1
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Pak D, Kamiya T, Greischar MA. Proliferation in malaria parasites: how resource limitation can prevent evolution of greater virulence. Evolution 2024:qpae057. [PMID: 38581661 DOI: 10.1093/evolut/qpae057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Indexed: 04/08/2024]
Abstract
For parasites, robust proliferation within hosts is crucial for establishing the infection and creating opportu- nities for onward transmission. While faster proliferation enhances transmission rates, it is often assumed to curtail transmission duration by killing the host (virulence), a tradeoff constraining parasite evolution. Yet in many diseases, including malaria, the preponderance of infections with mild or absent symptoms suggests that host mortality is not a sufficient constraint, raising the question of what restrains evolution towards faster proliferation. In malaria infections, the maximum rate of proliferation is determined by the burst size, the number of daughter parasites produced per infected red blood cell. Larger burst sizes should expand the pool of infected red blood cells that can be used to produce the specialized transmission forms needed to infect mosquitoes. We use a within-host model parameterized for rodent malaria parasites (Plasmodium chabaudi ) to project the transmission consequences of burst size, focusing on initial acute infection where re- source limitation and risk of host mortality are greatest. We find that resource limitation restricts evolution towards higher burst sizes below the level predicted by host mortality alone. Our results suggest resource lim- itation could represent a more general constraint than virulence-transmission tradeoffs, preventing evolution towards faster proliferation.
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Affiliation(s)
- Damie Pak
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Tsukushi Kamiya
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, Paris, 75001, France
- HRB Clinical Research Facility, University of Galway, Ireland
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
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2
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Greischar MA, Childs LM. Extraordinary parasite multiplication rates in human malaria infections. Trends Parasitol 2023; 39:626-637. [PMID: 37336700 DOI: 10.1016/j.pt.2023.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 05/18/2023] [Accepted: 05/19/2023] [Indexed: 06/21/2023]
Abstract
For pathogenic organisms, faster rates of multiplication promote transmission success, the potential to harm hosts, and the evolution of drug resistance. Parasite multiplication rates (PMRs) are often quantified in malaria infections, given the relative ease of sampling. Using modern and historical human infection data, we show that established methods return extraordinarily - and implausibly - large PMRs. We illustrate how inflated PMRs arise from two facets of malaria biology that are far from unique: (i) some developmental ages are easier to sample than others; (ii) the distribution of developmental ages changes over the course of infection. The difficulty of accurately quantifying PMRs demonstrates a need for robust methods and a subsequent re-evaluation of what is known even in the well-studied system of malaria.
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Affiliation(s)
- Megan A Greischar
- Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY, USA.
| | - Lauren M Childs
- Department of Mathematics, Virginia Tech, Blacksburg, VA, USA
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3
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Greischar MA. Modern Epidemics: From the Spanish Flu to COVID-19. Emerg Infect Dis 2021. [DOI: 10.3201/eid2712.1312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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4
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O'Donnell AJ, Greischar MA, Reece SE. Mistimed malaria parasites re-synchronize with host feeding-fasting rhythms by shortening the duration of intra-erythrocytic development. Parasite Immunol 2021; 44:e12898. [PMID: 34778983 PMCID: PMC9285586 DOI: 10.1111/pim.12898] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 11/08/2021] [Accepted: 11/09/2021] [Indexed: 12/24/2022]
Abstract
AIMS Malaria parasites exhibit daily rhythms in the intra-erythrocytic development cycle (IDC) that underpins asexual replication in the blood. The IDC schedule is aligned with the timing of host feeding-fasting rhythms. When the IDC schedule is perturbed to become mismatched to host rhythms, it readily reschedules but it is not known how. METHODS We intensively follow four groups of infections that have different temporal alignments between host rhythms and the IDC schedule for 10 days, before and after the peak in asexual densities. We compare how the duration, synchrony and timing of the IDC differs between parasites in control infections and those forced to reschedule by 12 hours and ask whether the density of parasites affects the rescheduling process. RESULTS AND CONCLUSIONS Our experiments reveal parasites shorten the IDC duration by 2-3 hours to become realigned to host feeding-fasting rhythms with 5-6 days, in a density-independent manner. Furthermore, parasites are able to reschedule without significant fitness costs for them or their hosts. Understanding the extent of, and limits on, plasticity in the IDC schedule may reveal targets for novel interventions, such as drugs to disrupt IDC regulation and preventing IDC dormancy conferring tolerance to existing drugs.
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Affiliation(s)
- Aidan J O'Donnell
- Institute of Evolutionary Biology, and Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, USA
| | - Sarah E Reece
- Institute of Evolutionary Biology, and Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
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5
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Kamiya T, Davis NM, Greischar MA, Schneider D, Mideo N. Linking functional and molecular mechanisms of host resilience to malaria infection. eLife 2021; 10:e65846. [PMID: 34636723 PMCID: PMC8510579 DOI: 10.7554/elife.65846] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Accepted: 08/16/2021] [Indexed: 12/30/2022] Open
Abstract
It remains challenging to understand why some hosts suffer severe illnesses, while others are unscathed by the same infection. We fitted a mathematical model to longitudinal measurements of parasite and red blood cell density in murine hosts from diverse genetic backgrounds to identify aspects of within-host interactions that explain variation in host resilience and survival during acute malaria infection. Among eight mouse strains that collectively span 90% of the common genetic diversity of laboratory mice, we found that high host mortality was associated with either weak parasite clearance, or a strong, yet imprecise response that inadvertently removes uninfected cells in excess. Subsequent cross-sectional cytokine assays revealed that the two distinct functional mechanisms of poor survival were underpinned by low expression of either pro- or anti-inflammatory cytokines, respectively. By combining mathematical modelling and molecular immunology assays, our study uncovered proximate mechanisms of diverse infection outcomes across multiple host strains and biological scales.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology and Evolutionary Biology, University of TorontoTorontoCanada
| | - Nicole M Davis
- Department of Microbiology and Immunology, Stanford UniversityStanfordUnited States
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, Cornell UniversityIthacaUnited States
| | - David Schneider
- Department of Microbiology and Immunology, Stanford UniversityStanfordUnited States
| | - Nicole Mideo
- Department of Ecology and Evolutionary Biology, University of TorontoTorontoCanada
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6
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Peters MAE, Greischar MA, Mideo N. Challenges in forming inferences from limited data: a case study of malaria parasite maturation. J R Soc Interface 2021; 18:20210065. [PMID: 33906391 DOI: 10.1098/rsif.2021.0065] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Inferring biological processes from population dynamics is a common challenge in ecology, particularly when faced with incomplete data. This challenge extends to inferring parasite traits from within-host infection dynamics. We focus on rodent malaria infections (Plasmodium berghei), a system for which previous work inferred an immune-mediated extension in the length of the parasite development cycle within red blood cells. By developing a system of delay-differential equations to describe within-host infection dynamics and simulating data, we demonstrate the potential to obtain biased estimates of parasite (and host) traits when key biological processes are not considered. Despite generating infection dynamics using a fixed parasite developmental cycle length, we find that known sources of measurement bias in parasite stage and abundance data can affect estimates of parasite developmental duration, with stage misclassification driving inferences about extended cycle length. We discuss alternative protocols and statistical methods that can mitigate such misestimation.
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Affiliation(s)
- Madeline A E Peters
- Department of Ecology and Evolutionary Biology, The University of Toronto, Toronto Ontario, Canada
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
| | - Nicole Mideo
- Department of Ecology and Evolutionary Biology, The University of Toronto, Toronto Ontario, Canada
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7
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Kamiya T, Greischar MA, Schneider DS, Mideo N. Uncovering drivers of dose-dependence and individual variation in malaria infection outcomes. PLoS Comput Biol 2020; 16:e1008211. [PMID: 33031367 PMCID: PMC7544130 DOI: 10.1371/journal.pcbi.1008211] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 07/31/2020] [Indexed: 01/01/2023] Open
Abstract
To understand why some hosts get sicker than others from the same type of infection, it is essential to explain how key processes, such as host responses to infection and parasite growth, are influenced by various biotic and abiotic factors. In many disease systems, the initial infection dose impacts host morbidity and mortality. To explore drivers of dose-dependence and individual variation in infection outcomes, we devised a mathematical model of malaria infection that allowed host and parasite traits to be linear functions (reaction norms) of the initial dose. We fitted the model, using a hierarchical Bayesian approach, to experimental time-series data of acute Plasmodium chabaudi infection across doses spanning seven orders of magnitude. We found evidence for both dose-dependent facilitation and debilitation of host responses. Most importantly, increasing dose reduced the strength of activation of indiscriminate host clearance of red blood cells while increasing the half-life of that response, leading to the maximal response at an intermediate dose. We also explored the causes of diverse infection outcomes across replicate mice receiving the same dose. Besides random noise in the injected dose, we found variation in peak parasite load was due to unobserved individual variation in host responses to clear infected cells. Individual variation in anaemia was likely driven by random variation in parasite burst size, which is linked to the rate of host cells lost to malaria infection. General host vigour in the absence of infection was also correlated with host health during malaria infection. Our work demonstrates that the reaction norm approach provides a useful quantitative framework for examining the impact of a continuous external factor on within-host infection processes.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
| | - Megan A. Greischar
- Department of Ecology Evolutionary Biology, Cornell University, United States of America
| | - David S. Schneider
- Program in Immunology, Stanford University, Stanford, California, United States of America
- Department of Microbiology and Immunology, Stanford University, Stanford, California, United States of America
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
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8
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Greischar MA, Alexander HK, Bashey F, Bento AI, Bhattacharya A, Bushman M, Childs LM, Daversa DR, Day T, Faust CL, Gallagher ME, Gandon S, Glidden CK, Halliday FW, Hanley KA, Kamiya T, Read AF, Schwabl P, Sweeny AR, Tate AT, Thompson RN, Wale N, Wearing HJ, Yeh PJ, Mideo N. Evolutionary consequences of feedbacks between within-host competition and disease control. Evol Med Public Health 2020; 2020:30-34. [PMID: 32099654 PMCID: PMC7027713 DOI: 10.1093/emph/eoaa004] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 01/21/2020] [Accepted: 01/22/2020] [Indexed: 11/14/2022]
Abstract
Lay Summary: Competition often occurs among diverse parasites within a single host, but control efforts could change its strength. We examined how the interplay between competition and control could shape the evolution of parasite traits like drug resistance and disease severity.
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Affiliation(s)
- Megan A Greischar
- Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks St., Toronto, ON M5S 3B2, Canada
| | - Helen K Alexander
- Department of Zoology, University of Oxford, Zoology Research and Administration Building, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Farrah Bashey
- Department of Biology, Indiana University, 1001 E. 3rd St., Bloomington, IN 47405, USA
| | - Ana I Bento
- Odum School of Ecology and the Center for the Ecology of Infectious Diseases, University of Georgia, 140 E Green St., Athens, GA 30602, USA
| | - Amrita Bhattacharya
- Department of Biology, Indiana University, 1001 E. 3rd St., Bloomington, IN 47405, USA
| | - Mary Bushman
- Department of Biology, Emory University, Atlanta, GA 30322, USA
| | - Lauren M Childs
- Department of Mathematics, McBryde Hall, Virginia Tech, Blacksburg, VA 24061, USA
| | - David R Daversa
- Institute of Integrative Biology, University of Liverpool, Liverpool, L69 3BX, UK.,Institute of Zoology, Zoological Society of London, Regent's Park, NW1 4RY, UK
| | - Troy Day
- Departments of Mathematics & Biology, Jeffery Hall, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Christina L Faust
- Institute of Biodiversity, Animal Health & Comparative Medicine, University of Glasgow, Glasgow G12 8QQ, UK
| | | | - Sylvain Gandon
- CEFE UMR 5175, CNRS - Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, 1919, Route de Mende, 34293 Montpellier Cedex 5, France
| | - Caroline K Glidden
- Department of Integrative Biology, Oregon State University, 3029 Cordley Hall Corvallis, OR 97331, USA
| | - Fletcher W Halliday
- Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, 8057, Switzerland
| | - Kathryn A Hanley
- Department of Biology, New Mexico State University, Foster Hall, Las Cruces, NM 88003, USA
| | - Tsukushi Kamiya
- Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks St., Toronto, ON M5S 3B2, Canada
| | - Andrew F Read
- Center for Infectious Disease Dynamics, Huck Institutes for the Life Sciences; Departments of Biology and Entomology, Pennsylvania State University, University Park, PA 16802, USA
| | - Philipp Schwabl
- Institute of Biodiversity, Animal Health & Comparative Medicine, University of Glasgow, Glasgow G12 8QQ, UK
| | - Amy R Sweeny
- Department of Zoology, University of Oxford, Zoology Research and Administration Building, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Ann T Tate
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA
| | - Robin N Thompson
- Department of Zoology, University of Oxford, Zoology Research and Administration Building, 11a Mansfield Road, Oxford OX1 3SZ, UK.,Mathematical Institute, University of Oxford, Woodstock Road, Oxford OX2 6GG, UK.,Christ Church, University of Oxford, St Aldates, Oxford OX1 1DP, UK
| | - Nina Wale
- Department of Ecology & Evolutionary Biology, University of Michigan, 1105 North University Ave, Biological Sciences Building, Ann Arbor, MI 48109, USA
| | - Helen J Wearing
- Departments of Biology and Mathematics & Statistics, The University of New Mexico, Albuquerque, NM 87131, USA
| | - Pamela J Yeh
- Department of Ecology & Evolutionary Biology, University of California, Los Angeles, 621 Charles E Young Dr South, Los Angeles, CA 90095, USA
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks St., Toronto, ON M5S 3B2, Canada
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9
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Kamiya T, Greischar MA, Wadhawan K, Gilbert B, Paaijmans K, Mideo N. Temperature-dependent variation in the extrinsic incubation period elevates the risk of vector-borne disease emergence. Epidemics 2019; 30:100382. [PMID: 32004794 DOI: 10.1016/j.epidem.2019.100382] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2019] [Revised: 11/29/2019] [Accepted: 12/01/2019] [Indexed: 12/24/2022] Open
Abstract
Identifying ecological drivers of disease transmission is central to understanding disease risks. For vector-borne diseases, temperature is a major determinant of transmission because vital parameters determining the fitness of parasites and vectors are highly temperature-sensitive, including the extrinsic incubation period required for parasites to develop within the vector. Temperature also underlies dramatic differences in the individual-level variation in the extrinsic incubation period, yet the influence of this variation in disease transmission is largely unexplored. We incorporate empirical estimates of dengue virus extrinsic incubation period and its variation across a range of temperatures into a stochastic model to examine the consequences for disease emergence. We find that such variation impacts the probability of disease emergence because exceptionally rapid, but empirically observed incubation - typically ignored by modelling only the average - increases the chance of disease emergence even at the limits of the temperature range for dengue transmission. We show that variation in the extrinsic incubation period causes the greatest proportional increase in the risk of disease emergence at cooler temperatures where the mean incubation period is long, and associated variation is large. Thus, ignoring EIP variation will likely lead to underestimation of the risk of vector-borne disease emergence in temperate climates.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada.
| | - Megan A Greischar
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
| | - Kiran Wadhawan
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
| | - Benjamin Gilbert
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
| | - Krijn Paaijmans
- Center for Evolution & Medicine, Biodesign Center for Immunotherapy, Vaccines and Virotherapy, School of Life Sciences, Arizona State University, Tempe, AZ, USA
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
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10
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Greischar MA, Beck-Johnson LM, Mideo N. Partitioning the influence of ecology across scales on parasite evolution. Evolution 2019; 73:2175-2188. [PMID: 31495911 DOI: 10.1111/evo.13840] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Accepted: 08/31/2019] [Indexed: 11/30/2022]
Abstract
Vector-borne parasites must succeed at three scales to persist: they must proliferate within a host, establish in vectors, and transmit back to hosts. Ecology outside the host undergoes dramatic seasonal and human-induced changes, but predicting parasite evolutionary responses requires integrating their success across scales. We develop a novel, data-driven model to titrate the evolutionary impact of ecology at multiple scales on human malaria parasites. We investigate how parasites invest in transmission versus proliferation, a life-history trait that influences disease severity and spread. We find that transmission investment controls the pattern of host infectiousness over the course of infection: a trade-off emerges between early and late infectiousness, and the optimal resolution of that trade-off depends on ecology outside the host. An expanding epidemic favors rapid proliferation, and can overwhelm the evolutionary influence of host recovery rates and mosquito population dynamics. If transmission investment and recovery rate are positively correlated, then ecology outside the host imposes potent selection for aggressive parasite proliferation at the expense of transmission. Any association between transmission investment and recovery represents a key unknown, one that is likely to influence whether the evolutionary consequences of interventions are beneficial or costly for human health.
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Affiliation(s)
- Megan A Greischar
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3B2, Canada
| | | | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3B2, Canada
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11
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Greischar MA, Reece SE, Savill NJ, Mideo N. The Challenge of Quantifying Synchrony in Malaria Parasites. Trends Parasitol 2019; 35:341-355. [PMID: 30952484 DOI: 10.1016/j.pt.2019.03.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 03/04/2019] [Accepted: 03/05/2019] [Indexed: 12/21/2022]
Abstract
Malaria infection is often accompanied by periodic fevers, triggered by synchronous cycles of parasite replication within the host. The degree of synchrony in parasite development influences the efficacy of drugs and immune defenses and is therefore relevant to host health and infectiousness. Synchrony is thought to vary over the course of infection and across different host-parasite genotype or species combinations, but the evolutionary significance - if any - of this diversity remains elusive. Standardized methods are lacking, but the most common metric for quantifying synchrony is the percentage of parasites in a particular developmental stage. We use a heuristic model to show that this metric is often unacceptably biased. Methodological challenges must be addressed to characterize diverse patterns of synchrony and their consequences for disease severity and spread.
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Affiliation(s)
- Megan A Greischar
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
| | - Sarah E Reece
- Institute of Evolutionary Biology and Institute of Immunology and Infection Research, University of Edinburgh, Edinburgh, UK
| | - Nicholas J Savill
- Institute of Evolutionary Biology and Institute of Immunology and Infection Research, University of Edinburgh, Edinburgh, UK
| | - Nicole Mideo
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
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12
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Francis EA, Moldowan PD, Greischar MA, Rollinson N. Anthropogenic nest sites provide warmer incubation environments than natural nest sites in a population of oviparous reptiles near their northern range limit. Oecologia 2019; 190:511-522. [PMID: 30953168 DOI: 10.1007/s00442-019-04383-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 03/12/2019] [Indexed: 11/27/2022]
Abstract
Oviposition site choice affects a host of offspring phenotypes and directly impacts maternal fitness. Recent evidence suggests that oviparous reptiles often select nest sites where the landscape has been altered by anthropogenic activity, whereas natural nest sites are less often used. We leverage a long-term study of snapping turtle (Chelydra serpentina) to identify natural nest sites and anthropogenic nest sites and to compare habitat variables among nest site types. Natural and anthropogenic nest sites did not differ in average canopy closure, distance to nearest water, substrate composition, or aspect. However, anthropogenic nest sites had less ground-level vegetation and greater soil brightness, and were 3.3 °C warmer than natural nests during incubation. We used the Schoolfield model of poikilotherm development to assess differences in development rate between natural and anthropogenic nests. Because of the difference in temperature, embryos in anthropogenic nests were predicted to have undergone nearly twice as much development as embryos in natural nests during incubation. We outline why the evolution of fast embryonic development rate cannot compensate indefinitely for the low temperature incubation regimes that become increasingly prevalent at northern range margins, thereby underlining why maternal nest site choice of relatively warm anthropogenic sites may help oviparous reptiles persist in thermally constrained environments. Future research should aim to quantify both the thermal benefits of anthropogenic nest sites, as well as associated fitness costs (e.g., increased adult mortality) to elucidate whether anthropogenic disturbance of the landscape can be an ecological trap or serve a net benefit to some reptiles in northern environments.
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Affiliation(s)
- Elizabeth Ann Francis
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
| | - Patrick D Moldowan
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Njal Rollinson
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
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13
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Birget PLG, Greischar MA, Reece SE, Mideo N. Altered life history strategies protect malaria parasites against drugs. Evol Appl 2018; 11:442-455. [PMID: 29636798 PMCID: PMC5891063 DOI: 10.1111/eva.12516] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 06/30/2017] [Indexed: 11/26/2022] Open
Abstract
Drug resistance has been reported against all antimalarial drugs, and while parasites can evolve classical resistance mechanisms (e.g., efflux pumps), it is also possible that changes in life history traits could help parasites evade the effects of treatment. The life history of malaria parasites is governed by an intrinsic resource allocation problem: specialized stages are required for transmission, but producing these stages comes at the cost of producing fewer of the forms required for within-host survival. Drug treatment, by design, alters the probability of within-host survival, and so should alter the costs and benefits of investing in transmission. Here, we use a within-host model of malaria infection to predict optimal patterns of investment in transmission in the face of different drug treatment regimes and determine the extent to which alternative patterns of investment can buffer the fitness loss due to drugs. We show that over a range of drug doses, parasites are predicted to adopt "reproductive restraint" (investing more in asexual replication and less in transmission) to maximize fitness. By doing so, parasites recoup some of the fitness loss imposed by drugs, though as may be expected, increasing dose reduces the extent to which altered patterns of transmission investment can benefit parasites. We show that adaptation to drug-treated infections could result in more virulent infections in untreated hosts. This work emphasizes that in addition to classical resistance mechanisms, drug treatment generates selection for altered parasite life history. Understanding how any shifts in life history will alter the efficacy of drugs, as well as any limitations on such shifts, is important for evaluating and predicting the consequences of drug treatment.
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Affiliation(s)
- Philip L. G. Birget
- Institutes of Evolutionary Biology, Immunology and Infection ResearchUniversity of EdinburghEdinburghUK
| | - Megan A. Greischar
- Department of Ecology & Evolutionary BiologyUniversity of TorontoTorontoONCanada
| | - Sarah E. Reece
- Institutes of Evolutionary Biology, Immunology and Infection ResearchUniversity of EdinburghEdinburghUK
| | - Nicole Mideo
- Department of Ecology & Evolutionary BiologyUniversity of TorontoTorontoONCanada
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14
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Kamiya T, Greischar MA, Mideo N. Epidemiological consequences of immune sensitisation by pre-exposure to vector saliva. PLoS Negl Trop Dis 2017; 11:e0005956. [PMID: 28991904 PMCID: PMC5648264 DOI: 10.1371/journal.pntd.0005956] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 10/19/2017] [Accepted: 09/12/2017] [Indexed: 11/25/2022] Open
Abstract
Blood-feeding arthropods—like mosquitoes, sand flies, and ticks—transmit many diseases that impose serious public health and economic burdens. When a blood-feeding arthropod bites a mammal, it injects saliva containing immunogenic compounds that facilitate feeding. Evidence from Leishmania, Plasmodium and arboviral infections suggests that the immune responses elicited by pre-exposure to arthropod saliva can alter disease progression if the host later becomes infected. Such pre-sensitisation of host immunity has been reported to both exacerbate and limit infection symptoms, depending on the system in question, with potential implications for recovery. To explore if and how immune pre-sensitisation alters the effects of vector control, we develop a general model of vector-borne disease. We show that the abundance of pre-sensitised infected hosts should increase when control efforts moderately increase vector mortality rates. If immune pre-sensitisation leads to more rapid clearance of infection, increasing vector mortality rates may achieve greater than expected disease control. However, when immune pre-sensitisation prolongs the duration of infection, e.g., through mildly symptomatic cases for which treatment is unlikely to be sought, vector control can actually increase the total number of infected hosts. The rising infections may go unnoticed unless active surveillance methods are used to detect such sub-clinical individuals, who could provide long-lasting reservoirs for transmission and suffer long-term health consequences of those sub-clinical infections. Sensitivity analysis suggests that these negative consequences could be mitigated through integrated vector management. While the effect of saliva pre-exposure on acute symptoms is well-studied for leishmaniasis, the immunological and clinical consequences are largely uncharted for other vector-parasite-host combinations. We find a large range of plausible epidemiological outcomes, positive and negative for public health, underscoring the need to quantify how immune pre-sensitisation modulates recovery and transmission rates in vector-borne diseases. Many diseases of health and economic importance are transmitted by arthropod vectors, like mosquitoes, sand flies, and ticks. When a blood-feeding arthropod bites a mammal, it injects saliva containing compounds that facilitate feeding. The immune responses elicited by previous exposure to vector saliva can alter disease severity if the host later becomes infected. Such pre-sensitisation of host immunity has been linked to either exacerbation or mitigation of symptoms in a number of disease systems. We develop a general model of vector-borne disease to examine how vector control efforts alter the frequency of immune pre-sensitisation and thus change the epidemiological impact of control. We show that the abundance of pre-sensitised infected hosts should increase when control efforts moderately increase vector mortality rates. When immune pre-sensitisation leads to longer infections—by generating sub-clinical cases for which treatment is not rapidly sought—killing vectors can lead to unexpected increases in the number of infected hosts. The rising case burden may go unnoticed unless sub-clinical individuals are tested for infection. Conversely, if immune pre-sensitisation leads to more rapid clearance of infection, increasing vector mortality rates may achieve greater than expected disease control. Our findings highlight the need to quantify how immune pre-sensitisation modulates clinical outcomes and parasite transmission in humans.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Megan A Greischar
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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Greischar MA, Mideo N, Read AF, Bjørnstad ON. Predicting optimal transmission investment in malaria parasites. Evolution 2016; 70:1542-58. [DOI: 10.1111/evo.12969] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Accepted: 05/07/2016] [Indexed: 01/07/2023]
Affiliation(s)
- Megan A. Greischar
- Center For Infectious Disease Dynamics, Departments of Entomology and Biology, The Pennsylvania State University; University Park; Pennsylvania 16802
- Department of Ecology and Evolutionary Biology; University of Toronto; Toronto ON M5S 3B2 Canada
| | - Nicole Mideo
- Department of Ecology and Evolutionary Biology; University of Toronto; Toronto ON M5S 3B2 Canada
| | - Andrew F. Read
- Center For Infectious Disease Dynamics, Departments of Entomology and Biology, The Pennsylvania State University; University Park; Pennsylvania 16802
- Fogarty International Center; National Institutes of Health; Bethesda Maryland 20892
| | - Ottar N. Bjørnstad
- Center For Infectious Disease Dynamics, Departments of Entomology and Biology, The Pennsylvania State University; University Park; Pennsylvania 16802
- Fogarty International Center; National Institutes of Health; Bethesda Maryland 20892
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Abstract
Malaria parasites exhibit great diversity in the coordination of their asexual life cycle within the host, ranging from asynchronous growth to tightly synchronized cycles of invasion and emergence from red blood cells. Synchronized reproduction should come at a high cost--intensifying competition among offspring--so why would some Plasmodium species engage in such behavior and others not? We use a delayed differential equation model to show that synchronized infections can be favored when (1) there is limited interference among parasites competing for red blood cells, (2) transmission success is an accelerating function of sexual parasite abundance, (3) the target of saturating immunity is short-lived, and (4) coinfections with asynchronous parasites are rare. As a consequence, synchrony may be beneficial or costly, in line with the diverse patterns of synchronization observed in natural and lab infections. By allowing us to characterize diverse temporal dynamics, the model framework provides a basis for making predictions about disease severity and for projecting evolutionary responses to interventions.
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Affiliation(s)
- Megan A Greischar
- Center for Infectious Disease Dynamics, Departments of Entomology and Biology, Pennsylvania State University, University Park, Pennsylvania 16802
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17
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Abstract
The study of parasite local adaptation, whereby parasites perform better on sympatric hosts than on allopatric hosts and/or better on their own host population than do other parasites, is of great importance to both basic and applied biology. Theoretical examination of host-parasite coevolution predicts that parasite migration rate, generation time and virulence all contribute to the pattern of parasite local adaptation, such that parasites with greater dispersal ability, more frequent reproduction and/or high virulence ought to exhibit increased infectivity on local hosts. Here, we present a meta-analysis of experimental work from 57 host-parasite systems across 54 local adaptation studies to directly test theoretical predictions concerning the effect of each attribute on parasite adaptation. As expected, we find that studies of parasites with higher migration rates than their hosts report local adaptation, as measured by infection success, significantly more often than studies of parasites with relatively low migration rates. Furthermore, this synthesis serves to identify biases in the current body of work and highlight areas with the greatest need for further study. We emphasize the importance of unifying the field with regard to experimental methods, local adaptation definitions and reported statistics for cross-infection studies.
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Affiliation(s)
- Megan A Greischar
- Department of Biology, Indiana University, 1001 E. 3rd St., Bloomington, IN 47405-3700, USA.
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