Vector relationships in the Trypanosomatidae

Prevalence and Diversity of Blood Parasites (Plasmodium, Leucocytozoon and Trypanosoma) in Backyard Chickens (Gallus gallus domesticus) Raised in Southern Thailand

Avian malaria and leucocytozoonosis can cause fatal diseases, whereas avian trypanosomiasis is reported to be harmless in chickens. Backyard chickens can be infected by several pathogens, including blood parasites, that may shed to industrial poultry production, with a consequently higher economic impact. This study aimed to investigate the presence of several blood parasites (Plasmodium, Leucocytozoon and Trypanosoma) in backyard chickens raised in Southern Thailand, using PCR-based detection and microscopic methods. From June 2021 to June 2022, 57 backyard chickens were sampled. Fresh thin blood smears were prepared from 11 individuals, and buffy coat smears were prepared from 55 of them. Both thin blood smears and buffy coat smears were used for microscopic analysis. Two nested PCR protocols that amplify a fragment of cytochrome b (cytb) and small subunit rRNA (SSU rRNA) genes were used to identify Haemosporida and Trypanosoma parasites, respectively. The number of positive samples was higher with the application of nested PCR than when buffy coat smears were used. Three new Plasmodium lineages (GALLUS47-49) and thirteen Leucocytozoon lineages (GALLUS50-62) were found. Trophozoites, meronts and gametocytes of Plasmodium gallinaceum (GALLUS01) were present in one thin blood smear. All thin blood smears revealed Leucocytozoon infections, but only three samples were a single infection. These three samples revealed the presence of fusiform host cell-parasite complexes, of which the morphological features resembled those of Leucocytozoon macleani (possible synonym is Leucocytozoon sabrazesi), while the cytb showed that this parasite is closely related to the lineage GALLUS06-07, described as Leucocytozoon schouteni. The Trypanosoma prevalence was 33.33%; it was present in only one of the thin blood smears, and it resembles Trypanosoma calmettei. This study showed the prevalence of a high diversity of Plasmodium (64.91%) and Leucocytozoon (89.47%) in Thai chickens. Both nested-PCR and buffy coat smear can be used as the diagnostic tool for the testing of Plasmodium, Leucocytozoon and Trypanosoma for parasitic control in backyard chickens and poultry farms. The information on the parasite species that can be found in chickens raised in Southern Thailand was also considered as the baseline information for further study.

Lotmaria passim (Kinetoplastea: Trypanosomatidae) in honey bees from Argentina

Lotmaria passim (Kinetoplastea) is considered the most prevalent as well as the most virulent trypanosomatid associated to the European honey bee Apis mellifera. We used qPCR to screen for the presence of this parasite in 57 samples from ten Argentinian provinces, and were able to detect its presence throughout most of the country with 41% of the samples testing positive. In a retrospective analysis, we detected L. passim in 73% of honey bee samples from 2006 showing that this flagellate has been widely present in Argentina for at least ~15 years. Additionally, three primer sets for L. passim detection were compared, with the pair that produced smallest PCR product having the best detection capability. Finally, we also found L. passim DNA in 100% (n = 6) of samples of the mite Varroa destructor. The role of this ectoparasite in the lifecycle of Lotmaria, if any, remains unrevealed.

Development of Trypanosoma everetti in Culicoides biting midges

Trypanosoma species (Trypanosomatida, Kinetoplastea) are almost exclusively heteroxenous flagellated parasites, which have been extensively studied as the causative agents of severe trypanosomiasis in humans and domestic animals. However, the biology of avian trypanosomes remains insufficiently known, particularly in wildlife, despite information that some species might be pathogenic and affect the fitness of intensively infected individuals. Avian trypanosomes are cosmopolitans. Due to regular bird seasonal migrations, this host-parasite system might provide new insight for better understanding mechanisms of transcontinental dispersal of pathogens, their ecological plasticity, specificity and speciation. Trypanosoma everetti parasitizes numerous bird species globally, but data on its biology are scarce and its vectors remain unknown. This study aimed to test experimentally whether widespread Culicoides (Diptera: Ceratopogonidae) biting midges are susceptible to infection with this parasite. Two common house martins Delichon urbicum and two sedge warblers Acrocephalus schoenobaenus naturally infected with T. everetti were caught in the wild after arrival from African wintering grounds. Laboratory reared Culicoides nubeculosus and wild-caught Culicoides impunctatus biting midges were exposed by allowing them to take infected blood meals. The experimentally infected and control insects were maintained in the laboratory and dissected at intervals to follow the development of the parasite. Infections were determined using microscopic examination and PCR-based testing. Four closely related haplotypes of T. everetti were found, and each was present in different individual parasite-donor birds. These parasites readily developed and produced metacyclic trypomastigotes in C. nubeculosus and C. impunctatus biting midges. Molecular characterisation of T. everetti was developed. According to Bayesian phylogenetic analysis using a DNA fragment encoding 18S rRNA, the five species of small avian trypanosomes were closely related. Wild caught Culicoides biting midges were also collected and screened for the presence of natural infections. In all, 6.8% of wild-caught biting midges belonging to five Culicoides species were PCR-positive for kinetoplastids, including Trypanosoma species. Culicoides biting midges are readily susceptible and likely naturally transmit avian trypanosomes and thus, should be targeted in epidemiology research of avian trypanosomiasis.

Correlates of blood parasitism in a threatened marshland passerine: infection by kinetoplastids of the genus Trypanosoma is related to landscape metrics of habitat edge

In birds, vector-borne parasites invading the bloodstream are important agents of disease, affect fitness and shape population viability, thus being of conservation interest. Here, we molecularly identified protozoan blood parasites in two populations of the threatened Aquatic Warbler Acrocephalus paludicola, a migratory passerine nesting in open marsh. We explored whether prevalence and lineage diversity of the parasites vary by population and whether infection status is explained by landscape metrics of habitat edge and individual traits (body mass, fat score, wing length and sex). Aquatic Warblers were infected by genera Plasmodium, Leucocytozoon and Trypanosoma, with seven, one and four lineages, and 29.9, 0.7 and 12.5% prevalence, respectively. No Haemoproteus infections were detected. Prevalence did not vary between the populations, but lineage diversity was higher in Polesie than in Biebrza for all the lineages pooled and for Plasmodium. Infection by Trypanosoma decreased with patch core area and increased with density of habitat edge. Infection status was not predicted by the individual traits. Our study is the first to show an association between edge-related landscape features and blood parasitism in an open habitat bird. This finding will support informed conservation measures for avian species of the globally shrinking marshland and other treeless habitats.

Workshop no. 7. Digestion in haematophagous arthropods

In vector-borne diseases it is generally the vector which determines the success of disease transmission and efforts to limit the incidence of such diseases generally involve control of the vector. The very nature of their feeding habits renders haematophagous arthropods prime candidates for disease transmission and a great deal is now known of the biology of the most important vectors. Nevertheless, there are many areas in which our knowledge is incomplete or about which conflieting views exist.

Flagellum couples cell shape to motility in Trypanosoma brucei

Trypanosoma brucei is a highly invasive pathogen capable of penetrating deeply into host tissues. To understand how flagellar motility facilitates cell penetration, we used cryo-electron tomography (cryo-ET) to visualize two genetically anucleate mutants with different flagellar motility behaviors. We found that the T. brucei cell body is highly deformable as defined by changes in cytoskeletal twist and spacing, in response to flagellar beating and environmental conditions. Based on the cryo-ET models, we proposed a mechanism of how flagellum motility is coupled to cell shape changes, which may facilitate penetration through size-limiting barriers.

In the unicellular parasite Trypanosoma brucei, the causative agent of human African sleeping sickness, complex swimming behavior is driven by a flagellum laterally attached to the long and slender cell body. Using microfluidic assays, we demonstrated that T. brucei can penetrate through an orifice smaller than its maximum diameter. Efficient motility and penetration depend on active flagellar beating. To understand how active beating of the flagellum affects the cell body, we genetically engineered T. brucei to produce anucleate cytoplasts (zoids and minis) with different flagellar attachment configurations and different swimming behaviors. We used cryo-electron tomography (cryo-ET) to visualize zoids and minis vitrified in different motility states. We showed that flagellar wave patterns reflective of their motility states are coupled to cytoskeleton deformation. Based on these observations, we propose a mechanism for how flagellum beating can deform the cell body via a flexible connection between the flagellar axoneme and the cell body. This mechanism may be critical for T. brucei to disseminate in its host through size-limiting barriers.

Haemoparasites of the pied flycatcher: inter-population variation in the prevalence and community composition

The prevalence and community composition of haemoparasites can substantially differ among avian host populations, which may lead to different selection pressures. Therefore, information about these parameters is crucial for understanding, e.g. the inter-population variation in host life history traits. Here, we molecularly screened a population of a long-distance migrant, the pied flycatcher Ficedula hypoleuca, from central Poland for the presence of three genera of blood parasites: Haemoproteus, Plasmodium and Trypanosoma. The infection rate in this population was the highest for haemosporidians (86·8%) and one of the highest for trypanosomes (39·7%) among the thus far screened breeding populations of this species. The haemosporidian community was composed of six Haemoproteus/Plasmodium lineages, and the trypanosome community - 4 species and a parasite assigned to genus level. Trypanosomes were dominated by T. culicavium, a recently described species, corroborating the prediction that insectivorous songbirds are vertebrate hosts of this parasite. Host sex and age did not explain variation in infection incidence except for the higher trypanosome infection rates in males. A comparison of the study population with three other breeding populations previously screened molecularly for haemosporidians showed some geographic differences. This study confirms the importance of examining local parasite communities across a host distribution range.

Blood parasites of penguins: a critical review

Blood parasites are considered some of the most significant pathogens for the conservation of penguins, due to the considerable morbidity and mortality they have been shown to produce in captive and wild populations of these birds. Parasites known to occur in the blood of penguins include haemosporidian protozoans (Plasmodium, Leucocytozoon, Haemoproteus), piroplamid protozoans (Babesia), kinetoplastid protozoans (Trypanosoma), spirochete bacteria (Borrelia) and nematode microfilariae. This review provides a critical and comprehensive assessment of the current knowledge on these parasites, providing an overview of their biology, host and geographic distribution, epidemiology, pathology and implications for public health and conservation.

Deforestation does not affect the prevalence of a common trypanosome in African birds

In spite of numerous reports of avian Trypanosoma spp. in birds throughout the world, patterns of the distribution and prevalence of these blood parasites remains insufficiently understood. It is clear that spatial heterogeneity influences parameters of parasite distributions in natural populations, but data regarding avian trypanosomes are scarce. Using microscopy and molecular diagnostic methods, we analysed the variation of prevalence of avian Trypanosoma parasites in two widespread African bird species, the yellow-whiskered greenbul Andropadus latirostris and the olive sunbird Cyanomitra olivacea. In all, 353 birds were captured in pristine forests and agroforest sites in Cameroon and Ghana. Overall, the prevalence of avian trypanosomes was 51.3%. Five morphospecies were reported (Trypanosoma everetti, T. anguiformis, T. avium, T. naviformis, T. ontarioensis). Trypanosoma everetti predominated, representing 98% of all Trypanosoma spp. reports, and it was present in both avian hosts. The prevalence of T. everetti was significantly less in the yellow-whiskered greenbul (19%) than olive sunbird (83%), and the same pattern of prevalence was reported in these avian hosts at different study sites. We found no interaction between sites and the prevalence of T. everetti. For both avian hosts, the prevalence did not differ significantly between pristine forests and agroforests. This indicates the same pattern of transmission at sites with different levels of deforestation and suggests that spatial heterogeneity related to deforestation does not affect the prevalence of avian Trypanosoma infections. It is likely that host-related factors, but not environmental conditions favour or reduce these parasite infections in forests of sub-Saharan Africa. Microscopic and PCR-based diagnostics showed the same sensitivity in diagnostics of T. everetti. We discuss the implications of these findings for the epidemiology of avian trypanosomiasis in natural populations.

The flagellar protein FLAG1/SMP1 is a candidate for Leishmania-sand fly interaction

Leishmaniasis is a serious problem that affects mostly poor countries. Various species of Leishmania are the agents of the disease, which take different clinical manifestations. The parasite is transmitted by sandflies, predominantly from the Phlebotomus genus in the Old World and Lutzomyia in the New World. During development in the gut, Leishmania must survive various challenges, which include avoiding being expelled with blood remnants after digestion. It is believed that attachment to the gut epithelium is a necessary step for vector infection, and molecules from parasites and sand flies have been implicated in this attachment. In previous work, monoclonal antibodies were produced against Leishmania. Among these an antibody was obtained against Leishmania braziliensis flagella, which blocked the attachment of Leishmania panamensis flagella to Phlebotomus papatasi guts. The protein recognized by this antibody was identified and named FLAG1, and the complete FLAG1 gene sequence was obtained. This protein was later independently identified as a small, myristoylated protein and called SMP1, so from now on it will be denominated FLAG1/SMP1. The FLAG1/SMP1 gene is expressed in all developmental stages of the parasite, but has higher expression in promastigotes. The anti-FLAG1/SMP1 antibody recognized the flagellum of all Leishmania species tested and generated the expected band by western blots. This antibody was used in attachment and infection blocking experiments. Using the New World vector Lutzomyia longipalpis and Leishmania infantum chagasi, no inhibition of attachment ex vivo or infection in vivo was seen. On the other hand, when the Old World vectors P. papatasi and Leishmania major were used, a significant decrease of both attachment and infection were seen in the presence of the antibody. We propose that FLAG1/SMP1 is involved in the attachment/infection of Leishmania in the strict vector P. papatasi and not the permissive vector L. longipalpis.

Epidemiology and molecular phylogeny of Babesia sp. in Little Penguins Eudyptula minor in Australia

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We examined blood smears from 263 wild little penguins in southeastern Australia.

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Babesia sp. was detected in penguins in New South Wales, Victoria and Tasmania.

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True prevalence is estimated between 3.4% and 4.5%.

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Babesia sp. from little penguins is closely related to B. poelea and B. uriae.

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Babesia infections were assymptomatic.

Blood parasites are potential threats to the health of penguins and to their conservation and management. Little penguins Eudyptula minor are native to Australia and New Zealand, and are susceptible to piroplasmids (Babesia), hemosporidians (Haemoproteus, Leucocytozoon, Plasmodium) and kinetoplastids (Trypanosoma). We studied a total of 263 wild little penguins at 20 sites along the Australian southeastern coast, in addition to 16 captive-bred little penguins. Babesia sp. was identified in seven wild little penguins, with positive individuals recorded in New South Wales, Victoria and Tasmania. True prevalence was estimated between 3.4% and 4.5%. Only round forms of the parasite were observed, and gene sequencing confirmed the identity of the parasite and demonstrated it is closely related to Babesia poelea from boobies (Sula spp.) and B. uriae from murres (Uria aalge). None of the Babesia-positive penguins presented signs of disease, confirming earlier suggestions that chronic infections by these parasites are not substantially problematic to otherwise healthy little penguins. We searched also for kinetoplastids, and despite targeted sampling of little penguins near the location where Trypanosoma eudyptulae was originally reported, this parasite was not detected.

Distribution, diversity and drivers of blood-borne parasite co-infections in Alaskan bird populations

Avian species are commonly infected by multiple parasites, however few studies have investigated the environmental determinants of the prevalence of co-infection over a large scale. Here we believe that we report the first, detailed ecological study of the prevalence, diversity and co-infections of four avian blood-borne parasite genera: Plasmodium spp., Haemoproteus spp., Leucocytozoon spp. and Trypanosoma spp. We collected blood samples from 47 resident and migratory bird species across a latitudinal gradient in Alaska. From the patterns observed at collection sites, random forest models were used to provide evidence of associations between bioclimatic conditions and the prevalence of parasite co-infection distribution. Molecular screening revealed a higher prevalence of haematozoa (53%) in Alaska than previously reported. Leucocytozoons had the highest diversity, prevalence and prevalence of co-infection. Leucocytozoon prevalence (35%) positively correlated with Trypanosoma prevalence (11%), negatively correlated with Haemoproteus prevalence (14%) and had no correlation with Plasmodium prevalence (7%). We found temperature, precipitation and tree cover to be the primary environmental drivers that show a relationship with the prevalence of co-infection. The results provide insight into the impacts of bioclimatic drivers on parasite ecology and intra-host interactions, and have implications for the study of infectious diseases in rapidly changing environments.

Evolution of parasitism in kinetoplastid flagellates

Kinetoplastid protists offer a unique opportunity for studying the evolution of parasitism. While all their close relatives are either photo- or phagotrophic, a number of kinetoplastid species are facultative or obligatory parasites, supporting a hypothesis that parasitism has emerged within this group of flagellates. In this review we discuss origin and evolution of parasitism in bodonids and trypanosomatids and specific adaptations allowing these protozoa to co-exist with their hosts. We also explore the limits of biodiversity of monoxenous (one host) trypanosomatids and some features distinguishing them from their dixenous (two hosts) relatives.

Trypanosoma (Megatrypanum) melophagium in the sheep ked Melophagus ovinus from organic farms in Croatia: phylogenetic inferences support restriction to sheep and sheep keds and close relationship with trypanosomes from other ruminant species

Trypanosoma (Megatrypanum) melophagium is a parasite of sheep transmitted by sheep keds, the sheep-restricted ectoparasite Melophagus ovinus (Diptera: Hippoboscidae). Sheep keds were 100% prevalent in sheep from five organic farms in Croatia, Southeastern Europe, whereas trypanosomes morphologically compatible with T. melophagium were 86% prevalent in the guts of the sheep keds. Multilocus phylogenetic analyses using sequences of small subunit rRNA, glycosomal glyceraldehyde-3-phosphate dehydrogenase, spliced leader, and internal transcribed spacer 1 of the rDNA distinguished T. melophagium from all allied trypanosomes from other ruminant species and placed the trypanosome in the subgenus Megatrypanum. Trypanosomes from sheep keds from Croatia and Scotland, the only available isolates for comparison, shared identical sequences. All biologic and phylogenetic inferences support the restriction of T. melophagium to sheep and, especially, to the sheep keds. The comparison of trypanosomes from sheep, cattle, and deer from the same country, which was never achieved before this work, strongly supported the host-restricted specificity of trypanosomes of the subgenus Megatrypanum. Our findings indicate that with the expansion of organic farms, both sheep keds and T. melophagium may re-emerge as parasitic infections of sheep.

Biodiversity of avian trypanosomes

We have studied the biodiversity of trypanosomes from birds and bloodsucking Diptera on a large number of isolates. We used two molecular approaches, random amplification of polymorphic DNA (RAPD) method, and sequence analysis of the small subunit ribosomal RNA (SSU rRNA) gene. RAPD method divided the isolates into 11 separate lineages. Phylogenetic analysis of the SSU rRNA gene was congruent with the RAPD. Morphometric analysis of kinetoplast width and cell length was in agreement with molecular data. Avian trypanosomes appeared polyphyletic on SSU rDNA tree; thus, they do not represent a taxonomic group. We propose that all lineages recovered by SSU analysis probably represent distinct species of avian trypanosomes. We discuss possible transmission ways and geographical distribution of new avian trypanosome lineages. Finally, we recommend methods that should be used for species determination of avian trypanosomes.

Two new Trypanosoma species from African birds, with notes on the taxonomy of avian trypanosomes

Trypanosoma anguiformis n. sp. and Trypanosoma polygranularis n. sp. are described from the African olive sunbird, Cyanomitra olivacea, and Latham's forest francolin, Francolinus lathami, respectively, based on the morphology of their hematozoic trypomastigotes and partial sequences of the small subunit ribosomal RNA gene. Both new species belong to the group of small non-striated avian trypanosomes (<30 µm in length on average) with the kinetoplast situated close to the posterior end of the body. Trypanosoma anguiformis can be readily distinguished from other small avian trypanosomes due to its markedly attenuated (snake-shaped) form of the hematozoic trypomastigotes and the dumbbell-shaped nucleus of the parasite. Trypanosoma polygranularis is readily distinguishable due to the markedly off-center (anteriorly) located nucleus, numerous azurophilic granules that are arranged in a line following the undulating membrane, and the large kinetoplast (with an area up to 1.7 µm(2) [1.1 µm(2) on average]). Illustrations of hematozoic trypomastigotes of the new species are given, and DNA lineages associated with these parasites are reported. The current situation in species taxonomy of avian trypanosomes is discussed. We call for the redescription of valid species of avian trypanosomes from their type vertebrate hosts and type localities by using morphological and polymerase chain reaction-based techniques as an initial essential step towards revising the species composition of avian trypanosomes and reconstructing the taxonomy of these organisms.

Natural infections of man-biting sand flies by Leishmania and Trypanosoma species in the northern Peruvian Andes

The natural infection of sand flies by Leishmania species was studied in the Andean areas of Peru where cutaneous leishmaniasis caused by Leishmania (Viannia) peruviana is endemic. Sand flies were captured by human bait and Center for Disease Control (CDC) light trap catches at Nambuque and Padregual, Department of La Libertad, Peru, and morphologically identified. Among 377 female sand flies dissected, the two dominant man-biting species were Lutzomyia (Helcocyrtomyia) peruensis (211 flies) and Lutzomyia (Helcocyrtomyia) caballeroi (151 flies). Another sand fly species captured by light trap was Warileya phlebotomanica (15 flies). The natural infection of sand flies by flagellates was detected in 1.4% of Lu. (H.) peruensis and 2.6% of Lu. (H.) caballeroi, and the parasite species were identified as Le. (V.) peruviana and Trypanosoma avium, respectively, by molecular biological methods. The results indicated that the vector species responsible for the transmission of leishmaniasis in the study areas is Lu. (H.) peruensis. In addition, the presence of Trypanosoma in man-biting sand fly species means that more careful consideration is necessary for vector research in areas of Andean Peru where leishmaniasis is endemic.

Host—parasite relationships ofBlastocrithidia familiarisinLygaeus pandurusScop. (Hemiptera: Lygaeidae)

Blastocrithidia familiariswere found to be parasitic in the midgut, ileum and rectum ofLygaeus pandurus. The host—parasite relationship is described. Attachment of parasites in the midgut and ileum occurs by interdigitation of expanded flagella over and between the microvilli. No attachment to microvilli was observed where extracellular membranes form well-organized layers which lie parallel to the gut wall and completely separate the microvilli border from the lumen. The extracellular membranes originate from delamination of the outer unit membrane of microvilli which consists of a double plasma membrane. The function of the extracellular membrane layers and their possible role as a peritrophic membrane in preventing parasite attachment is discussed in relation to previous studies on midgut cells in Hemiptera with a similar apical coat on midgut microvilli. In the rectum, parasites attach to the cuticle of the gland cells and not to the rest of the rectal wall. Attachment to the cuticle occurs by the formation of hemidesmosomes. A comparison of the relationship ofB. familiarisand its host to previous ultrastructural studies of associations between kinetoplastid flagellates and their respective hosts is discussed.

Leishmania: origin, evolution and future since the Precambrian

This brief review discusses the history of leishmaniasis, considering its origin from the Paleoartic, Neoartic or Neotropic. We reassess some of the theories of the likely origin of this protozoan since the beginning of life on Earth, passing through the Mesozoic and continuing to the appearance of humans. The relationship between this parasite or its ancestors, possible vectors and hosts with regard to ecological modifications is discussed. Recent molecular techniques have helped to elucidate some of the evolutionary questions regarding Leishmania, but have also brought doubts about the origin and evolution of this human parasite. PCR has been used for studies in the new discipline of paleoparasitology, helping to elucidate some of the remaining evolutionary questions. Understanding of this global condition is fundamental in determining the best approach to use against the parasite, specifically for the development of an efficient vaccine.

Blood parasites of chickens in Uganda and Cameroon with molecular descriptions of Leucocytozoon schoutedeni and Trypanosoma gallinarum

Using microscopy and PCR, we determined the prevalence of blood parasites in village chickens in Uganda and Cameroon. Of 148 individuals tested, 18.3% were infected with Leucocytozoon schoutedeni (Haemosporida, Leucocytozoidae) and 4.1% were infected with Trypanosoma gallinarum (Kinetoplastida, Trypanosomatidae). No other blood parasites were detected. Subsequent phylogenetic analysis of the cytochrome b gene of L. schoutedeni identified 2 distinct lineages that were found at all 3 sampling locations in Uganda. The sequence divergence between these 2 lineages is 1.5%. One of these lineages was also found in chickens in Cameroon, nearly 2,000 km distant. There are no morphological differences between blood stages of the parasites represented by the 2 different lineages, suggesting that cytochrome b gene sequence divergence can be as high as 1.5% within a single well-defined morphospecies of Leucocytozoon. We sequenced a portion of the small subunit ribosomal RNA gene (SSU rRNA) of T. gallinarum, and redescribe T. gallinarum for the first time since its discovery in 1911. These are the first assignments of DNA sequence data to these morphospecies of Leucocytozoon and Trypanosoma and may represent an example of intraspecific sequence divergence.

Molecular trees of trypanosomes incongruent with fossil records of hosts

Molecular trees of trypanosomes have confirmed conventionally accepted genera, but often produce topologies that are incongruent with knowledge of the evolution, systematics, and biogeography of hosts and vectors. These distorted topologies result largely from incorrect assumptions about molecular clocks. A host-based phylogenetic tree could serve as a broad outline against which the reasonability of molecular phylogenies could be evaluated. The host-based tree of trypanosomes presented here supports the " invertebrate first " hypothesis of trypanosome evolution, supports the monophyly of Trypanosomatidae, and indicates the digenetic lifestyle arose three times. An area cladogram of Leishmania supports origination in the Palaearctic during the Palaeocene.

Pathogenicity of trypanosomatids on insects

More and more effects of trypanosomatids on insects have been recognized in the past few years. Here, Günter A. Schaub reviews such effects, classifying the flagellates according to the intensity of the effects on the insect host into pathogenic, subpathogenic and apathogenic trypanosomatids. He emphasizes that subpathogenic trypanosomatids which cause only minor effects under optimal conditions might act synergistically with natural stressors, thereby being an important regulatory factor in insect populations.

Host specificity and incidence of Trypanosoma in some African rainforest birds: a molecular approach

Studies of host-parasite interactions in birds have contributed greatly to our understanding of the evolution and ecology of disease. Here we employ molecular techniques to determine the incidence and study the host-specificity of parasitic trypanosomes in the African avifauna. We developed a polymerase chain reaction (PCR)-based diagnostic test that amplified the small subunit ribosomal RNA gene (SSU rRNA) of Trypanosoma from avian blood samples. This nested PCR assay complements and corroborates information obtained by the traditional method of blood smear analysis. The test was used to describe the incidence of trypanosomes in 479 host individuals representing 71 rainforest bird species from Cameroon, the Ivory Coast and Equatorial Guinea. Forty-two (59%) of these potential host species harboured trypanosomes and 189 individuals (35%) were infected. To examine host and geographical specificity, we examined the morphology and sequenced a portion of the SSU rRNA gene from representative trypanosomes drawn from different hosts and collecting locations. In traditional blood smear analyses we identified two trypanosome morphospecies, T. avium and T. everetti. Our molecular and morphological results were congruent in that these two morphospecies had highly divergent SSU rRNA sequences, but the molecular assay also identified cryptic variation in T. avium, in which we found seven closely allied haplotypes. The pattern of sequence diversity within T. avium provides evidence for widespread trypanosome mixing across avian host taxa and across geographical locations. For example, T. avium lineages with identical haplotypes infected birds from different families, whereas single host species were infected by T. avium lineages with different haplotypes. Furthermore, some conspecific hosts from geographically distant sampling locations were infected with the same trypanosome lineage, but other individuals from those locations harboured different trypanosome lineages. This apparent lack of host or geographical specificity may have important consequences for the evolutionary and ecological interactions between parasitic trypanosomes and their avian hosts.

New data from old Trypanosomatid preparations

Assessing the diversity of the Trypanosomatidae is difficult because of the relatively small number of species that can be cultured. This same problem thwarts efforts to identify the hosts and insect vectors of Phytomonas, a genus of parasites of plants that includes species responsible for devastating epiphytotics of economically important plantations. Here, Myrna Serrano, Marta Teixeira and Erney Camargo review the studies that have led to the development of a PCR-based technique for processing insect and plant juices fixed on glass slides. The method overcomes the need for cultivation, facilitates field collections and also permits the molecular examination of archival smears of Phytomonas. In principle, the method can be adapted to any trypanosomatid as well as to any fastidious parasitic or free-living organism.

Phytomonas and other trypanosomatid parasites of plants and fruit

Trypanosomatid parasites are fairly common in the latex, phloem, fruit sap, seed albumen, and even in the nectar, of many plant families. They are transmitted to the plants in the saliva of phytophagous hemipterous bugs (Insecta). Morphologically, plant trypanosomatids have no special characteristic, except perhaps a very twisted cell body. Most occur in plants as promastigotes and a few as choanomastigotes. It is still controversial whether or not they are pathogenic in lactiferous plants or fruit, but it is certain that the phloem parasites are pathogenic in coconut palms and coffee bushes. In these plants, they cause lethal diseases responsible for the destruction of many plantations in Central and South America, but fortunately nowhere else in the world. Probably more than one genus of Trypanosomatidae is represented among the plant parasites. The most important is certainly Phytomonas, but Leptomonas, Crithidia and Herpetomonas may also be present. The distinction between them is difficult and only recently have molecular markers become available to help in their identification. At present, Phytomonas can be identified by DNA hybridization with a specific probe (SL3') complementary to a sequence of the mini-exon or spliced leader gene. The development of a polymerase chain reaction coupled to SL3' hybridization has facilitated the detection of Phytomonas in plants. The phylogeny of Phytomonas is still being worked out. For the moment it can only be said that the genus is very close to Herpetomonas.

Factors influencing the prevalence of trypanosome infection of Glossina pallidipes on the Ruvu flood plain of Eastern Tanzania

We report the pattern of infection of Glossina pallidipes with Trypanosoma vivax and T. congolense at a site in the Coast region of eastern Tanzania, studied between November 1993 and December 1994. Of the 2315 flies dissected 114 (4.9%) were T. congolense positive, 77 (3.3%) were T. vivax positive and 2 (0.1%) were T. brucei positive. Fly age was determined by the pteridine fluorescence method. Prevalence of infection was most strongly affected by month and the linear effect of age with the interaction of month and age having an effect for T. congolense-type infections. Sex and sex by month also have some predictive capacity when data for T. congolense and T. vivax-type infections are combined. In contrast to other similar studies our results suggest that the infection rate is non-linearly related to age of the tsetse fly, with older flies having progressively more chance of infection. The potential biological factors underpinning these interactions are discussed.

Vectors of cutaneous leishmaniasis in north-central Venezuela

An entomological survey was undertaken from January 1991 to February 1992 in El Ingenio, Miranda State, Venezuela, an endemic area of cutaneous leishmaniasis: prevalence of 10.7 cases per 100,000 inhabitants. A total of 4863 female sandflies (Phlebotominae) of fourteen species were collected in Shannon traps, then dissected and examined for leishmanial infections. Lutzomyia ovallesi (85.4%) and Lu. gomezi (11.2%) were the predominant anthropophilic species of sandfly. Fifty-one (1.19%) Lu.ovallesi and two (0.47%) Lu.gomezi had natural infection with Leishmania promastigotes. Identification of the parasites was done by using the polymerase chain reaction (PCR) and DNA hybridization. Two isolates from Lu.gomezi and forty-nine from Lu.ovallesi were typed as Leishmania braziliensis and three of the latter reacted with Le.mexicana also. This is the first report of Lu.gomezi with parasites typed as Le.braziliensis. We concluded that Lu.ovallesi is the primary vector of cutaneous leishmaniasis in the north-central area of Venezuela and Lu.gomezi should be regarded as an additional vector.

Evolutionary factors influencing the nature of parasite specificity

This article considers how specificity patterns are shaped during the course of parasite evolution. Parasites are first and foremost specific to site, or microhabitat; host ranges are far more subject to change than is microhabitat. Specificity results from a number of convergent phenomena starting with habits (microhabitat and feeding styles) of free-living progenitors and the way in which the parasitic association arises (e.g., passive oral contamination as opposed to intrusive entry). These bias the types of interaction parasites have with the host, and, through this, the way specificity develops. Host ecology acts as an external factor affecting specificity and predominates in parasites that interact minimally with the hosts physiological and immune systems. Coevolutionary factors are more important in parasites that feed on host tissues or occur in extraintestinal sites. Here, parasites must present the right cues, and respond appropriately to the host defense system. The ability to generalize these cues and responses across host boundaries may act as a constraint on host range. The functional role of the host in the parasite life history also affects the degree of specificity; thus, parasites may act as host generalists in hosts that act as trophic channels to the final host. The role of competition in determining specificity is difficult to assess. However, competition has been reported to influence microhabitat and host distribution through interactive site selection and/or competitive seclusion.

Leishmania infections damage the feeding mechanism of the sandfly vector and implement parasite transmission by bite

Leishmania parasites are transmitted by the bites of infected female sandflies by a mechanism that has not been clarified. Leishmania infections in the vector develop only in the gut, and the parasites' exit is through the food channel in the proboscis. The problem is how during the bite, when blood flows in, parasites are emitted through the same channel in the opposite direction. It is well documented that infected sandflies maintained on sugar diets are potent vectors, whereas transmission fails after constant feeding on blood. Hence to study the mechanism of transmission, we fed these diets to Phlebotomus papatasi infected with L. major. Histological examination demonstrated that only in the sugar-fed flies did the cuticle lining of the cardiac valve detach and other valve tissues degenerate gradually. The injury of the main valve of the food pumps hindered gorging of most flies when force-fed from capillaries, and they regurgitated the gut contents with fluids from the capillaries. We suggest that infections are caused by parasites regurgitated from the stomach that are deposited in the host tissue. We found that secretion of chitinolytic enzymes by cultured L. major parasites is inhibited by blood or hemoglobin, and hence these enzymes are apparently absent from the blood-fed infected flies, where the cardiac valve appears undamaged. We therefore presume that lysis of the chitin in the cuticle lining of the valve leads to exposure and degeneration of the underlying tissues.

Ultrastructural study of the host-parasite relationship of trypanosomatids in the housefly

The course of experimental oral infection of Musca domestica with Herpetomonas samuelpessoai and two new isolates from houseflies was followed for up to 40 days using optical and electron microscopy. The fly's rectum was found to be the preferential site of colonization by flagellates, mainly at places near papillar insertions but not on the papillae themselves. Midgut infection was transient, and infection of the crop did not last longer than 1 week. Promastigotes were the predominant colonizing forms and could be seen either free in the gut lumen or attached via hemidesmosomes to the rectum wall. Adherent flagellates exhibited flagellar projections and surface membrane blebs. Many flagellates displayed longitudinal body foldings yielding star-like images in cross sections. Opisthomastigotes could be seen in small numbers as free swimmers, mainly in the rectum.

Avian trypanosomes as models of hemoflagellate evolution

In the 15 years since the last review on avian trypanosomes(1), there has been a steady accrual of information on the distribution and dynamics of trypanosome infections in wild bird populations. Recent immunological and biochemical studies provide evidence that several trypanosome species can parasitize an ecological guild of host species but the relative roles of avian host phylogeny and vector ecology remain unanswered. In this article, Victor Apanius reviews the habitat preferences and behavior of trypanosomes within the avian host and attempts to draw similarities in the strategy employed by the parasite for persistence in different vertebrate classes. Next, the question of host specificity is raised and recent evidence on the subject is examined with an eye toward understanding the distribution of trypanosome species in host communities.

Avian trypanosomes in Simulium and sparrowhawks (Accipiter nisus)

Isolates of avian trypanosomes from nestling sparrowhawks (Accipiter nisus) and from Simulium latipes were compared by isoenzyme electrophoresis with the previously described avian trypanosomes Trypanosoma corvi and T. everetti. Simulium isolates developed into trypomastigotes in semi-defined medium at 37 degrees C confirming that they belong to the genus Trypanosoma. Cellulose acetate electrophoresis (CAE) and polyacrylamide gel electrophoresis (PAGE) methods were employed. A total of 11 enzymes was examined, of which 8 gave satisfactory results for all lysates (MDH, ICD, PGM, 6PGD, SOD, PEP I, PEP II and PEP D). The zymograms of 3 isolates from Simulium and 4 from A. nisus were similar indicating that they were the same organism and the isoenzyme patterns coincided with those of T. corvi. It is concluded that A. nisus and S. latipes are infected with T. corvi. Flagellate infections were found in the midgut, hindgut and rectum of Simulium where large numbers of epimastigotes were found in the lumen and attached to the cuticular intima of the rectal ampullae by hemidesmosomes at the distal end of an expanded flagellum. Out of 285 nestling sparrowhawks 13 (5%) were infected with trypanosomes. In view of their age and inability to preen themselves it is suggested they became infected via infected prey.

The effect of Blastocrithidia triatomae (Trypanosomatidae) on the midgut of the reduviid bug Triatoma infestans

The pathogenic flagellate Blastocrithidia triatomae disrupts the digestion of Triatoma infestans; the midgut ultrastructure of bugs infected with the flagellate and of uninfected bugs is compared. Third or fourth instar larvae were dissected either unfed or 1 week after feeding. In all uninfected bugs extracellular membrane layers (e.m.l.) covered the apical microvillar border of the epithelial cells. Some midgut regions of bugs infected with B. triatomae appeared normal but often adjacent cells showed pathological effects. In affected cells the e.m.l. and the microvilli and finally the cells themselves were reduced or destroyed. Correlated with these observations of pathogenicity the method of attachment of parasites changed. When the e.m.l. were present only rarely were flagella found, but on extracellular membrane-free cells B. triatomae attached by flagellar enlargement to the microvillar border or, if this was reduced, to the apical host cell membrane. No hemidesmosome-like plaques were found at the attachment site. Although some flagella were inserted into the apical region of the cells no intracellular flagellates were observed.

Zymogram and life-history studies on trypanosomes of the subgenus Megatrypanum

Of 13 Swedish dairy cows examined, 12 (92.3%) were found to be infected with trypanosomes by cultivation of blood samples. Of the two species of tabanid fly caught close to the cattle, 33.3% of the Tabanus bromius and 8.6% of the Haematopota pluvialis were also found to be infected with trypanosomes on dissection. Isoenzyme patterns of trypanosome isolates from one H. pluvialis and from six cattle were identical, incriminating this fly species as a vector of the trypanosome. Comparison of these isolates with other Megatrypanum isolates indicated that the Swedish parasites were a form of Trypanosoma theileri and that T. theileri and the badger parasite T. pestanai are closely related. An isolate of a Megatrypanum from a buffalo (Syncerus caffer) in Kenya was entirely different from T. theileri.

Isolation of leishmanial parasites from a wild caught Anopheles gambiae mosquito in Kenya

A total of 232 mosquitoes were collected and dissected for leishmanial parasites in the Baringo District, Kenya. Anopheles gambiae sensu lato comprised 90.9% of the sample. One female A. gambiae was found to be infected with leishmanial promastigotes. The parasites when injected into Balb C mice caused skin lesions characterized by heavy amastigote infections. The average size of the parasite was: body length, 11.7 +/- 0.19 microns; width, 1.3 +/- 0.04 microns; flagellum length, 15.5 +/- 0.28 microns.

Host-parasite relationship of Trypanosoma corvi in Ornithomyia avicularia

The first description of an electron microscopic study of Trypanosoma corvi in the vector Ornithomyia avicularia is reported. There is a close association between vector and parasite in the midgut, ileum and rectum of the vector. The midgut distribution of parasites is determined by the peritrophic membrane, which confines the early infection to the endoperitrophic space. Parasites escape from the ruptured region of the peritrophic membrane at the pylorus to gain access to the ectoperitrophic space, where intense multiplication occurs. The resulting, smaller epimastigotes attach to the cuticle in the pylorus, ileum and rectum, where they continue multiplying to give rise to mature, short, stumpy trypomastigotes (metacyclics) that are not attached. Attachment to these cuticularly lined regions occurs by the formation of dense, hemidesmosome-like plaques at the extremities of the expanded flagella. A fibrous matrix surrounds the parasites in the ileum. For the first time, intracellular midgut forms are reported for T. corvi in O. avicularia. These parasites enter the cells between the microvilli and penetrate deeply between the folds of the midgut. In the midgut of O. avicularia, the cells of a mycetome region are packed with Rickettsia-like organisms. The significance of these intracellular parasites in the relationship of T. corvi in O. avicularia remains unknown.

Recent studies of the biology of Trypanosoma vivax

Recent biological investigations of the African trypanosomes have been moving away from their previous preoccupation with the phenomenon of antigenic variation. The feeling has arisen that antigenic variation, as demonstrated by the Trypanozoon and Nannomonas subgenera of trypanosomes, is too extensive, the number of serodemes too large and the coexistence of different species in many areas too complicated, to allow any immunoprophylaxis based on antibodies to variable antigens. This is, of course, not to rule out possible biochemical intervention in the biosynthesis or export of VSG molecules by trypanosomes. However, in the case of T. vivax, more information is required concerning antigenic variation and coat structure in this organism before these avenues of investigation are discarded. Ways of improving the yield of mature metacyclic trypanosomes in vitro must be found, so that the contribution of metacyclic variable antigens to the induction of immunity in T. vivax infection can be elucidated. The number of bloodstream VATs must be determined (perhaps by genetic rather than serological means), as there is evidence both for VAT exhaustion contributing to the self-cure of infected hosts, and for a possible limit to the number of VATs which can be expressed in infections in Africa. In South America nothing is known of the number of serodemes of T. vivax which exist, although such knowledge is obviously required, especially if immunity to bloodstream variants is the more important mechanism of inducing immunity to this trypanosome and true cyclical transmission is rare in, or absent from, that subcontinent. Further, in a fragile organism, with a coat of suspect integrity, the method of VSG packing and the relative exposure of underlying surface molecules seems to hold out even more hope for an immunological intervention based on cell surface but invariant molecules than is the case with T. brucei or T. congolense, although this is being attempted with the latter species. In T. brucei infections the appearance of the non-dividing stumpy population acts as a stimulus to the induction of humoral immune responses. In ruminants, antibody responses to T. vivax, at least as judged from lysis tests, lag behind the appearance of the different VATs by some days. It would be important to determine, therefore, whether, if late bloodstream forms could be induced more frequently in the ruminant, the speed of anti-VAT responses could be enhanced. Whilst self-cure appears to be relatively common in T. vivax infections, it is unlikely that it results in sterile immunity.(ABSTRACT TRUNCATED AT 400 WORDS)

Chitin derivatives as novel substrates for Trypanosoma brucei brucei attachment in vitro

Procyclic trypomastigotes of Trypanosoma brucei brucei, cultured in Cunningham's medium with 20% heat-inactivated foetal calf serum at 27 degrees C, attached to chitosan and to gels of N-acetyl chitosan and glycol chitosan. Following attachment, epimastigotes, metacyclic-like trypomastigotes and multinucleate parasites appeared in the culture supernatant.

Trypanosoma (Megatrypanum) incertum from Pipistrellus pipistrellus: development and transmission by cimicid bugs

Trypanosoma (Megatrypanum) incertum Pittaluga 1905 was found in 33 out of 206 Pipistrellus pipistrellus caught at various sites in Britain. The trypanosome is described from blood smears. Development took place in laboratory-reared Cimex pipistrelli and Cimex lectularius. Epimastigote forms initially multiplied rapidly in the ventriculus and midgut of Cimex. Metacyclic trypanosomes were found in the rectum of both species of Cimex after 8 days when bugs were maintained at 20 degrees C and as early as 3 days at 30 degrees C. Electron microscopy of infected bugs revealed that there was no attachment to epithelial cells of the ventriculus or midgut, but within the rectum epimastigotes were attached by their flagella to the cuticle of the rectum by hemidesmosomes. Transmission was achieved by feeding experimentally infected bugs to bats kept in the laboratory. These bats were negative as judged by xenodiagnosis using laboratory-reared Cimex. Bats which had been caught in the wild demonstrated low-grade or sub-patent parasitaemias (positive in xenodiagnosis) for up to 400 days after the day of capture. Despite an extensive search of impression smears of tissues immediately after trypanosomes first appeared in the blood of experimentally infected bats no multiplicative stages were found.