Plasmodium (Haemamoeba) cathemerium gene sequences for phylogenetic analysis of malaria parasites

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.

The nuclear 18S ribosomal DNAs of avian haemosporidian parasites

Background

Plasmodium species feature only four to eight nuclear ribosomal units on different chromosomes, which are assumed to evolve independently according to a birth-and-death model, in which new variants originate by duplication and others are deleted throughout time. Moreover, distinct ribosomal units were shown to be expressed during different developmental stages in the vertebrate and mosquito hosts. Here, the 18S rDNA sequences of 32 species of avian haemosporidian parasites are reported and compared to those of simian and rodent Plasmodium species.

Methods

Almost the entire 18S rDNAs of avian haemosporidians belonging to the genera Plasmodium (7), Haemoproteus (9), and Leucocytozoon (16) were obtained by PCR, molecular cloning, and sequencing ten clones each. Phylogenetic trees were calculated and sequence patterns were analysed and compared to those of simian and rodent malaria species. A section of the mitochondrial CytB was also sequenced.

Results

Sequence patterns in most avian Plasmodium species were similar to those in the mammalian parasites with most species featuring two distinct 18S rDNA sequence clusters. Distinct 18S variants were also found in Haemoproteus tartakovskyi and the three Leucocytozoon species, whereas the other species featured sets of similar haplotypes. The 18S rDNA GC-contents of the Leucocytozoon toddi complex and the subgenus Parahaemoproteus were extremely high with 49.3% and 44.9%, respectively. The 18S sequences of several species from all three genera showed chimeric features, thus indicating recombination.

Conclusion

Gene duplication events leading to two diverged main sequence clusters happened independently in at least six out of seven avian Plasmodium species, thus supporting evolution according to a birth-and-death model like proposed for the ribosomal units of simian and rodent Plasmodium species. Patterns were similar in the 18S rDNAs of the Leucocytozoon toddi complex and Haemoproteus tartakovskyi. However, the 18S rDNAs of the other species seem to evolve in concerted fashion like in most eukaryotes, but the presence of chimeric variants indicates that the ribosomal units rather evolve in a semi-concerted manner. The new data may provide a basis for studies testing whether differential expression of distinct 18S rDNA also occurs in avian Plasmodium species and related haemosporidian parasites.

Indel-informed Bayesian analysis suggests cryptic population structure between Plasmodium knowlesi of humans and long-tailed macaques (Macaca fascicularis) in Malaysian Borneo

Plasmodium knowlesi is an important causative agent of malaria in humans of Southeast Asia. Macaques are natural hosts for this parasite, but little is conclusively known about its patterns of transmission within and between these hosts. Here, we apply a comprehensive phylogenetic approach to test for patterns of cryptic population genetic structure between P. knowlesi isolated from humans and long-tailed macaques from the state of Sarawak in Malaysian Borneo. Our approach differs from previous investigations through our exhaustive use of archival 18S Small Subunit rRNA (18S) gene sequences from Plasmodium and Hepatocystis species, our inclusion of insertion and deletion information during phylogenetic inference, and our application of Bayesian phylogenetic inference to this problem. We report distinct clades of P. knowlesi that predominantly contained sequences from either human or macaque hosts for paralogous A-type and S-type 18S gene loci. We report significant partitioning of sequence distances between host species across both types of loci, and confirmed that sequences of the same locus type showed significantly biased assortment into different clades depending on their host species. Our results support the zoonotic potential of Plasmodium knowlesi, but also suggest that humans may be preferentially infected with certain strains of this parasite. Broadly, such patterns could arise through preferential zoonotic transmission of some parasite lineages or a disposition of parasites to transmit within, rather than between, human and macaque hosts. Available data are insufficient to address these hypotheses. Our results suggest that the epidemiology of P. knowlesi may be more complicated than previously assumed, and highlight the need for renewed and more vigorous explorations of transmission patterns in the fifth human malarial parasite.

WITHDRAWN: Indel-informed bayesian analysis suggests cryptic divisions between Plasmodium knowlesi of humans and long-tailed macaques (Macaca fascicularis) in Malaysian Borneo

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Keys to the avian malaria parasites

BACKGROUND

Malaria parasites (genus Plasmodium) are widespread in birds. These pathogens cause pathology of blood and various organs, often resulting in severe avian malaria. Numerous recent studies have reported DNA sequences of avian malaria parasites, indicating rich genetic diversity and the possible existence of many undescribed species. However, the majority of reported Plasmodium lineages remain unidentified to species level, and molecular characterization is unavailable for the majority of described Plasmodium parasites. During the past 15 years, numerous new Plasmodium species have been described. However, keys for their identification are unavailable or incomplete. Identification of avian malaria parasites remains a difficult task even for experts, and this precludes development of avian malariology, particularly in wildlife. Here, keys for avian malaria parasites have been developed as a baseline for assisting academic and veterinary medicine researchers in identification of these pathogens. The main obstacles and future research priorities have been defined in the taxonomy of avian Plasmodium species.

METHODS

The data were considered from published articles and type and voucher material, which was accessed in museums in Europe, the USA and Australia. Blood films containing various blood stages of the majority of described species were examined and used for the development of dichotomous keys for avian Plasmodium species.

RESULTS

In all, 164 published articles were included in this review. Blood stages of avian Plasmodium parasites belonging to subgenera Haemamoeba, Giovannolaia, Novyella, Bennettinia and Huffia were analysed and compared. Illustrated keys for identification of subgenera and species of these parasites were developed. Lists of invalid and synonymous Plasmodium parasite names as well as names of doubtful identity were composed.

CONCLUSION

This study shows that 55 described species of avian Plasmodium can be readily identified using morphological features of their blood stages. These were incorporated in the keys. Numerous synonymous names of Plasmodium species and also the names belonging to the category species inquirenda exist, and they can be used as reserves for future taxonomy studies. Molecular markers are unavailable for 58% of described Plasmodium parasites, raising a task for the current avian malaria researchers to fill up this gap.

Prevalence and diversity of avian Haemosporida infecting songbirds in southwest Michigan

Avian blood parasites from the genera Plasmodium, Haemoproteus, and Leucocytozoon (Haemosporida) affect hosts in numerous ways. They influence species interactions, host behavior, reproductive success, and cause pathology and mortality in birds. The Great Lakes region of North America has extensive aquatic and wetland habitat and supports a diverse vector community. Here we describe the community of bird-infecting Haemosporida in southwest Michigan and their host associations by measuring parasite prevalence, diversity, and host breadth across a diverse community of avian hosts. Over 700 songbirds of 55 species were screened for Haemosporida infection across southwest Michigan, including 11 species that were targeted for larger sample sizes. In total, 71 parasite lineages infected over 40% of birds. Of these, 42 were novel, yet richness estimates suggest that approximately half of the actual parasite diversity in the host community was observed despite intensive sampling of multiple host species. Parasite prevalence varied among parasite genera (7-24%) and target host species (0-85%), and parasite diversity was consistently high across most target species. Host breadth varied widely across the most prevalent parasite lineages, and we detected around 60% of host species richness for these parasite lineages. We report many new lineages and novel host-parasite associations, but substantial parasite diversity remains undiscovered in the Midwest.

A method to preserve low parasitaemia Plasmodium-infected avian blood for host and vector infectivity assays

Background

Avian malaria vector competence studies are needed to understand more succinctly complex avian parasite-vector-relations. The lack of vector competence trials may be attributed to the difficulty of obtaining gametocytes for the majority of Plasmodium species and lineages. To conduct avian malaria infectivity assays for those Plasmodium spp. and lineages that are refractory to in vitro cultivation, it is necessary to obtain and preserve for short periods sufficient viable merozoites to infect naïve donor birds to be used as gametocyte donors to infect mosquitoes. Currently, there is only one described method for long-term storage of Plasmodium spp.—infected wild avian blood and it is reliable at a parasitaemia of at least 1 %. However, most naturally infected wild-caught birds have a parasitaemia of much less that 1 %. To address this problem, a method for short-term storage of infected wild avian blood with low parasitaemia (even ≤0.0005 %) has been explored and validated.

Methods

To obtain viable infective merozoites, blood was collected from wild birds using a syringe containing the anticoagulant and the red blood cell preservative citrate phosphate dextrose adenine solution (CPDA). Each blood sample was stored at 4 °C for up to 48 h providing sufficient time to determine the species and parasitaemia of Plasmodium spp. in the blood by morphological examination before injecting into donor canaries. Plasmodium spp.—infected blood was inoculated intravenously into canaries and once infection was established, Culex stigmatosoma, Cx. pipiens and Cx. quinquefasciatus mosquitoes were then allowed to feed on the infected canaries to validate the efficacy of this method for mosquito vector competence assays.

Results

Storage of Plasmodium spp.—infected donor blood at 4 °C yielded viable parasites for 48 h. All five experimentally-infected canaries developed clinical signs and were infectious. Pathologic examination of three canaries that later died revealed splenic lesions typical of avian malaria infection. Mosquito infectivity assays demonstrated that Cx. stigmatosoma and Cx. pipiens were competent vectors for Plasmodium cathemerium.

Conclusions

A simple method of collecting and preserving avian whole blood with malaria parasites of low parasitaemia (≤0.0005 %) was developed that remained viable for further experimental bird and mosquito infectivity assays. This method allows researchers interested in conducting infectivity assays on target Plasmodium spp. to collect these parasites directly from nature with minimal impact on wild birds.

Local parasite lineage sharing in temperate grassland birds provides clues about potential origins of Galapagos avian Plasmodium

Oceanic archipelagos are vulnerable to natural introduction of parasites via migratory birds. Our aim was to characterize the geographic origins of two Plasmodium parasite lineages detected in the Galapagos Islands and in North American breeding bobolinks (Dolichonyx oryzivorus) that regularly stop in Galapagos during migration to their South American overwintering sites. We used samples from a grassland breeding bird assemblage in Nebraska, United States, and parasite DNA sequences from the Galapagos Islands, Ecuador, to compare to global data in a DNA sequence registry. Homologous DNA sequences from parasites detected in bobolinks and more sedentary birds (e.g., brown‐headed cowbirds Molothrus ater, and other co‐occurring bird species resident on the North American breeding grounds) were compared to those recovered in previous studies from global sites. One parasite lineage that matched between Galapagos birds and the migratory bobolink, Plasmodium lineage B, was the most common lineage detected in the global MalAvi database, matching 49 sequences from unique host/site combinations, 41 of which were of South American origin. We did not detect lineage B in brown‐headed cowbirds. The other Galapagos‐bobolink match, Plasmodium lineage C, was identical to two other sequences from birds sampled in California. We detected a close variant of lineage C in brown‐headed cowbirds. Taken together, this pattern suggests that bobolinks became infected with lineage B on the South American end of their migratory range, and with lineage C on the North American breeding grounds. Overall, we detected more parasite lineages in bobolinks than in cowbirds. Galapagos Plasmodium had similar host breadth compared to the non‐Galapagos haemosporidian lineages detected in bobolinks, brown‐headed cowbirds, and other grassland species. This study highlights the utility of global haemosporidian data in the context of migratory bird–parasite connectivity. It is possible that migratory bobolinks bring parasites to the Galapagos and that these parasites originate from different biogeographic regions representing both their breeding and overwintering sites.

Host compatibility rather than vector-host-encounter rate determines the host range of avian Plasmodium parasites

Blood-feeding arthropod vectors are responsible for transmitting many parasites between vertebrate hosts. While arthropod vectors often feed on limited subsets of potential host species, little is known about the extent to which this influences the distribution of vector-borne parasites in some systems. Here, we test the hypothesis that different vector species structure parasite-host relationships by restricting access of certain parasites to a subset of available hosts. Specifically, we investigate how the feeding patterns of Culex mosquito vectors relate to distributions of avian malaria parasites among hosts in suburban Chicago, IL, USA. We show that Plasmodium lineages, defined by cytochrome b haplotypes, are heterogeneously distributed across avian hosts. However, the feeding patterns of the dominant vectors (Culex restuans and Culex pipiens) are similar across these hosts, and do not explain the distributions of Plasmodium parasites. Phylogenetic similarity of avian hosts predicts similarity in their Plasmodium parasites. This effect was driven primarily by the general association of Plasmodium parasites with particular host superfamilies. Our results suggest that a mosquito-imposed encounter rate does not limit the distribution of avian Plasmodium parasites across hosts. This implies that compatibility between parasites and their avian hosts structure Plasmodium host range.

Multiple host-switching of Haemosporidia parasites in bats

Background

There have been reported cases of host-switching in avian and lizard species of Plasmodium (Apicomplexa, Haemosporidia), as well as in those infecting different primate species. However, no evidence has previously been found for host-swapping between wild birds and mammals.

Methods

This paper presents the results of the sampling of blood parasites of wild-captured bats from Madagascar and Cambodia. The presence of Haemosporidia infection in these animals is confirmed and cytochrome b gene sequences were used to construct a phylogenetic analysis.

Results

Results reveal at least three different and independent Haemosporidia evolutionary histories in three different bat lineages from Madagascar and Cambodia.

Conclusion

Phylogenetic analysis strongly suggests multiple host-switching of Haemosporidia parasites in bats with those from avian and primate hosts.

Bayesian analysis of new and old malaria parasite DNA sequence data demonstrates the need for more phylogenetic signal to clarify the descent of Plasmodium falciparum

Molecular systematic studies published during the last 15 years to clarify the phylogenetic relationships among the malaria parasites have led to two major hypotheses on the descent of Plasmodium falciparum: One supports an avian origin as a result of a relatively recent host switch, and another one favours the evolutionary development of P. falciparum together with its human host from primate ancestors. In this paper, we present phylogenetic analyses of three different Plasmodium genes, the nuclear 18 small sub-unit (SSU) ribosomal ribonucleic acid (rRNA), the mitochondrial cytochrome b (cyt b) and the plastid caseinolytic protease C (ClpC) gene, using numerous haemosporidian parasite DNA sequences obtained from the GenBank as well as several new sequences for major malaria parasites including the avian one Plasmodium cathemerium, which has never been considered in molecular phylogenetic analyses before. Most modern and sophisticated DNA substitution models based on Bayesian inference analysis were applied to estimate the cyt b and ClpC phylogenetic trees, whereas the 18 SSU rRNA gene was examined with regards to its secondary structure using PHASE software. Our results indicate that the data presently available are generally neither sufficient in number nor in information to solve the problem of the phylogenetic origin of P. falciparum.

Linkage between mitochondrial cytochrome b lineages and morphospecies of two avian malaria parasites, with a description of Plasmodium (Novyella) ashfordi sp. nov

Numerous lineages of avian malaria parasites of the genus Plasmodium have been deposited in GenBank. However, only seven morphospecies have been linked to these lineages. This study linked two molecular sequences with morphospecies of malaria parasites. Two species of Plasmodium (mitochondrial cytochrome b gene lineages P-GRW2 and P-GRW4) were isolated from naturally infected adult great reed warblers (Acrocephalus arundinaceus) and inoculated to naive juvenile individuals of the same host species. Heavy parasitemia developed in the subinoculated birds, which enable identification of the species and deposition of their voucher specimens. Parasites of the lineage P-GRW2 were described as a new species, Plasmodium (Novyella) ashfordi, which is characterized primarily by the fan-like mature erythrocytic meronts containing seven to eight merozoites and the terminal position of clumped pigment granules in the gametocytes. Illustrations of the blood stages of the new species and Plasmodium (Haemamoeba) relictum (lineage P-GRW4) are given. The parasites of both lineages are transmitted in Africa and probably not in northern Europe. Other lineages closely related to P. ashfordi and P. relictum are identified. This study establishes the value of PCR-based identification of avian malaria parasites.

Complete nucleotide sequences of the mitochondrial genomes of two avian malaria protozoa, Plasmodium gallinaceum and Plasmodium juxtanucleare

We analyzed mitochondrial genomes of two avian malaria protozoa, Plasmodium gallinaceum and Plasmodium juxtanucleare. Both mitochondrial genomes were estimated to be 6,002 and 6,014 bp in length, respectively, and to have the identical gene organization and contents to that of other Plasmodium species previously analyzed; three functional genes for cytochrome c oxidase subunit I, III, and cytochrome (cyt b), with following sets of discontinuous and scrambled 15 ribosomal subunit RNA (rRNA) genes. Similarities of the three protein-coding genes showed closer relationship within avian malaria protozoa rather than mammalian Plasmodium species. In addition, we showed the tandem repeated structure of each mitochondrial genome of both P. gallinaceum and P. juxtanucleare as well as previously found in mammalian Plasmodium species. This study revealed the complete sequences and structure of the mitochondrial genomes of avian malaria protozoa for the first time.