Host-parasite interaction explains variation in the prevalence of avian haemosporidians at the community level

Do specialist haemoparasites induce tolerance in their hosts?

Generalist and specialist parasites are predicted to trade off transmission efficiency with host virulence, depending on host range. However, very few empirical studies test this trade-off in parasites at both ends of this spectrum simultaneously. Here, we examine parasitaemia (as a proxy for transmission efficiency) and virulence (assessed through 2 metrics of host immunity) in birds infected by a generalist lineage of Haemoproteus , comparing these with birds infected by more specialist Haemoproteus lineages, and birds uninfected by any haemoparasite. We compared the same metrics for specialist-infected birds, depending on whether a species was a ‘usual’ host or ‘spillover’ host. Immune metrics of specialist-infected birds did not differ from those of uninfected birds, but generalist-infected birds had elevated heterophil:lymphocyte (H:L) ratios and elevated white blood cell (WBC) counts compared to both other groups. Parasitaemia of specialist lineages was nearly 5 times higher than that of generalist lineages. Moreover, specialist-infected spillover hosts had higher H:L ratios and higher WBC counts compared to usual hosts for these lineages, with parasitaemia nearly 10 times lower in spillover hosts compared to usual hosts, although sample sizes of spillover hosts are, by definition, small. Our data provide support for the evolution of tolerance in specialist host-parasite interactions, with increased transmission efficiency for the parasite and reduced impacts on the host.

Do specialist and generalist parasites differ in their prevalence and intensity of infection? A test of the niche breadth and trade-off hypotheses

Studying host specificity is crucial to understanding the ability of parasites to spread to new hosts and trigger disease emergence events. The relationship between host specificity and parasite prevalence and infection intensity, has typically been studied in the context of two opposing hypotheses. According to the trade-off hypothesis generalist parasites, which can infect a broad range of hosts, will reach a lower prevalence and infection intensity than more specialist parasites due to the higher costs to adapt to multiple host immune systems. In contrast, the niche breadth hypothesis proposes that generalists' ability to infect more host species makes them more efficient in colonising host communities and thus they are found at higher prevalences and infection intensities. This study aims to test these hypotheses using the widespread avian malaria parasites of the genera Plasmodium and the related malaria-like parasite Haemoproteus. Overall, 1188 wild house sparrows from 17 localities in southwestern Spain were screened for parasite presence and intensity of infection. For each lineage found infecting house sparrows, we estimated host specificity as i) the number of different bird taxa infected by that lineage according to the MalAvi database and ii) an index that accounts for the phylogenetic relatedness between the host species. Parasite infections were recorded in 419 house sparrows, and eight Plasmodium and three Haemoproteus lineages were identified. Prevalence was positively associated with the number of host species. Lineages found in more localities showed both higher prevalence and host range. Overall, these results support the niche breadth hypothesis in relation to blood parasites infecting house sparrows.

Diversity and Host Specificity of Avian Haemosporidians in an Afrotropical Conservation Region

Afrotropical regions have high bird diversity, yet few studies have attempted to unravel the prevalence of avian haemosporidia in conservation areas. The diversity and host specificity of parasites in biodiversity hotspots is crucial to understanding parasite distribution and potential disease emergence. We test the hypothesis that biodiverse regions are associated with highly diverse parasites. By targeting the cytochrome b (Cytb) gene, we molecularly screened 1035 blood samples from 55 bird species for avian haemosporidia infections to determine its prevalence and diversity on sites inside and adjacent to the Kruger National Park. Overall infection prevalence was 28.41%. Haemoproteus, Leucocytozoon, and Plasmodium presented prevalences of 17.39%, 9.24%, and 4.64%, respectively. One hundred distinct parasite lineages were detected, of which 56 were new lineages. Haemoproteus also presented the highest diversity compared to Leucocytozoon and Plasmodium with varying levels of specificity. Haemoproteus lineages were found to be specialists while Plasmodium and Leucocytozoon lineages were generalists. We also found a positive relationship between avian host diversity and parasite diversity, supporting an amplification effect. These findings provide insight data for host-parasite and co-evolutionary relationship models.

The Impact of Avian Haemosporidian Infection on Feather Quality and Feather Growth Rate of Migratory Passerines

Bird feathers have several functions, including flight, insulation, communication, and camouflage. Since feathers degrade over time, birds need to moult regularly to maintain these functions. However, environmental factors like food scarcity, stress, and parasite infections can affect feather quality and moult speed. This study examined the impact of avian haemosporidian infection and uropygial gland volume, as well as feather quality and feather growth rate in two migratory hirundine species captured in southwestern Spain-the house martin (Delichon urbicum) and sand martin (Riparia riparia). Our findings showed that the prevalence of infection varied among species, with house martins having the highest rates, possibly due to their larger colony size. Moreover, haemosporidian infection had a different impact on each species; infected house martins exhibited lower feather quality than healthy individuals, although this outcome was not observed in sand martins. Furthermore, no effect of infection on feather growth rate was observed in both hirundinids. Additionally, feather growth rate only correlated positively with feather quality in house martins. Finally, no link was observed between uropygial gland volume and feather quality or feather growth rate in any of the species in this study. These findings highlight the effect of haemosporidian infections on the plumage of migratory birds, marking, for the first time, how avian haemosporidian infection is shown to adversely impact feather quality. Even so, further research is needed to explore these relationships more deeply.

Molecular survey and genetic diversity of Plasmodium sp. infesting domestic poultry in northeastern Thailand

Introduction

Haemosporidian parasites are prevalent worldwide and can cause economic losses in poultry production. These parasites are arousing interest in Thailand and are found in many avian species. There is insufficient information on the genetic diversity of these alveolates from the largest families - Plasmodidae, Haemoprotidae and Leucocytozoidae - specifically parasitising ducks, turkeys, and geese.

Material and Methods

Blood samples from 116 backyard poultry (60 ducks, 36 turkeys and 20 geese) in northeastern Thailand were investigated for Plasmodium spp., Haemoproteus spp. and Leucocytozoon spp. infections using microscopic examination and molecular approaches.

Results

A total of 37/116 birds (31.9%) had confirmed Plasmodium infections. The prevalence was 69.4% (25/36) in turkeys, 18.3% (11/60) in ducks, and 5.0% (1/20) in geese. Of these 37 positives, 86.5% were Plasmodium sp., 10.8% were P. gallinaceum and 2.7% were P. juxtanucleare. Sequence analysis based on the cytochrome b gene identified seven lineages, of which two were new lineages in backyard poultry.

Conclusion

This is the first report on the prevalence of haemosporidian parasites in backyard poultry in northeastern Thailand. The results provide important data for better understanding the molecular epidemiology of haemosporidian parasites infection in poultry in this region, which will be helpful in controlling these blood parasites.

Avian haemosporidians of breeding birds in the Davis Mountains sky-islands of west Texas, USA

Avian haemosporidians are protozoan parasites transmitted by insect vectors that infect birds worldwide, negatively impacting avian fitness and survival. However, the majority of haemosporidian diversity remains undescribed. Quantifying this diversity is critical to determining parasite–host relationships and host-switching potentials of parasite lineages as climate change induces both host and vector range shifts. In this study, we conducted a community survey of avian haemosporidians found in breeding birds on the Davis Mountains sky islands in west Texas, USA. We determined parasite abundance and host associations and compared our results to data from nearby regions. A total of 265 birds were screened and infections were detected in 108 birds (40.8%). Most positive infections were identified as Haemoproteus (36.2%), followed by Plasmodium (6.8%) and Leucocytozoon (0.8%). A total of 71 haemosporidian lineages were detected of which 39 were previously undescribed. We found that regional similarity influenced shared lineages, as a higher number of lineages were shared with avian communities in the sky islands of New Mexico compared to south Texas, the Texas Gulf Coast and central Mexico. We found that migratory status of avian host did not influence parasite prevalence, but that host phylogeny is likely an important driver.

Unravelling the mosquito-haemosporidian parasite-bird host network in the southwestern Iberian Peninsula: insights into malaria infections, mosquito community and feeding preferences

BAKGROUND

Vector-borne diseases affecting humans, wildlife and livestock have significantly increased their incidence and distribution in the last decades. Because the interaction among vectors-parasite-vertebrate hosts plays a key role driving vector-borne disease transmission, the analyses of the diversity and structure of vector-parasite networks and host-feeding preference may help to assess disease risk. Also, the study of seasonal variations in the structure and composition of vector and parasite communities may elucidate the current patterns of parasite persistence and spread as well as facilitate prediction of how climate variations may impact vector-borne disease transmission. Avian malaria and related haemosporidian parasites constitute an exceptional model to understand the ecology and evolution of vector-borne diseases. However, the characterization of vector-haemosporidian parasite-bird host assemblages is largely unknown in many regions.

METHODS

Here, we analyzed 5859 female mosquitoes captured from May to November in five localities from southwestern Spain to explore the composition and seasonal variation of the vector-parasite-vertebrate host network.

RESULTS

We showed a gradual increase in mosquito abundance, peaking in July. A total of 16 different haemosporidian lineages were found infecting 13 mosquito species. Of these assemblages, more than 70% of these vector-parasite associations have not been described in previous studies. Moreover, three Haemoproteus lineages were reported for the first time in this study. The prevalence of avian malaria infections in mosquitoes varied significantly across the months, reaching a maximum in November. Mosquito blood-feeding preference was higher for mammals (62.5%), whereas 37.5% of vectors fed on birds, suggesting opportunistic feeding behavior.

CONCLUSION

These outcomes improve our understanding of disease transmission risk and help tovector control strategies.

Exo-erythrocytic development of two Haemoproteus species (Haemosporida, Haemoproteidae), with description of Haemoproteus dumbbellus, a new blood parasite of bunting birds (Emberizidae)

Avian haemosporidians are widespread parasites categorized into four families of the order Haemosporida (Apicomplexa). Species of the subgenus Parahaemoproteus (genus Haemoproteus) belong to the Haemoproteidae and are transmitted by Culicoides biting midges. Reports of death due to tissue damage during haemoproteosis in non-adapted birds have raised concerns about these pathogens, especially as their exo-erythrocytic development is known for only a few Haemoproteus spp. More research is needed to better understand the patterns of the parasites' development in tissues and their impact on avian hosts. Yellowhammers Emberiza citrinella (Emberizidae) and common house martins Delichon urbicum (Hirundinidae) were screened for Haemoproteus parasites by microscopic examination of blood films and PCR-based testing. Individuals with single infection were selected for histological investigations. H & E-stained sections were screened for detection and characterization of the exo-erythrocytic stages, while chromogenic in situ hybridization (CISH) and phylogenetic analysis were performed to confirm the Haemoproteus origin and their phylogenetic relationships. Haemoproteus dumbbellus n. sp. was discovered in Emberiza citrinella single-infected with the lineage hEMCIR01. Meronts of H. dumbbellus n. sp. developed in various organs of five of six tested individuals, a pattern which was reported in other Haemoproteus species clustering in the same clade, suggesting this could be a phylogenetic trait. By contrast, in Delichon urbicum infected with the Haemoproteus lineage hDELURB2, which was linked to the more distantly related parasite Haemoproteus hirundinis, only megalomeronts were found in the pectoral muscles of two of six infected individuals. All exo-erythrocytic stages were confirmed to be Haemoproteus parasites by CISH using a Haemoproteus genus-specific probe. While the development of meronts seems to be typical for species of the clade containing H. dumbbellus, further investigations and data from more species are needed to explore whether a phylogenetic pattern occurs in meront or megalomeront formation.

Prevalence of haemosporidia in Asian Glossy Starling with discovery of misbinding of Haemoproteus-specific primer to Plasmodium genera in Sarawak, Malaysian Borneo

BACKGROUND

Plasmodium, Haemoproteus and Leucocytozoon are three mainly studied blood parasites known to cause malarial and pseudomalarial infections in avian worldwide. Although Sarawak is a biodiversity hotspot, molecular data on blood parasite diversity in birds are absent. The objective of the study is to determine the prevalence of blood parasite in Asian Glossy Starlings (AGS), an urban bird with high population density in Sarawak and to elucidate the phylogenetic relationship with other blood parasite.

METHODS

Twenty-nine carcasses of juvenile AGS that were succumbed to death due to window collision were collected around the vicinity of Universiti Malaysia Sarawak. Nested-multiplex and nested PCR targeting the Cytochrome B gene were used to detect Plasmodium and Haemoproteus, and Leucocytozoon respectively. Two primer sets were used for Haemoproteus detection to increase detection sensitivity, with one being a genus-specific primer.

RESULTS

Fourteen samples (prevalence rate: 48.28%) were found positive for avian Plasmodium. Phylogenetic analysis divided our sequences into five lineages, pFANTAIL01, pCOLL4, pACCBAD01, pALPSIS01 and pALPSIS02, with two lineages being novel. No Haemoproteus and Leucocytozoon was found in this study. However, Haemoproteus-specific primer used amplified our Plasmodium samples, making the primer non-specific to Haemoproteus only.

CONCLUSION

This is the first blood parasite detection study on AGS using carcasses and blood clot as sample source in Sarawak. Due to the scarcity of longer sequences from regions with high genetic plasticity, usage of genus-specific primers should be validated with sequencing to ensure correct prevalence interpretation.

Contrasting haemoparasite prevalence in larid species with divergent ecological niches and migration patterns

Haemoparasites represent a diverse group of vector-borne parasites that infect a wide range of vertebrate hosts. In birds, haemoparasite infection rates may be associated with various ecological and life history traits, including habitat choice, colony size and migration distance. Here, we molecularly assessed the prevalence of 3 main haemoparasite genera (Plasmodium, Haemoproteus and Leucocytozoon) in 2 bird species with different habitat preferences and migratory behaviour: black-headed gulls (Chroicocephalus ridibundus) and common terns (Sterna hirundo). We found that gulls showed a much higher prevalence and diversity of Plasmodium or Haemoproteus (ca. 60% of individuals infected) than terns (zero prevalence). The prevalence of Leucocytozoon was low in both species (<3%). The differences in haemoparasite prevalences may be primarily driven by varying vector encounter rate resulting from different habitat preferences, as black-headed gulls mainly use vector-rich vegetated freshwater habitats, whereas common terns often use vector-poor coastal and brackish habitats. Since common terns migrate further than black-headed gulls, our results did not provide support for an association between haemoparasite prevalence and migratory distance. In gulls, we found a negative association between colony size and infection rates, suggestive of an ideal despotic distribution, and phylogenetic analyses of detected haemoparasite lineages provided evidence for higher host specificity in Haemoproteus than Plasmodium. Our results suggest that the preference for coastal areas and less vegetated habitats in terns may reduce haemoparasite infection rates compared to other larids, regardless of their migratory distance, emphasizing the role of ecological niches in parasite exposure.

Reciprocal positive effects on parasitemia between coinfecting haemosporidian parasites in house sparrows

BACKGROUND

Hosts are often simultaneously infected with several parasite species. These co-infections can lead to within-host interactions of parasites, including mutualism and competition, which may affect both virulence and transmission. Birds are frequently co-infected with different haemosporidian parasites, but very little is known about if and how these parasites interact in natural host populations and what consequences there are for the infected hosts. We therefore set out to study Plasmodium and Haemoproteus parasites in house sparrows Passer domesticus with naturally acquired infections using a protocol where the parasitemia (infection intensity) is quantified by qPCR separately for the two parasites. We analysed infection status (presence/absence of the parasite) and parasitemia of parasites in the blood of both adult and juvenile house sparrows repeatedly over the season.

RESULTS

Haemoproteus passeris and Plasmodium relictum were the two dominating parasite species, found in 99% of the analyzed Sanger sequences. All birds were infected with both Plasmodium and Haemoproteus parasites during the study period. Seasonality explained infection status for both parasites in the adults: H. passeris was completely absent in the winter while P. relictum was present all year round. Among adults infected with H. passeris there was a positive effect of P. relictum parasitemia on H. passeris parasitemia and likewise among adults infected with P. relictum there was a positive effect of H. passeris parasitemia on P. relictum parasitemia. No such associations on parasitemia were seen in juvenile house sparrows.

CONCLUSIONS

The reciprocal positive relationships in parasitemia between P. relictum and H. passeris in adult house sparrows suggests either mutualistic interactions between these frequently occurring parasites or that there is variation in immune responses among house sparrow individuals, hence some individuals suppress the parasitemia of both parasites whereas other individuals suppress neither. Our detailed screening of haemosporidian parasites over the season shows that co-infections are very frequent in both juvenile and adult house sparrows, and since co-infections often have stronger negative effects on host fitness than the single infection, it is imperative to use screening systems with the ability to detect multiple parasites in ecological studies of host-parasite interactions.

Phylogeographic Patterns of Haemoproteid Assemblages of Selected Avian Hosts: Ecological and Evolutionary Implications

BACKGROUND

While the dynamics of disease emergence is driven by host-parasite interactions, the structure and dynamics of these interactions are still poorly understood. Here we study the phylogenetic and morphological clustering of haemosporidian parasite lineages in a local avian host community. Subsequently, we examine geographical patterns of parasite assemblages in selected avian hosts breeding in Europe.

METHODS

We conduct phylogenetic and haplotype network analyses of Haemoproteus (Parahaemoproteus) lineages based on a short and an extended cytochrome b barcode region. Ordination analyses are used to examine changes in parasite assemblages with respect to climate type and geography.

RESULTS

We reveal relatively low phylogenetic clustering of haemoproteid lineages in a local avian host community and identify a potentially new Haemoproteus morphospecies. Further, we find that climate is effectively capturing geographical changes in parasite assemblages in selected widespread avian hosts. Moreover, parasite assemblages are found to vary distinctly across the host's breeding range, even within a single avian host.

CONCLUSIONS

This study suggests that a few keystone hosts can be important for the local phylogenetic and morphological clustering of haemoproteid parasites. Host spatio-temporal dynamics, both for partially and long-distance migratory birds, appear to explain geographical variation in haemoproteid parasite assemblages. This study also gives support to the idea that climate variation in terms of rainfall seasonality can be linked to the propensity for host switching in haemosporidians.

Ecological specificity explains infection parameters of anuran parasites at different scales

Understanding the determinants of parasite infection in different hosts is one of the main goals of disease ecology. Evaluating the relationship between parasite–host specificity and infection parameters within host communities and populations may contribute to this understanding. Here we propose two measures of specificity that encompasses phylogenetic and ecological relatedness among hosts and investigated how such metrics explain parasite infection prevalence and mean infection intensity (MII). We analysed the parasites associated with an anuran community in an area of Atlantic Forest and used the number of infected hosts and the net relatedness index to calculate the phylogenetic and ecological specificities of the parasites. These specificity measures were related to infection metrics (prevalence and MII) with generalized linear mixed models at community (all hosts) and population (infected host species) scales. Parasite prevalence was correlated with the number of infected hosts and, when considering only multi-host parasites, was positively related to parasite ecological specificity at community and population scales. Thus, parasite species have similar prevalences in ecologically closer hosts. No relationship was found for parasite MII. Incorporating ecological characteristics of hosts in parasite specificity analyses improves the detection of patterns of specificity across scales.

Massive Infection of Lungs with Exo-Erythrocytic Meronts in European Robin Erithacus rubecula during Natural Haemoproteus attenuatus Haemoproteosis

Simple Summary

Haemoproteus parasites are cosmopolitan bird pathogens belonging to the order Haemosporida (Apicomplexa). A majority of the described species are transmitted by Culicoides biting midges, which inject infective stages (sporozoites) in birds during blood meals. The sporozoites initiate tissue merogony, resulting in numerous merozoites, part of which penetrate red blood cells and produce blood stages (gametocytes), which are infective for vectors. The blood stages of Haemoproteus parasites have been relatively well-investigated, although tissue stages and patterns of their development remain unidentified in the majority of Haemoproteus species. Nevertheless, they often damage various organs which makes them important for bird health. This study contributes new knowledge about tissue merogony of Haemoproteus attenuatus, which parasitize birds of the Muscicapidae. Naturally infected European robins Erithacus rubecula were caught in Lithuania during autumnal migration. Parasites were identified using morphological features of gametocytes and DNA sequence analysis. Organs of infected birds were examined using histological methods. Tissue stages (meronts) were present only in the lungs, where they were numerous and markedly varied in shape, size and maturation stage. Description of meronts was provided and molecular phylogenetic analysis identified closely related lineages that could present similar exo-erythrocytic development in lungs. Lung damage caused by meronts of H. attenuatus and closely related lineages is worth attention due to their possible implications on a bird’s health.

Abstract

Haemoproteus species are widespread avian blood parasites belonging to Haemoproteidae (Haemosporida). Blood stages of these pathogens have been relatively well-investigated, though exo-erythrocytic (tissue) stages remain unidentified for the majority of species. However, recent histopathological studies show that haemoproteins markedly affect bird organs during tissue merogony. This study investigated the exo-erythrocytic development of Haemoproteus (Parahaemoproteus) attenuatus (lineage hROBIN1), the common parasite of flycatchers (Muscicapidae). Naturally infected European robins Erithacus rubecula were examined. Parasite species and lineage were identified using microscopic examination of blood stages and DNA sequence analysis. Parasitaemia intensity varied between 0.8 and 26.5% in seven host individuals. Organs of infected birds were collected and processed for histological examination. Tissues stages (meronts) were seen in six birds and were present only in the lungs. The parasites were usually located in groups and were at different stages of maturation, indicating asynchronous exo-erythrocytic development. In most parasitized individuals, 100 meronts were observed in 1 cm² section of lungs. The largest meronts reached 108 µm in length. Mature meronts contained numerous roundish merozoites of approximately 0.8 µm in diameter. Megalomeronts were not observed. Massive merogony and resulting damage of lungs is a characteristic feature during H. attenuatus infections and might occur in related parasite lineages, causing haemoproteosis.

Ecological Effects on the Dynamics of West Nile Virus and Avian Plasmodium: The Importance of Mosquito Communities and Landscape

Humans and wildlife are at risk from certain vector-borne diseases such as malaria, dengue, and West Nile and yellow fevers. Factors linked to global change, including habitat alteration, land-use intensification, the spread of alien species, and climate change, are operating on a global scale and affect both the incidence and distribution of many vector-borne diseases. Hence, understanding the drivers that regulate the transmission of pathogens in the wild is of great importance for ecological, evolutionary, health, and economic reasons. In this literature review, we discuss the ecological factors potentially affecting the transmission of two mosquito-borne pathogens circulating naturally between birds and mosquitoes, namely, West Nile virus (WNV) and the avian malaria parasites of the genus Plasmodium. Traditionally, the study of pathogen transmission has focused only on vectors or hosts and the interactions between them, while the role of landscape has largely been ignored. However, from an ecological point of view, it is essential not only to study the interaction between each of these organisms but also to understand the environmental scenarios in which these processes take place. We describe here some of the similarities and differences in the transmission of these two pathogens and how research into both systems may facilitate a greater understanding of the dynamics of vector-borne pathogens in the wild.

Avian haemosporidia in native and invasive sparrows at an Afrotropical region

Bio-invasions are a major threat to biodiversity and ecosystems globally and may contribute to the proliferation of emerging infectious diseases. We examined the prevalence and phylogenetic diversity of avian haemosporidian parasites infecting the non-native house sparrows (Passer domesticus) and the native southern grey-headed sparrows (Passer diffusus). Blood samples from 104 sparrows (74 house sparrows and 30 southern grey-headed sparrows) mist-netted inside and around the Kruger National Park were used. Genomic DNA was extracted from each blood sample and subjected to nested PCR analyses, Sanger sequencing and phylogenetic analyses. Overall, 35.57% (37/104) of the birds sampled were infected with at least one haemosporidian parasites. Southern grey-headed sparrows had a higher parasite prevalence (60%) than house sparrows (24.3%). A total of 16 parasite lineages were identified, of which eight were novel lineages. Whereas Haemoproteus spp. showed the highest lineage diversity, Leucocytozoon spp. were the most prevalent parasites, albeit with significant differences between sparrow species. A single Plasmodium sp. infection was recorded in a southern grey-headed sparrow. In support of the enemy release hypothesis, we found that prevalence on non-native house sparrows was lower than prevalence recorded in their region of origin and also that they were infected only by indigenous parasites lineages.

Prevalence and Genetic Diversity of Avian Haemosporidian Parasites in Southern Iran

Avian haemosporidians are widespread and diverse and are classified in the genera Plasmodium, Haemoproteus, Leucocytozoon, and Fallisia. These species are known to cause haemosporidiosis and decreased fitness of their hosts. Despite the high diversity of habitats and animal species in Iran, only few studies have addressed avian haemosporidians in this geographic area. This study was performed in the south and southeast of Iran during the bird breeding seasons in 2017 and 2018, with the aim to partly fill in this gap. Blood samples of 237 passerine birds belonging to 41 species and 20 families were collected. Parasite infections were identified using a nested PCR protocol targeting a 479-base-pair fragment of the mitochondrial cytochrome b (cytb) gene of Haemoproteus, Plasmodium and Leucocytozoon species. The overall prevalence of haemosporidian parasites was 51.1%, and 55 different lineages were identified, of which 15 cytb lineages were new globally. The lineages of Haemoproteus predominated (63.6% of all detected lineages), followed by Leucocytozoon and Plasmodium. Nineteen new host records of haemosporidian cytb lineages were identified, and the majority of them were found in resident bird species, indicating local transmission. Thirteen co-infections (9.8% of infected individuals) of Haemoproteus and Leucocytozoon parasites in seven host species were observed. This study shows the presence of active local transmission of parasites to resident bird species in the southeast of Iran and contributes to the knowledge on haemosporidian parasite biodiversity in this poorly studied region of the world.

Co-infections of Plasmodium relictum lineages pSGS1 and pGRW04 are readily distinguishable by broadly used PCR-based protocols, with remarks on global distribution of these malaria parasites

Plasmodium relictum is the most common generalist avian malaria parasite, which was reported in over 300 bird species of different orders, particularly often in passerines. This malaria infection is often severe in non-accustomed avian hosts. Currently, five distinct cytochrome b gene lineages have been assigned to P. relictum, with the lineages pSGS1 and pGRW04 being the most common. Based on molecular screenings, the transmission of these two parasite lineages might occur in sympatry, particularly often in sub-Saharan Africa, but they also have been reported to have different areas of transmission globally, with the lineages pSGS1 and pGRW04 being of low (if at all) transmission in huge regions of Americas and Europe, respectively. It remains unclear why these lineages are more often reported in some geographical areas, even though their susceptible vertebrate hosts and vectors are present globally. Co-infections of malaria parasites and other haemosporidians belonging to different species and subgenera are prevalent and even predominate in many bird populations, however, PCR-based protocols using commonly used primers often do not read such co-infections. Because information about the sensitivity of these protocols to read co-infections of the lineages pSGS1 and pGRW04 is absent, this study aimed to unravel this issue experimentally. Blood samples of birds experimentally infected with the single parasite lineages pSGS1 and pGRW04 were used to prepare various combinations of mixes, which were tested by two PCR-based protocols, which have been often used in current avian malaria research. Single infections of the same lineages were used as controls. Careful examination of the sequence electropherograms showed the presence of clear double peaks on polymorphic sites, indicating co-infections. This experiment shows that the broadly used PCR-based protocols can readily distinguish co-infections of these parasite lineages. In other words, the available information about patterns of the geographical distribution of the P. relictum lineages pSGS1 and pGRW04 likely mirrors the existing epidemiological situation but is not a result of the bias due to preferable DNA amplification of one of these lineages during their possible co-infections. This calls for further ecological research aiming determination of factors associated with the transmission of the lineages pSGS1 and pGRW04 in different regions of the globe.

Spatially different annual cycles but similar haemosporidian infections in distant populations of collared sand martins

Background

Populations of long-distance migratory birds experience different environments and are consequently exposed to different parasites throughout their annual cycles. Though, specific whereabouts and accompanied host-parasite interactions remain unknown for most migratory passerines. Collared sand martins (Riparia riparia) breeding in the western Palaearctic spend the nonbreeding period in Africa, but it is not yet clear whether specific populations differ in overwintering locations and whether these also result in varying infections with vector-transmitted endoparasites.

Results

Geolocator tracking revealed that collared sand martins from northern-central and central-eastern Europe migrate to distant nonbreeding sites in West Africa and the Lake Chad basin in central Africa, respectively. While the ranges of these populations were clearly separated throughout the year, they consistently spent up to 60% of the annual cycle in Africa. Ambient light recorded by geolocators further indicated unsheltered roosting during the nonbreeding season in Africa compared to the breeding season in Europe.

We found 5–26% prevalence of haemosporidian parasites in three breeding populations and one migratory passage population that was only sampled but not tracked. In total, we identified seven Plasmodium and nine Haemoproteus lineages (incl. two and seven new lineages, respectively), the latter presumably typical for swallows (Hirundinae) hosts. 99.5% of infections had a low intensity, typical for chronic infection stages, whereas three individuals (0.5%) showed high parasitaemia typical for acute infections during spring migration and breeding.

Conclusions

Our study shows that blood parasite infections are common in several western Palaearctic breeding populations of collared sand martins who spent the nonbreeding season in West Africa and the lake Chad region. Due to long residency at the nonbreeding grounds blood parasite transmissions may mainly occur at host population-specific residences sites in Europe and Africa; the latter being likely facilitated by unsheltered roosting and thus high vulnerability to hematophagous insects. The rare cases of high parasitaemia during spring migration and breeding further indicates either relapses of chronic infection or primary infections which occurred shortly before migration and during breeding.

Diversity and host assemblage of avian haemosporidians in different terrestrial ecoregions of Peru

Characterizing the diversity and structure of host–parasite communities is crucial to understanding their eco-evolutionary dynamics. Malaria and related haemosporidian parasites are responsible for fitness loss and mortality in bird species worldwide. However, despite exhibiting the greatest ornithological biodiversity, avian haemosporidians from Neotropical regions are quite unexplored. Here, we analyze the genetic diversity of bird haemosporidian parasites (Plasmodium and Haemoproteus) in 1,336 individuals belonging to 206 bird species to explore for differences in diversity of parasite lineages and bird species across 5 well-differentiated Peruvian ecoregions. We detected 70 different haemosporidian lineages infecting 74 bird species. We showed that 25 out of the 70 haplotypes had not been previously recorded. Moreover, we also identified 81 new host–parasite interactions representing new host records for these haemosporidian parasites. Our outcomes revealed that the effective diversity (as well as the richness, abundance, and Shannon–Weaver index) for both birds and parasite lineages was higher in Amazon basin ecoregions. Furthermore, we also showed that ecoregions with greater diversity of bird species also had high parasite richness, hence suggesting that host community is crucial in explaining parasite richness. Generalist parasites were found in ecoregions with lower bird diversity, implying that the abundance and richness of hosts may shape the exploitation strategy followed by haemosporidian parasites. These outcomes reveal that Neotropical region is a major reservoir of unidentified haemosporidian lineages. Further studies analyzing host distribution and specificity of these parasites in the tropics will provide important knowledge about phylogenetic relationships, phylogeography, and patterns of evolution and distribution of haemosporidian parasites.

Prevalence and Diversity of Avian Haemosporidians May Vary with Anthropogenic Disturbance in Tropical Habitats in Myanmar

Avian malaria and related haemosporidians (genera Haemoproteus, Plasmodium and Leucocytozoon) infect most clades of bird. Although these parasites are present in almost all continents, they have been irregularly studied across different geographical regions. Despite the high bird diversity in Asia, the diversity of avian haemosporidians in this region is largely unknown. Moreover, anthropogenic changes to habitats in tropical regions may have a profound impact on the overall composition of haemosporidian communities. Here we analyzed the diversity and host association of bird haemosporidians from areas with different degrees of anthropogenic disturbance in Myanmar, revealing an unexplored diversity of these parasites (27% of newly-discovered haemosporidian lineages, and 64% of new records of host–parasite assemblages) in these tropical environments. This newly discovered diversity will be valuable for detecting host range and transmission areas of haemosporidian parasites. We also found slightly higher haemosporidian prevalence and diversity in birds from paddy fields than in individuals from urban areas and hills, thus implying that human alteration of natural environments may affect the dynamics of vector-borne diseases. These outcomes provide valuable insights for biodiversity conservation management in threatened tropical ecosystems.

Avian Haemosporidian Diversity on Sardinia: A First General Assessment for the Insular Mediterranean

The Western Palearctic is one of the most investigated regions for avian haemosporidian parasites (Haemoproteus, Plasmodium and Leucocytozoon), yet geographic gaps in our regional knowledge remain. Here, we report the first haemosporidian screening of the breeding birds from Sardinia (the second-largest Mediterranean Island and a biodiversity hotspot), and the first for the insular Mediterranean in general. We examined the occurrence of haemosporidians by amplifying their mtDNA cytb gene in 217 breeding birds, belonging to 32 species. The total prevalence of infected birds was 55.3%, and of the 116 haplotypes recovered, 84 were novel. Despite the high number of novel lineages, phylogenetic analysis did not highlight Sardinia-specific clades; instead, some Sardinian lineages were more closely related to lineages previously recovered from continental Europe. Host-parasite network analysis indicated a specialized host-parasite community. Binomial generalized linear models (GLMs), performed at the community level, suggested an elevational effect on haemosporidian occurrence probability (negative for Haemoproteus; positive for Leucocytozoon) likely due to differences in the abundance of insect vectors at different elevations. Furthermore, a GLM revealed that sedentary birds showed a higher probability of being infected by novel haplotypes and long-distance migrants showed a lower probability of novel haplotype infection. We hypothesize that the high diversity of haemosporidians is linked to the isolation of breeding bird populations on Sardinia. This study adds to the growing knowledge on haemosporidians lineage diversity and distribution in insular environments and presents new insights on potential host-parasite associations.

Detection of haemosporidian parasites in wild and domestic birds in northern and central provinces of Iran: Introduction of new lineages and hosts

Haemosporidian parasites characterize multi-host and multi-parasite structures which are prevalent among wild bird populations. Here, determination of host records, estimation of the prevalence and diversity of haemosporidian lineages were performed in wild and domestic birds in 11 provinces in Iran. To our knowledge, for the first time in this region, molecular characterization of haemosporidians in migratory water birds, raptors, and domestic birds was carried out: blood or tissue samples were collected from 246 birds belonging to 36 species, 12 families, and 11 orders. The prevalence of Plasmodium, Haemoproteus, and Leucocytozoon were documented as 1.21%, 3.65%, and 0.4%, respectively. Of 36 birds' species inspected in this investigation, 13 individuals of 9 species were parasitized by blood parasites. To our knowledge, five lineages including hANACRE03, hAYTFER01, hAYTFER02, hAQUCYR01, and hSTAL06 were found as un-described lineages, while six known lineages of hLK03, pLK05, lTUSW04, pSW5, hMILANS02, and hHAECOL1 were recorded in hosts within novel geographical regions. Such results are required to fill the gaps in understanding the geographical distribution patterns of wildlife related vector-borne parasites in migratory birds as potential carriers, raptors with high vulnerability, and domestic birds as pet or with economic value.

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Molecular characterization of haemosporidians in migratory, raptors, and domestic birds.

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Eleven avian haemosporidian lineages discovered in new geographical regions of West Asia.

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Novelhost records of blood parasites in Iran.

Prevalence and genetic diversity of avian haemosporidian parasites at an intersection point of bird migration routes: Sultan Marshes National Park, Turkey

Avian haemosporidians (Haemosporida) represent a globally distributed, species-rich multiparasite-multihost host-parasite system. Each year, many of these parasite lineages are carried between temperate and tropical regions by migratory birds. While several factors can limit the transmission of avian haemosporidians to new areas, recent studies have shown that some abundant parasites can sometimes disperse and be transmitted in new areas to become emerging infectious diseases. In this study, we investigated the prevalence and diversity of avian haemosporidian parasites in Sultan Marshes National Park (SMNP), a major stopover site in the eastern Mediterranean flyway, and we evaluated the potential for avian haemosporidians in SMNP to be transmitted to areas outside of their known distributions. We sampled a total of 565 migratory and resident birds belonging to 39 species and 23 families. We applied both molecular and microscopic methods to detect and identify avian haemosporidian infections and also quantified the frequency of potential abortive infections. We identified a total of 52 different mitochondrial cytochrome b (cyt b) parasite lineages belonging to the genera Plasmodium (N = 12), Haemoproteus (N = 31), and Leucocytozoon (N = 9) in 193 (34.2%) infected birds. Ten of the lineages were reported for the first time. Our findings show that numerous parasite lineages are actively transmitted among resident bird species of SMNP. Our findings also revealed new parasite-host interactions while considering the role of possible abortive infections. The relatively high frequency of presumed abortive infections suggests that analyses of datasets generated only by PCR-based methods should be interpreted with caution. We also compared the prevalence and distribution of avian haemosporidian infections in both resident and migratory bird species and showed that haemosporidian prevalence was related to bird migratory behavior. The results of this study contribute to a better understanding of the ecological and genetic adaptations associated with changes in transmission areas of avian haemosporidian parasites.

Evolution of vector transmitted parasites by host switching revealed through sequencing of Haemoproteus parasite mitochondrial genomes

Parasite species evolve by switching to new hosts, cospeciating with their current hosts, or speciating on their current hosts. Vector transmitted parasites are expected to speciate by host switching, but confirming this hypothesis has proved challenging. Parasite DNA can be difficult to sequence, thus well resolved parasite phylogenies that are needed to distinguish modes of parasite speciation are often lacking. Here, we studied speciation in vector transmitted avian haemosporidian parasites in the genus Haemoproteus and their warbler hosts (family Acrocephalidae). We overcome the difficulty of generating parasite genetic data by combining nested long-range PCR with next generation sequencing to sequence whole mitochondrial genomes from 19 parasite haplotypes confined to Acrocephalidae warblers, resulting in a well-supported parasite phylogeny. We also generated a well-supported host phylogeny using five genes from published sources. Our phylogenetic analyses confirm that these parasites have speciated by host switching. We also found that closely related host species shared parasites which themselves were not closely related. Sharing of parasites by closely related host species is not due to host geographic range overlap, but may be the result of phylogenetically conserved host immune systems.

Exploring the adjustment to parasite pressure hypothesis: differences in uropygial gland volume and haemosporidian infection in palearctic and neotropical birds

Parasites are globally widespread pathogenic organisms, which impose important selective forces upon their hosts. Thus, in accordance with the Adjustment to parasite pressure hypothesis, it is expected that defenses among hosts vary relative to the selective pressure imposed by parasites. According to the latitudinal gradient in diversity, species richness and abundance of parasites peak near the equator. The uropygial gland is an important defensive exocrine gland against pathogens in birds. Size of the uropygial gland has been proposed to vary among species of birds because of divergent selection by pathogens on their hosts. Therefore, we should expect that bird species from the tropics should have relatively larger uropygial glands for their body size than species from higher latitudes. However, this hypothesis has not yet been explored. Here, we analyze the size of the uropygial gland of 1719 individual birds belonging to 36 bird species from 3 Neotropical (Peru) and 3 temperate areas (Spain). Relative uropygial gland volume was 12.52% larger in bird species from the tropics than from temperate areas. This finding is consistent with the relative size of this defensive organ being driven by selective pressures imposed by parasites. We also explored the potential role of this gland as a means of avoiding haemosporidian infection, showing that species with large uropygial glands for their body size tend to have lower mean prevalence of haemosporidian infection, regardless of their geographical origin. This result provides additional support for the assumption that secretions from the uropygial gland reduce the likelihood of becoming infected with haemosporidians.

Molecular characterization of swallow haemoproteids, with description of one new Haemoproteus species

Haemoproteus species (Haemosporida, Haemoproteidae) are cosmopolitan bird blood parasites, which often cause relatively benign infections in adapted avian hosts, but severe and even lethal haemoproteosis might develop due to internal organ damage if these pathogens inhabit non-adapted (wrong) hosts. Haemoproteids of swallows (Hirundinidae) remain fragmentarily investigated, with only two haemoproteid species reported in this bird family, which members are cosmopolitan, diverse and inhabit various terrestrial ecosystems, particularly in tropical countries. This study describes and provides molecular characterization of Haemoproteus parahirundinis n. sp. (cytochrome b lineage hHIRUS05), parasite of the most broadly distributed swallow, the Barn swallow Hirundo rustica. Gametocytes, gametes and ookinetes of the new species were examined and compared with other haemoproteids described in swallows. The phylogenetic analysis indicated the existence of a largely undescribed Haemoproteus species diversity in birds of the Hirundinidae and also suggests that all lineages of haemoproteids reported in swallows are transmitted by Culicoides biting midges, but not louse flies of the Hippoboscidae, which often inhabit their nests. The biting midges should be the first targets in vectors research of swallow haemoproteids. This study indicates existence of Haemoproteus species, which are readily distinct based on morphological characters of their blood and sporogonic stages, but differ only negligently in partial cytochrome b sequences, the main markers broadly used in molecular characterization of haemoproteids. That calls for further taxonomic research on haemoproteid in swallows, many species of which are endangered or even threatened with extinction because of habitat degradation.

Drivers of community turnover differ between avian hemoparasite genera along a North American latitudinal gradient

The latitudinal diversity gradient (LDG) is an established macroecological pattern, but is poorly studied in microbial organisms, particularly parasites. In this study, we tested whether latitude, elevation, and host species predicted patterns of prevalence, alpha diversity, and community turnover of hemosporidian parasites. We expected parasite diversity to decrease with latitude, alongside the diversity of their hosts and vectors. Similarly, we expected infection prevalence to decrease with latitude as vector abundances decrease. Lastly, we expected parasite community turnover to increase with latitudinal distance and to be higher between rather than within host species. We tested these hypotheses by screening blood and tissue samples of three closely related avian species in a clade of North American songbirds (Turdidae: Catharus, n = 466) across 17.5° of latitude. We used a nested PCR approach to identify parasites in hemosporidian genera that are transmitted by different dipteran vectors. Then, we implemented linear-mixed effects and generalized dissimilarity models to evaluate the effects of latitude, elevation, and host species on parasite metrics. We found high diversity of hemosporidian parasites in Catharus thrushes (n = 44 lineages) but no evidence of latitudinal gradients in alpha diversity or prevalence. Parasites in the genus Leucocytozoon were most prevalent and lineage rich in this study system; however, there was limited turnover with latitude and host species. Contrastingly, Plasmodium parasites were less prevalent and diverse than Leucocytozoon parasites, yet communities turned over at a higher rate with latitude and host species. Leucocytozoon communities were skewed by the dominance of one or two highly prevalent lineages with broad latitudinal distributions. The few studies that evaluate the hemosporidian LDG do not find consistent patterns of prevalence and diversity, which makes it challenging to predict how they will respond to global climate change.

Morphological and molecular characterization of Plasmodium cathemerium (lineage PADOM02) from the sparrow Passer domesticus with complete sporogony in Culex pipiens complex

Avian malaria is a mosquito-borne disease caused by Plasmodium spp. protozoa. Although these parasites have been extensively studied in North America and Eurasia, knowledge on the diversity of Plasmodium, its vectors and avian hosts in Africa is scarce. In this study, we report on natural malarial infections in free-ranging sparrows (Passer domesticus) sampled at Giza Governorate, Egypt. Parasites were morphologically characterized as Plasmodium cathemerium based on the examination of thin blood smears from the avian host. Sequencing a fragment of the mitochondrial cytochrome b gene showed that the parasite corresponded to lineage PADOM02. Phylogenetic analysis showed that this parasite is closely related to the lineages SERAU01 and PADOM09, both of which are attributed to P. cathemerium. Experimental infection of Culex pipiens complex was successful, with ookinetes first detected at 1-day post infection (dpi), oocysts at 4 dpi and sporozoites at 6 dpi. The massive infection of the salivary glands by sporozoites corroborates that Cx. pipiens complex is a competent vector of PADOM02. Our findings confirm that Plasmodium lineage PADOM02 infects sparrows in urban areas along the Nile River, Egypt, and corroborate that Cx. pipiens complex is a highly competent vector for these parasites. Furthermore, our results demonstrate that this lineage corresponds to the morphospecies P. cathemerium and not P. relictum as previously believed.

Evolutionary ecology, taxonomy, and systematics of avian malaria and related parasites

Haemosporidian parasites of the genera Plasmodium, Leucocytozoon, and Haemoproteus are one of the most prevalent and widely studied groups of parasites infecting birds. Plasmodium is the most well-known haemosporidian as the avian parasite Plasmodium relictum was the original transmission model for human malaria and was also responsible for catastrophic effects on native avifauna when introduced to Hawaii. The past two decades have seen a dramatic increase in research on avian haemosporidian parasites as a model system to understand evolutionary and ecological parasite-host relationships. Despite haemosporidians being one the best studied groups of avian parasites their specialization among avian hosts and variation in prevalence amongst regions and host taxa are not fully understood. In this review we focus on describing the current phylogenetic and morphological diversity of haemosporidian parasites, their specificity among avian and vector hosts, and identifying the determinants of haemosporidian prevalence among avian species. We also discuss how these parasites might spread across regions due to global climate change and the importance of avian migratory behavior in parasite dispersion and subsequent diversification.

Differential gene expression of Plasmodium homocircumflexum (lineage pCOLL4) across two experimentally infected passerine bird species

Plasmodium parasites are present in a wide range of host species, some of which tend to be more susceptible than others, potentially as an outcome of evolved tolerance or resistance. Common starlings seem to cope with malaria infection while common crossbills are more susceptible to the same infections. That raises the question if the parasites rely on the same molecular mechanisms regardless of host species or do Plasmodium parasites change gene-expressions in accordance to the environment different hosts might provide? We used RNA-sequencing from starlings and crossbills, experimentally infected with Plasmodium homocircumflexum (lineage pCOLL4). The assembled transcriptome contained a total of 26,733 contigs. Parasite expression patterns differed between bird species. Parasites had higher expression of cell-invasion genes when infecting crossbills compared to starlings whereas in starlings genes related to apoptosis or/and oxidative stress showed higher expression levels. This article reveals how a Plasmodium parasite might adjust its expression and gene function depending on the host species infected.

Sporogony of four Haemoproteus species (Haemosporida: Haemoproteidae), with report of in vitro ookinetes of Haemoproteus hirundinis: phylogenetic inference indicates patterns of haemosporidian parasite ookinete development

BACKGROUND

Haemoproteus (Parahaemoproteus) species (Haemoproteidae) are widespread blood parasites that can cause disease in birds, but information about their vector species, sporogonic development and transmission remain fragmentary. This study aimed to investigate the complete sporogonic development of four Haemoproteus species in Culicoides nubeculosus and to test if phylogenies based on the cytochrome b gene (cytb) reflect patterns of ookinete development in haemosporidian parasites. Additionally, one cytb lineage of Haemoproteus was identified to the species level and the in vitro gametogenesis and ookinete development of Haemoproteus hirundinis was characterised.

METHODS

Laboratory-reared C. nubeculosus were exposed by allowing them to take blood meals on naturally infected birds harbouring single infections of Haemoproteus belopolskyi (cytb lineage hHIICT1), Haemoproteus hirundinis (hDELURB2), Haemoproteus nucleocondensus (hGRW01) and Haemoproteus lanii (hRB1). Infected insects were dissected at intervals in order to detect sporogonic stages. In vitro exflagellation, gametogenesis and ookinete development of H. hirundinis were also investigated. Microscopic examination and PCR-based methods were used to confirm species identity. Bayesian phylogenetic inference was applied to study the relationships among Haemoproteus lineages.

RESULTS

All studied parasites completed sporogony in C. nubeculosus. Ookinetes and sporozoites were found and described. Development of H. hirundinis ookinetes was similar both in vivo and in vitro. Developing ookinetes of this parasite possess long outgrowths, which extend longitudinally and produce the apical end of the ookinetes. A large group of closely related Haemoproteus species with a similar mode of ookinete development was determined. Bayesian analysis indicates that this character has phylogenetic value. The species identity of cytb lineage hDELURB2 was determined: it belongs to H. hirundinis.

CONCLUSIONS

Culicoides nubeculosus is susceptible to and is a likely natural vector of numerous species of Haemoproteus parasites, thus worth attention in haemoproteosis epidemiology research. Data about in vitro development of haemoproteids provide valuable information about the rate of ookinete maturation and are recommended to use as helpful step during vector studies of haemosporidian parasites, particularly because they guide proper dissection interval of infected insects for ookinete detection during in vivo experiments. Additionally, in vitro studies readily identified patterns of morphological ookinete transformations, the characters of which are of phylogenetic value in haemosporidian parasites.