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Byrne A, Bissonnette N, Ollier S, Tahlan K. Investigating in vivo Mycobacterium avium subsp. paratuberculosis microevolution and mixed strain infections. Microbiol Spectr 2023; 11:e0171623. [PMID: 37584606 PMCID: PMC10581078 DOI: 10.1128/spectrum.01716-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 07/10/2023] [Indexed: 08/17/2023] Open
Abstract
Mycobacterium avium subsp. paratuberculosis (MAP) causes Johne's Disease (JD) in ruminants, which is responsible for significant economic loss to the global dairy industry. Mixed strain infection (MSI) refers to the concurrent infection of a susceptible host with genetically distinct strains of a pathogen, whereas within-host changes in an infecting strain leading to genetically distinguishable progeny is called microevolution. The two processes can influence host-pathogen dynamics, disease progression and outcomes, but not much is known about their prevalence and impact on JD. Therefore, we obtained up to 10 MAP isolates each from 14 high-shedding animals and subjected them to whole-genome sequencing. Twelve of the 14 animals examined showed evidence for the presence of MSIs and microevolution, while the genotypes of MAP isolates from the remaining two animals could be attributed solely to microevolution. All MAP isolates that were otherwise isogenic had differences in short sequence repeats (SSRs), of which SSR1 and SSR2 were the most diverse and homoplastic. Variations in SSR1 and SSR2, which are located in ORF1 and ORF2, respectively, affect the genetic reading frame, leading to protein products with altered sequences and computed structures. The ORF1 gene product is predicted to be a MAP surface protein with possible roles in host immune modulation, but nothing could be inferred regarding the function of ORF2. Both genes are conserved in Mycobacterium avium complex members, but SSR1-based modulation of ORF1 reading frames seems to only occur in MAP, which could have potential implications on the infectivity of this pathogen. IMPORTANCE Johne's disease (JD) is a major problem in dairy animals, and concerns have been raised regarding the association of Mycobacterium avium subsp. paratuberculosis (MAP) with Crohn's disease in humans. MAP is an extremely slow-growing bacterium with low genome evolutionary rates. Certain short sequence repeats (SSR1 and SSR2) in the MAP chromosome are highly variable and evolve at a faster rate than the rest of the chromosome. In the current study, multiple MAP isolates with genetic variations such as single-nucleotide polymorphisms, and more noticeably, diverse SSRs, could simultaneously infect animals. Variations in SSR1 and SSR2 affect the products of the respective genes containing them. Since multiple MAP isolates can infect the same animal and the possibility that the pathogen undergoes further changes within the host due to unstable SSRs, this could provide a compensative mechanism for an otherwise slow-evolving pathogen to increase phenotypic diversity for overcoming host responses.
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Affiliation(s)
- Alexander Byrne
- Department of Biology, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador, Canada
| | - Nathalie Bissonnette
- Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, Quebec, Canada
| | - Séverine Ollier
- Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, Quebec, Canada
| | - Kapil Tahlan
- Department of Biology, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador, Canada
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2
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Agonhossou R, Akoton R, Lagnika H, Djihinto OY, Sovegnon PM, Saizonou HD, Ntoumi F, Wondji CS, Borrmann S, Adegnika AA, Djogbénou LS. P. falciparum msp1 and msp2 genetic diversity in P. falciparum single and mixed infection with P. malariae among the asymptomatic population in Southern Benin. Parasitol Int 2022; 89:102590. [PMID: 35472441 DOI: 10.1016/j.parint.2022.102590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 04/17/2022] [Accepted: 04/19/2022] [Indexed: 10/18/2022]
Abstract
Plasmodium falciparum and Plasmodium malariae infections are prevalent in malaria-endemic countries. However, very little is known about their interactions especially the effect of P. malariae on P. falciparum genetic diversity. This study aimed to assess P. falciparum genetic diversity in P. falciparum and mixed infection P. falciparum/P. malariae isolates among the asymptomatic populations in Southern Benin. Two hundred and fifty blood samples (125 of P. falciparum and 125 P. falciparum/P. malariae isolates) were analysed by a nested PCR amplification of msp1 and msp2 genes. The R033 allelic family was the most represented for the msp1 gene in mono and mixed infection isolates (99.2% vs 86.4%), while the K1 family had the lowest frequency (38.3% vs 20.4%). However, with the msp2 gene, the two allelic families displayed similar frequencies in P. falciparum isolates while the 3D7 allelic family was more represented in P. falciparum/P. malariae isolates (88.7%). Polyclonal infections were also lower (62.9%) in P. falciparum/P. malariae isolates (p < 0.05). Overall, 96 individual alleles were identified (47 for msp1 and 49 for msp2) in P. falciparum isolates while a total of 50 individual alleles were identified (23 for msp1 and 27 for msp2) in P. falciparum/P. malariae isolates. The Multiplicity of Infection (MOI) was lower in P. falciparum/P. malariae isolates (p < 0.05). This study revealed a lower genetic diversity of P. falciparum in P. falciparum/P. malariae isolates using msp1 and msp2 genes among the asymptomatic population in Southern Benin.
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Affiliation(s)
- Romuald Agonhossou
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin; Fondation Pour la Recherche Scientifique (FORS), ISBA, BP 88, Cotonou, Bénin.
| | - Romaric Akoton
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin; Fondation Pour la Recherche Scientifique (FORS), ISBA, BP 88, Cotonou, Bénin
| | - Hamirath Lagnika
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin
| | - Oswald Y Djihinto
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin
| | - Pierre M Sovegnon
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin
| | - Helga D Saizonou
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin
| | - Francine Ntoumi
- Fondation Congolaise pour la Recherche Médicale (FCRM), Brazzaville, Congo; Institute for Tropical Medicine (ITM), University of Tübingen, Tübingen, Germany
| | - Charles S Wondji
- Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK; Department of Parasitology and Medical Entomology, Centre for Research in Infectious Diseases (CRID), Yaoundé, Centre Region, 237, Cameroon
| | - Steffen Borrmann
- Institute for Tropical Medicine (ITM), University of Tübingen, Tübingen, Germany; German Center for Infection Research (DZIF), Tübingen, Germany
| | - Ayola A Adegnika
- Fondation Pour la Recherche Scientifique (FORS), ISBA, BP 88, Cotonou, Bénin; Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon; Institute for Tropical Medicine (ITM), University of Tübingen, Tübingen, Germany; Eberhard Karls Universität Tübingen, Tübingen, Germany; German Center for Infection Research (DZIF), Tübingen, Germany
| | - Luc S Djogbénou
- Tropical Infectious Diseases Research Centre (TIDRC), University of Abomey-Calavi, 01BP 526, Cotonou, Benin; Institut Régional de Santé Publique/Université d'Abomey-Calavi, BP 384 Ouidah, Bénin
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3
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Arias CF, Acosta FJ, Fernandez-Arias C. Killing the competition: a theoretical framework for liver-stage malaria. Open Biol 2022; 12:210341. [PMID: 35350863 PMCID: PMC8965401 DOI: 10.1098/rsob.210341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The first stage of malaria infections takes place inside the host's hepatocytes. Remarkably, Plasmodium parasites do not infect hepatocytes immediately after reaching the liver. Instead, they migrate through several hepatocytes before infecting their definitive host cells, thus increasing their chances of immune destruction. Considering that malaria can proceed normally without cell traversal, this is indeed a puzzling behaviour. In fact, the role of hepatocyte traversal remains unknown to date, implying that the current understanding of malaria is incomplete. In this work, we hypothesize that the parasites traverse hepatocytes to actively trigger an immune response in the host. This behaviour would be part of a strategy of superinfection exclusion aimed to reduce intraspecific competition during the blood stage of the infection. Based on this hypothesis, we formulate a comprehensive theory of liver-stage malaria that integrates all the available knowledge about the infection. The interest of this new paradigm is not merely theoretical. It highlights major issues in the current empirical approach to the study of Plasmodium and suggests new strategies to fight malaria.
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Affiliation(s)
- Clemente F. Arias
- Centro de Investigaciones Biológicas (CSIC), Madrid, Spain,Grupo Interdisciplinar de Sistemas Complejos de Madrid, Spain
| | | | - Cristina Fernandez-Arias
- Departamento de Inmunología, Universidad Complutense de Madrid, Spain,Instituto de Medicina Molecular, Universidade de Lisboa, Portugal
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4
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Li Y, Akimoto SI. Self and non-self recognition affects clonal reproduction and competition in the pea aphid. Proc Biol Sci 2021; 288:20210787. [PMID: 34187194 PMCID: PMC8242831 DOI: 10.1098/rspb.2021.0787] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Accepted: 06/04/2021] [Indexed: 11/12/2022] Open
Abstract
The spatial interaction of clonal organisms is an unsolved but crucial topic in evolutionary biology. We evaluated the interactions between aphid clones using a colour mutant (yellow) and an original (green) clone. Colonies founded by two aphids of the same clone and mixed colonies, founded by a green aphid and a yellow aphid, were set up to observe population growth for 15 days. We confirmed positive competition effects, with mixed colonies increasing in size more rapidly than clonal colonies. In mixed colonies where reproduction started simultaneously, green aphids overwhelmed yellow aphids in number, and yellow aphids restrained reproduction. However, when yellow aphids started to reproduce earlier, they outnumbered the green aphids. To test whether aphids have the ability to control reproduction according to the densities of self and non-self clones, one yellow aphid or one antennae-excised yellow aphid was transferred into a highly dense green clone colony. Intact yellow aphids produced fewer nymphs in crowded green colonies, whereas the fecundity of antennae-excised aphids did not change. Thus, we conclude that aphid clones can discriminate between self and non-self clones, and can regulate their reproduction, depending on whether they are superior or inferior in number to their competitors.
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Affiliation(s)
- Yang Li
- Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
- College of Biology and Agriculture, Zunyi Normal University, Zunyi Guizhou 563006, People's Republic of China
| | - Shin-ichi Akimoto
- Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
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5
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Milutinović B, Stock M, Grasse AV, Naderlinger E, Hilbe C, Cremer S. Social immunity modulates competition between coinfecting pathogens. Ecol Lett 2020; 23:565-574. [PMID: 31950595 DOI: 10.1111/ele.13458] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 10/31/2019] [Accepted: 12/14/2019] [Indexed: 12/18/2022]
Abstract
Coinfections with multiple pathogens can result in complex within-host dynamics affecting virulence and transmission. While multiple infections are intensively studied in solitary hosts, it is so far unresolved how social host interactions interfere with pathogen competition, and if this depends on coinfection diversity. We studied how the collective disease defences of ants - their social immunity - influence pathogen competition in coinfections of same or different fungal pathogen species. Social immunity reduced virulence for all pathogen combinations, but interfered with spore production only in different-species coinfections. Here, it decreased overall pathogen sporulation success while increasing co-sporulation on individual cadavers and maintaining a higher pathogen diversity at the community level. Mathematical modelling revealed that host sanitary care alone can modulate competitive outcomes between pathogens, giving advantage to fast-germinating, thus less grooming-sensitive ones. Host social interactions can hence modulate infection dynamics in coinfected group members, thereby altering pathogen communities at the host level and population level.
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Affiliation(s)
- Barbara Milutinović
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Miriam Stock
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Anna V Grasse
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Elisabeth Naderlinger
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Christian Hilbe
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Sylvia Cremer
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
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Host food quality and quantity differentially affect Ascogregarina barretti parasite burden, development and within-host competition in the mosquito Aedes triseriatus. Parasitology 2019; 146:1665-1672. [PMID: 31362793 DOI: 10.1017/s0031182019000994] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Host condition depends in large part on the quality and quantity of available food and heavily influences the outcome of parasite infection. Although parasite fitness traits such as growth rate and size may depend on host condition, whether host food quality or quantity is more important to parasite fitness and within-host interactions is poorly understood. We provided individual mosquito hosts with a standard dose of a gregarine parasite and reared mosquitoes on two food types of different quality and two quantities. We measured host size, total parasite count and area, and average size of parasites within each treatment. Food quality significantly influenced the number of parasites in a host; hosts fed a low-quality diet were infected with more parasites than those provided a high-quality diet. In addition, we found evidence of within-host competition; there was a negative relationship between parasite size and count though this relationship was dependent on host food quality. Host food quantity significantly affected total parasite area and parasite size; lower food quantity resulted in smaller parasites and reduced overall parasite area inside the host. Thus both food quality and quantity have the potential to influence parasite fitness and population dynamics.
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Sondo P, Derra K, Lefevre T, Diallo-Nakanabo S, Tarnagda Z, Zampa O, Kazienga A, Valea I, Sorgho H, Ouedraogo JB, Guiguemde TR, Tinto H. Genetically diverse Plasmodium falciparum infections, within-host competition and symptomatic malaria in humans. Sci Rep 2019; 9:127. [PMID: 30644435 PMCID: PMC6333925 DOI: 10.1038/s41598-018-36493-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Accepted: 11/16/2018] [Indexed: 11/17/2022] Open
Abstract
There is a large genetic diversity of Plasmodium falciparum strains that infect people causing diverse malaria symptoms. This study was carried out to explore the effect of mixed-strain infections and the extent to which some specific P. falciparum variants are associated with particular malaria symptoms. P. falciparum isolates collected during pharmacovigilance study in Nanoro, Burkina Faso were used to determine allelic variation in two polymorphic antigens of the merozoite surface (msp1 and msp2). Overall, parasite density did not increase with additional strains, suggesting the existence of within-host competition. Parasite density was influenced by msp1 allelic families with highest parasitaemia observed in MAD20 allelic family. However, when in mixed infections with allelic family K1, MAD20 could not grow to the same levels as it would alone, suggesting competitive suppression in these mixed infections. Host age was associated with parasite density. Overall, older patients exhibited lower parasite densities than younger patients, but this effect varied with the genetic composition of the isolates for the msp1 gene. There was no effect of msp1 and msp2 allelic family variation on body temperature. Haemoglobin level was influenced by msp2 family with patients harboring the FC27 allele showing lower haemoglobin level than mono-infected individuals by the 3D7 allele. This study provides evidence that P. falciparum genetic diversity influenced the severity of particular malaria symptoms and supports the existence of within-host competition in genetically diverse P. falciparum.
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Affiliation(s)
- Paul Sondo
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso.
| | - Karim Derra
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso
| | - Thierry Lefevre
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso.,MIVEGEC, IRD, CNRS, University of Montpellier, Montpellier, France
| | - Seydou Diallo-Nakanabo
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso
| | - Zekiba Tarnagda
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso
| | - Odile Zampa
- Centre Muraz of Bobo-Dioulasso, Bobo-Dioulasso, Burkina Faso
| | - Adama Kazienga
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso
| | - Innocent Valea
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso.,Centre Muraz of Bobo-Dioulasso, Bobo-Dioulasso, Burkina Faso
| | - Hermann Sorgho
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso
| | - Jean-Bosco Ouedraogo
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso
| | | | - Halidou Tinto
- Institut de Recherche en Sciences de la Santé (IRSS)/Clinical Research Unit of Nanoro (CRUN), Nanoro, Burkina Faso.,Centre Muraz of Bobo-Dioulasso, Bobo-Dioulasso, Burkina Faso
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8
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Wale N, Sim DG, Read AF. A nutrient mediates intraspecific competition between rodent malaria parasites in vivo. Proc Biol Sci 2018; 284:rspb.2017.1067. [PMID: 28747479 PMCID: PMC5543226 DOI: 10.1098/rspb.2017.1067] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 06/21/2017] [Indexed: 12/02/2022] Open
Abstract
Hosts are often infected with multiple strains of a single parasite species. Within-host competition between parasite strains can be intense and has implications for the evolution of traits that impact patient health, such as drug resistance and virulence. Yet the mechanistic basis of within-host competition is poorly understood. Here, we demonstrate that a parasite nutrient, para-aminobenzoic acid (pABA), mediates competition between a drug resistant and drug susceptible strain of the malaria parasite, Plasmodium chabaudi. We further show that increasing pABA supply to hosts infected with the resistant strain worsens disease and changes the relationship between parasite burden and pathology. Our experiments demonstrate that, even when there is profound top-down regulation (immunity), bottom-up regulation of pathogen populations can occur and that its importance may vary during an infection. The identification of resources that can be experimentally controlled opens up the opportunity to manipulate competitive interactions between parasites and hence their evolution.
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Affiliation(s)
- Nina Wale
- Center for Infectious Disease Dynamics and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Derek G Sim
- Center for Infectious Disease Dynamics and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Andrew F Read
- Center for Infectious Disease Dynamics and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.,Department of Entomology, The Pennsylvania State University, University Park, PA 16802, USA
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Antibody-independent mechanisms regulate the establishment of chronic Plasmodium infection. Nat Microbiol 2017; 2:16276. [PMID: 28165471 DOI: 10.1038/nmicrobiol.2016.276] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 12/22/2016] [Indexed: 01/15/2023]
Abstract
Malaria is caused by parasites of the genus Plasmodium. All human-infecting Plasmodium species can establish long-lasting chronic infections1-5, creating an infectious reservoir to sustain transmission1,6. It is widely accepted that the maintenance of chronic infection involves evasion of adaptive immunity by antigenic variation7. However, genes involved in this process have been identified in only two of five human-infecting species: Plasmodium falciparum and Plasmodium knowlesi. Furthermore, little is understood about the early events in the establishment of chronic infection in these species. Using a rodent model we demonstrate that from the infecting population, only a minority of parasites, expressing one of several clusters of virulence-associated pir genes, establishes a chronic infection. This process occurs in different species of parasites and in different hosts. Establishment of chronicity is independent of adaptive immunity and therefore different from the mechanism proposed for maintenance of chronic P. falciparum infections7-9. Furthermore, we show that the proportions of parasites expressing different types of pir genes regulate the time taken to establish a chronic infection. Because pir genes are common to most, if not all, species of Plasmodium10, this process may be a common way of regulating the establishment of chronic infections.
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10
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Multistrain Infections with Lyme Borreliosis Pathogens in the Tick Vector. Appl Environ Microbiol 2017; 83:AEM.02552-16. [PMID: 27836839 DOI: 10.1128/aem.02552-16] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2016] [Accepted: 11/08/2016] [Indexed: 12/16/2022] Open
Abstract
Mixed or multiple-strain infections are common in vector-borne diseases and have important implications for the epidemiology of these pathogens. Previous studies have mainly focused on interactions between pathogen strains in the vertebrate host, but little is known about what happens in the arthropod vector. Borrelia afzelii and Borrelia garinii are two species of spirochete bacteria that cause Lyme borreliosis in Europe and that share a tick vector, Ixodes ricinus Each of these two tick-borne pathogens consists of multiple strains that are often differentiated using the highly polymorphic ospC gene. For each Borrelia species, we studied the frequencies and abundances of the ospC strains in a wild population of I. ricinus ticks that had been sampled from the same field site over a period of 3 years. We used quantitative PCR (qPCR) and 454 sequencing to estimate the spirochete load and the strain diversity within each tick. For B. afzelii, there was a negative relationship between the two most common ospC strains, suggesting the presence of competitive interactions in the vertebrate host and possibly the tick vector. The flat relationship between total spirochete abundance and strain richness in the nymphal tick indicates that the mean abundance per strain decreases as the number of strains in the tick increases. Strains with the highest spirochete load in the nymphal tick were the most common strains in the tick population. The spirochete abundance in the nymphal tick appears to be an important life history trait that explains why some strains are more common than others in nature. IMPORTANCE Lyme borreliosis is the most common vector-borne disease in the Northern Hemisphere and is caused by spirochete bacteria that belong to the Borrelia burgdorferi sensu lato species complex. These tick-borne pathogens are transmitted among vertebrate hosts by hard ticks of the genus Ixodes Each Borrelia species can be further subdivided into genetically distinct strains. Multiple-strain infections are common in both the vertebrate host and the tick vector and can result in competitive interactions. To date, few studies on multiple-strain vector-borne pathogens have investigated patterns of cooccurrence and abundance in the arthropod vector. We demonstrate that the abundance of a given strain in the tick vector is negatively affected by the presence of coinfecting strains. In addition, our study suggests that the spirochete abundance in the tick is an important life history trait that can explain why some strains are more common in nature than others.
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11
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Heterologous Infection of Pregnant Mice Induces Low Birth Weight and Modifies Offspring Susceptibility to Malaria. PLoS One 2016; 11:e0160120. [PMID: 27467392 PMCID: PMC4965193 DOI: 10.1371/journal.pone.0160120] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Accepted: 07/12/2016] [Indexed: 11/20/2022] Open
Abstract
Pregnancy malaria (PM) is associated with poor pregnancy outcomes, and can arise due to relapse, recrudescence or a re-infection with heterologous parasites. We have used the Plasmodium chabaudi model of pregnancy malaria in C57BL/6 mice to examine recrudescence and heterologous infection using CB and AS parasite strains. After an initial course of patent parasitemia and first recrudescence, CB but not AS parasites were observed to recrudesce again in most animals that became pregnant. Pregnancy exacerbated heterologous CB infection of AS-experienced mice, leading to mortality and impaired post-natal growth of pups. Parasites were detected in placental blood without evidence of sequestration, unlike P. falciparum but similar to other malaria species that infect pregnant women. Inflammatory cytokine levels were elevated in pregnant females during malaria, and associated with intensity of infection and with poor outcomes. Pups born to dams during heterologous infection were more resistant to malaria infections at 6–7 weeks of age, compared to pups born to malaria-experienced but uninfected dams or to malaria-naïve dams. In summary, our mouse model reproduces several features of human PM, including recrudescences, heterologous infections, poor pregnancy outcomes associated with inflammatory cytokines, and modulation of offspring susceptibility to malaria. This model should be further studied to explore mechanisms underlying PM pathogenesis.
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Bushman M, Morton L, Duah N, Quashie N, Abuaku B, Koram KA, Dimbu PR, Plucinski M, Gutman J, Lyaruu P, Kachur SP, de Roode JC, Udhayakumar V. Within-host competition and drug resistance in the human malaria parasite Plasmodium falciparum. Proc Biol Sci 2016; 283:20153038. [PMID: 26984625 PMCID: PMC4810865 DOI: 10.1098/rspb.2015.3038] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 02/16/2016] [Indexed: 11/12/2022] Open
Abstract
Infections with the malaria parasite Plasmodium falciparum typically comprise multiple strains, especially in high-transmission areas where infectious mosquito bites occur frequently. However, little is known about the dynamics of mixed-strain infections, particularly whether strains sharing a host compete or grow independently. Competition between drug-sensitive and drug-resistant strains, if it occurs, could be a crucial determinant of the spread of resistance. We analysed 1341 P. falciparum infections in children from Angola, Ghana and Tanzania and found compelling evidence for competition in mixed-strain infections: overall parasite density did not increase with additional strains, and densities of individual chloroquine-sensitive (CQS) and chloroquine-resistant (CQR) strains were reduced in the presence of competitors. We also found that CQR strains exhibited low densities compared with CQS strains (in the absence of chloroquine), which may underlie observed declines of chloroquine resistance in many countries following retirement of chloroquine as a first-line therapy. Our observations support a key role for within-host competition in the evolution of drug-resistant malaria. Malaria control and resistance-management efforts in high-transmission regions may be significantly aided or hindered by the effects of competition in mixed-strain infections. Consideration of within-host dynamics may spur development of novel strategies to minimize resistance while maximizing the benefits of control measures.
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Affiliation(s)
- Mary Bushman
- Department of Biology, Emory University, Atlanta, GA 30322, USA Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
| | - Lindsay Morton
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
| | - Nancy Duah
- Epidemiology Department, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana
| | - Neils Quashie
- Epidemiology Department, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana
| | - Benjamin Abuaku
- Epidemiology Department, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana
| | - Kwadwo A Koram
- Epidemiology Department, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana
| | | | - Mateusz Plucinski
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
| | - Julie Gutman
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
| | - Peter Lyaruu
- Ifakara Health Institute, Dar es Salaam, Tanzania
| | - S Patrick Kachur
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
| | | | - Venkatachalam Udhayakumar
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
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13
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Clerc M, Ebert D, Hall MD. Expression of parasite genetic variation changes over the course of infection: implications of within-host dynamics for the evolution of virulence. Proc Biol Sci 2015; 282:20142820. [PMID: 25761710 DOI: 10.1098/rspb.2014.2820] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
How infectious disease agents interact with their host changes during the course of infection and can alter the expression of disease-related traits. Yet by measuring parasite life-history traits at one or few moments during infection, studies have overlooked the impact of variable parasite growth trajectories on disease evolution. Here we show that infection-age-specific estimates of host and parasite fitness components can reveal new insight into the evolution of parasites. We do so by characterizing the within-host dynamics over an entire infection period for five genotypes of the castrating bacterial parasite Pasteuria ramosa infecting the crustacean Daphnia magna. Our results reveal that genetic variation for parasite-induced gigantism, host castration and parasite spore loads increases with the age of infection. Driving these patterns appears to be variation in how well the parasite maintains control of host reproduction late in the infection process. We discuss the evolutionary consequences of this finding with regard to natural selection acting on different ages of infection and the mechanism underlying the maintenance of castration efficiency. Our results highlight how elucidating within-host dynamics can shed light on the selective forces that shape infection strategies and the evolution of virulence.
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Affiliation(s)
- Melanie Clerc
- Institute of Evolutionary Biology, University of Edinburgh, Ashworth Labs, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK Zoological Institute, University of Basel, Vesalgasse 1, Basel 4051, Switzerland
| | - Dieter Ebert
- Zoological Institute, University of Basel, Vesalgasse 1, Basel 4051, Switzerland
| | - Matthew D Hall
- Zoological Institute, University of Basel, Vesalgasse 1, Basel 4051, Switzerland School of Biological Sciences, Monash University, Melbourne 3800, Australia
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14
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Ulrich Y, Schmid-Hempel P. The distribution of parasite strains among hosts affects disease spread in a social insect. INFECTION GENETICS AND EVOLUTION 2015; 32:348-53. [PMID: 25858120 DOI: 10.1016/j.meegid.2015.04.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Revised: 03/28/2015] [Accepted: 04/01/2015] [Indexed: 11/26/2022]
Abstract
Social insects present highly interesting and experimentally amenable systems for the study of disease transmission because they naturally live in dense groups of frequently interacting individuals. Using experimental inoculations of five trypanosomatid strains into groups of its natural host, the bumblebee Bombus terrestris, we investigate the effects of the initial parasite strain distribution across group members on the establishment and transmission success of the different strains to new hosts. For a given number of parasite strains circulating within a host group, transmission to new hosts was increased when the strains were initially inoculated as mixed infections (as opposed to separate single infections), presumably because mixed infections generally favored fast replicating strains. In contrast, separate single infections reduced transmission at least in part through a precedence effect, whereby weak strains appeared to persist by making their host unavailable to superinfection. These results suggest that host groups could benefit from 'compartmentalizing' infections by different parasite strains across different group members, which might be achieved in social insects, for example, by division of labor.
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Affiliation(s)
- Yuko Ulrich
- ETH Zurich, Institute of Integrative Biology (IBZ), ETH-Zentrum CHN, Universitätsstrasse 16, CH-8092 Zurich, Switzerland; Laboratory of Insect Social Evolution, The Rockefeller University, 1230 York Avenue, 10065 New York, NY, USA.
| | - Paul Schmid-Hempel
- ETH Zurich, Institute of Integrative Biology (IBZ), ETH-Zentrum CHN, Universitätsstrasse 16, CH-8092 Zurich, Switzerland
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15
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Pérez-Rodríguez A, de la Hera I, Fernández-González S, Pérez-Tris J. Global warming will reshuffle the areas of high prevalence and richness of three genera of avian blood parasites. GLOBAL CHANGE BIOLOGY 2014; 20:2406-2416. [PMID: 24488566 DOI: 10.1111/gcb.12542] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 01/23/2014] [Indexed: 06/03/2023]
Abstract
The importance of parasitism for host populations depends on local parasite richness and prevalence: usually host individuals face higher infection risk in areas where parasites are most diverse, and host dispersal to or from these areas may have fitness consequences. Knowing how parasites are and will be distributed in space and time (in a context of global change) is thus crucial from both an ecological and a biological conservation perspective. Nevertheless, most research articles focus just on elaborating models of parasite distribution instead of parasite diversity. We produced distribution models of the areas where haemosporidian parasites are currently highly diverse (both at community and at within-host levels) and prevalent among Iberian populations of a model passerine host: the blackcap Sylvia atricapilla; and how these areas are expected to vary according to three scenarios of climate change. On the basis of these models, we analysed whether variation among populations in parasite richness or prevalence are expected to remain the same or change in the future, thereby reshuffling the geographic mosaic of host-parasite interactions as we observe it today. Our models predict a rearrangement of areas of high prevalence and richness of parasites in the future, with Haemoproteus and Leucocytozoon parasites (today the most diverse genera in blackcaps) losing areas of high diversity and Plasmodium parasites (the most virulent ones) gaining them. Likewise, the prevalence of multiple infections and parasite infracommunity richness would be reduced. Importantly, differences among populations in the prevalence and richness of parasites are expected to decrease in the future, creating a more homogeneous parasitic landscape. This predicts an altered geographic mosaic of host-parasite relationships, which will modify the interaction arena in which parasite virulence evolves.
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Affiliation(s)
- Antón Pérez-Rodríguez
- Departamento de Zoología y Antropología Física, Universidad Complutense de Madrid, Madrid, E-28040, Spain
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16
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Motz VL, Lewis WD, Vardo-Zalik AM. Leukocyte profiles for western fence lizards, Sceloporus occidentalis, naturally infected by the malaria parasite Plasmodium mexicanum. J Parasitol 2014; 100:592-7. [PMID: 24945903 DOI: 10.1645/13-371.1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Plasmodium mexicanum is a malaria parasite that naturally infects the western fence lizard, Sceloporus occidentalis , in northern California. We set out to determine whether lizards naturally infected with this malaria parasite have different leukocyte profiles, indicating an immune response to infection. We used 29 naturally infected western fence lizards paired with uninfected lizards based on sex, snout-to-vent length, tail status, and the presence-absence of ectoparasites such as ticks and mites, as well as the presence-absence of another hemoparasite, Schellackia occidentalis. Complete white blood cell (WBC) counts were conducted on blood smears stained with Giemsa, and the proportion of granulocytes per microliter of blood was estimated using the Avian Leukopet method. The abundance of each WBC class (lymphocytes, monocytes, heterophils, eosinophils, and basophils) in infected and uninfected lizards was compared to determine whether leukocyte densities varied with infection status. We found that the numbers of WBCs and lymphocytes per microliter of blood significantly differed (P < 0.05) between the 2 groups for females but not for males, whereas parasitemia was significantly correlated with lymphocyte counts for males, but not for females. This study supports the theory that infection with P. mexicanum stimulates the lizard's immune response to increase the levels of circulating WBCs, but what effect this has on the biology of the parasite remains unclear.
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Affiliation(s)
- Victoria L Motz
- The Pennsylvania State University, York Campus, 1031 Edgecomb Avenue, York, Pennsylvania 17403. Correspondence should be sent to:
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17
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Dynamics of clonal diversity in natural infections of the malaria parasite Plasmodium mexicanum in its free-ranging lizard host. Parasitol Res 2014; 113:2059-67. [PMID: 24647987 DOI: 10.1007/s00436-014-3854-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 03/05/2014] [Indexed: 10/25/2022]
Abstract
Within mixed-genotype infections of malaria parasites (Plasmodium), the number of genetic clones present is associated with variation in important life history traits of the infection, including virulence. Although the number of clones present is important, how the proportion of those clones varies over time is poorly known. Clonal proportions of the lizard malaria parasite, Plasmodium mexicanum, were assessed in naturally infected free-ranging lizards followed in a mark-recapture program over as long as two warm seasons, the typical life span of the lizard. Clonal proportions were determined by amplifying two microsatellite markers, a method previously verified for accuracy. Most blood samples had been stored for over a decade, so a verification test determined that these samples had not degraded. Although the environment experienced by the parasite (its host) varies over the seasons and transmission occurs over the entire warm season, 68% of infections were stable over time, harboring a single clone (37% of infections) or multiple clones changing only 1-12% maximum comparing any two samples (31% of infections). The maximum change seen in any infection (comparing any two sample periods) was only 30%. A new clone entered three infections (only once successfully), and a clone was lost in only three infections. These results mirror those seen for a previous study of experimentally induced infections that showed little change in relative proportions over time. The results of this study, the first look at how clonal proportions vary over time for any malaria parasite of a nonhuman vertebrate host for natural infections, were surprising because experimental studies show clones of P. mexicanum appear to interact, yet relative proportions of clones typically remain constant over time.
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18
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Giraudeau M, Mousel M, Earl S, McGraw K. Parasites in the city: degree of urbanization predicts poxvirus and coccidian infections in house finches (Haemorhous mexicanus). PLoS One 2014; 9:e86747. [PMID: 24503816 PMCID: PMC3913573 DOI: 10.1371/journal.pone.0086747] [Citation(s) in RCA: 85] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 12/13/2013] [Indexed: 01/21/2023] Open
Abstract
Background Urbanization can strongly impact the physiology, behavior, and fitness of animals. Conditions in cities may also promote the transmission and success of animal parasites and pathogens. However, to date, no studies have examined variation in the prevalence or severity of several distinct pathogens/parasites along a gradient of urbanization in animals or if these infections increase physiological stress in urban populations. Methodology/Principal Findings Here, we measured the prevalence and severity of infection with intestinal coccidians (Isospora sp.) and the canarypox virus (Avipoxvirus) along an urban-to-rural gradient in wild male house finches (Haemorhous mexicanus). In addition, we quantified an important stress indicator in animals (oxidative stress) and several axes of urbanization, including human population density and land-use patterns within a 1 km radius of each trapping site. Prevalence of poxvirus infection and severity of coccidial infection were significantly associated with the degree of urbanization, with an increase of infection in more urban areas. The degrees of infection by the two parasites were not correlated along the urban-rural gradient. Finally, levels of oxidative damage in plasma were not associated with infection or with urbanization metrics. Conclusion/Significance These results indicate that the physical presence of humans in cities and the associated altered urban landscape characteristics are associated with increased infections with both a virus and a gastrointestinal parasite in this common songbird resident of North American cities. Though we failed to find elevations in urban- or parasite/pathogen-mediated oxidative stress, humans may facilitate infections in these birds via bird feeders (i.e. horizontal disease transmission due to unsanitary surfaces and/or elevations in host population densities) and/or via elevations in other forms of physiological stress (e.g. corticosterone, nutritional).
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Affiliation(s)
- Mathieu Giraudeau
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
- * E-mail:
| | - Melanie Mousel
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - Stevan Earl
- Global Institute of Sustainability, Arizona State University, Tempe, Arizona, United States of America
| | - Kevin McGraw
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
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19
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Fairlie-Clarke KJ, Allen JE, Read AF, Graham AL. Quantifying variation in the potential for antibody-mediated apparent competition among nine genotypes of the rodent malaria parasite Plasmodium chabaudi. INFECTION, GENETICS AND EVOLUTION : JOURNAL OF MOLECULAR EPIDEMIOLOGY AND EVOLUTIONARY GENETICS IN INFECTIOUS DISEASES 2013; 20:270-5. [PMID: 24056014 PMCID: PMC3898986 DOI: 10.1016/j.meegid.2013.09.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 09/10/2013] [Accepted: 09/11/2013] [Indexed: 01/01/2023]
Abstract
Within-host competition among parasite genotypes affects epidemiology as well as the evolution of virulence. In the rodent malaria Plasmodium chabaudi, competition among genotypes, as well as clone-specific and clone-transcending immunity are well documented. However, variation among genotypes in the induction of antibodies is not well understood, despite the important role of antibodies in the clearance of malaria infection. Here, we quantify the potential for antibodies induced by one clone to bind another (i.e., to cause antibody-mediated apparent competition) for nine genetically distinct P. chabaudi clones. We hypothesised that clones would vary in the strength of antibody induction, and that the propensity for clone-transcending immunity between a pair of clones would increase with increasing genetic relatedness at key antigenic loci. Using serum collected from mice 35 days post-infection, we measured titres of antibody to an unrelated antigen, Keyhole Limpet Haemocyanin (KLH), and two malaria antigens: recombinant Apical Membrane Antigen-1 (AMA-1) and Merozoite Surface Protein-119 (MSP-119). Amino acid sequence homology within each antigenic locus was used as a measure of relatedness. We found significant parasite genetic variation for the strength of antibody induction. We also found that relatedness at MSP-119 but not AMA-1 predicted clone-transcending binding. Our results help explain the outcome of chronic-phase mixed infections and generate testable predictions about the pairwise competitive ability of P. chabaudi clones.
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Affiliation(s)
- Karen J Fairlie-Clarke
- Institutes of Evolution, Immunology and Infection Research, School of Biological Sciences, King's Buildings, University of Edinburgh, Edinburgh, UK.
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20
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Salathé R, Tognazzo M, Schmid-Hempel R, Schmid-Hempel P. Probing mixed-genotype infections I: extraction and cloning of infections from hosts of the trypanosomatid Crithidia bombi. PLoS One 2012; 7:e49046. [PMID: 23155449 PMCID: PMC3498296 DOI: 10.1371/journal.pone.0049046] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Accepted: 10/03/2012] [Indexed: 11/25/2022] Open
Abstract
We here present an efficient, precise and reliable method to isolate and cultivate healthy and viable single Crithidia bombi cells from bumblebee faeces using flow cytometry. We report a precision of >99% in obtaining single trypanosomatid cells for further culture and analysis (“cloning”). In the study, we have investigated the use of different liquid media to cultivate C. bombi and present an optimal medium for obtaining viable clones from all tested, infected host donors. We show that this method can be applied to genotype a collection of clones from natural infections. Furthermore, we show how to cryo-preserve C. bombi cells to be revived to become infective clones after at least 4 years of storage. Considering the high prevalence of infections in natural populations, our method provides a powerful tool in studying the level and diversity of these infections, and thus enriches the current methodology for the studies of complex host-parasite interactions.
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Affiliation(s)
- Rahel Salathé
- Institute of Integrative Biology (IBZ), ETH Zürich, Zürich, Switzerland
- * E-mail: (RS); (PSH)
| | | | | | - Paul Schmid-Hempel
- Institute of Integrative Biology (IBZ), ETH Zürich, Zürich, Switzerland
- * E-mail: (RS); (PSH)
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21
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Chung E, Petit E, Antonovics J, Pedersen AB, Hood ME. Variation in resistance to multiple pathogen species: anther smuts of Silene uniflora. Ecol Evol 2012; 2:2304-14. [PMID: 23139888 PMCID: PMC3488680 DOI: 10.1002/ece3.346] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Revised: 07/10/2012] [Accepted: 07/14/2012] [Indexed: 11/10/2022] Open
Abstract
The occurrence of multiple pathogen species on a shared host species is unexpected when they exploit the same micro-niche within the host individual. One explanation for such observations is the presence of pathogen-specific resistances segregating within the host population into sites that are differentially occupied by the competing pathogens. This study used experimental inoculations to test whether specific resistances may contribute to the maintenance of two species of anther-smut fungi, Microbotryum silenes-inflatae and Microbotryum lagerheimii, in natural populations of Silene uniflora in England and Wales. Overall, resistance to the two pathogens was strongly positively correlated among host populations and to a lesser degree among host families within populations. A few instances of specific resistance were also observed and confirmed by replicated inoculations. The results suggest that selection for resistance to one pathogen may protect the host from the emergence via host shifts of related pathogen species, and conversely that co-occurrence of two species of pathogens may be dependent on the presence of host genotypes susceptible to both.
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Affiliation(s)
- Erin Chung
- Department of Biology, Amherst College Amherst, Massachusetts
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22
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Klein EY, Smith DL, Laxminarayan R, Levin S. Superinfection and the evolution of resistance to antimalarial drugs. Proc Biol Sci 2012; 279:3834-42. [PMID: 22787024 DOI: 10.1098/rspb.2012.1064] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
A major issue in the control of malaria is the evolution of drug resistance. Ecological theory has demonstrated that pathogen superinfection and the resulting within-host competition influences the evolution of specific traits. Individuals infected with Plasmodium falciparum are consistently infected by multiple parasites; however, while this probably alters the dynamics of resistance evolution, there are few robust mathematical models examining this issue. We developed a general theory for modelling the evolution of resistance with host superinfection and examine: (i) the effect of transmission intensity on the rate of resistance evolution; (ii) the importance of different biological costs of resistance; and (iii) the best measure of the frequency of resistance. We find that within-host competition retards the ability and slows the rate at which drug-resistant parasites invade, particularly as the transmission rate increases. We also find that biological costs of resistance that reduce transmission are less important than reductions in the duration of drug-resistant infections. Lastly, we find that random sampling of the population for resistant parasites is likely to significantly underestimate the frequency of resistance. Considering superinfection in mathematical models of antimalarial drug resistance may thus be important for generating accurate predictions of interventions to contain resistance.
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Affiliation(s)
- Eili Y Klein
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
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23
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Wacker MA, Turnbull LB, Walker LA, Mount MC, Ferdig MT. Quantification of multiple infections of Plasmodium falciparum in vitro. Malar J 2012; 11:180. [PMID: 22646748 PMCID: PMC3483182 DOI: 10.1186/1475-2875-11-180] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Accepted: 03/13/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Human malaria infections caused by the parasite Plasmodium falciparum often contain more than one genetically distinct parasite. Despite this fact, nearly all studies of multiple strain P. falciparum infections have been limited to determining relative densities of each parasite within an infection. In light of this, new methods are needed that can quantify the absolute number of parasites within a single infection. METHODS A quantitative PCR (qPCR) method was developed to track the dynamic interaction of P. falciparum infections containing genetically distinct parasite clones in cultured red blood cells. Allele-specific primers were used to generate a standard curve and to quantify the absolute concentration of parasite DNA within multi-clonal infections. Effects on dynamic growth relationships between parasites under drug pressure were examined by treating mixed cultures of drug sensitive and drug resistant parasites with the anti-malarial drug chloroquine at different dosing schedules. RESULTS An absolute quantification method was developed to monitor the dynamics of P. falciparum cultures in vitro. This method allowed for the observation of competitive suppression, the reduction of parasites numbers due to the presence of another parasite, and competitive release, the improved performance of a parasite after the removal of a competitor. These studies demonstrated that the presence of two parasites led to the reduction in density of at least one parasite. The introduction of drug to a mixed culture containing both a drug resistant and drug sensitive parasites resulted in an increased proportion of the drug resistant parasite. Moreover, following drug treatment, the resistant parasite experienced competitive release by exhibiting a fitness benefit greater than simply surviving drug treatment, due to the removal of competitive suppression by the sensitive parasite. CONCLUSIONS The newly developed assay allowed for the examination of the dynamics of two distinct clones in vitro; both competitive suppression and release were observed. A deeper understanding of the dynamic growth responses of multiple strain P. falciparum infections, with and without drug pressure, can improve the understanding of the role of parasite interactions in the spread of drug resistant parasites, perhaps suggesting different treatment strategies.
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Affiliation(s)
- Mark A Wacker
- Eck Institute of Global Health, Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA
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24
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Huijben S, Sim DG, Nelson WA, Read AF. The fitness of drug-resistant malaria parasites in a rodent model: multiplicity of infection. J Evol Biol 2011; 24:2410-22. [PMID: 21883612 PMCID: PMC3304104 DOI: 10.1111/j.1420-9101.2011.02369.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Malaria infections normally consist of more than one clonally replicating lineage. Within-host interactions between sensitive and resistant parasites can have profound effects on the evolution of drug resistance. Here, using the Plasmodium chabaudi mouse malaria model, we ask whether the costs and benefits of resistance are affected by the number of co-infecting strains competing with a resistant clone. We found strong competitive suppression of resistant parasites in untreated infections and marked competitive release following treatment. The magnitude of competitive suppression depended on competitor identity. However, there was no overall effect of the diversity of susceptible parasites on the extent of competitive suppression or release. If these findings generalize, then transmission intensity will impact on resistance evolution because of its effect on the frequency of mixed infections, not because of its effect on the distribution of clones per host. This would greatly simplify the computational problems of adequately capturing within-host ecology in models of drug resistance evolution in malaria.
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Affiliation(s)
- S Huijben
- Department of Biology, Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA 16802, USA.
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25
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The evolution of drug resistance and the curious orthodoxy of aggressive chemotherapy. Proc Natl Acad Sci U S A 2011; 108 Suppl 2:10871-7. [PMID: 21690376 DOI: 10.1073/pnas.1100299108] [Citation(s) in RCA: 183] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The evolution of drug-resistant pathogens is a major challenge for 21st century medicine. Drug use practices vigorously advocated as resistance management tools by professional bodies, public health agencies, and medical schools represent some of humankind's largest attempts to manage evolution. It is our contention that these practices have poor theoretical and empirical justification for a broad spectrum of diseases. For instance, rapid elimination of pathogens can reduce the probability that de novo resistance mutations occur. This idea often motivates the medical orthodoxy that patients should complete drug courses even when they no longer feel sick. Yet "radical pathogen cure" maximizes the evolutionary advantage of any resistant pathogens that are present. It could promote the very evolution it is intended to retard. The guiding principle should be to impose no more selection than is absolutely necessary. We illustrate these arguments in the context of malaria; they likely apply to a wide range of infections as well as cancer and public health insecticides. Intuition is unreliable even in simple evolutionary contexts; in a social milieu where in-host competition can radically alter the fitness costs and benefits of resistance, expert opinion will be insufficient. An evidence-based approach to resistance management is required.
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26
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Prevalence, diversity, and interaction patterns of avian haemosporidians in a four-year study of blackcaps in a migratory divide. Parasitology 2011; 138:824-35. [PMID: 21518466 DOI: 10.1017/s0031182011000515] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Migratory birds contribute to the movement of avian parasites between distant locations, thereby influencing parasite distribution and ecology. Here we analyse the prevalence, diversity and interaction patterns of Haemosporida parasites infecting Blackcap (Sylvia atricapilla) populations in a recently established migratory divide of southwestern Germany across 4 years. We hypothesize that the temporal and spatial isolation provided by 2 sympatric Blackcap breeding populations (migratory divide) might modify ecological interactions and thus create differences in the structure of the parasite community according to migratory route. We used a fragment of the mitochondrial DNA cytochrome b gene to determine haemosporidian haplotypes. We detected an overall infection prevalence of 70.3% (348 out of 495 blackcaps sampled from 2006 to 2009), and prevalence rates were significantly different among years and seasons. We observed a total of 27 parasite haplotypes infecting blackcaps, from them 6 new rare Haemoproteus haplotypes were found in 2 mixed infections. H. parabelopolskyi haplotypes SYAT01 (35.7%) and SYAT02 (20.8%) comprised most of the infections. An association analysis suggests that SYAT01 and SYAT02 are interacting negatively, implying that they are either competing directly for host resources, or indirectly by eliciting a cross-immune response. Molecular data show no clear difference between the parasite communities infecting blackcaps with different migratory routes, despite some temporal and spatial isolation between the two sympatric blackcap populations.
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27
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Ford AF, Schall JJ. Relative clonal proportions over time in mixed-genotype infections of the lizard malaria parasite Plasmodium mexicanum. Int J Parasitol 2011; 41:731-8. [PMID: 21396372 DOI: 10.1016/j.ijpara.2011.01.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2010] [Revised: 01/20/2011] [Accepted: 01/25/2011] [Indexed: 11/15/2022]
Abstract
Vertebrate hosts of malaria parasites (Plasmodium) often harbour two or more genetically distinct clones of a single species, and interaction among these co-existing clones can play an important role in Plasmodium biology. However, how relative clonal proportions vary over time in a host is still poorly known. Experimental mixed-clone infections of the lizard malaria parasite, Plasmodium mexicanum, were followed in its natural host, the western fence lizard using microsatellite markers to determine the relative proportions of two to five co-existing clones over time (2-3 months). Results for two markers, and two PCR primer pairs for one of those, matched very closely, supporting the efficacy of the method. Of the 54 infections, 67% displayed stable relative clonal proportions, with the others showing a shift in proportions, usually with one clone outpacing the others. Infections with rapidly increasing or slowly increasing parasitemia were stable, showing that all clones within these infections reproduced at the same rapid or slow rate. Replicate infections containing the same clones did not always reveal the same growth rate, final parasitemia or dominant clone; thus there was no clone effect for these life history measures. The rate of increase in parasitemia was not associated with stable versus unstable relative proportions, but infections with four to five clones were more likely to be unstable than those with two to three clones. This rare look into events in genetically complex Plasmodium infections suggests that parasite clones may be interacting in complex and unexpected ways.
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Affiliation(s)
- Alice Flynn Ford
- Department of Biology, University of Vermont, Burlington, VT 05405, USA
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O'Donnell AJ, Schneider P, McWatters HG, Reece SE. Fitness costs of disrupting circadian rhythms in malaria parasites. Proc Biol Sci 2011; 278:2429-36. [PMID: 21208950 PMCID: PMC3125626 DOI: 10.1098/rspb.2010.2457] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Circadian biology assumes that biological rhythms maximize fitness by enabling organisms to coordinate with their environment. Despite circadian clocks being such a widespread phenomenon, demonstrating the fitness benefits of temporal coordination is challenging and such studies are rare. Here, we tested the consequences--for parasites--of being temporally mismatched to host circadian rhythms using the rodent malaria parasite, Plasmodium chabaudi. The cyclical nature of malaria infections is well known, as the cell cycles across parasite species last a multiple of approximately 24 h, but the evolutionary explanations for periodicity are poorly understood. We demonstrate that perturbation of parasite rhythms results in a twofold cost to the production of replicating and transmission stages. Thus, synchronization with host rhythms influences in-host survival and between-host transmission potential, revealing a role for circadian rhythms in the evolution of host-parasite interactions. More generally, our results provide a demonstration of the adaptive value of circadian rhythms and the utility of using an evolutionary framework to understand parasite traits.
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Affiliation(s)
- Aidan J O'Donnell
- Institute of Evolution, Institute of Immunology and Infection Research, University of Edinburgh, Edinburgh EH9 3JT, UK
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29
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Choisy M, de Roode J. Mixed Infections and the Evolution of Virulence: Effects of Resource Competition, Parasite Plasticity, and Impaired Host Immunity. Am Nat 2010; 175:E105-18. [DOI: 10.1086/651587] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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30
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Leung TLF, Keeney DB, Poulin R. Genetics, intensity-dependence, and host manipulation in the trematodeCurtuteria australis: following the strategies of others? OIKOS 2010. [DOI: 10.1111/j.1600-0706.2009.17840.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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31
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Balmer O, Stearns SC, Schötzau A, Brun R. Intraspecific competition between co-infecting parasite strains enhances host survival in African trypanosomes. Ecology 2009; 90:3367-78. [DOI: 10.1890/08-2291.1] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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32
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Fox JW, Rauch G. Partitioning the mechanisms by which genetic diversity of parasite infections affects total parasite load. OIKOS 2009. [DOI: 10.1111/j.1600-0706.2009.17547.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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33
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Vardo-Zalik AM. Clonal diversity of a malaria parasite, Plasmodium mexicanum, and its transmission success from its vertebrate-to-insect host. Int J Parasitol 2009; 39:1573-9. [PMID: 19523471 DOI: 10.1016/j.ijpara.2009.05.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 05/13/2009] [Accepted: 05/15/2009] [Indexed: 11/18/2022]
Abstract
Infections of the lizard malaria parasite Plasmodium mexicanum are often genetically complex within their fence lizard host (Sceloporus occidentalis) harbouring two or more clones of parasite. The role of clonal diversity in transmission success was studied for P. mexicanum by feeding its sandfly vectors (Lutzomyia vexator and Lutzomyia stewarti) on experimentally infected lizards. Experimental infections consisted of one, two, three or more clones, assessed using three microsatellite markers. After 5days, vectors were dissected to assess infection status, oocyst burden and genetic composition of the oocysts. A high proportion (92%) of sandflies became infected and carried high oocyst burdens (mean of 56 oocysts) with no influence of clonal diversity on these two measures of transmission success. Gametocytemia was positively correlated with transmission success and the more common vector (L. vexator) developed more oocysts on midguts. A high proportion ( approximately 74%) of all alleles detected in the lizard blood was found in infected vectors. The relative proportion of clones within mixed infections, determined by peak heights on pherograms produced by the genetic analyser instrument, was very similar for the lizard's blood and infections in the vectors. These results demonstrate that P. mexicanum achieves high transmission success, with most clones making the transition from vertebrate-to-insect host, and thus explains in part the high genetic diversity of the parasite among all hosts at the study site.
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Affiliation(s)
- A M Vardo-Zalik
- Program in Public Health, College of Health Sciences, University of California at Irvine, Room 3501 Hewitt Hall, Irvine, CA 92697-4050, USA.
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Vardo-Zalik AM, Schall JJ. Clonal diversity alters the infection dynamics of a malaria parasite (Plasmodium mexicanum) in its vertebrate host. Ecology 2009; 90:529-36. [PMID: 19323236 DOI: 10.1890/07-1866.1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Ecological and evolutionary theory predicts that genetic diversity of microparasites within infected hosts will influence the parasite replication rate, parasitemia, transmission strategy, and virulence. We manipulated clonal diversity (number of genotypes) of the malaria parasite, Plasmodium mexicanum, in its natural lizard host and measured important features of the infection dynamics, the first such study for any natural Plasmodium-host association. Hosts harboring either a single P. mexicanum clone or various combinations of clones (scored via three microsatellite markers) were established. Production of asexually replicating stages (meronts) and maximal meront parasitemia did not differ by clonal diversity, nor did timing of first production of transmission stages (gametocytes). However, mean rate of gametocyte increase and maximal gametocyte parasitemia were greater for hosts with mixed-clone infections. Characteristics of infections were more variable in hosts with mixed-clone infections than with single-clone infections except for first production of gametocytes. One or more of the parasite reproductive traits were extreme in 20 of 52 hosts with mixed-clone infections. This was not associated with specific clones, but diversity itself. The overall pattern from studies of clonal diversity for human, rodent, and now reptile malaria parasites confirms that the genetic diversity of infections in the vertebrate host is of central importance for the ecology of Plasmodium.
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Affiliation(s)
- Anne M Vardo-Zalik
- Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.
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35
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Reece SE, Ramiro RS, Nussey DH. Plastic parasites: sophisticated strategies for survival and reproduction? Evol Appl 2009; 2:11-23. [PMID: 20305703 PMCID: PMC2836026 DOI: 10.1111/j.1752-4571.2008.00060.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Accepted: 11/26/2008] [Indexed: 11/28/2022] Open
Abstract
Adaptive phenotypic plasticity in life history traits, behaviours, and strategies is ubiquitous in biological systems. It is driven by variation in selection pressures across environmental gradients and operates under constraints imposed by trade-offs. Phenotypic plasticity has been thoroughly documented for multicellular taxa, such as insects, birds and mammals, and in many cases the underlying selective pressures are well understood. Whilst unicellular parasites face many of the same selective pressures and trade-offs, plasticity in their phenotypic traits has been largely overlooked and remains poorly understood. Here, we demonstrate that evolutionary theory, developed to explain variation observed in the life-history traits of multicellular organisms, can be applied to parasites. Though our message is general - we can expect the life-histories of all parasites to have evolved phenotypic plasticity - we focus our discussion on malaria parasites. We use an evolutionary framework to explain the trade-offs that parasites face and how plasticity in their life history traits will be expressed according to changes in their in-host environment. Testing whether variation in parasites traits is adaptive will provide new and fundamental insights into the basic biology of parasites, their epidemiology and the processes of disease during individual infections.
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Clonal diversity within infections and the virulence of a malaria parasite, Plasmodium mexicanum. Parasitology 2008; 135:1363-72. [PMID: 18937882 DOI: 10.1017/s0031182008004964] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Both verbal and mathematical models of parasite virulence predict that genetic diversity of microparasite infections will influence the level of costs suffered by the host. We tested this idea by manipulating the number of co-existing clones of Plasmodium mexicanum in its natural vertebrate host, the fence lizard Sceloporus occidentalis. We established replicate infections of P. mexicanum made up of 1, 2, 3, or >3 clones (scored using 3 microsatellite loci) to observe the influence of clone number on several measures of parasite virulence. Clonal diversity did not affect body growth or production of immature erythrocytes. Blood haemoglobin concentration was highest for the most genetically complex infections (equal to that of non-infected lizards), and blood glucose levels and rate of blood clotting was highest for the most diverse infections (with greater glucose and more rapid clotting than non-infected animals). Neither specific clones nor parasitaemia were associated with virulence. In this first experiment that manipulated the clonal diversity of a natural Plasmodium-host system, the cost of infection with 1 or 2 clones of P. mexicanum was similar to that previously reported for infected lizards, but the most complex infections had either no cost or could be beneficial for the host.
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Mideo N, Barclay VC, Chan BHK, Savill NJ, Read AF, Day T. Understanding and predicting strain-specific patterns of pathogenesis in the rodent malaria Plasmodium chabaudi. Am Nat 2008; 172:214-38. [PMID: 18834302 DOI: 10.1086/591684] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Despite considerable success elucidating important immunological and resource-based mechanisms that control the dynamics of infection in some diseases, little is known about how differences in these mechanisms result in strain differences in patterns of pathogenesis. Using a combination of data and theory, we disentangle the role of ecological factors (e.g., resource abundance) in the dynamics of pathogenesis for the malaria species Plasmodium chabaudi in CD4+ T cell-depleted mice. We build a series of nested models to systematically test a number of potential regulatory mechanisms and determine the "best" model using statistical techniques. The best-fit model is further tested using an independent data set from mixed-clone competition experiments. We find that parasites preferentially invade older red blood cells even when they are more fecund in younger reticulocytes and that inoculum size has a strong effect on burst size in reticulocytes. Importantly, the results suggest that strain-specific differences in virulence arise from differences in red blood cell age-specific invasion rates and burst sizes, since these are lower for the less virulent strain, as well as from differences in levels of erythropoesis induced by each strain. Our analyses highlight the importance of model selection and validation for revealing new biological insights.
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Affiliation(s)
- Nicole Mideo
- Department of Biology, Queen's University, Kingston, Ontario K7L3N6,
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38
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Barclay VC, Råberg L, Chan BHK, Brown S, Gray D, Read AF. CD4+T cells do not mediate within-host competition between genetically diverse malaria parasites. Proc Biol Sci 2008; 275:1171-9. [PMID: 18292054 PMCID: PMC2373868 DOI: 10.1098/rspb.2007.1713] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Ecological interactions between microparasite populations in the same host are an important source of selection on pathogen traits such as virulence and drug resistance. In the rodent malaria model Plasmodium chabaudi in laboratory mice, parasites that are more virulent can competitively suppress less virulent parasites in mixed infections. There is evidence that some of this suppression is due to immune-mediated apparent competition, where an immune response elicited by one parasite population suppress the population density of another. This raises the question whether enhanced immunity following vaccination would intensify competitive interactions, thus strengthening selection for virulence in Plasmodium populations. Using the P. chabaudi model, we studied mixed infections of virulent and avirulent genotypes in CD4+T cell-depleted mice. Enhanced efficacy of CD4+T cell-dependent responses is the aim of several candidate malaria vaccines. We hypothesized that if immune-mediated interactions were involved in competition, removal of the CD4+T cells would alleviate competitive suppression of the avirulent parasite. Instead, we found no alleviation of competition in the acute phase, and significant enhancement of competitive suppression after parasite densities had peaked. Thus, the host immune response may actually be alleviating other forms of competition, such as that over red blood cells. Our results suggest that the CD4+-dependent immune response, and mechanisms that act to enhance it such as vaccination, may not have the undesirable affect of exacerbating within-host competition and hence the strength of this source of selection for virulence.
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39
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Grech K, Chan BHK, Anders RF, Read AF. THE IMPACT OF IMMUNIZATION ON COMPETITION WITHINPLASMODIUMINFECTIONS. Evolution 2008; 62:2359-71. [DOI: 10.1111/j.1558-5646.2008.00438.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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40
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Alizon S. Decreased overall virulence in coinfected hosts leads to the persistence of virulent parasites. Am Nat 2008; 172:E67-79. [PMID: 18582168 DOI: 10.1086/588077] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Multiple infections are known to affect virulence evolution. Some studies even show that coinfections may decrease the overall virulence (the disease-induced mortality of a coinfected host). Yet, epidemiological studies tend to overlook the overall virulence, and within-host models tend to ignore epidemiological processes. Here, I develop an epidemiological model where overall virulence is an explicit function of the virulence of the coinfecting strains. I show that in most cases, a unique strain is evolutionarily stable (in accordance with the model I use here). However, when the overall virulence is lower than the virulence of each of the coinfecting strains (i.e., when coinfections decrease virulence), the evolutionary equilibrium may be invaded by highly virulent strains, leading to the coexistence of two strains on an evolutionary timescale. This model has theoretical and experimental implications: it underlines the importance of overall virulence and of epidemiological feedbacks on virulence evolution.
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Affiliation(s)
- Samuel Alizon
- Department of Mathematics and Statistics, Queen's University, Jeffery Hall, Kingston, Ontario K7L 3N6, Canada.
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MARZAL A, BENSCH S, REVIRIEGO M, BALBONTIN J, DE LOPE F. Effects of malaria double infection in birds: one plus one is not two. J Evol Biol 2008; 21:979-87. [DOI: 10.1111/j.1420-9101.2008.01545.x] [Citation(s) in RCA: 181] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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42
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Wargo AR, de Roode JC, Huijben S, Drew DR, Read AF. Transmission stage investment of malaria parasites in response to in-host competition. Proc Biol Sci 2007; 274:2629-38. [PMID: 17711832 PMCID: PMC1975767 DOI: 10.1098/rspb.2007.0873] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Conspecific competition occurs in a multitude of organisms, particularly in parasites, where several clones are commonly sharing limited resources inside their host. In theory, increased or decreased transmission investment might maximize parasite fitness in the face of competition, but, to our knowledge, this has not been tested experimentally. We developed and used a clone-specific, stage-specific, quantitative PCR protocol to quantify Plasmodium chabaudi replication and transmission stage densities in mixed-clone infections. We co-infected mice from two strains with an avirulent and virulent parasite clone and found competitive suppression of in-host (blood-stage) parasite densities and generally corresponding reductions in transmission stage production, with the virulent clone obtaining overall competitive superiority. In response to competitive suppression, there was little evidence of any alteration in transmission stage investment, apart from a small reduction by one of the two clones in one of the two host strains. This alteration did not result in a competitive advantage, although it might have reduced the disadvantage. This study supports much of the current literature, which predicts that conspecific in-host competition will result in a competitive advantage and positive selection for virulent clones and thus the evolution of higher virulence.
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Affiliation(s)
- Andrew R Wargo
- Institutes of Evolution, Immunology and Infection Research, Ashworth Laboratories, School of Biological Sciences, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK.
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Drew DR, Reece SE. Development of reverse-transcription PCR techniques to analyse the density and sex ratio of gametocytes in genetically diverse Plasmodium chabaudi infections. Mol Biochem Parasitol 2007; 156:199-209. [PMID: 17889948 PMCID: PMC3818572 DOI: 10.1016/j.molbiopara.2007.08.004] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2007] [Revised: 08/07/2007] [Accepted: 08/10/2007] [Indexed: 11/29/2022]
Abstract
We have developed cross-genotype and genotype-specific quantitative reverse-transcription PCR (qRT-PCR) assays to detect and quantify the number of parasites, transmission stages (gametocytes) and male gametocytes in blood stage Plasmodium chabaudi infections. Our cross-genotype assays are reliable, repeatable and generate counts that correlate strongly (R(2)s>90%) with counts expected from blood smears. Our genotype-specific assays can distinguish and quantify different stages of genetically distinct parasite clones (genotypes) in mixed infections and are as sensitive as our cross-genotype assays. Using these assays we show that gametocyte density and gametocyte sex ratios vary during infections for two genetically distinct parasite lines (genotypes) and present the first data to reveal how sex ratio is affected when each genotype experiences competition in mixed-genotype infections. Successful infection of mosquito vectors depends on both gametocyte density and their sex ratio and we discuss the implications of competition in genetically diverse infections for transmission success.
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Affiliation(s)
| | - Sarah E. Reece
- Corresponding author. Tel.: +44 131 650 5547; fax: +44 131 650 6564.
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44
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Kurtz J, Hammerschmidt K. Resistance against heterogeneous sequential infections: experimental studies with a tapeworm and its copepod host. J Helminthol 2007; 80:199-206. [PMID: 16768863 DOI: 10.1079/joh2006349] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Parasite heterogeneity is thought to be an important factor influencing the likelihood and the dynamics of infection. Previous studies have demonstrated that simultaneous exposure of hosts to a heterogeneous mixture of parasites might increase infection success. Here this view is extended towards the effect of parasite heterogeneity on subsequent infections. Using a system of the tapeworm Schistocephalus solidus and its copepod intermediate host, heterogeneity of the tapeworm surface carbohydrates is investigated, i.e. structures that are potentially recognized by the invertebrate host's immune system. With lectin labelling, a significant proportion of variation in surface carbohydrates is related to differences in worm sibships (i.e. families). Tapeworm sibships were used for experimental exposure of copepods to either homogeneous combinations of tapeworm larvae, i.e. worms derived from the same sibship or heterogeneous mixtures of larvae, and copepods were subsequently challenged with an unrelated larva to study re-infection. Contrary to expectation, neither an effect of parasite heterogeneity on the current infection, nor on re-infection were found. The effect of parasitic heterogeneity on host immunity is therefore complex, potentially involving increased cross-protection on the one hand, with higher costs of raising a more heterogeneous immune response on the other.
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Affiliation(s)
- J Kurtz
- Department of Evolutionary Ecology, Max Planck Institute of Limnology, August-Thienemann-Str. 2, 24306 Plön, Germany.
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45
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Wedekind C, Walker M, Little TJ. The separate and combined effects of MHC genotype, parasite clone, and host gender on the course of malaria in mice. BMC Genet 2006; 7:55. [PMID: 17118203 PMCID: PMC1664581 DOI: 10.1186/1471-2156-7-55] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Accepted: 11/21/2006] [Indexed: 11/25/2022] Open
Abstract
Background The link between host MHC (major histocompatibility complex) genotype and malaria is largely based on correlative data with little or no experimental control of potential confounding factors. We used an experimental mouse model to test for main effects of MHC-haplotypes, MHC heterozygosity, and MHC × parasite clone interactions. We experimentally infected MHC-congenic mice (F2 segregants, homo- and heterozygotes, males and females) with one of two clones of Plasmodium chabaudi and recorded disease progression. Results We found that MHC haplotype and parasite clone each have a significant influence on the course of the disease, but there was no significant host genotype by parasite genotype interaction. We found no evidence for overdominance nor any other sort of heterozygote advantage or disadvantage. Conclusion When tested under experimental conditions, variation in the MHC can significantly influence the course of malaria. However, MHC heterozygote advantage through overdominance or dominance of resistance cannot be assumed in the case of single-strain infections. Future studies might focus on the interaction between MHC heterozygosity and multiple-clone infections.
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Affiliation(s)
- Claus Wedekind
- Department of Ecology and Evolution, University of Lausanne, Biophore, 1015 Lausanne, Switzerland
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, Scotland, UK
| | - Mirjam Walker
- Institute of Zoo and Wildlife Biology, 10252 Berlin, Germany
- Natural History Museum Bern, 3005 Bern, Switzerland
- ZLB Behring AG, Wankdorfstr. 10, 3022 Bern, Switzerland
| | - Tom J Little
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, Scotland, UK
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Abstract
Parasite virulence, i.e. the damage done to the host, may be a by-product of the parasite's effort to maximize its fitness. Accordingly, several life-history trade-offs may explain interspecific differences in virulence, but such constraints remain little tested in an evolutionary context. In this phylogenetic study of primate malarias, I investigated the relationship between virulence and other parasite life-history traits. I used peak parasitaemia as a proxy for virulence, because it reflected parasite reproductive success and parasite-induced mortality. Peak parasitaemia was higher in specialist than in generalist species, even when confounding life-history traits were controlled. While there was a significant phylogenetic relationship between the number of competitors per host and host specialization, peak parasitaemia was unrelated to within-host competition. Therefore, the key evolutionary factor that favours virulence is host specialization, and the evolutionary success of virulent parasites, such as Plasmodium falciparum, may be better understood when the trade-off in virulence between different hosts is considered. Such phylogenetic results may help us design better protection programmes against malaria.
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Affiliation(s)
- László Zsolt Garamszegi
- Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
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47
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Bell AS, Roode JC, Sim D, Read AF. WITHIN-HOST COMPETITION IN GENETICALLY DIVERSE MALARIA INFECTIONS: PARASITE VIRULENCE AND COMPETITIVE SUCCESS. Evolution 2006. [DOI: 10.1111/j.0014-3820.2006.tb01215.x] [Citation(s) in RCA: 185] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Raberg L, de Roode JC, Bell AS, Stamou P, Gray D, Read AF. The Role of Immune‐Mediated Apparent Competition in Genetically Diverse Malaria Infections. Am Nat 2006; 168:41-53. [PMID: 16874614 DOI: 10.1086/505160] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2005] [Accepted: 03/17/2006] [Indexed: 11/03/2022]
Abstract
Competitive interactions between coinfecting genotypes of the same pathogen can impose selection on virulence, but the direction of this selection depends on the mechanisms behind the interactions. Here, we investigate how host immune responses contribute to competition between clones in mixed infections of the rodent malaria parasite Plasmodium chabaudi. We studied single and mixed infections of a virulent and an avirulent clone and compared the extent of competition in immunodeficient and immunocompetent mice (nude mice and T cell-reconstituted nude mice, respectively). In immunocompetent mice, the avirulent clone suffered more from competition than did the virulent clone. The competitive suppression of the avirulent clone was alleviated in immunodeficient mice. Moreover, the relative density of the avirulent clone in mixed infections was higher in immunodeficient than in immunocompetent mice. We conclude that immune-mediated interactions contributed to competitive suppression of the avirulent clone, although other mechanisms, presumably competition for resources such as red blood cells, must also be important. Because only the avirulent clone suffered from immune-mediated competition, this mechanism should contribute to selection for increased virulence in mixed infections in this host-parasite system. As far as we are aware, this is the first direct experimental evidence of immune-mediated apparent competition in any host-parasite system.
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Affiliation(s)
- Lars Raberg
- Institutes of Evolution, Immunology, and Infection Research, School of Biological Sciences, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JT, Scotland, United Kingdom.
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Abstract
The question why different host individuals within a population differ with respect to infection resistance is of fundamental importance for understanding the mechanisms of parasite-mediated selection. We addressed this question by infecting wild-caught captive male greenfinches with intestinal coccidian parasites originating either from single or multiple hosts. Birds with naturally low pre-experimental infection retained their low infection status also after reinfection with multiple strains, indicating that natural infection intensities confer information about the phenotypic ability of individuals to resist novel strains. Exposure to novel strains did not result in protective immunity against the subsequent infection with the same strains. Infection with multiple strains resulted in greater virulence than single-strain infection, indicating that parasites originating from different host individuals are genetically diverse. Our experiment thus demonstrates the validity of important but rarely tested assumptions of many models of parasite-mediated selection in a wild bird species and its common parasite.
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Affiliation(s)
- P Hõrak
- Institute of Zoology and Hydrobiology, Tartu University, Tartu, Estonia.
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50
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Bell AS, de Roode JC, Sim D, Read AF. WITHIN-HOST COMPETITION IN GENETICALLY DIVERSE MALARIA INFECTIONS: PARASITE VIRULENCE AND COMPETITIVE SUCCESS. Evolution 2006. [DOI: 10.1554/05-611.1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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