Diptera vectors of avian Haemosporidian parasites: untangling parasite life cycles and their taxonomy

Haemoproteus infections (Haemosporida, Haemoproteidae) kill bird-biting mosquitoes

Haemoproteus parasites (Haemosporida, Haemoproteidae) are widespread; some species cause severe diseases in avian hosts. Heavy Haemoproteus infections are often lethal for biting midges (Ceratopogonidae), which transmit avian haemoproteids, but there is no information regarding detrimental effect on other blood-sucking insects. We examined effects of Haemoproteus tartakovskyi (lineage hSISKIN1), Haemoproteus lanii (lineages hRB1and hRBS2) and Haemoproteus balmorali (lineage hCOLL3) on the survival of Ochlerotatus cantans, a widespread Eurasian mosquito. Wild-caught females were infected by allowing them to feed on naturally infected birds with light (0.01%) and high (3.0-9.6%) parasitaemia. Mosquitoes fed on uninfected birds were used as controls. Both experimental and control groups were maintained under the same laboratory conditions until 20 days post-exposure (dpe). Dead insects were counted daily and used for parasitological examination and PCR-based testing. No difference was discernible in the survival rate of control mosquitoes and those fed on meal with light parasitaemia. There was a highly significant difference in the survival rate between the control group and all groups fed on meals with high parasitaemia, with the greatest mortality reported 1-3 dpe. For 4 dpe, the percentage of survived control mosquitoes (88%) was 2.2-, 3.6- and 4-fold greater than that of groups fed on meals with high parasitaemia of H. balmorali, H. tartakovskyi and H. lanii, respectively. Numerous ookinetes were observed in the gut area and adjacent tissues located in the head, thorax and abdomen of infected insects 0.5-1 dpe. The migrating parasites damage organs throughout the entire body of mosquitoes; that is the main reason of mortality. To the end of this study, 46% of mosquitoes survived in control group, but the survival rates of experimental mosquitoes fed on meals with high parasitaemia were between 2.6- and 5.8-fold lower. This study indicates that widespread Haemoproteus infections are markedly virulent for bird-biting mosquitoes, which rapidly die after feeding on heavily infected blood meals.

Associations of forest type, parasitism and body condition of two European passerines, Fringilla coelebs and Sylvia atricapilla

Human-induced forest modification can alter parasite-host interactions and might change the persistence of host populations. We captured individuals of two widespread European passerines (Fringilla coelebs and Sylvia atricapilla) in southwestern Germany to disentangle the associations of forest types and parasitism by haemosporidian parasites on the body condition of birds. We compared parasite prevalence and parasite intensity, fluctuating asymmetries, leukocyte numbers, and the heterophil to lymphocyte ratio (H/L-ratio) among individuals from beech, mixed-deciduous and spruce forest stands. Based on the biology of bird species, we expected to find fewer infected individuals in beech or mixed-deciduous than in spruce forest stands. We found the highest parasite prevalence and intensity in beech forests for F. coelebs. Although, we found the highest prevalence in spruce forests for S. atricapilla, the highest intensity was detected in beech forests, partially supporting our hypothesis. Other body condition or health status metrics, such as the heterophil to lymphocyte ratio (H/L-ratio), revealed only slight differences between bird populations inhabiting the three different forest types, with the highest values in spruce for F. coelebs and in mixed-deciduous forests for S. atricapilla. A comparison of parasitized versus non-parasitized individuals suggests that parasite infection increased the immune response of a bird, which was detectable as high H/L-ratio. Higher infections with blood parasites for S. atricapilla in spruce forest indicate that this forest type might be a less suitable habitat than beech and mixed-deciduous forests, whereas beech forests seem to be a suboptimal habitat regarding parasitism for F. coelebs.

Finding the appropriate variables to model the distribution of vector-borne parasites with different environmental preferences: climate is not enough

Understanding how environmental variation influences the distribution of parasite diversity is critical if we are to anticipate disease emergence risks associated with global change. However, choosing the relevant variables for modelling current and future parasite distributions may be difficult: candidate predictors are many, and they seldom are statistically independent. This problem often leads to simplistic models of current and projected future parasite distributions, with climatic variables prioritized over potentially important landscape features or host population attributes. We studied avian blood parasites of the genera Plasmodium, Haemoproteus and Leucocytozoon (which are viewed as potential emergent pathogens) in 37 Iberian blackcap Sylvia atricapilla populations. We used Partial Least Squares regression to assess the relative importance of a wide array of putative determinants of variation in the diversity of these parasites, including climate, landscape features and host population migration. Both prevalence and richness of parasites were predominantly related to climate (an effect which was primarily, but not exclusively driven by variation in temperature), but landscape features and host migration also explained variation in parasite diversity. Remarkably, different models emerged for each parasite genus, although all parasites were studied in the same host species. Our results show that parasite distribution models, which are usually based on climatic variables alone, improve by including other types of predictors. Moreover, closely related parasites may show different relationships to the same environmental influences (both in magnitude and direction). Thus, a model used to develop one parasite distribution can probably not be applied identically even to the most similar host-parasite systems.

Description and molecular characterization of Plasmodium (Novyella) unalis sp. nov. from the Great Thrush (Turdus fuscater) in highland of Colombia

Plasmodium (Novyella) unalis sp. nov. was found in the Great Thrush, Turdus fuscater (Passeriformes, Turdidae) in Bogotá, Colombia, at 2,560 m above sea level where the active transmission occurs. This parasite is described based on the morphology of its blood stages and a fragment of the mitochondrial cytochrome b gene (lineage UN227). Illustrations of blood stages of new species are given, and the phylogenetic analysis identifies closely related species and lineages of avian malaria parasites. The new species is most similar to Plasmodium (Novyella) vaughani (lineage SYAT05), a cosmopolitan avian malaria parasite; these parasites are also closely related genetically, with a genetic difference of 3.2% between them. P. unalis can be readily distinguished from the latter species morphologically, primarily due to the (1) presence of a single large, circular shaped pigment granule in the erythrocytic trophozoites and meronts; (2) presence of prominent vacuoles in trophozoites and growing meronts; and (3) presence of predominantly fan-like shaped erythrocytic meronts. Cytochrome b lineages with high similarity to the new species have been reported in Costa Rica, Brazil, Chile, and USA. It is probable that the new species of malaria parasite is widely distributed in the New World. This parasite has been reported only in the Great Thrush at the study site and might have a narrow range of avian hosts. Records of P. unalis are of particular theoretical interest due to its active transmission at highlands in Andes. Possible influence of urbanization on transmission of this malaria parasite in Bogotá is discussed.

Urban forests as hubs for novel zoonosis: blood meal analysis, seasonal variation in Culicoides (Diptera: Ceratopogonidae) vectors, and avian haemosporidians

Culicoides vectors can transmit a diverse array of parasites and are globally distributed. We studied feeding preferences and seasonal variation of Culicoides (Diptera: Ceratopogonidae) vectors in an urban forest of Germany to determine whether humans living nearby are readily exposed to vector-borne parasites from wild animals. We used a fragment of the mtDNA COI gene to identify hosts from blood meals. We amplified a fragment of the mtDNA cyt b to detect haemosporidian infections in Culicoides abdomens and thoraxes. We detected a total of 22 Culicoides species. Fifty-eight blood meals (84%) were from humans, 10 from birds, and one from livestock. We found Culicoides kibunensis (considered ornithophilic) with 29 human blood meals. Host generalist Culicoides festivipennis and Culicoides obsoletus had 14 human blood meals. Culicoides clastrieri and Culicoides semimaculatus fed on birds; previously humans were their only known host. Six thoraxes and three abdomens were infected with either Haemoproteus pallidulus or Haemoproteus parabelopolskyi. There were changes in Culicoides community structure across months. Culicoides pictipennis was the dominant species during spring, C. kibunensis and C. clastrieri were dominant during summer, and C. obsoletus was dominant by early autumn. All dominant species were generalists feeding on birds, livestock and humans. Our results indicate that humans can serve as a blood source for dominant Culicoides species instead of the normal wild animal hosts in urban areas.

Culicoides biting midges, arboviruses and public health in Europe

The emergence of multiple strains of bluetongue virus (BTV) and the recent discovery of Schmallenberg virus (SBV) in Europe have highlighted the fact that exotic Culicoides-borne arboviruses from remote geographic areas can enter and spread rapidly in this region. This review considers the potential for this phenomenon to impact on human health in Europe, by examining evidence of the role of Culicoides biting midges in the zoonotic transmission and person-to-person spread of arboviruses worldwide. To date, the only arbovirus identified as being primarily transmitted by Culicoides to and between humans is Oropouche virus (OROV). This member of the genus Orthobunyavirus causes major epidemics of febrile illness in human populations of South and Central America and the Caribbean. We examine factors promoting sustained outbreaks of OROV in Brazil from an entomological perspective and assess aspects of the epidemiology of this arbovirus that are currently poorly understood, but may influence the risk of incursion into Europe. We then review the secondary and rarely reported role of Culicoides in the transmission of high-profile zoonotic infections, while critically reviewing evidence of this phenomenon in endemic transmission and place this in context with the presence of other potential vector groups in Europe. Scenarios for the incursions of Culicoides-borne human-to-human transmitted and zoonotic arboviruses are then discussed, along with control measures that could be employed to reduce their impact. These measures are placed in the context of legislative measures used during current and ongoing outbreaks of Culicoides-borne arboviruses in Europe, involving both veterinary and public health sectors.

On the study of the transmission networks of blood parasites from SW Spain: diversity of avian haemosporidians in the biting midge Culicoides circumscriptus and wild birds

Background

Blood-sucking flying insects play a key role in the transmission of pathogens of vector-borne diseases. However, at least for the case of avian malaria parasites, the vast majority of studies focus on the interaction between parasites and vertebrate hosts, but there is a lack of information regarding the interaction between the parasites and the insect vectors. Here, we identified the presence of malaria and malaria-like parasite lineages harbored by the potential vector Culicoides circumscriptus (Kieffer). Also, we identified some nodes of the transmission network connecting parasite lineages, potential insect vectors and avian hosts by comparing Haemoproteus and Plasmodium lineages isolated from insects with those infecting wild birds in this and previous studies.

Methods

Using a molecular approach, we analysed the presence of blood parasites in a total of 97 biting midges trapped in the Doñana National Park (SW Spain) and surrounding areas. Also, 123 blood samples from 11 bird species were analyzed for the presence of blood parasite infections. Blood parasites Haemoproteus and Plasmodium were identified by amplification of a 478 bp fragment of the mitochondrial cytochrome b gen.

Results

Thirteen biting midges harboured blood parasites including six Haemoproteus and two Plasmodium lineages, supporting the potential role of these insects on parasite transmission. Moreover, ten (8.1%) birds carried blood parasites. Seven Plasmodium and one Haemoproteus lineages were isolated from birds. Overall, six new Haemoproteus lineages were described in this study. Also, we identified the transmission networks of some blood parasites. Two Haemoproteus lineages, hCIRCUM03 and GAGLA03, were identical to those isolated from Corvus monedula in southern Spain and Garrulus glandarius in Bulgaria, respectively. Furthermore, the new Haemoproteus lineage hCIRCUM05 showed a 99% similarity with a lineage found infecting captive penguins in Japan.

Conclusions

The comparison of the parasite lineages isolated in this study with those previously found infecting birds allowed us to identify some potential nodes in the transmission network of avian blood parasite lineages. These results highlight the complexity of the transmission networks of blood parasites in the wild that may involve a high diversity of susceptible birds and insect vectors.

Avian Plasmodium in Culex and Ochlerotatus Mosquitoes from Southern Spain: Effects of Season and Host-Feeding Source on Parasite Dynamics

Haemosporidians, a group of vector-borne parasites that include Plasmodium, infect vertebrates including birds. Although mosquitoes are crucial elements in the transmission of avian malaria parasites, little is known of their ecology as vectors. We examined the presence of Plasmodium and Haemoproteus lineages in five mosquito species belonging to the genera Culex and Ochlerotatus to test for the effect of vector species, season and host-feeding source on the transmission dynamics of these pathogens. We analyzed 166 blood-fed individually and 5,579 unfed mosquitoes (grouped in 197 pools) from a locality in southern Spain. In all, 15 Plasmodium and two Haemoproteus lineages were identified on the basis of a fragment of 478 bp of the mitochondrial cytochrome b gene. Infection prevalence of blood parasites in unfed mosquitoes varied between species (range: 0-3.2%) and seasons. The feeding source was identified in 91 mosquitoes where 78% were identified as bird. We found that i) several Plasmodium lineages are shared among different Culex species and one Plasmodium lineage is shared between Culex and Ochlerotatus genera; ii) mosquitoes harboured Haemoproteus parasites; iii) pools of unfed females of mostly ornithophilic Culex species had a higher Plasmodium prevalence than the only mammophylic Culex species studied. However, the mammophylic Ochlerotatus caspius had in pool samples the greatest Plasmodium prevalence. This relative high prevalence may be determined by inter-specific differences in vector survival, susceptibility to infection but also the possibility that this species feeds on birds more frequently than previously thought. Finally, iv) infection rate of mosquitoes varies between seasons and reaches its maximum prevalence during autumn and minimum prevalence in spring.

Molecular characterization and distribution of Haemoproteus minutus (Haemosporida, Haemoproteidae): a pathogenic avian parasite

Recently, the lineage hTURDUS2 of Haemoproteus minutus (Haemosporida, Haemoproteidae) was reported to cause mortality in captive parrots. This parasite lineage is widespread and prevalent in the blackbird Turdus merula throughout its entire distribution range. Species identity of other closely related lineages recently reported in dead parrots remains unclear, but will be important to determine for a better understanding of the epidemiology of haemoproteosis. Using polymerase chain reaction (PCR)-based and microscopic methods, we analyzed 265 blood samples collected from 52 species of wild birds in Eurasia (23 samples from Kamchatka Peninsula, 73 from Sakhalin Island, 150 from Ekaterinburg and 19 from Irkutsk regions of Russia). Single infections of the lineages hTURDUS2 (hosts are redwing Turdus iliacus and fieldfare Turdus pilaris), hTUPHI1 (song thrush Turdus philomelos) and hTUCHR01 (fieldfare, redwing, song thrush and brown-headed thrush Turdus chysolaus) were detected. We identified species of these haemoproteids based on morphology of their blood stages and conclude that these lineages belong to H. minutus, a widespread parasite of different species of thrushes (genus Turdus), which serve as reservoir hosts of this haemoproteid infection. Phylogenetic analysis shows that the lineages hTURDUS2, hTUCHR01 and hTUPHI1 of H. minutus are closely related to Haemoproteus pallidus (lineages hPFC1 and hCOLL2), Haemoproteus pallidulus (hSYAT03), and Haemoproteus sp. (hMEUND3); genetic distance among their mitochondrial cytochrome b (cyt b) lineages is small (<1% or<4 nucleotides). All these blood parasites are different in many morphological characters, but are similar due to one feature, which is the pale staining of their macrogametocytes' cytoplasm with Giemsa. Because of the recent publications about mortality caused by the lineages hTUPHI1 and hTURDUS2 of H. minutus in captive parrots in Europe, H. minutus and the closely related H. pallidus and H. pallidulus are worth more attention as these are possible agents of haemoproteosis in exotic birds. The present study provides barcodes for molecular detection of different lineages of H. minutus, and extends information about the distribution of this blood parasite.

Identification of Plasmodium (Haemamoeba) lutzi (Lucena, 1939) from Turdus fuscater (Great Thrush) in Colombia

This study reports a broadening of the altitudinal range and a new host for Plasmodium (Haemamoeba) lutzi in Colombia. The study was conducted in the city of Bogotá, located in the Eastern Cordillera of Colombia at 2,560 m asl (meters above sea level) with an average annual temperature of 15 C. In total, 156 specimens of birds belonging to 25 species and 14 families were captured using mist nets. The blood samples were collected through venipuncture and analyzed by light microscopy. Plasmodium (H.) lutzi was only found in 2 individuals of Turdus fuscater (Great Thrush). This parasite has previously been reported in Aramides cajaneus (before: Aramides cajanea) (Grey-Necked Wood Rail), a bird found in the lowlands of Brazil, Venezuela, and Colombia. This finding provides evidence for a broad host range for P. lutzi that include 2 different orders, Gruiformes and Passeriformes, and also altitudinal expansion of its distribution. The blood stages were compared with the parasite's original descriptions, and the sequence of the parasite's mitochondrial genome (mtDNA) confirms that P. lutzi is a sister taxa of Plasmodium relictum, as previously proposed.

Two new Haemoproteus species (Haemosporida: Haemoproteidae) from columbiform birds

Here we describe Haemoproteus (Haemoproteus) multivolutinus n. sp. from a tambourine dove (Turtur timpanistria) of Uganda and Haemoproteus (Haemoproteus) paramultipigmentatus n. sp. (Haemosporida, Haemoproteidae) from the Socorro common ground dove (Columbina passerina socorroensis) of Socorro Island, Mexico. These parasites are described based on the morphology of their blood stages and segments of the mitochondrial cytochrome b gene that can be used for molecular identification and diagnosis of these species. Gametocytes of H. multivolutinus possess rod-like pigment granules and are evenly packed with volutin, which masks pigment granules and darkly stains both macro- and microgametocytes in the early stages of their development. Based on these 2 characters, H. multivolutinus can be readily distinguished from other species of hemoproteids parasitizing columbiform (Columbiformes) birds. Haemoproteus paramultipigmentatus resembles Haemoproteus multipigmentatus; it can be distinguished from the latter parasite primarily due to the broadly ovoid shape of its young gametocytes and significantly fewer pigment granules in its fully developed gametocytes. We provide illustrations of blood stages of the new species, and phylogenetic analyses identify DNA lineages closely related to these parasites. Cytochrome b lineages of Haemoproteus multivolutinus and H. paramultipigmentatus cluster with hippoboscid-transmitted lineages of hemoproteids; thus these parasites likely belong to the subgenus Haemoproteus. We emphasize the importance of using cytochrome b sequences in conjunction with thorough microscopic descriptions to facilitate future identification of these and other avian hemosporidian species.