Sex-dependent differences in avian malaria prevalence and consequences of infections on nestling growth and adult condition in the Tawny pipit, Anthus campestris

Higher body condition with infection by Haemoproteus parasites in Bananaquits (Coereba flaveola)

Parasite transmission is a heterogenous process in host-parasite interactions. This heterogeneity is particularly apparent in vector-borne parasite transmission where the vector adds an additional level of complexity. Haemosporidian parasites, a widespread protist, cause a malaria-like disease in birds globally, but we still have much to learn about the consequences of infection to hosts' health. In the Caribbean, where malarial parasites are endemic, studying host-parasites interactions may give us important insights about energetic trade-offs involved in malarial parasites infections in birds. In this study, we tested the consequences of Haemoproteus infection on the Bananaquit, a resident species of Puerto Rico. We also tested for potential sources of individual heterogeneity in the consequences of infection such as host age and sex. To quantify the consequences of infection to hosts' health we compared three complementary body condition indices between infected and uninfected individuals. Our results showed that Bananaquits infected by Haemoproteus had higher body condition than uninfected individuals. This result was consistent among the three body condition indices. Still, we found no clear evidence that this effect was mediated by host age or sex. We discuss a set of non-mutually exclusive hypotheses that may explain this pattern including metabolic syndrome, immunological responses leading to host tolerance or resistance to infection, and potential changes in consumption rates. Overall, our results suggest that other mechanisms, may drive the consequences of avian malarial infection.

Global prevalence of Plasmodium infection in wild birds: A systematic review and meta-analysis

Avian malaria is a vector-borne parasitic disease caused by Plasmodium infection transmitted to birds by mosquitoes. The aim of this systematic review was to analyze the global prevalence of malaria and risk factors associated with infection in wild birds. A systematic search of the databases CNKI, WanFang, VIP, PubMed, and ScienceDirect was performed from database inception to 24 February 2023. The search identified 3181 retrieved articles, of which 52 articles met predetermined inclusion criteria. Meta-analysis was performed using the random-effects model. The estimated pooled global prevalence of Plasmodium infection in wild birds was 16%. Sub-group analysis showed that the highest prevalence was associated with adult birds, migrant birds, North America, tropical rainforest climate, birds captured by mist nets, detection of infection by microscopy, medium quality studies, and studies published after 2016. Our study highlights the need for more understanding of Plasmodium prevalence in wild birds and identifying risk factors associated with infection to inform future infection control measures.

The influence of the host sex on parasitemia of parasite lineages belonging to Haemoproteus majoris in a natural bird community

Immunological capability shows a sexual dimorphism in diverse animal species. Females are generally more immunocompetent than males, leading to the higher susceptibility of males to infection compared to females and thus greater infection-related pathology in males. These sex-differences in immunity remain understudied in birds. Here, we compared the percentage of parasitemia of three different parasite lineages belonging to the morphological species Haemoproteus majoris (namely, PARUS1, PHSIB1 and WW2) in terms of the sex of birds living in a natural community. We found that parasitemia (percentage of erythrocytes infected with parasites) of WW2 lineage, but not of the other two lineages of H. majoris, is higher in male birds compared to female birds. Similarly, we showed that the total parasitemia of these three H. majoris lineages is higher in male birds compared to female birds. Our study points out that male birds at the community level may be more susceptible to infection by certain parasites than female birds. We propose that sexual dimorphism in parasitemia of certain parasites in host birds might be more common than previously thought, similar to what is observed in other species, influencing host population dynamics in a sex-specific manner. Therefore, it can be speculated that infection by certain parasites might differentially affect male and female birds, possibly resulting in a bias in survival rates between sexes due to infections, in certain contexts.

The Pathology of Fatal Avian Malaria Due to Plasmodium elongatum (GRW6) and Plasmodium matutinum (LINN1) Infection in New Zealand Kiwi (Apteryx spp.)

Avian malaria caused by Plasmodium species is a known cause of mortality in avifauna worldwide, however reports within New Zealand kiwi (Apteryx spp.) are scant. Postmortem reports from kiwi were obtained from the Massey University/Te Kunenga ki Pūrehuroa School of Veterinary Science Pathology Register from August 2010-August 2020. Gross lesions were described from postmortem reports, and archived H.E.-stained slides used for histological assessment. Nested PCR testing was performed on formalin-fixed paraffin-embedded tissue samples to assess the presence of Plasmodium spp. and Toxoplasma gondii DNA and cases with a PCR-positive result were sequenced to determine the lineage involved. Of 1005 postmortem reports, 23 cases of confirmed or suspected avian malaria were included in this study. The most consistent gross lesions included splenomegaly, hepatomegaly, and interstitial pneumonia with oedema. Histological lesions were characterised by severe interstitial pneumonia, pulmonary oedema, interstitial myocarditis, hepatic sinusoidal congestion and hypercellularity, and splenic macrophage hyperplasia and hyperaemia/congestion with numerous haemosiderophages. Cytoplasmic meronts were consistently found within endothelial cells of a variety of tissues, and within tissue macrophages of the liver, lung and spleen. A diagnosis of avian malaria was confirmed via PCR testing in 13 cases, with sequencing revealing P. matutinum (LINN1) and P. elongatum (GRW6) as the species involved. This is the largest case series describing the pathology of avian malaria as a cause of mortality in endemic New Zealand avifauna.

Haemosporidians from a Neglected Group of Terrestrial Wild Birds in the Peruvian Amazonia

Haemosporidians are a widespread group of blood parasites transmitted by vectors. Despite their relevance for bird conservation, few studies have been conducted in the Amazonia and even less in terrestrial wild birds. We analysed blood samples from 168 game birds, collected from 2008 to 2015 by subsistence hunters of an indigenous rural community in the Peruvian Amazonia. DNA was tested for Haemoproteus spp., Plasmodium spp. and Leucocytozoon spp. and positive amplicons were sequenced and curated for phylogenetic analysis. Haemosporidian prevalence was 72% overall, 66.7% for Haemoproteus spp. and 5.4% for Plasmodium spp. and respectively by bird species: Spix's Guan (Penelope jacquacu, n = 72) 87.5% and 0%, Razor-billed Curassow (Mitu tuberosum, n = 45) 77.8% and 6.7%, White-winged Trumpeter (Psophia leucoptera, n = 20) 6.3% and 12.5%, Blue-throated Piping-guan (Pipile cumanensis, n = 16) 73.3% and 6.7%, and Great Tinamou (Tinamus major, n = 15) 10% and 15%. Leucocytozoon spp. was not found. P. leucoptera and T. major were less likely to be infected with Haemoproteus spp. Fruit abundance had a negative association with Haemoproteus spp. prevalence and precipitation was negatively associated with Plasmodium spp. prevalence. The 106 sequences examined represented 29 lineages, 82.8% of them were new lineages (Plasmodium n = 3, Haemoproteus n = 21). Novel host-parasite associations and lineages were unveiled, including probably new species of Plasmodium spp. Our results highlight the scientific value of alternative sampling methods and the collaboration with local communities.

High Blood Parasite Infection Rate and Low Fitness Suggest That Forest Water Bodies Comprise Ecological Traps for Pied Flycatchers

Blood parasites are considered to have strong negative effects on host fitness. Negative fitness consequences may be associated with proximity to areas where blood parasite vectors reproduce. This study tested for relationships between haemosporidian infection prevalence, parasitemia, and fitness parameters of breeding Pied Flycatchers (Ficedula hypoleuca) at different distances from forest water bodies. Prevalence and parasitemias (the intensity of infection) of haemosporidians and vector abundance generally decreased with increasing distance from forest lakes, streams, and bogs. Fledgling numbers were lower, and their condition was worse in the vicinity of water bodies, compared with those located one kilometer away from lakes and streams. At the beginning of the breeding season, adult body mass was not related to distance to the nearest water body, whereas at the end of the breeding season body mass was significantly lower closer to water bodies. Forest areas around water bodies may represent ecological traps for Pied Flycatchers. Installing nest boxes in the vicinity of forest water bodies creates unintended ecological traps that may have conservation implications.

The Impact of Temperature on the Sporogonic Development of the Tropical Avian Malaria Parasite Plasmodium relictum (Genetic Lineage pGRW4) in Culex pipiens Form molestus Mosquitoes

The avian malaria parasite Plasmodium relictum (genetic lineage pGRW4) is known to cause severe pathology in nonadapted vertebrate hosts. This parasite is prevalent in some bird species in Northern Europe, however the records obtained are only from adult long-distance migrant birds after their return from the wintering grounds. A recent experimental study showed that this parasite completes sporogonic development in the local European vector Culex pipiens at a controlled mean temperature of 19 °C. Thereby, temperature limits for the transmission of this parasite in Northern Europe remain unknown. In this study, we took a step further and tested the impact of different temperature conditions, including some extreme fluctuations between 23 °C down to 7 °C, on the sporogonic development of P. relictum (pGRW4) in the vector Culex pipiens form molestus. Mosquitoes were exposed to infection and kept under different air-temperature conditions: (i) constant warm temperature, (ii) natural outdoor temperatures and (iii) temporary exposure to low temperatures. Plasmodium relictum (pGRW4) completed sporogony in mosquitoes of all experimental groups, however different patterns of the sporogonic development depending on temperature conditions were observed. Based on these results, we conclude that the cool air temperature of Northern Europe in summer is not a limiting factor in successful development of the parasite. However, delayed sporogony caused by low summer temperatures may have a detrimental impact on the active transmission of this parasite in Northern Europe.

Impacts of selective logging on haemosporidian infection and physiological correlates in tropical birds

Tropical forest degradation affects host-parasite interactions, determining the probability of animals acquiring an infection. The activation of an immune response to fight off infections requires energy and other resources such as antioxidants which may be redirected from growth and reproduction. A key question is how selective logging-the most common form of tropical forest degradation-impacts the prevalence of avian haemosporidian infection and its correlated physiological responses (nutritional and oxidative status markers). We investigated the prevalence of Plasmodium, Haemoproteus, and Leucocytozoon parasites in 14 understorey bird species in lowland, logged and unlogged, old-growth forests of Borneo. Prevalences of infections were similar between selectively logged and unlogged forests. To explore nutritional and oxidative status effects of haemosporidian infections, we examined associations between infections and plasma proteins, plasma triglycerides, and multiple blood-based markers of oxidative status, testing for an impact of selective logging on those markers. Birds infected with Plasmodium showed higher levels of plasma proteins and non-enzymatic antioxidant capacity, and lower levels of plasma triglycerides and glutathione, compared with haemosporidian-free individuals. Conversely, birds infected with Haemoproteus showed no changes in nutritional or physiological markers compared with uninfected individuals. These results indicate higher metabolic and physiological costs of controlling Plasmodium infection, compared with Haemoproteus, possibly due to higher pathogenicity of Plasmodium. Selectively logged forests had no effect on the responses of birds to infection, suggesting that the environmental conditions of degraded forests do not appear to induce any appreciable physiological demands in parasitised birds.

A field test of the dilution effect hypothesis in four avian multi-host pathogens

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens-three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)-and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.

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.

Sex and nest type influence avian blood parasite prevalence in a high-elevation bird community

Background

The prevalence of avian haemosporidian parasites and the factors influencing infection in the Colorado Rocky Mountains are largely unknown. With climate change expected to promote the expansion of vector and avian blood parasite distributions, baseline knowledge and continued monitoring of the prevalence and diversity of these parasites is needed.

Methods

Using an occupancy modeling framework, we conducted a survey of haemosporidian parasite species infecting an avian community in the Colorado Rocky Mountains in order to estimate the prevalence and diversity of blood parasites and to investigate species-level and individual-level characteristics that may influence infection.

Results

We estimated the prevalence and diversity of avian Haemosporidia across 24 bird species, detecting 39 parasite haplotypes. We found that open-cup nesters have higher Haemoproteus prevalence than cavity or ground nesters. Additionally, we found that male Ruby-crowned Kinglets, White-crowned Sparrows, and Wilson’s Warblers have higher Haemoproteus prevalence compared to other host species. Plasmodium prevalence was relatively low (5%), consistent with the idea that competent vectors may be rare at high altitudes.

Conclusions

Our study presents baseline knowledge of haemosporidian parasite presence, prevalence, and diversity among avian species in the Colorado Rocky Mountains and adds to our knowledge of host–parasite relationships of blood parasites and their avian hosts.

Physiological and morphological correlates of blood parasite infection in urban and non-urban house sparrow populations

In the last decade, house sparrow populations have shown a general decline, especially in cities. Avian malaria has been recently suggested as one of the potential causes of this decline, and its detrimental effects could be exacerbated in urban habitats. It was initially thought that avian malaria parasites would not have large negative effects on wild birds because of their long co-evolution with their hosts. However, it is now well-documented that they can have detrimental effects at both the primo- and chronical infection stages. In this study, we examined avian malaria infection and its physiological and morphological consequences in four populations of wild house sparrows (2 urban and 2 rural). We did not find any relationship between the proportions of infected individuals and the urbanisation score calculated for our populations. However, we observed that the proportion of infected individuals increased during the course of the season, and that juveniles were less infected than adults. We did not detect a strong effect of malaria infection on physiological, morphological and condition indexes. Complex parasite dynamics and the presence of confounding factors could have masked the potential effects of infection. Thus, longitudinal and experimental studies are needed to understand the evolutionary ecology of this very common, but still poorly understood, wild bird parasite.

Using a multistate occupancy approach to determine molecular diagnostic accuracy and factors affecting avian haemosporidian infections

The use of a sensitive and accurate parasite detection methodology is crucial in studies exploring prevalence of parasites in host populations or communities, and uncertainty in identifying parasite genera and/or lineages may limit the understanding of host-parasite interactions. Here, we used a multistate occupancy approach that accounts for imperfect detection to assess whether sex and breeding season influenced the prevalence of a specific Haemoproteus lineage (TARUF02) in a white-lined tanager population. Likewise, we explored whether the probability of detecting the target parasite in an infected bird using PCR and sequencing analyses may be influenced by season and host sex. We found little evidence that sex influenced the probability of an individual host being infected by a haemosporidian parasite. Conversely, we found that the probability of infection by Haemoproteus TARUF02 was ~30% higher during the breeding season, reflecting a higher prevalence of this parasite in this season. The probability that PCR detects DNA of haemosporidian parasite was higher for female birds, suggesting that they are more prone to be parasitized with parasitemia levels that are more successfully detected by molecular analysis. Sequencing successfully determined the Haemoproteus TARUF02 lineage in 60% of samples collected during the breeding season and 84% of samples collected during the non-breeding season. Understanding the ecology of hosts and aspects of their physiology that may influence the parasite infection is essential to better understanding of hemoparasite infections and how parasites influence their native hosts, through decreasing reproductive success, lifespan, and/or survival.

Sex-biased parasitism in vector-borne disease: Vector preference?

Sex-biased infections are a recurrent observation in vertebrates. In many species, males are more parasitized than females. Two potentially complementary mechanisms are often suggested to explain this pattern: sexual differences in susceptibility mainly caused by the effect of sex hormones on immunity and differential exposure to parasites. Exposure is mostly a consequence of host behavioural traits, but vector-borne parasitic infections involve another degree of complexity due to the active role of vectors in transmission. Blood-sucking insects may make choices based on cues produced by hosts. Regarding malaria, several studies highlighted a male-biased infection by Plasmodium sp in great tits (Parus major). We hypothesize that the mosquito vector, Culex pipiens, might at least partially cause this bias by being more attracted to male birds. Intrinsic variation associated to bird sex would explain a preference of mosquitoes for males. To test this hypothesis, we provide uninfected mosquitoes with a choice between uninfected male and female nestlings. Mosquito choice is assessed by sex typing of the ingested blood. We did not observe any preference for a given sex. This result does not support our prediction of a preference of mosquitoes for male great tits during the nestling period. In conclusion, mosquitoes do not seem to have an intrinsic preference for male nestlings. However, sexually divergent traits (e.g. behaviour, odour, metabolic rate) present in adults may play a role in the attraction of mosquitoes and should be investigated.

Louse flies of Eleonora's falcons that also feed on their prey are evolutionary dead-end hosts for blood parasites

Host shifts are widespread among avian haemosporidians, although the success of transmission depends upon parasite‐host and parasite‐vector compatibility. Insular avifaunas are typically characterized by a low prevalence and diversity of haemosporidians, although the underlying ecological and evolutionary processes remain unclear. We investigated the parasite transmission network in an insular system formed by Eleonora's falcons (the avian host), louse flies that parasitize the falcons (the potential vector), and haemosporidians (the parasites). We found a great diversity of parasites in louse flies (16 Haemoproteus and 6 Plasmodium lineages) that did not match with lineages previously found infecting adult falcons (only one shared lineage). Because Eleonora's falcon feeds on migratory passerines hunted over the ocean, we sampled falcon kills in search of the origin of parasites found in louse flies. Surprisingly, louse flies shared 10 of the 18 different parasite lineages infecting falcon kills. Phylogenetic analyses revealed that all lineages found in louse flies (including five new lineages) corresponded to Haemoproteus and Plasmodium parasites infecting Passeriformes. We found molecular evidence of louse flies feeding on passerines hunted by falcons. The lack of infection in nestlings and the mismatch between the lineages isolated in adult falcons and louse flies suggest that despite louse flies’ contact with a diverse array of parasites, no successful transmission to Eleonora's falcon occurs. This could be due to the falcons’ resistance to infection, the inability of parasites to develop in these phylogenetically distant species, or the inability of haemosporidian lineages to complete their development in louse flies.

Effects of host sex, body mass and infection by avian Plasmodium on the biting rate of two mosquito species with different feeding preferences

BACKGROUND

The transmission of mosquito-borne pathogens is strongly influenced by the contact rates between mosquitoes and susceptible hosts. The biting rates of mosquitoes depend on different factors including the mosquito species and host-related traits (i.e. odour, heat and behaviour). However, host characteristics potentially affecting intraspecific differences in the biting rate of mosquitoes are poorly known. Here, we assessed the impact of three host-related traits on the biting rate of two mosquito species with different feeding preferences: the ornithophilic Culex pipiens and the mammophilic Ochlerotatus (Aedes) caspius. Seventy-two jackdaws Corvus monedula and 101 house sparrows Passer domesticus were individually exposed to mosquito bites to test the effect of host sex, body mass and infection status by the avian malaria parasite Plasmodium on biting rates.

RESULTS

Ochlerotatus caspius showed significantly higher biting rates than Cx. pipiens on jackdaws, but non-significant differences were found on house sparrows. In addition, more Oc. caspius fed on female than on male jackdaws, while no differences were found for Cx. pipiens. The biting rate of mosquitoes on house sparrows increased through the year. The bird infection status and body mass of both avian hosts were not related to the biting rate of both mosquito species.

CONCLUSIONS

Host sex was the only host-related trait potentially affecting the biting rate of mosquitoes, although its effect may differ between mosquito and host species.

Blood parasite infection linked to condition of spring-migrating Lesser Scaup (Aythya affinis)

Numerous organisms exhibit carry-over effects, in which previous environmental conditions impact current performance. For example, reproductive output for many migratory birds can be impacted by events during the preceding migration. Lesser Scaup (Aythya affinis (Eyton, 1838); hereafter scaup) declined dramatically during 1970s–2000s, and there is evidence linking reduced reproductive output to reduced body condition during spring migration. In addition to food availability and quality, haemosporidian parasites (Plasmodium spp., Haemoproteus spp.) may be associated with condition of spring-migrating birds. We examined whether haemosporidian parasite infection status was linked to measures of size (mass, wing length, tarsus length, and keel length) and condition (body fat, size-corrected mass, wing-loading) in female spring-migrating scaup. Infection prevalence varied by year (21.7% in 2014; 47.1% in 2015) and percent body fat was negatively associated with the probability of infection. Body fat levels declined from 2014 to 2015, but at a similar rate for infected and uninfected birds. This pattern suggests that the increased prevalence in 2015 may have been related to the greater proportion of poor-condition birds being more susceptible to infection or recrudescence of latent infections. In light of forecasted range shifts and expansions of avian malaria vectors, the impact of haemosporidian parasites on migratory waterfowl condition warrants further investigation.

Molecular characterization of avian malaria in the spotless starling (Sturnus unicolor)

We studied the prevalence and genetic diversity of malaria parasites in the poorly investigated spotless starling (Sturnus unicolor) breeding in central Spain, aiming to describe the phylogenetic relationships among them and with other haemosporidians infecting the genus Sturnus. A total of 180 nestlings and 180 adult individuals from four different breeding seasons were screened for haemosporidian parasites using a nested PCR approach for the genera Plasmodium and Haemoproteus. Although the malaria prevalence ranged between years, the overall prevalence was 6.94%. Adults had a higher prevalence than chicks: 12.77 vs. 1.11%, respectively. We molecularly characterized avian malaria isolated in peripheral blood samples taken from malaria-infected individuals. Sequence analyses revealed four unique Plasmodium lineages of avian malaria (STURUNI01, STURUNI02, SYAT05, SGS1) in our spotless starling population. The phylogenetic analysis showed a well-supported clade comprised by STURUNI01, STURUNI02, and SYAT05. The most common lineage (SYAT05) has been previously found in 26 other avian host species, including populations of spotless starling in Portugal. Because this sedentary species is widely distributed throughout the Iberian Peninsula, we suggest that the local transmission of these lineages might place migratory birds at infection risk.

Haemosporidian infections affect antioxidant defences in great tits Parus major but are not related to exposure to aerial pollutants

Haemosporidian parasites are widespread in avian species and modulate their ecology, behaviour, life-history and fitness. The prevalence of these vector-transmitted parasites varies with host intrinsic and extrinsic factors, such as host resistance and behaviour, and habitat-related characteristics. In this study, we evaluated the prevalence of avian haemosporidians in great tit Parus major populations inhabiting two areas with different degrees of exposure to aerial emissions from pulp mills, to assess if this type of pollution impacted parasite prevalence. We also compared the physiological condition of infected and uninfected individuals. Haemosporidian infection prevalence was high (58%), varied seasonally, but was not associated with air pollution exposure. Fledged birds presented higher infection rates than nestlings and infected fledged birds had higher levels of blood glutathione peroxidase activity. These results allow us to infer that infection by blood parasites may activate antioxidant defences, possibly to protect the organism from the negative oxidative stress side-effects of immune activation against parasites. Because oxidative stress is one of the mechanisms responsible for ageing and senescence and may affect fitness, the relationship between parasitism and oxidative stress markers should be further investigated through studies that include experimental manipulation of infection in model organisms.

High rates of infection by blood parasites during the nestling phase in UK Columbids with notes on ecological associations

Studies of blood parasite infection in nestling birds rarely find a high prevalence of infection. This is likely due to a combination of short nestling periods (limiting the age at which nestlings can be sampled) and long parasite prepatent periods before gametocytes can be detected in peripheral blood. Here we examine rates of blood parasite infection in nestlings from three Columbid species in the UK. We use this system to address two key hypotheses in the epidemiology of avian haemoparasites: first, that nestlings in open nests have a higher prevalence of infection; and second, that nestlings sampled at 14 days old have a higher apparent infection rate than those sampled at 7 days old. Open-nesting individuals had a 54% infection rate compared with 25% for box-nesters, probably due to an increased exposure of open-nesting species to dipteran vectors. Nestlings sampled at 14 days had a 68% infection rate compared with 32% in nestlings sampled at 7 days, suggesting that rates of infection in the nest are high. Further work should examine nestlings post-fledging to identify rates of successful parasite infection (as opposed to abortive development within a dead-end host) as well as impacts on host post-fledging survival and behaviour.