Haemosporidian vector research: marriage of molecular and microscopical approaches is essential

A Literature Review on the Role of the Invasive Aedes albopictus in the Transmission of Avian Malaria Parasites

The Asian tiger mosquito (Aedes albopictus) is an invasive mosquito species with a global distribution. This species has populations established in most continents, being considered one of the 100 most dangerous invasive species. Invasions of mosquitoes such as Ae. albopictus could facilitate local transmission of pathogens, impacting the epidemiology of some mosquito-borne diseases. Aedes albopictus is a vector of several pathogens affecting humans, including viruses such as dengue virus, Zika virus and Chikungunya virus, as well as parasites such as Dirofilaria. However, information about its competence for the transmission of parasites affecting wildlife, such as avian malaria parasites, is limited. In this literature review, we aim to explore the current knowledge about the relationships between Ae. albopictus and avian Plasmodium to understand the role of this mosquito species in avian malaria transmission. The prevalence of avian Plasmodium in field-collected Ae. albopictus is generally low, although studies have been conducted in a small proportion of the affected countries. In addition, the competence of Ae. albopictus for the transmission of avian malaria parasites has been only proved for certain Plasmodium morphospecies under laboratory conditions. Therefore, Ae. albopictus may play a minor role in avian Plasmodium transmission in the wild, likely due to its mammal-biased blood-feeding pattern and its reduced competence for the development of different avian Plasmodium. However, further studies considering other avian Plasmodium species and lineages circulating under natural conditions should be carried out to properly assess the vectorial role of Ae. albopictus for the Plasmodium species naturally circulating in its distribution range.

Sympatry in a nightingale contact zone has no effect on host-specific blood parasite prevalence and lineage diversity

Parasites are a key driving force behind many ecological and evolutionary processes. Prevalence and diversity of parasites, as well as their effects on hosts, are not uniform across host species. As such, the potential parasite spillover between species can significantly influence outcomes of interspecific interactions. We screened two species of Luscinia nightingales for haemosporidian blood parasites (Plasmodium, Leucocytozoon and Haemoproteus) along an approximately 3000 km transect in Europe, incorporating areas of host distant allopatry, close allopatry and sympatry. We found significant differences in infection rates between the two host species, with common nightingales having much lower parasite prevalence than thrush nightingales (36.7% versus 83.8%). This disparity was mostly driven by Haemoproteus prevalence, which was significantly higher in thrush nightingales while common nightingales had a small, but significantly higher, Plasmodium prevalence. Furthermore, we found no effect of proximity to the contact zone on infection rate in either host species. Despite having lower infection prevalence, common nightingales were infected with a significantly higher diversity of parasite lineages than thrush nightingales, and lineage assemblages differed considerably between the two species, even in sympatry. This pattern was mostly driven by the large diversity of comparatively rare lineages, while the most abundant lineages were shared between the two host species. This suggests that, despite the close evolutionary relationships between the two nightingales, there are significant differences in parasite prevalence and diversity, regardless of the distance from the contact zone. This suggests that spillover of haemosporidian blood parasites is unlikely to contribute towards interspecific interactions in this system.

New insight into avian malaria vectors in New Zealand

BACKGROUND

Mosquitoes (Culicidae) are vectors for most malaria parasites of the Plasmodium species and are required for Plasmodium spp. to complete their life cycle. Despite having 16 species of mosquitoes and the detection of many Plasmodium species in birds, little is known about the role of different mosquito species in the avian malaria life cycle in New Zealand.

METHODS

In this study, we used nested polymerase chain reaction (PCR) and real-time PCR to determine Plasmodium spp. prevalence and diversity of mitochondrial cytochrome b gene sequences in wild-caught mosquitoes sampled across ten sites on the North Island of New Zealand during 2012-2014. The mosquitoes were pooled by species and location collected, and the thorax and abdomens were examined separately for Plasmodium spp. DNA. Akaike information criterion (AIC) modeling was used to test whether location, year of sampling, and mosquito species were significant predictors of minimum infection rates (MIR).

RESULTS

We collected 788 unengorged mosquitoes of six species, both native and introduced. The most frequently caught mosquito species were the introduced Aedes notoscriptus and the native Culex pervigilans. Plasmodium sp DNA was detected in 37% of matched thorax and abdomen pools. When considered separately, 33% of abdomen and 23% of thorax pools tested positive by nested PCR. The MIR of the positive thorax pools from introduced mosquito species was 1.79% for Ae. notoscriptus and 0% for Cx. quinquefasciatus, while the MIR for the positive thorax pools of native mosquito species was 4.9% for Cx. pervigilans and 0% for Opifex fuscus. For the overall MIR, site and mosquito species were significant predictors of Plasmodium overall MIR. Aedes notoscriptus and Cx. pervigilans were positive for malaria DNA in the thorax samples, indicating that they may play a role as avian malaria vectors. Four different Plasmodium lineages (SYAT05, LINN1, GRW6, and a new lineage of P (Haemamoeba) sp. AENOT11) were identified in the pooled samples.

CONCLUSIONS

This is the first detection of avian Plasmodium DNA extracted from thoraxes of native Culex and introduced Aedes mosquito species in New Zealand and therefore the first study providing an indication of potential vectors in this country.

Landscape and mosquito community impact the avian Plasmodium infection in Culex pipiens

Avian malaria parasites provide an important model for studying host-pathogen interactions, yet understanding their dynamics in vectors under natural conditions is limited. We investigated the effect of vector abundance, species richness and diversity, and habitat characteristics on avian Plasmodium prevalence and lineage richness in Culex pipiens across 45 urban, natural, and rural localities in southern Spain. Analyzing 16,574 mosquitoes grouped in 768 mosquito pools, 32.7% exhibited parasite presence. 13 different Plasmodium lineages were identified, with the lineage SYAT05 being the most commonly found. Parasite prevalence positively correlated with the distance to saltmarshes and rivers, but negatively with the distance to total water source. Parasite lineage diversity was higher in natural than in rural areas and positively correlated with mosquito species richness. These results emphasize the complex dynamics of avian Plasmodium in the wild, with habitat characteristics and vector community driving the parasite transmission by mosquito vectors.

Avian haemosporidian parasites in captive and free-ranging, wild birds from zoological institutions in Switzerland: Molecular characterization and clinical importance

Avian haemosporidian parasites are widespread and infect birds from a broad variety of avian families with diverse consequences ranging from subclinical infections to severe and fatal disease. This study aimed to determine the occurrence and diversity of avian haemosporidia including associated clinical signs and pathomorphological lesions in captive and free-ranging, wild birds from two zoos and the near environment in Switzerland. Blood samples from 475 birds, including 230 captive and 245 free-ranging, wild individuals belonging to 42 different avian species from 15 orders were examined for the presence of avian haemosporidian DNA by a one-step multiplex PCR designed to simultaneously detect and discriminate the genera Plasmodium, Haemoproteus and Leucocytozoon by targeting mitochondrial genome sequences. Positive samples were additionally tested using a nested PCR targeting the cytochrome b gene of Plasmodium and Haemoproteus. The obtained amplicons were bidirectionally sequenced. This study revealed haemosporidian DNA in 42 samples, belonging to ten host species. The most commonly detected lineage was Plasmodium relictum SGS1, which was identified in 29 birds (Phoenicopterus roseus: n = 24, Alectoris graeca: n = 1, Lamprotornis superbus: n = 1, Somateria mollissima: n = 1, Spheniscus demersus: n = 1, Tetrao urogallus crassirostris: n = 1), followed by Haemoproteus sp. STRURA03 in six avian hosts (Bubo bubo: n = 5, Bubo scandiacus = 1), Plasmodium relictum GRW11 in four individuals (Phoenicopterus roseus: n = 3, Spheniscus demersus: n = 1) and Plasmodium elongatum GRW06 in one Alectura lathami lathami. A Phalacrocorax carbo was infected with Plasmodium relictum, but the exact lineage could not be determined. One mixed infection with P. relictum and Haemoproteus sp. was detected in a Bubo scandiacus. Only five individuals (Spheniscus demersus: n = 2, Somateria mollissima: n = 1, Bubo scandiacus: n = 1, Alectoris graeca: n = 1) showed clinical and pathomorphological evidence of a haemosporidian infection.

Molecular Identification of Host Blood Meals and Detection of Blood Parasites in Culicoides Latreille (Diptera: Ceratopogonidae) Collected from Phatthalung Province, Southern Thailand

Five hundred and fifty-nine female biting midges were collected, and seventeen species in six subgenera (Avaritia, Haemophoructus, Hoffmania, Meijerehelea, Remmia, and Trithecoides) and two groups (Clavipalpis and Shortti) were identified. The dominant Culicoides species was C. peregrinus (30.94%), followed by C. subgenus Trithecoides. From blood meal analysis of engorged biting midges, they were found to feed on cows, dogs, pigs, and avians. The majority of blood preferences of biting midges (68%; 49/72) displayed a mixed pattern of host blood DNA (cow and avian). The overall non-engorged biting midge field infectivity rate was 1.44 % (7/487). We detected Leucocytozoon sp. in three Culicoides specimens, one from each species: C. fulvus, C. oxystoma, and C. subgenus Trithecoides. Crithidia sp. was found in two C. peregrinus specimens, and Trypanosoma sp. and P. juxtanucleare were separately found in two C. guttifer. More consideration should be paid to the capacity of biting midges to transmit pathogens such as avian haemosporidian and trypanosomatid parasites. To demonstrate that these biting midges are natural vectors of trypanosomatid parasites, additional research must be conducted with a greater number of biting midges in other endemic regions.

Is Haemoproteus gabaldoni a valid species? An approach from morphology and molecular tools applied to parasites of Anseriformes

Currently, there are three recognized species of haemoproteids infecting Anseriformes: Haemoproteus nettionis, H. macrovacuolatus, and H. greineri. Unfortunately, genetic information associated with a morphotype is available only for H. macrovacuolatus. We recently found a parasite morphologically compatible with Haemoproteus gabaldoni, a species Bennet (1993) described in a Cairina moschata (Muscovy duck) from Venezuela. This species was synonymized to H. nettionis by Valkiūnas (2005), arguing not enough morphological differentiation between them; it was said that H. greineri could be as well a synonym of H. nettionis. In this study, we aimed to provide evidence to determine if Haemoproteus gabaldoni is a different species of H. nettionis and help to clarify other species status. We first performed morphological and morphometrical analyses and compared this information against the parahapantotypes of H. greineri, H. gabaldoni and material diagnosed as H. nettionis provided by the International Reference center for Avian Haematozoa (IRCAH), and H. macrovacuolatus from the Host-Parasite Relationship Study Group (GERPH, in Spanish Grupo de Estudio Relación Parásito Hospedero) biological collection. We used Principal Component Analysis (PCA) of dimensionless standard morphometrical variables from gametocytes. Furthermore, we amplified a small fragment of cytochrome b (cyt b) to compare the sequence with information in GenBank and Malavi through phylogenetic analyses and haplotype networks. PCA analyses revealed the presence of three distinct groups in the samples studied, supported in the morphological traits of each parasite species analyzed; phylogenetic analyses grouped parasite lineages separately according to the host and continent of provenance. Such results indicate that, H. gabaldoni, is a different species from H. nettionis. One more time, it is demonstrated the importance of linking barcode surveys to morphological studies. Finally, it is highlighted the importance of biological collections as repositories of worldwide biodiversity.

Molecular detection of avian haemosporidian parasites in biting midges (Diptera: Ceratopogonidae) from Thailand

Culicoides biting midges are vectors of many haemosporidian parasite species. These parasites are found in several wild and domestic avian species in Thailand but knowledge of the insect vectors is very limited. In this study, a molecular approach was used to detect haemosporidian parasites in six biting midge species in Thailand. A total of fifteen cytochrome b haplotypes of three haemosporidian parasites were detected from 1,165 specimens of six different Culicoides species. Comparisons of these sequences with those recorded in a public database revealed that they were comprised sequences of three species, Leucocytozoon sp., Plasmodium juxtanucleare and P. gallinaceum. All of these haemosporidian parasite species were detected in Culicoides mahasarakhamense Pramual, Jomkumsing, Piraonapicha, & Jumpato while P. juxtanucleare was also detected in C. huffi Causey and C. guttifer Meijere and Leucocytozoon sp. were also detected in C. guttifer. All of these parasites are commonly found in chickens in agreement with information that these biting midge species will bite chickens. Detection DNA of Leucocytozoon sp. in biting midges reported here provides the second record of this parasitic genus infecting Culicoides. This study also provides the first records of P. juxtanucleare and P. gallinaceum in biting midge species. Further investigation is required to determine whether Culicoides biting midge species are competent vectors of these parasites.

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.

Impact of Subclinical Haemoproteus columbae Infection on Farmed Domestic Pigeons from Central Java (Yogyakarta), Indonesia, with Special Reference to Changes in the Hemogram

Pigeon haemoproteosis caused by Haemoproteus columbae (Apicomplexa: Haemosporida: Haemoproteidae) is globally prevalent in rock doves (Columba livia), although little is known regarding this disease in pigeons and doves in Indonesia. Blood samples of 35 farmed domestic pigeons (C. livia f. domestica) from four localities in Yogyakarta Special Region, Central Java, Indonesia, were collected from March to June, 2016, subjected to a hemogram, and analyzed for the presence of hemoprotozoan infections. Microscopic examination of blood smears revealed a prevalence of 62.5–100% of H. columbae at the four localities (n = 8–10 for each locality), and geometric means of 3.0–5.6% of erythrocytes were parasitized by young and mature gametocytes, suggesting that all infected pigeons were in the chronic phase of infection with repeated recurrences and/or reinfections. Nucleotide sequencing of mitochondrial cytochrome b gene (cytb) for haemosporidian species demonstrated the distribution of four major cytb lineages of H. columbae (mainly HAECOL1, accompanied by COLIV03, COQUI05, and CXNEA02 according to the MalAvi database). Hemogram analysis, involving the estimation of packed cell volume, erythrocyte counts, mean corpuscular volume, mean corpuscular hemoglobin concentration, and plasma protein and fibrinogen levels of 20 parasitized pigeons and five non-infected pigeons demonstrated significant macrocytic hypochromic anemia with hypoproteinemia and hyperfibrinogenemia in the infected pigeons. This study shows the profound impact of long-lasting subclinical pigeon haemoproteosis caused by H. columbae on the health of farmed domestic pigeons.

Assessing Diversity, Plasmodium Infection and Blood Meal Sources in Mosquitoes (Diptera: Culicidae) from a Brazilian Zoological Park with Avian Malaria Transmission

Avian malaria parasites are widespread parasites transmitted by Culicidae insects belonging to different genera. Even though several studies have been conducted recently, there is still a lack of information about potential vectors of Plasmodium parasites, especially in Neotropical regions. Former studies with free-living and captive animals in São Paulo Zoo showed the presence of several Plasmodium and Haemoproteus species. In 2015, a pilot study was conducted at the zoo to collect mosquitoes in order to find out (i) which species of Culicidae are present in the study area, (ii) what are their blood meal sources, and (iii) to which Plasmodium species might they be potential vectors. Mosquitoes were morphologically and molecularly identified. Blood meal source and haemosporidian DNA were identified using molecular protocols. A total of 25 Culicidae species were identified, and 6 of them were positive for Plasmodium/Haemoproteus DNA. Ten mosquito species had their source of blood meal identified, which were mainly birds, including some species that were positive for haemosporidian parasites in the former study mentioned. This study allowed us to expand the list of potential vectors of avian malaria parasites and to improve our knowledge of the evolutionary and ecological relationships between the highly diverse communities of birds, parasites, and vectors present at São Paulo Zoo.

Effects of Mosquito Microbiota on the Survival Cost and Development Success of Avian Plasmodium

Both intrinsic and extrinsic factors affect the capacity of mosquitoes for the transmission of vector-borne pathogens. Among them, mosquito microbiota may play a key role determining the development of pathogens in mosquitoes and the cost of infections. Here, we used a wild avian malaria-mosquito assemblage model to experimentally test the role of vector microbiota on the cost of infection and their consequences for parasite development. To do so, a cohort of Culex pipiens mosquitoes were treated with antibiotics, including gentamicin sulfate and penicillin-streptomycin, to alter their microbiota, and other cohort was treated with sterilized water as controls. Subsequently, both cohorts were allowed to feed on Plasmodium infected or uninfected house sparrows (Passer domesticus). The antibiotic treatment significantly increased the survival rate of mosquitoes fed on infected birds while this was not the case of mosquitoes fed on uninfected birds. Additionally, a higher prevalence of Plasmodium in the saliva of mosquitoes was found in antibiotic treated mosquitoes than in mosquitoes of the control group at 20 days post exposure (dpe). Analyses of the microbiota of a subsample of mosquitoes at 20 dpe suggest that although the microbiota diversity did not differ between individuals of the two treatments, microbiota in control mosquitoes had a higher number of unique features and enriched in biochemical pathways related to the immune system than antibiotic treated ones. In sum, this study provides support for the role of mosquito microbiota on mosquito survival and the presence of parasite DNA in their saliva.

The role of different Culex mosquito species in the transmission of West Nile virus and avian malaria parasites in Mediterranean areas

Vector-borne diseases, especially those transmitted by mosquitoes, have severe impacts on public health and economy. West Nile virus (WNV) and avian malaria parasites of the genus Plasmodium are mosquito-borne pathogens that may produce severe disease and illness in humans and birds, respectively, and circulate in an endemic form in southern Europe. Here, we used field-collected data to identify the impact of Culex pipiens, Cx. perexiguus and Cx. modestus, on the circulation of both WNV and Plasmodium in Andalusia (SW Spain) using mathematical modelling of the basic reproduction number (R₀ ). Models were calibrated with field-collected data on WNV seroprevalence and Plasmodium infection in wild house sparrows, presence of WNV and Plasmodium in mosquito pools, and mosquito blood-feeding patterns. This approach allowed us to determine the contribution of each vector species to pathogen amplification. Overall, 0.7% and 29.6% of house sparrows were positive to WNV antibodies and Plasmodium infection, respectively. In addition, the prevalence of Plasmodium was higher in Cx. pipiens (2.0%), followed by Cx. perexiguus (1.8%) and Cx. modestus (0.7%). Three pools of Cx. perexiguus were positive to WVN. Models identified Cx. perexiguus as the most important species contributing to the amplification of WNV in southern Spain. For Plasmodium models, R₀ values were higher when Cx. pipiens was present in the population, either alone or in combination with the other mosquito species. These results suggest that the transmission of these vector-borne pathogens depends on different Culex species, and consequently, their transmission niches will present different spatial and temporal patterns. For WNV, targeted surveillance and control of Cx. perexiguus populations appear as the most effective measure to reduce WNV amplification. Also, preventing Culex populations near human settlements, or reducing the abundance of these species, are potential strategies to reduce WNV spillover into human populations in southern Spain.

Mosquitoes in an Urban Zoo: Identification of Blood Meals, Flight Distances of Engorged Females, and Avian Malaria Infections

Zoological gardens are home to a large number of vertebrate species and as such are suitable sites for both mosquito breeding and maintenance. They are excellent places for entomological studies of mosquito phenology, diversity, and blood-feeding patterns, as well as for xenomonitoring. During 2016, we sampled mosquitoes in Barcelona Zoo and used molecular methods to determine their blood-feeding patterns and the prevalence and diversity of avian malaria parasites. We also estimated the flight distance of engorged mosquitoes in the area. Overall, 1,384 adult Culex pipiens s.l., Culiseta longiareolata, and Aedes albopictus were captured. Birds dominated the diet of Cx. pipiens s.l. (n = 87) and Cs. longiareolata (n = 6), while humans were the only blood-meal source of Ae. albopictus (n = 3). Mosquitoes had a mean flight distance of 95.67 m after feeding on blood (range 38.71–168.51 m). Blood parasites were detected in the abdomen of 13 engorged Cx. pipiens s.l., eight of which had fed on magpies. Four Plasmodium lineages and a single lineage of the malaria-like parasite Haemoproteus were identified. These results suggest that Cx. pipiens s.l. is involved in the local transmission of avian Plasmodium, which potentially affects the circulation of parasites between and within wildlife and enclosed animals. Vigilance regarding possible mosquito breeding sites in this zoo is thus recommended.

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.

Dynamics of prevalence and distribution pattern of avian Plasmodium species and its vectors in diverse zoogeographical areas - A review

Avian Plasmodium is of special interest to health care scientists and veterinarians due to the potency of causing avian malaria in non-adapted birds and their evolutionary phylogenetic relationship with human malaria species. This article aimed to provide a comprehensive list of the common avian Plasmodium parasites in the birds and mosquitoes, to specify the common Plasmodium species and lineages in the selected regions of West of Asia, East of Europe, and North of Africa/Middle East, and to determine the contribution of generalist and host-specific Plasmodium species and lineages. The final list of published infected birds includes 146 species, among which Passer domesticus was the most prevalent in the studied areas. The species of Acrocephalus arundinaceus and Sylvia atricapilla were reported as common infected hosts in the examined regions of three continents. The highest numbers of common species of infected birds between continent pairs were from Asia and Europe, and no common record was found from Europe and Africa. The species of Milvus migrans and Upupa epops were recorded as common species from Asia and Africa. The lineage of GRW11 and species of P. relictum were the most prevalent parasites among all the infection records in birds. The most prevalent genus of vectors of avian malaria belonged to Culex and species of Cx. pipiens. The lineage SGS1 with the highest number of occurrence has been found in various vectors comprising Cx. pipiens, Cx. modestus, Cx. theileri, Cx. sasai, Cx. perexiguus, Lutzia vorax, and Culicoides alazanicus. A total of 31 Plasmodium species and 59 Plasmodium lineages were recorded from these regions. SGS1, GRW04, and GRW11, and P. relictum and P. vaughani are specified as common generalist avian malaria parasites from these three geographic areas. The presence of avian Plasmodium parasites in distant geographic areas and various hosts may be explained by the movement of the infected birds through the migration routes. Although most recorded lineages were from Asia, investigating the distribution of lineages in some of the countries has not been done. Thus, the most important outcome of this review is the determination of the distribution pattern of parasite and vector species that shed light on gaps requiring further studies on the monitoring of avian Plasmodium and common vectors extension. This task could be achieved through scientific field and laboratory networking, performing active surveillance and designing regional/continental control programs of birds' malaria and other zoonotic diseases.

Plasmodium transmission differs between mosquito species and parasite lineages

Factors such as the particular combination of parasite-mosquito species, their co-evolutionary history and the host's parasite load greatly affect parasite transmission. However, the importance of these factors in the epidemiology of mosquito-borne parasites, such as avian malaria parasites, is largely unknown. Here, we assessed the competence of two mosquito species [Culex pipiens and Aedes (Ochlerotatus) caspius], for the transmission of four avian Plasmodium lineages (Plasmodium relictum SGS1 and GRW11 and Plasmodium cathemerium-related lineages COLL1 and PADOM01) naturally infecting wild house sparrows. We assessed the effects of parasite identity and parasite load on Plasmodium transmission risk through its effects on the transmission rate and mosquito survival. We found that Cx. pipiens was able to transmit the four Plasmodium lineages, while Ae. caspius was unable to transmit any of them. However, Cx. pipiens mosquitoes fed on birds infected by P. relictum showed a lower survival and transmission rate than those fed on birds infected by parasites related to P. cathemerium. Non-significant associations were found with the host-parasite load. Our results confirm the existence of inter- and intra-specific differences in the ability of Plasmodium lineages to develop in mosquito species and their effects on the survival of mosquitoes that result in important differences in the transmission risk of the different avian malaria parasite lineages studied.

From Africa to Europe: evidence of transmission of a tropical Plasmodium lineage in Spanish populations of house sparrows

Background

Avian malaria parasites are a highly diverse group that commonly infect birds and have deleterious effects on their hosts. Some parasite lineages are geographically widespread and infect many host species in many regions. Bird migration, natural dispersal, invasive species and human-mediated introductions into areas where competent insect vectors are present, are probably the main drivers of the current distribution of avian malaria parasites.

Methods

A total of 412 and 2588 wild house sparrows (Passer domesticus) were captured in 2012 and 2013 in two areas of the Iberian Peninsula (central and southern Spain, respectively). Genomic DNA was extracted from blood samples; parasite lineages were sequenced and identified by comparing with GenBank and/or MalAvi databases.

Results

Thirteen Plasmodium lineages were identified in house sparrows corresponding to three major clades. Five individuals were infected by the African Plasmodium lineage PAGRI02, which has been proposed to actively circulate only in Africa.

Conclusions

Despite the low prevalence of PAGRI02 in sparrows in Spain, our results suggest that the area of transmission of this parasite is more widespread than previously thought and covers both Africa and Europe. Further studies of the global distribution of Plasmodium lineages infecting wild birds are required to identify the current transmission areas of these parasites. This is vital given the current scenario of global change that is providing new opportunities for avian malaria transmission into areas where parasites were previously absent.

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.

Occurrence and diversity of avian haemosporidia in Afrotropical landbirds

Avian haemosporidian infections are widespread and can result in the decline of wild bird populations or in some cases contribute to extinction of species. We determined the prevalence and genetic diversity of avian haemosporidia in 93 samples from 22 landbird species from South Africa (N = 76) and West Africa (N = 17), of which six are intra-African migrants and one is a Palearctic migrant. The samples were analysed for the presence of avian haemosporidian DNA using real-time quantitative PCR (qPCR) and nested PCR assays targeting specific mitochondrial genes of these parasites. The cytochrome b (cytb) gene was sequenced for all samples that tested positive and phylogenetic analysis was conducted in order to determine the relationship of the new sequences with previously published sequences from the MalAvi database. The overall prevalence of avian haemosporidiosis was 68.82% (95% CI: 56.4%-78.87%) and 82.80% (95% CI: 65.68%-86.11%) as determined by qPCR and nested PCR respectively. Eighteen (19.36%; 95% CI; 10.78%-29.97%) samples had mixed infections. Infection prevalence of all haemosporidian spp. were significantly higher (p < 0.05) in samples from West Africa. Forty-six mitochondrial sequences obtained from 14 avian species grouped into three distinct clusters of Haemoproteus (36), Leucocytozoon (8) and Plasmodium (2). These represent eight published and nine new cytb lineages. The most common lineage was Haemoproteus sp. (VIMWE1) which was identified in two bird species from West Africa and seven bird species from South Africa. This study adds to our knowledge of host-parasite relationships of avian haemosporidia of Afrotropical birds.

Culicoides species community composition and infection status with parasites in an urban environment of east central Texas, USA

BACKGROUND

Despite their importance as vectors of zoonotic parasites that can impact human and animal health, Culicoides species distribution across different habitat types is largely unknown. Here we document the community composition of Culicoides found in an urban environment including developed and natural sites in east central Texas, a region of high vector diversity due to subtropical climates, and report their infection status with haemoparasites.

RESULTS

A total of 251 individual Culicoides were collected from May to June 2016 representing ten Culicoides species, dominated by C. neopulicaris followed by C. crepuscularis. We deposited 63 sequences to GenBank among which 25 were the first deposition representative for six Culicoides species: C. arboricola (n = 1); C. nanus (n = 4); C. debilipalpis (n = 2); C. haematopotus (n = 14); C. edeni (n = 3); and C. hinmani (n = 1). We also record for the first time the presence of C. edeni in Texas, a species previously known to occur in the Bahamas, Florida and South Carolina. The urban environments with natural area (sites 2 and 4) had higher species richness than sites more densely populated or in a parking lot (sites 1 and 3) although a rarefaction analysis suggested at least two of these sites were not sampled sufficiently to characterize species richness. We detected a single C. crepuscularis positive for Onchocercidae gen. sp. DNA and another individual of the same species positive for Haemoproteus sacharovi DNA, yielding a 2.08% prevalence (n = 251) for both parasites in this species.

CONCLUSIONS

We extend the knowledge of the Culicoides spp. community in an urban environment of Texas, USA, and contribute to novel sequence data for these species. Additionally, the presence of parasite DNA (Onchocercidae gen. sp. and H. sacharovi) from C. crepuscularis suggests the potential for this species to be a vector of these parasites.

Culicoides paolae and C. circumscriptus as potential vectors of avian haemosporidians in an arid ecosystem

BACKGROUND

Haemosporidians are the most important vector-borne parasites due to their cosmopolitan distribution and their wide range of hosts, including humans. Identification of their vectors is critical to highlight ecologically and epidemiologically relevant features such as host specificity or transmission routes. Biting midges of the genus Culicoides are considered the main vectors of Haemoproteus spp., yet important information on aspects such as vector feeding preferences or vector-host specificity involving haemosporidian parasites is frequently missing.

METHODS

We assessed the abundance of Culicoides circumscriptus and C. paolae and blood sources of the latter at the nests of cavity-nesting bird species (mainly the European roller Coracias garrulus) and in their surroundings. We also explored the prevalence and genetic diversity of avian haemosporidians in parous females of both species.

RESULTS

Both C. circumscriptus and C. paolae were abundant in the study area and common at European roller nests. Culicoides paolae had a diverse ornithophilic diet, feeding on at least seven bird species. Human DNA was also detected in the blood meal of some individuals. Four Haemoproteus lineages, including a new one reported here for the first time, were isolated from parous females of both biting midges.

CONCLUSIONS

Culicoides circumscriptus and C. paolae can play a locally important role in the transmission dynamics of Haemoproteus parasites in a community of cavity-nesting bird species in an arid ecosystem.

From Galapagos doves to passerines: Spillover of Haemoproteus multipigmentatus

Haemoproteus (Haemoproteus) multipigmentatus, a haemosporidian parasite thought to be specific to columbiform birds, was detected in passeriform birds on Santiago Island in the Galapagos archipelago. We surveyed birds along an altitudinal gradient on the islands of Santa Cruz, Isabela and Santiago between June 2013 and July 2015. Molecular screening of 2254 individuals from 25 species of endemic and introduced birds revealed clusters of passerine birds positive for H. multipigmentatus on Santiago Island that coincide with captures of Galapagos doves at sampled sites. Of 507 individuals from 10 species of endemic passerines sampled on Santiago, 58 individuals from 6 species were found positive (11% prevalence). However, no gametocytes were found in the blood smears of positive passerines, suggesting that these species are not competent hosts for the parasite. All 31 doves captured were positive and gametocytes were found upon microscopic examination of all thin blood smears (averaging 357 gametocytes per 10,000 erythrocytes). These findings indicate parasite spillover from doves to passerines, but that passerines are possibly not competent hosts for further parasite transmission. The endemic Galapagos dove acts as a reservoir host for the introduced H. multipigmentatus, however the effect of this parasite on passerines has not been studied. We report on these findings because parasites can have large effects on individual host populations and on the ecology of a community, but may go undetected.

The widespread biting midge Culicoides impunctatus (Ceratopogonidae) is susceptible to infection with numerous Haemoproteus (Haemoproteidae) species

Background

Haemoproteus parasites are widespread, and some species cause disease in wild and domestic birds. However, the insect vectors remain unknown for the majority of species and genetic lineages of avian Haemoproteus. This information is crucial for better understanding the biology of haemoproteids, the epidemiology of haemoproteosis, and the development of morphological characters of sporogonic stages in wildlife haemosporidian parasites. It remains unclear whether the specificity of Haemoproteus parasites for vectors is broad or the transmission of a given parasite can be restricted to a single or few species of vectors. The aim of this study was to examine the sporogonic development of four species of common European avian haemoproteids in the common biting midge Culicoides impunctatus.

Methods

Wild-caught females of C. impunctatus were infected experimentally by allowing them to take blood meals on naturally infected Muscicapa striata, Cyanistes caeruleus, Ficedula hypoleuca and Motacilla flava harbouring mature gametocytes of Haemoproteus balmorali (genetic lineage hSFC9), H. majoris (hPARUS1), H. motacillae (hYWT1) and H. pallidus (hPFC1), respectively. Infected insects were collected, maintained under laboratory conditions and dissected daily in order to detect the development of ookinetes, oocysts and sporozoites. Microscopic examination and polymerase chain reaction based methods were used to detect the parasites. Bayesian analysis was applied to identify phylogenetic relationships among Haemoproteus lineages.

Results

All investigated parasites completed sporogony in C. impunctatus, indicating broad susceptibility of this biting midge for numerous Haemoproteus parasites. Ookinetes, oocysts and sporozoites were reported, described and compared morphologically. The investigated parasite species can be distinguished at the sporogony stage, particularly with regards to the morphology and rate of development of mature ookinetes. Analysis of data from the literature, and this study, shows that 12 genetically distantly related Haemoproteus parasites complete sporogony in C. impunctatus.

Conclusions

Susceptibility of C. impunctatus is broad for Haemoproteus parasites, indicating that this biting midge is an important natural vector of numerous species of avian haemoproteids in Europe. Some Haemoproteus species can be readily distinguished using morphological characters of ookinetes and sporozoites, as well as the rate of ookinete development. These characters can be used for the identification of Haemoproteus species during sporogony in vectors, and are worth more attention in these parasite taxonomy studies at the species levels.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2317-z) contains supplementary material, which is available to authorized users.

Mosquito Vectors of Avian Malaria in Mississippi: A First Look

The vectors of avian malaria (Haemosporida) are an understudied component of wildlife disease ecology. Most studies of avian malaria have focused on the intermediate bird hosts. This bias leaves a significant gap in our knowledge and understanding of the insect hosts. This study investigates the diversity of malaria parasites carried by mosquitoes (Diptera, Culicidae) in the state of Mississippi. With the use of molecular techniques, haemosporidian infection rates were determined and parasites were identified. A total of 27,157 female mosquitoes representing 15 species were captured. Five of those species tested positive for malaria parasites with an overall infection rate of 4 per 1,000 mosquitoes infected. Mosquitoes were shown to harbor Plasmodium and Haemoproteus ( Parahaemoproteus) parasites. A unique lineage of parasites was discovered in Anopheles mosquitoes, potentially representing a new genus of haemosporidian parasites, reinforcing the need to continue investigating this diverse group of parasites.

Do mosquitoes transmit the avian malaria-like parasite Haemoproteus? An experimental test of vector competence using mosquito saliva

Background

The life-cycle of many vector-borne pathogens includes an asexual replication phase in the vertebrate host and sexual reproduction in the insect vector. However, as only a small array of parasites can successfully develop infective phases inside an insect, few insect species are competent vectors for these pathogens. Molecular approaches have identified the potential insect vectors of blood parasites under natural conditions. However, the effectiveness of this methodology for verifying mosquito competence in the transmission of avian malaria parasites and related haemosporidians is still under debate. This is mainly because positive amplifications of parasite DNA in mosquitoes can be obtained not only from sporozoites, the infective phase of the malaria parasites that migrate to salivary glands, but also from different non-infective parasite forms in the body of the vector. Here, we assessed the vectorial capacity of the common mosquito Culex pipiens in the transmission of two parasite genera.

Methods

A total of 1,560 mosquitoes were allowed to feed on five house sparrows Passer domesticus naturally infected by Haemoproteus or co-infected by Haemoproteus/Plasmodium. A saliva sample of the mosquitoes that survived after 13 days post-exposure was taken to determine the presence of parasite DNA by PCR.

Results

Overall, 31.2% mosquito’s head-thorax and 5.8% saliva samples analysed showed positive amplifications for avian malaria parasites. In contrast to Haemoproteus DNA, which was not found in either the body parts or the saliva, Plasmodium DNA was detected in both the head-thorax and the saliva of mosquitoes. Parasites isolated from mosquitoes feeding on the same bird corresponded to the same Plasmodium lineage.

Conclusions

Our experiment provides good evidence for the competence of Cx. pipiens in the transmission of Plasmodium but not of Haemoproteus. Molecular analyses of saliva are an effective method for testing the vector competence of mosquitoes and other insects in the transmission of vector-borne pathogens.

Searching for putative avian malaria vectors in a Seasonally Dry Tropical Forest in Brazil

Background

Haemosporidian parasites of the genera Plasmodium and Haemoproteus can have detrimental effects on individual birds and populations. Despite recent investigations into the distribution and richness of these parasites and their vertebrate hosts, little is known about their dipteran vectors. The Neotropics has the highest diversity of mosquitoes in the world, but few studies have tried to identify vectors in this area, hampering the understanding of the ecology of avian malaria in the highly diverse Neotropical environments.

Methods

Shannon traps and active collection were used to capture 27,110 mosquitoes in a Seasonally Dry Tropical Forest in southeastern Brazil, a highly endangered ecosystem.

Results

We screened 17,619 mosquito abdomens from 12 different species and several unidentified specimens of Culex, grouped into 1,913 pools, for the presence of haemosporidians. Two pools (out of 459) of the mosquito Mansonia titillans and one pool (out of 29) of Mansonia pseudotitillans were positive for Plasmodium parasites, with the detection of a new parasite lineage in the former species. Detected Plasmodium lineages were distributed in three different clades within the phylogenetic tree revealing that Mansonia mosquitoes are potential vectors of genetically distant parasites. Two pools of Culex spp. (out of 43) were positive for Plasmodium gallinaceum and closely related lineages. We found a higher abundance of these putative vectors in pasture areas, but they were also distributed in areas at intermediate and late successional stages. One pool of the mosquito Psorophora discrucians (out of 173) was positive for Haemoproteus.

Conclusions

The occurrence of different Plasmodium lineages in Mansonia mosquitoes indicates that this genus encompasses potential vectors of avian malaria parasites in Brazil, even though we did not find positive thoraces among the samples tested. Additional evidence is required to assign the role of Mansonia mosquitoes in avian malaria transmission and further studies will add information about evolutionary and ecological aspects of avian haemosporidia and untangle the diversity of their vectors in Brazil.

Nest ecology of blood parasites in the European roller and its ectoparasitic carnid fly

Haemosporidian parasites are considered the most important vector-borne parasites. However, vector identity and ecology is unknown for most such host-vector-parasite systems. In this study, we employ microscopic and molecular analyses to examine haemosporidian prevalence in a migratory, cavity-nesting bird, European roller Coracias garrulus, and its nidicolous blood-feeding ectoparasite Carnus hemapterus. This system is unique in that the ectoparasite is confined to a near-closed environment, in contrast to the free-wandering system of haematophagous dipterans such as mosquitoes. Blood film analysis confirms previous works in that Haemoproteus parasites are widely prevalent in adult rollers and belong to a single species, Haemoproteus coraciae. Leucocytozoon sp. and Trypanosoma sp. also are detected in adult rollers at low intensities with this technique. By means of molecular analysis, we report for the first time Plasmodium sp. presence in C. garrulus. Based on PCR results, Plasmodium parasites are relatively less prevalent than Haemoproteus parasites (20% vs. 31%) in rollers. In contrast, haemosporidian prevalences show the opposite trend for Carnus flies: Plasmodium sp. occurrence (62%) clearly predominates over that of Haemoproteus sp. (5%). A comparison between roller and Carnus samples reveals a significantly higher prevalence of Plasmodium sp. in Carnus samples. Insect survey and phylogenetic analysis suggest Culicoides flies as Haemoproteus sp. vectors, which appear to readily transmit the parasite in southern Spain. This study does not find support for Carnus flies to serve as biological or mechanical vectors of haemosporidians. In spite of this, nidicolous blood-feeding ectoparasites, such as carnid flies, appear as a suitable model for studies on the occurrence and temporal dynamics of avian haemosporidians such as Plasmodium sp. present at low intensities.

Sporogony and sporozoite rates of avian malaria parasites in wild Culex pipiens pallens and C. inatomii in Japan

Background

Malaria infection in mosquitoes is traditionally detected by microscopic examination for Plasmodium oocysts and sporozoites. Although PCR is now widely used, the presence of parasite DNA in a mosquito does not prove that sporogony is achieved. Thus, detection of sporozoites by microscopy is still required to definitively identify vector mosquitoes. The aim of this study was to confirm sporogony of avian Plasmodium spp. in Culex pipiens pallens and C. inatomii caught from the wild.

Findings

Mosquitoes collected at two sites in Japan were dissected and examined by microscopy for Plasmodium oocysts and sporozoites. DNA was extracted from the midgut and salivary gland of infected mosquitoes, and the infecting Plasmodium species was identified by sequencing 478 bp of cytochrome b. Oocysts, or both oocysts and sporozoites, were found in 3.94 and 0.46 % of C. p. pallens and C. inatomii, respectively. Four (CXPIP09, GRW4, GRW11 and SGS1) and three cytochrome b lineages (CXINA01, CXINA02 and CXQUI01) were confirmed to achieve sporogony in C. p. pallens and C. inatomii, respectively. One mosquito each of C. p. pallens and C. inatomii was co-infected with two different Plasmodium lineages.

Conclusions

These findings demonstrate that C. p. pallens and C. inatomii are natural vectors of four and three lineages of avian Plasmodium spp., respectively. The data indicate that a systematic procedure combining microscopy and PCR is a feasible and reliable approach to identify natural vectors of wildlife malaria.

Haemosporidian infections in the Tengmalm's Owl (Aegolius funereus) and potential insect vectors of their transmission

Sedentary bird species are suitable model hosts for identifying potential vectors of avian blood parasites. We studied haemosporidian infections in the Tengmalm's Owl (Aegolius funereus) in the Ore Mountains of the Czech Republic using molecular detection methods. Sex of owl nestlings was scored using molecular sexing based on fragment analysis of PCR-amplified CHD1 introns. Observed infection prevalences in nestlings and adult owls were 51 and 86 %, respectively. Five parasite lineages were detected. Most of the infections comprised the Leucocytozoon AEFUN02 and STOCC06 lineages that probably refer to distinct Leucocytozoon species. Other lineages were detected only sporadically. Mixed infections were found in 49 % of samples. The main factor affecting the probability of infection was host age. No effect of individual sex on infection probability was evidenced. The youngest infected nestling was 12 days old. High parasite prevalence in the Tengmalm's Owl nestlings suggests that insect vectors must enter nest boxes to transmit parasites before fledging. Hence, we placed sticky insect traps into modified nest boxes, collected potential insect vectors, and examined them for the presence of haemosporidian parasites using molecular detection. We trapped 201 insects which were determined as biting midges from the Culicoides genus and two black fly species, Simulium (Nevermannia) vernum and Simulium (Eusimulium) angustipes. Six haemosporidian lineages were detected in the potential insect vectors, among which the Leucocytozoon lineage BT2 was common to the Tengmalm's Owl and the trapped insects. However, we have not detected the most frequently encountered Tengmalm's Owl Leucocytozoon lineages AEFUN02 and STOCC06 in insects.

Avian malaria parasites in the last supper: identifying encounters between parasites and the invasive Asian mosquito tiger and native mosquito species in Italy

BACKGROUND

The invasive Asian tiger mosquito Aedes albopictus has dramatically expanded its distribution range, being catalogued as one of the world's 100 worst invasive alien species. As vectors of pathogens, Ae. albopictus may create novel epidemiological scenarios in the invaded areas.

METHODS

Here, the frequency of encounters of Ae. albopictus with the avian malaria parasite Plasmodium and the related Haemoproteus was studied in an area with established populations in northeastern Italy and compared with those from four native mosquito species, Anopheles maculipennis s.l., Culex hortensis, Culex pipiens, and Ochlerotatus caspius. The abdomens of mosquitoes with a recent blood meal were used to identify both the blood meal source and the parasites harboured.

RESULTS

Aedes albopictus had a clear antropophilic behaviour while An. maculipennis and Oc. caspius fed mainly on non-human mammals. Birds were the most common hosts of Cx. pipiens and reptiles of Cx. hortensis. Parasites were isolated from three mosquito species, with Cx. pipiens (30%) showing the highest parasite prevalence followed by Cx. hortensis (9%) and Ae. albopictus (5%).

CONCLUSIONS

These results are the first identifying the avian malaria parasites harboured by mosquitoes in Italy and represent the first evidence supporting that, although Ae. albopictus could be involved in the transmission of avian malaria parasites, the risk of avian malaria parasite spread by this invasive mosquito in Europe would be minimal.

Fur or feather? Feeding preferences of species of Culicoides biting midges in Europe

Understanding the feeding preferences of haematophagous insects is critical to depicting the amplification and transmission networks of pathogens and identifying key vector species for surveillance programs. In the case of species from genus Culicoides, many of which are important vectors of pathogens causing animal diseases, information from molecular studies on the feeding habits of females is expanding but still limited for a significant fraction of competent vectors of Culicoides-borne pathogens. In spite of these limitations, recent studies highlight that most Culicoides species are able to feed on several vertebrate species, but present clear preferences for mammals or birds.

Degree of associations among vectors of the genus Culicoides (Diptera: Ceratopogonidae) and host bird species with respect to haemosporidian parasites in NE Bulgaria

The occurrence of haemosporidians in biting midges of the genus Culicoides is examined in North-East Bulgaria in order to reveal their potential role for parasite transmission. A PCR-based technique amplifying part of the mitochondrial cytochrome b gene of the parasite is applied on naturally infected biting midges. Totally, 640 parous individuals of four species and 95 blood-fed individuals of six species of Culicoides are examined for the presence of DNA of haemosporidians. Haemosporidian genetic lineages are identified in individuals of three insect species: Culicoides alazanicus (12 lineages, nine lineages of Haemoproteus and three lineages of Plasmodium), Culicoides festivipennis and Culicoides circumscriptus (with two and one lineages of Haemoproteus, respectively). Two genetic lineages of Haemoproteus are recorded in more than one vector species. These results demonstrate variations in the specificity of Haemoproteus genetic lineages to their potential vectors, since some lineages are recorded in a single vector species and others occur in two or more vector species.

Dynamics of prevalence and diversity of avian malaria infections in wild Culex pipiens mosquitoes: the effects of Wolbachia, filarial nematodes and insecticide resistance

Background

Identifying the parasites transmitted by a particular vector and the factors that render this vector susceptible to the parasite are key steps to understanding disease transmission. Although avian malaria has become a model system for the investigation of the ecological and evolutionary dynamics of Plasmodium parasites, little is still known about the field prevalence, diversity and distribution of avian Plasmodium species within the vectors, or about the extrinsic factors affecting Plasmodium population dynamics in the wild.

Methods

We examined changes in avian malaria prevalence and Plasmodium lineage composition in female Culex pipiens caught throughout one field season in 2006, across four sampling sites in southern France. Using site occupancy models, we correct the naive estimates of Plasmodium prevalence to account for PCR-based imperfect detection. To establish the importance of different factors that may bear on the prevalence and diversity of avian Plasmodium in field mosquitoes, we focus on Wolbachia and filarial parasite co-infections, as well as on the insecticide resistance status of the mosquito.

Results

Plasmodium prevalence in Cx. pipiens increased from February (0%) to October (15.8%) and did not vary significantly among the four sampling sites. The application of site occupancy models leads to a 4% increase in this initial (naive) estimate of prevalence. The parasite community was composed of 15 different haemosporidian lineages, 13 of which belonged to the Plasmodium genus, and 2 to the Haemoproteus genus. Neither the presence of different Wolbachia types and of filarial parasites co-infecting the mosquitoes, nor their insecticide resistance status were found to affect the Plasmodium prevalence and diversity.

Conclusion

We found that haemosporidian parasites are common and diverse in wild-caught Cx. pipiens mosquitoes in Southern France. The prevalence of the infection in mosquitoes is unaffected by Wolbachia and filarial co-infections as well as the insecticide resistant status of the vector. These factors may thus have a negligible impact on the transmission of avian malaria. In contrast, the steady increase in prevalence from February to October indicates that the dynamics of avian malaria is driven by seasonality and supports that infected birds are the reservoir of a diverse community of lineages in southern France.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-437) contains supplementary material, which is available to authorized users.

Natural malaria infection reduces starvation resistance of nutritionally stressed mosquitoes

In disease ecology, there is growing evidence that environmental quality interacts with parasite and host to determine host susceptibility to an infection. Most studies of malaria parasites have focused on the infection costs incurred by the hosts, and few have investigated the costs on mosquito vectors. The interplay between the environment, the vector and the parasite has therefore mostly been ignored and often relied on unnatural or allopatric Plasmodium/vector associations. Here, we investigated the effects of natural avian malaria infection on both fecundity and survival of field-caught female Culex pipiens mosquitoes, individually maintained in laboratory conditions. We manipulated environmental quality by providing mosquitoes with different concentrations of glucose-feeding solution prior to submitting them to a starvation challenge. We used molecular-based methods to assess mosquitoes' infection status. We found that mosquitoes infected with Plasmodium had lower starvation resistance than uninfected ones only under low nutritional conditions. The effect of nutritional stress varied with time, with the difference of starvation resistance between optimally and suboptimally fed mosquitoes increasing from spring to summer, as shown by a significant interaction between diet treatment and months of capture. Infected and uninfected mosquitoes had similar clutch size, indicating no effect of infection on fecundity. Overall, this study suggests that avian malaria vectors may suffer Plasmodium infection costs in their natural habitat, under certain environmental conditions. This may have major implications for disease transmission in the wild.

Multiple lineages of Avian malaria parasites (Plasmodium) in the Galapagos Islands and evidence for arrival via migratory birds

Haemosporidian parasites in the genus Plasmodium were recently detected through molecular screening in the Galapagos Penguin (Spheniscus mendiculus). We summarized results of an archipelago-wide screen of 3726 endemic birds representing 22 species for Plasmodium spp. through a combination of molecular and microscopy techniques. Three additional Plasmodium lineages were present in Galapagos. Lineage A-infected penguins, Yellow Warblers (Setophaga petechia aureola), and one Medium Ground Finch (Geospiza fortis) and was detected at multiple sites in multiple years [corrected]. The other 3 lineages were each detected at one site and at one time; apparently, they were transient infections of parasites not established on the archipelago. No gametocytes were found in blood smears of infected individuals; thus, endemic Galapagos birds may be dead-end hosts for these Plasmodium lineages. Determining when and how parasites and pathogens arrive in Galapagos is key to developing conservation strategies to prevent and mitigate the effects of introduced diseases. To assess the potential for Plasmodium parasites to arrive via migratory birds, we analyzed blood samples from 438 North American breeding Bobolinks (Dolichonyx oryzivorus), the only songbird that regularly migrates through Galapagos. Two of the ephemeral Plasmodium lineages (B and C) found in Galapagos birds matched parasite sequences from Bobolinks. Although this is not confirmation that Bobolinks are responsible for introducing these lineages, evidence points to higher potential arrival rates of avian pathogens than previously thought. Linajes Múltiples de Parásitos de Malaria Aviar (Plasmodium) en las Islas Galápagos y Evidencia de su Arribo por Medio de Aves Migratorias.

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.

The pathology and pathogenicity of a novel Haemoproteus spp. infection in wild Little Penguins (Eudyptula minor)

One hundred and thirty four Little Penguin (Eudyptula minor) carcases found since 2004 in south west Australia were necropsied. The livers and spleens from ten of the penguins exhibited varying degrees of multifocal, randomly scattered areas of necrosis and varying numbers of parasites were associated with these areas. Hepatomegaly and splenomegaly were noted in many of these ten cases. Necrosis and parasites were also observed in the cardiac muscle of four of the cases and in the lung tissue in one of the penguins. Using PCR, the parasites were positively identified in four of the cases as Haemoproteus spp. and morphologically identical tissue stage parasites associated with histopathological changes were observed in all ten dead penguins. This is the first study to demonstrate both the in situ presence of the Haemoproteus parasite in any member of the Sphensicidae family and mortality due to its presence. We postulate the involvement of anomalous environmental conditions in a potential increase in local vectors.

Seroprevalence of malarial antibodies in Galapagos penguins (Spheniscus mendiculus)

A parasite species of the genus Plasmodium has recently been documented in the endangered Galapagos penguin (Spheniscus mendiculus). Avian malaria causes high mortality in several species after initial exposure and there is great concern for the conservation of the endemic Galapagos penguin. Using a Plasmodium spp. circumsporozoite protein antigen, we standardized an enzyme-linked immunosorbent assay to test the level of exposure in this small population, as indicated by seroprevalence. Sera from adult and juvenile Galapagos penguins collected between 2004 and 2009 on the Galapagos archipelago were tested for the presence of anti- Plasmodium spp. antibodies. Penguins were also tested for the prevalence of avian malaria parasite DNA using a polymerase chain reaction (PCR) screening. Total seroprevalence of malarial antibodies in this sample group was 97.2%, which suggests high exposure to the parasite and low Plasmodium-induced mortality. However, total prevalence of Plasmodium parasite DNA by PCR screening was 9.2%, and this suggests that parasite prevalence may be under-detected through PCR screening. Multiple detection methods may be necessary to measure the real extent of Plasmodium exposure on the archipelago.

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.

Haemosporidian parasites of a European passerine wintering in South Asia: diversity, mixed infections and effect on host condition

We studied haemosporidian parasites in the scarlet rosefinch Carpodacus erythrinus in a small isolated semicolony during an eight-year period using molecular methods of parasite detection. The scarlet rosefinch is an interesting model of parasite host species. It winters in South Asia which represents a rare exception among European passerines. Males express yellow to red carotenoid-based plumage ornament which is a good predictor of male reproductive success. In 240 blood samples originating from 199 adult individuals, the total parasite prevalence reached 60%. Prevalence varied among years from 36 to 81% in Haemoproteus, 8 to 22% in Plasmodium, and 0 to 14% in Leucocytozoon. Twenty parasite lineages were detected (Haemoproteus: 5 lineages, Plasmodium: 10 lineages, and Leucocytozoon: 5 lineages). Among them, the Haemoproteus ROFI2 lineage, which is a host-specific parasite lineage of the scarlet rosefinch, was the most frequently found. Parasite lineages showed varying degree of lineage specificity. While Haemoproteus lineages detected in the scarlet rosefinch have relatively narrow host breadth restricted mainly to Fringillidae family, Leucocytozoon and Plasmodium lineages generally showed wider host range. The presence of some parasite lineages hitherto detected in sedentary European passerines (SISKIN1, CCF3, BT2) or in Culicoides biting midges at the same locality (ROFI1) suggest local transmission. On the contrary, lineages LK05 and FANTAIL1 that were previously reported exclusively from Asian hosts imply parasite transmission at the scarlet rosefinch wintering sites in South Asia. Mixed infections were found in 17% of infected samples and comprised mainly the most frequent lineages. The pattern of concomitant infections seemed to be rather random and matched expected levels based on lineage frequencies. Between-year comparisons revealed that in a majority of the repeatedly captured individual hosts the infection status remained unchanged (individuals stayed uninfected or possessed the same parasite lineages). However, 16 gains and 8 losses of lineages were also reported. We have not found any effect of haemosporidians on male carotenoid ornament expression or host body mass.

Avian haemosporidians in haematophagous insects in the Czech Republic

The degree to which avian haemosporidian parasites can exploit different vectors as a definitive host has ecological implications for their transmission and biogeography. Studies targeting haemosporidian parasites using precise molecular detection methods are almost lacking in Central Europe, however. Here, we utilized PCR-based molecular methods to detect avian haemosporidians in insect vectors in the Czech Republic. Nine lineages of parasites belonging to three genera, Haemoproteus, Plasmodium, and Leucocytozoon, were detected in pooled samples of insect individuals, of which three lineages had not yet been discovered in previous studies. All three Leucocytozoon lineages were found exclusively in black flies, while five Haemoproteus lineages were found in biting midges. The most abundant insect species Culicoides kibunensis harbored three Haemoproteus lineages, and the second-most numerous species Culicoides segnis even four. The positive mosquitoes of Culex pipiens complex hosted two parasite lineages, one Plasmodium and one Haemoproteus, the latter of which, however, could suggest the aberrant development of this parasite in an unusual invertebrate host. The co-occurrence of Haemoproteus ROFI1 and TURDUS2 lineages in both insects and birds at the same study plot suggests a transmission of these lineages during breeding season of birds.

Patterns in avian malaria at founder and source populations of an endemic New Zealand passerine

Significant progress in our understanding of disease transmission in the wild can be made by examining variation in host-parasite-vector interactions after founder events of the host. This study is the first to document patterns in avian malaria, Plasmodium spp., infecting an endemic New Zealand passerine, Anthornis melanura, at multiple-host subpopulations simultaneously. We assess the Beaudoin hypothesis of bimodal seasonality and use AIC model selection to determine host factors associated with disease prevalence. We had the rare opportunity to test the enemy release hypothesis (ERH) after a recent colonisation event of the bellbird host. Four Plasmodium species were found to infect bellbirds. Temporal patterns of three exotic parasite lineages, including GRW06 Plasmodium (Huffia) elongatum, SYAT05 Plasmodium (Novyella) vaughani and a Plasmodium (Haemamoeba) relictum, were sporadic with low prevalence year round. The fourth species was an endemic parasite, an unresolved Plasmodium (Novyella) sp. here called ANME01, which exhibited a strong winter peak at the source subpopulations possibly indicating greater immune stressors at the densely populated source site. At the colonies, we observed bimodal seasonality in the prevalence of ANME01 with autumn and spring peaks. These infection peaks were male-biased, and the amplitude of sex bias was more pronounced at the newer colony perhaps due to increased seasonal competition resulting from territory instability. We observed a decrease in parasite species diversity and increase in body condition from source to founder sites, but statistical differences in the direct relationship between body condition and malaria prevalence between source and colony were weak and significant only during winter. Though our data did not strongly support the ERH, we highlight the benefits of 'conspecific release' associated with decreased population density and food competition. Our findings contribute to the identification of ecological and environmental drivers of variability in malaria transmission, which is valuable for predicting the consequences of both natural range expansions, as well as host re-introductions resulting from intensive conservation practices.

High prevalence and lineage diversity of avian malaria in wild populations of great tits (Parus major) and mosquitoes (Culex pipiens)

Avian malaria studies have taken a prominent place in different aspects of evolutionary ecology. Despite a recent interest in the role of vectors within the complex interaction system of the malaria parasite, they have largely been ignored in most epidemiological studies. Epidemiology of the disease is however strongly related to the vector's ecology and behaviour, and there is a need for basic investigations to obtain a better picture of the natural associations between Plasmodium lineages, vector species and bird hosts.

The aim of the present study was to identify the mosquito species involved in the transmission of the haemosporidian parasites Plasmodium spp. in two wild populations of breeding great tits (Parus major) in western Switzerland. Additionally, we compared Plasmodium lineages, based on mitochondrial DNA cytochrome b sequences, between the vertebrate and dipteran hosts, and evaluated the prevalence of the parasite in the mosquito populations. Plasmodium spp. were detected in Culex pipiens only, with an overall 6.6% prevalence. Among the six cytochrome b lineages of Plasmodium identified in the mosquitoes, three were also present in great tits. The results provide evidence for the first time that C. pipiens can act as a natural vector of avian malaria in Europe and yield baseline data for future research on the epidemiology of avian malaria in European countries.

Novel Haemoproteus species (Haemosporida: Haemoproteidae) from the swallow-tailed gull (Lariidae), with remarks on the host range of hippoboscid-transmitted avian hemoproteids

Haemoproteus (Haemoproteus) jenniae n. sp. (Haemosporida: Haemoproteidae) is described from a Galapagos bird, the swallow-tailed gull Creagrus furcatus (Charadriiformes, Laridae), based on the morphology of its blood stages and segments of the mitochondrial cytochrome b (cyt b) gene. The most distinctive features of H. jenniae development are the circumnuclear gametocytes occupying all cytoplasmic space in infected erythrocytes and the presence of advanced, growing gametocytes in which the pellicle is closely appressed to the erythrocyte envelope but does not extend to the erythrocyte nucleus. This parasite is distinguishable from Haemoproteus larae, which produces similar gametocytes and parasitizes closely related species of Laridae. Haemoproteus jenniae can be distinguished from H. larae primarily due to (1) the predominantly amoeboid outline of young gametocytes, (2) diffuse macrogametocyte nuclei which do not possess distinguishable nucleoli, (3) the consistent size and shape of pigment granules, and (4) the absence of rod-like pigment granules from gametocytes. Additionally, fully-grown gametocytes of H. jenniae cause both the marked hypertrophy of infected erythrocytes in width and the rounding up of the host cells, which is not the case in H. larae. Phylogenetic analyses identified the DNA lineages that are associated with H. jenniae and showed that this parasite is more closely related to the hippoboscid-transmitted (Hippoboscidae) species than to the Culicoides spp.-transmitted (Ceratopogonidae) species of avian hemoproteids. Genetic divergence between morphologically well-differentiated H. jenniae and the hippoboscid-transmitted Haemoproteus iwa, the closely related parasite of frigatebirds (Fregatidae, Pelecaniformes), is only 0.6%; cyt b sequences of these parasites differ only by 1 base pair. This is the first example of such a small genetic difference in the cyt b gene between species of the subgenus Haemoproteus. In a segment of caseinolytic protease C gene (ClpC), genetic divergence is 4% between H. jenniae and H. iwa. This study corroborates the conclusion that hippoboscid-transmitted Haemoproteus parasites infect not only Columbiformes birds but also infect marine birds belonging to Pelecaniformes and Charadriiformes. We conclude that the vertebrate host range should be used cautiously in identification of subgenera of avian Haemoproteus species and that the phylogenies based on the cyt b gene provide evidence for determining the subgeneric position of avian hemoproteids.