Blood meal sources and bacterial microbiome diversity in wild-caught tsetse flies

Machine Learning Predicts Non-Preferred and Preferred Vertebrate Hosts of Tsetse Flies (Glossina spp.) Based on Skin Volatile Emission Profiles

Tsetse fly vectors of African trypanosomosis preferentially feed on certain vertebrates largely determined by olfactory cues they emit. Previously, we established that three skin-derived ketones including 6-methyl-5-hepten-2-one, acetophenone and geranyl acetone accounted for avoidance of zebra by tsetse flies. Here, we tested the hypothesis that these three ketones serve as biomarkers for tsetse flies to distinguish between non-preferred- and preferred-vertebrate hosts. We used coupled gas chromatography/mass spectrometry to analyze and compare the skin volatile emissions of two non-preferred- (waterbuck and zebra) and four preferred- (buffalo, donkey, horse, warthog) vertebrate hosts in two wildlife parks in Kenya. We detected a total of 96 volatile organic compounds (VOCs) in the skin emissions composed mainly of aldehydes, ketones, alcohols, phenols and alkanes, which varied with the vertebrate host. Using random forest analysis, we found a weak correlation between the three skin-odor repellent ketones and non-preferred and preferred vertebrate hosts. However, we found that the three repellent ketones plus skin background odors may be more sensitive chemical signals for tsetse flies to discriminate vertebrate hosts. These results contribute to understanding tsetse fly vertebrate host preferences in their natural habitat across geographic scales.

Investigating the influence of blood meal sources on the composition of culturable haemolytic gut bacteria of a wild-caught BTV vector Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae)

Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae) transmits many pathogens, including seven viruses, four protozoa and one nematode. This species has a wide distribution range across northern Afro-tropical, Palearctic, Australian, Indo-Malayan realms with a broad host spectrum, including cattle, buffaloes, sheep, pigs, dogs, horses and even humans. The heterogeneous nature of Culicoides' blood-feeding patterns is well documented, but the influence of various host blood meal sources on gut bacterial composition remains scant. Adult midges were collected during April (2023) by operating UV light traps in cattle, buffalo sheds and poultry farm in Purulia (India). Besides C. oxystoma, eleven Culicoides species were collected across the sheds and farm, seven of which are vectors. Culicoides liui Wirth and Hubert and C. thurmanae Wirth and Hubert are reported from India for the first time. In all the sheds, engorged females of C. oxystoma were ubiquitous. Identification of culturable gut bacteria and the host blood meal of C. oxystoma were done through the polymerase chain reaction (PCR)-based method. Blood meal analysis confirmed the following hosts: cattle, buffaloes and humans. Identification of blood meal of engorged C. oxystoma caught from poultry farm showed positive results for humans but not for birds. Among bacteria, Bacillus cereus was abundant in all of the engorged females. Bacillus paramycoides and Enterococcus faecium were identified from females feeding on cattle and buffaloes' blood, while Alcaligenes faecalis was found in the gut contents of females that fed on cattle and human blood. The gut bacteria Alcaligenes faecalis exhibited alpha haemolytic activity. In contrast, Bacillus sp., B. cereus, B. flexus, B. licheniformis, B. thuringiensis, B. paramycoides, E. faecium, Paenibacillus sp. and Pseudomonas sp. exhibited beta haemolysis. This is the first report on the composition of gut bacteria, with particular emphasis on the haemolytic bacteria of C. oxystoma with different host blood meals. The pathogenic bacteria B. cereus, B. licheniformis and A. faecalis within the females could potentially impact pathogen acquisition and increase the probability of their zoonotic transmissibility.

An Overview of Tsetse Fly Repellents: Identification and Applications

Tsetse flies are vectors of the parasite trypanosoma that cause the neglected tropical diseases human and animal African trypanosomosis. Semiochemicals play important roles in the biology and ecology of tsetse flies. Previous reviews have focused on olfactory-based attractants of tsetse flies. Here, we present an overview of the identification of repellents and their development into control tools for tsetse flies. Both natural and synthetic repellents have been successfully tested in laboratory and field assays against specific tsetse fly species. Thus, these repellents presented as innovative mobile tools offer opportunities for their use in integrated disease management strategies.

Species richness and abundance of wild tsetse flies collected from selected human-wildlife-livestock interface in Tanzania

The successful control of tsetse flies largely depends on understanding of the species available and abundance. This study assessed the species richness, abundance and apparent density of wild collected tsetse flies from selected human-wildlife-livestock interface in Tanzania. Seasonal trapping using baited NZI, Pyramidal and Biconical traps was done across selected wards. Traps were set at 200 m apart, emptied after every 24 h then rotated to the next sites after 72 h. Collected flies were identified morphologically and letter confirmed using the Polymerase Chain Reaction (PCR). Only two Glossina species; Glossina pallidipes (n = 371; 47.32 %) and Glossina morsitans morsitans (n = 413; 52.68 %) were identified. Among them, 96 flies (80 Female, 16 Male) were blood fed; 57(48 Female and 9 Male) G. pallidipes and 39(32 Female and 7 Male) G.m. morsitans. Tsetse fly abundance varied across wards (χ2 = 4.597, df = 1, p = 0.032), villages (χ2 = 9.491, df = 3, p = 0.023), habitats (χ2 = 17.239, df = 2, p < 0.001), months (χ2 = 13.507, df = 3, p = 0.004) and deployed traps (χ2 = 6.348, df = 2, p = 0.04). About 78.82 % of the total catch occurred in Kisaki ward (n = 618; p < 0.001) and 21.17 % (n = 166; p = 0.032) in Bwakila chini. Similarly, 62.37 % of the catch occurred in Mbojoge village. NZI traps (n = 422; 54 %; 4.98 FTD) were most successful traps. Moreover, 78.06 % of the catch occurred in bushed grassland habitat (n = 612; 55.41 FTD) while 5.48 % in farmland (n = 43; 7.17 FTD). This study recommends NZI and Pyramidal traps for tsetse flies control at the interface and proposes wet season as appropriate time for successful trapping of the flies. Finally, it attracts a need for assessing tsetse flies' blood meal sources and the infection status to establish the prevalence to inform existing trypanosome control programs.

Domestic dogs as reservoirs for African trypanosomiasis in Mambwe district, eastern Zambia

The control of African trypanosomiasis (AT) in Eastern and Southern Africa, including Zambia, faces huge challenges due to the involvement of wild and domestic animal reservoirs. Free-roaming dogs in wildlife-populated and tsetse-infested villages of Zambia's Mambwe district are exposed to infectious tsetse bites. Consuming fresh raw game meat and bones further exacerbates their risk of contracting AT. We focus on the reservoir role of such dogs in maintaining and transmitting diverse species of trypanosomes that are infective to humans and livestock in Zambia's Mambwe district. A cohort of 162 dogs was enrolled for follow-up at 3 different time points from June to December 2018 in selected villages of Malama, Mnkhanya, and Nsefu chiefdoms of Mambwe district, eastern Zambia. Blood and serum were screened for AT by microscopy, GM6 ELISA, PCR (ITS1 and SRA), and Sanger sequencing. Out of the 162 dogs in the cohort, 40 were lost to follow-up and only 122 remained traceable at the end of the study. GM6 ELISA detected Trypanosoma antibodies in 121 dogs (74.7%) and ITS1-PCR detected DNA involving single and mixed infections of T. congolense, T. brucei, and suspected T. simiae or T. godfreyi in 115 dogs (70.9%). The human-infective T. b. rhodesiense was detected by SRA PCR in 67 dogs (41.4%), and some sequence data that support the findings of this study have been deposited in the GenBank under accession numbers OL961811, OL961812, and OL961813. Our study demonstrates that the Trypanosoma reservoir community in Zambia is wider than was thought and includes domesticated dogs. As dogs are active carriers of human and livestock-infective trypanosomes, they pose a risk of transmitting AT in endemic villages of Mambwe district as they are neglected and left untreated. To fully bring AT under control, countries such as Zambia where the role of animal reservoirs is important, should not limit their prevention and treatment efforts to livestock (especially cattle) but also include dogs that play an integral part in most rural communities.

A scoping review on tsetse fly blood meal sources and its assay methods since 1956 to 2022

BACKGROUND

Tsetse flies (Glossina spp.) are the definitive biological vectors of African trypanosomes in humans and animals. Controlling this vector is the most promising method of preventing trypanosome transmission. This requires a comprehensive understanding of tsetse biology and host preference to inform targeted design and management strategies, such as the use of olfaction and visual cues in tsetse traps. No current review exists on host preference and blood meal analyses of tsetse flies.

METHODS

This review presents a meta-analysis of tsetse fly blood meal sources and the methodologies used to identify animal hosts from 1956 to August 2022. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRIMA-ScR) was applied. This focused on tsetse-endemic countries, blood meal analysis methodologies and the blood meal hosts identified. The articles were retrieved and screened from databases using predetermined eligibility criteria.

RESULTS

Only 49/393 of the articles retrieved matched the inclusion criteria. Glossina's main hosts in the wild included the bushbuck, buffalo, elephant, warthog, bushpig and hippopotamus. Pigs, livestock and humans were key hosts at the domestic interface. The least studied species included Glossina fuscipleuris, G. fusca, G. medicorum, G. tabaniformis and G. austeni. In the absence of preferred hosts, Glossina fed opportunistically on a variety of hosts. Precipitin, haemagglutination, disc diffusion, complement fixation, ELISA and PCR-based assays were used to evaluate blood meals. Cytochrome b (Cyt b) was the main target gene in PCR to identify the vertebrate hosts.

CONCLUSIONS

Tsetse blood meal sources have likely expanded because of ecological changes that could have rendered preferred hosts unavailable. The major approaches for analysing tsetse fly blood meal hosts targeted Cyt b gene for species identification by Sanger sequencing. However, small-fragment DNAs, such as the mammalian 12S and 16S rRNA genes, along with second- and third-generation sequencing techniques, could increase sensitivity for host identification in multiple host feeders that Sanger sequencing may misidentify as "noise". This review of tsetse fly blood meal sources and approaches to host identification could inform strategies for tsetse control.

Microbiomes of Blood-Feeding Triatomines in the Context of Their Predatory Relatives and the Environment

The importance of gut microbiomes has become generally recognized in vector biology. This study addresses microbiome signatures in North American Triatoma species of public health significance (vectors of Trypanosoma cruzi) linked to their blood-feeding strategy and the natural habitat. To place the Triatoma-associated microbiomes within a complex evolutionary and ecological context, we sampled sympatric Triatoma populations, related predatory reduviids, unrelated ticks, and environmental material from vertebrate nests where these arthropods reside. Along with five Triatoma species, we have characterized microbiomes of five reduviids (Stenolemoides arizonensis, Ploiaria hirticornis, Zelus longipes, and two Reduvius species), a single soft tick species, Ornithodoros turicata, and environmental microbiomes from selected sites in Arizona, Texas, Florida, and Georgia. The microbiomes of predatory reduviids lack a shared core microbiota. As in triatomines, microbiome dissimilarities among species correlate with dominance of a single bacterial taxon. These include Rickettsia, Lactobacillus, "Candidatus Midichloria," and Zymobacter, which are often accompanied by known symbiotic genera, i.e., Wolbachia, "Candidatus Lariskella," Asaia, Gilliamella, and Burkholderia. We have further identified a compositional convergence of the analyzed microbiomes in regard to the host phylogenetic distance in both blood-feeding and predatory reduviids. While the microbiomes of the two reduviid species from the Emesinae family reflect their close relationship, the microbiomes of all Triatoma species repeatedly form a distinct monophyletic cluster highlighting their phylosymbiosis. Furthermore, based on environmental microbiome profiles and blood meal analysis, we propose three epidemiologically relevant and mutually interrelated bacterial sources for Triatoma microbiomes, i.e., host abiotic environment, host skin microbiome, and pathogens circulating in host blood. IMPORTANCE This study places microbiomes of blood-feeding North American Triatoma vectors (Reduviidae) into a broader evolutionary and ecological context provided by related predatory assassin bugs (Reduviidae), another unrelated vector species (soft tick Ornithodoros turicata), and the environment these arthropods coinhabit. For both vectors, microbiome analyses suggest three interrelated sources of bacteria, i.e., the microbiome of vertebrate nests as their natural habitat, the vertebrate skin microbiome, and the pathobiome circulating in vertebrate blood. Despite an apparent influx of environment-associated bacteria into the arthropod microbiomes, Triatoma microbiomes retain their specificity, forming a distinct cluster that significantly differs from both predatory relatives and ecologically comparable ticks. Similarly, within the related predatory Reduviidae, we found the host phylogenetic distance to underlie microbiome similarities.

Host Associations of Culicoides Biting Midges in Northeastern Kansas, USA

Culicoides biting midges (Diptera: Ceratopogonidae) are hematophagous flies that transmit several viruses of veterinary concern to livestock. Understanding blood feeding behaviors is integral towards identification of putative vector species and preventing the transmission of these pathogens. PCR-based blood meal analysis was conducted on 440 blood-engorged Culicoides midges collected in northeastern Kansas, with 316 (71.8%) returning non-human vertebrate identifications at the ≥95% identity match level. Broadly, Culicoides sonorensis, Culicoides stellifer, and Culicoides variipennis were found to feed heavily on mammalian hosts, while Culicoides crepuscularis and Culicoides haematopotus fed on avian hosts. The blood meals in all specimens were graded prior to DNA extraction to determine whether blood meal size or digestion status significantly impacted the likelihood of a quality host match. Size had a significant impact on the likelihood of a quality match at grades 3-5, whereas digestion only significantly impacted outcomes at the most extreme grade. These vector-host dynamics have not previously been studied in Culicoides collected in Kansas, which represents a unique tallgrass prairie biome within the United States that is heavily interspersed with livestock operations. Based on these data, the highly abundant species C. crepuscularis and C. haematopotus are unlikely to be major vectors of mammalian viruses.

Using haematophagous fly blood meals to study the diversity of blood-borne pathogens infecting wild mammals

Many emerging infectious diseases originate from wild animals, so there is a profound need for surveillance and monitoring of their pathogens. However, the practical difficulty of sample acquisition from wild animals tends to limit the feasibility and effectiveness of such surveys. Xenosurveillance, using blood-feeding invertebrates to obtain tissue samples from wild animals and then detect their pathogens, is a promising method to do so. Here, we describe the use of tsetse fly blood meals to determine (directly through molecular diagnostic and indirectly through serology), the diversity of circulating blood-borne pathogens (including bacteria, viruses and protozoa) in a natural mammalian community of Tanzania. Molecular analyses of captured tsetse flies (182 pools of flies totalizing 1728 flies) revealed that the blood meals obtained came from 18 different vertebrate species including 16 non-human mammals, representing approximately 25% of the large mammal species present in the study area. Molecular diagnostic demonstrated the presence of different protozoa parasites and bacteria of medical and/or veterinary interest. None of the six virus species searched for by molecular methods were detected but an ELISA test detected antibodies against African swine fever virus among warthogs, indicating that the virus had been circulating in the area. Sampling of blood-feeding insects represents an efficient and practical approach to tracking a diversity of pathogens from multiple mammalian species, directly through molecular diagnostic or indirectly through serology, which could readily expand and enhance our understanding of the ecology and evolution of infectious agents and their interactions with their hosts in wild animal communities.

Beyond canonical models: why a broader understanding of Diptera-microbiota interactions is essential for vector-borne disease control

Vector-borne diseases constitute a major global public health threat. The most significant arthropod disease vectors are predominantly comprised of members of the insect order Diptera (true flies), which have long been the focus of research into host-pathogen dynamics. Recent studies have revealed the underappreciated diversity and function of dipteran-associated gut microbial communities, with important implications for dipteran physiology, ecology, and pathogen transmission. However, the effective parameterization of these aspects into epidemiological models will require a comprehensive study of microbe-dipteran interactions across vectors and related species. Here, we synthesize recent research into microbial communities associated with major families of dipteran vectors and highlight the importance of development and expansion of experimentally tractable models across Diptera towards understanding the functional roles of the gut microbiota in modulating disease transmission. We then posit why further study of these and other dipteran insects is not only essential to a comprehensive understanding of how to integrate vector-microbiota interactions into existing epidemiological frameworks, but our understanding of the ecology and evolution of animal-microbe symbiosis more broadly.

Facultative cleaning of spiral-horned antelope by the African paradise flycatcher (Terpsiphone viridis)

In cleaning associations, individuals known as "cleaners" remove and feed on parasites and pests found on, or around, other animals known as "clients." While best documented in marine environments and as mutualisms, cleaning associations are widespread in terrestrial systems and range along a spectrum of obligate to facultative associations. In African savannas, cleaning associations primarily comprise facultative interactions between mammals and birds that remove attached parasites. Few reports, however, exist on cleaning associations that involve the removal of unattached pests. In this short note, I report a novel facultative bird-ungulate cleaning association involving the removal of unattached pests, between the African paradise flycatcher (Terpsiphone viridis) and two species of spiral-horned antelope (Tragelaphus spp.): greater kudu (Tragelaphus strepsiceros) and Cape bushbuck (Tragelaphus sylvaticus). On multiple occasions, I observed African paradise flycatchers hawking flying insects around greater kudu and a Cape bushbuck during the dry season at the Mpala Research Centre in Laikipia, Kenya. These observations document a rare feeding strategy for the African paradise flycatcher and are among the few records on cleaning interactions involving the removal of unattached pests.

Parasites and blood-meal hosts of the tsetse fly in Tanzania: a metagenomics study

Background

Tsetse flies can transmit various Trypanosoma spp. that cause trypanosomiasis in humans, wild animals, and domestic animals. Amplicon deep sequencing of the 12S ribosomal RNA (rRNA) gene can be used to detect mammalian tsetse hosts, and the 18S rRNA gene can be used to detect all associated eukaryotic pathogens, including Trypanosoma spp.

Methods

Tsetse flies were collected from the Serengeti National Park (n = 48), Maswa Game Reserve (n = 42), and Tarangire National Park (n = 49) in Tanzania in 2012–13. Amplicon deep sequencing targeting mammal-specific 12S rRNA and 18S rRNA genes was performed to screen the blood-feeding sources of tsetse flies and eukaryotic parasites in tsetse flies, respectively.

Results

12S rRNA gene deep sequencing revealed that various mammals were blood-feeding sources of the tsetse flies, including humans, common warthogs, African buffalos, mice, giraffes, African elephants, waterbucks, and lions. Genes of humans were less frequently detected in Serengeti (P = 0.0024), whereas African buffaloes were detected more frequently as a blood-feeding source (P = 0.0010). 18S rRNA gene deep sequencing showed that six tsetse samples harbored the Trypanosoma gene, which was identified as Trypanosoma godfreyi and Trypanosoma simiae in subsequent ITS1 gene sequencing.

Conclusions

Through amplicon deep sequencing targeting the 12S rRNA and 18S rRNA genes, various mammalian animals were identified as blood-meal sources, and two Trypanosoma species were detected in tsetse flies collected from the Maswa Game Reserve, Serengeti National Park, and Tarangire National Park in Tanzania. This study illustrates the patterns of parasitism of tsetse fly, wild animals targeted by the fly, and Trypanosoma spp. carried by the fly in Tanzania. It may provide essential data for formulating better strategies to control African trypanosomes.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05344-1.

DNA metabarcoding across disciplines: sequencing our way to greater understanding across scales of biological organization

DNA metabarcoding describes the use of targeted DNA (i.e., amplicon) sequencing to identify community constituents from a complex sample containing genetic material from multiple organisms, such as water, soil, gut contents, microbiomes, or biofilms. This molecular approach for characterizing mixed DNA samples relies on the development of "universal primers" that allow for effective amplification of target sequences across a broad range of taxa. Armed with optimized lab protocols and rigorous bioinformatics tools, DNA metabarcoding can produce a wealth of information about the hidden biodiversity of various sample types by probing for organisms' molecular footprints. DNA metabarcoding has received considerable popular press over the last few years because of gut microbiome studies in humans and beyond. However, there are many other applications that are continually integrating molecular biology with other fields of study to address questions that have previously been unanswerable, for both prokaryotic and eukaryotic targets. For example, we can now sample mostly-digested gut contents from virtually any organism to learn about ontogeny and foraging ecology. Water samples collected from different locations can be filtered to extract eDNA (i.e., environmental DNA), revealing the biodiversity of fishes and other taxa targeted by carefully selected primer sets. This universal primer metabarcoding approach has even been extended to looking at diverse gene families within single species, which is particularly useful for complex immune system genetics. The purpose of this SICB symposium was to bring together researchers using DNA metabarcoding approaches to (a) showcase the diversity of applications of this technique for addressing questions spanning ecology, evolution, and physiology, and (b) to spark connections among investigators from different fields that are utilizing similar approaches to facilitate optimization and standardization of metabarcoding methods and analyses. The resulting manuscripts from this symposium represent a great diversity of metabarcoding applications and taxonomic groups of interest.

USING SURFACE WASHING TO REMOVE THE ENVIRONMENTAL COMPONENT FROM FLEA MICROBIOME ANALYSIS

Microbial metabarcoding is a common method to study the biology of blood-feeding arthropods and identify patterns of potential pathogen transmission. Before DNA extraction, specimens are often surface washed to remove environmental contaminants. While surface washing is common, its effects on microbial diversity remain unclear. We characterized the microbiome of the flea species Ceratophyllus idius, an avian ectoparasite, and a potential vector of pathogens, using high-throughput 16S rRNA sequencing. Half of the nests from which fleas were collected were subjected to an environmental manipulation in which nesting materials were periodically replaced. In a crossed study design we surface washed half of the flea samples from each environmental condition to produce 4 experimental conditions. Environmental manipulations resulted in significant differences in the diversity and structure of the flea microbiome, but these differences were unapparent when specimens were surface washed. Furthermore, differential abundance testing of the experimental groups revealed that surface washing predominantly affected the abundance of bacterial groups that are characterized as environmental contaminants. These findings suggest that environmental changes primarily affect the surface microbiome of arthropods and that surface washing is a useful tool to reduce the footprint of the external microbiome on analysis.

Overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors

This article presents an overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors. It first briefly summarises some of the disease-causing pathogens vectored by insects and emphasises the need for innovative control methods to counter the threat of resistance by both the vector insect to pesticides and the pathogens to therapeutic drugs. Subsequently, the state of art of paratransgenesis is described, which is a particularly ingenious method currently under development in many important vector insects that could provide an additional powerful tool for use in integrated pest control programmes. The requirements and recent advances of the paratransgenesis technique are detailed and an overview is given of the microorganisms selected for genetic modification, the effector molecules to be expressed and the environmental spread of the transgenic bacteria into wild insect populations. The results of experimental models of paratransgenesis developed with triatomines, mosquitoes, sandflies and tsetse flies are analysed. Finally, the regulatory and safety rules to be satisfied for the successful environmental release of the genetically engineered organisms produced in paratransgenesis are considered.

Tsetse Bloodmeal Analyses Incriminate the Common Warthog Phacochoerus africanus as an Important Cryptic Host of Animal Trypanosomes in Smallholder Cattle Farming Communities in Shimba Hills, Kenya

Trypanosomes are endemic and retard cattle health in Shimba Hills, Kenya. Wildlife in the area act as reservoirs of the parasites. However, wild animal species that harbor and expose cattle to tsetse-borne trypanosomes are not well known in Shimba Hills. Using xeno-monitoring surveillance to investigate wild animal reservoirs and sources of trypanosomes in Shimba Hills, we screened 696 trypanosome-infected and uninfected tsetse flies for vertebrate DNA using multiple-gene PCR-High Resolution Melting analysis and amplicon sequencing. Results revealed that tsetse flies fed on 13 mammalian species, preferentially Phacochoerus africanus (warthogs) (17.39%, 95% CI: 14.56–20.21) and Bos taurus (cattle) (11.35%, 95% CI: 8.99–13.71). Some tsetse flies showed positive cases of bloodmeals from multiple hosts (3.45%, 95% CI: 2.09–4.81), including warthog and cattle (0.57%, 95% CI: 0.01–1.14). Importantly, tsetse flies that took bloodmeals from warthog had significant risk of infections with Trypanosoma vivax (5.79%, 95% CI: 1.57–10.00), T. congolense (7.44%, 95% CI: 2.70–12.18), and T. brucei sl (2.48%, 95% CI: −0.33–5.29). These findings implicate warthogs as important reservoirs of tsetse-borne trypanosomes affecting cattle in Shimba Hills and provide valuable epidemiological insights to underpin the parasites targeted management in Nagana vector control programs in the area.

Blood meal analysis of tsetse flies ( Glossina pallidipes: Glossinidae) reveals higher host fidelity on wild compared with domestic hosts

Background: Changes in climate and land use can alter risk of transmission of parasites between domestic hosts and wildlife, particularly when mediated by vectors that can travel between populations. Here we focused on tsetse flies (genus Glossina), the cyclical vectors for both Human African Trypanosomiasis (HAT) and Animal African Trypanosomiasis (AAT). The aims of this study were to investigate three issues related to G. palldipes from Kenya: 1) the diversity of vertebrate hosts that flies fed on; 2) whether host feeding patterns varied in relation to type of hosts, tsetse feeding behaviour, site or tsetse age and sex; and 3) if there was a relationship between trypanosome detection and host feeding behaviours or host types. Methods: Sources of blood meals of Glossina pallidipes were identified by sequencing of the mitochondrial cytochrome b gene and analyzed in relationship with previously determined trypanosome detection in the same flies. Results: In an area dominated by wildlife but with seasonal presence of livestock (Nguruman), 98% of tsetse fed on single wild host species, whereas in an area including a mixture of resident domesticated animals, humans and wildlife (Shimba Hills), 52% of flies fed on more than one host species. Multiple Correspondence Analysis revealed strong correlations between feeding pattern, host type and site but these were resolved along a different dimension than trypanosome status, sex and age of the flies. Conclusions: Our results suggest that individual G. pallidipes in interface areas may show higher feeding success on wild hosts when available but often feed on both wild and domesticated hosts. This illustrates the importance of G. pallidipes as a vector connecting the sylvatic and domestic cycles of African trypanosomes.

How monoxenous trypanosomatids revealed hidden feeding habits of their tsetse fly hosts

Tsetse flies are well-known vectors of trypanosomes pathogenic for humans and livestock. For these strictly blood-feeding viviparous flies, the host blood should be the only source of nutrients and liquids, as well as any exogenous microorganisms colonising their intestine. Here we describe the unexpected finding of several monoxenous trypanosomatids in their gut. In a total of 564 individually examined Glossina (Austenia) tabaniformis (Westwood) (436 specimens) and Glossina (Nemorhina) fuscipes fuscipes (Newstead) (128 specimens) captured in the Dzanga-Sangha Protected Areas, Central African Republic, 24 (4.3%) individuals were infected with monoxenous trypanosomatids belonging to the genera Crithidia Léger, 1902; Kentomonas Votýpka, Yurchenko, Kostygov et Lukeš, 2014; Novymonas Kostygov et Yurchenko, 2020; Obscuromonas Votýpka et Lukeš, 2021; and Wallacemonas Kostygov et Yurchenko, 2014. Moreover, additional 20 (3.5%) inspected tsetse flies harboured free-living bodonids affiliated with the genera Dimastigella Sandon, 1928; Neobodo Vickerman, 2004; Parabodo Skuja, 1939; and Rhynchomonas Klebs, 1892. In the context of the recently described feeding behaviour of these dipterans, we propose that they become infected while taking sugar meals and water, providing indirect evidence that blood is not their only source of food and liquids.

A novel vehicle-mounted sticky trap; an effective sampling tool for savannah tsetse flies Glossina morsitans morsitans Westwood and Glossina morsitans centralis Machado

BACKGROUND

Black screen fly round (BFR) is a mobile sampling method for Glossina morsitans. This technique relies on the ability of operator(s) to capture flies landing on the screen with hand nets. In this study, we aimed to evaluate a vehicle-mounted sticky panel trap (VST) that is independent of the operator's ability to capture flies against BFR, for effective and rapid sampling of G. m. morsitans Westwood and G. m. centralis Machado. We also determined the influence of the VST colour (all-blue, all-black or 1:1 blue-black), orientation and presence of odour attractants on tsetse catch.

METHODOLOGY/PRINCIPAL FINDINGS

Using randomised block design experiments conducted in Zambia, we compared and modelled the number of tsetse flies caught in the treatment arms using negative binomial regression. There were no significant differences in the catch indices of the three colour designs and for in-line or transversely oriented panels for both subspecies (P > 0.05). When baited with butanone and 1-octen-3-ol, VST caught 1.38 (1.11-1.72; P < 0.01) times more G. m. centralis flies than the un-baited trap. Attractants did not significantly increase the VST catch index for G. m. morsitans (P > 0.05). Overall, the VST caught 2.42 (1.91-3.10; P < 0.001) and 2.60 (1.50-3.21; P < 0.001) times more G. m. centralis and G. m. morsitans respectively, than the BFR. The VST and BFR took 10 and 35 min respectively to cover a 1 km transect.

CONCLUSION/SIGNIFICANCE

The VST is several times more effective for sampling G. m. morsitans and G. m. centralis than the BFR and we recommend its use as an alternative sampling tool.

Host Bloodmeal Identification in Cave-Dwelling Ornithodoros turicata Dugès (Ixodida: Argasidae), Texas, USA

Tick-host bloodmeal associations are important factors when characterizing risks of associated pathogen transmission and applying appropriate management strategies. Despite their biological importance, comparatively little is known about soft tick (Argasidae) host associations in the United States compared to hard ticks (Ixodidae). In this study, we evaluated a PCR and direct Sanger sequencing method for identifying the bloodmeal hosts of soft ticks. We collected 381 cave-associated Ornithodoros turicata near San Antonio, Texas, USA, and also utilized eight colony-reared specimens fed artificially on known host blood sources over 1.5 years ago. We correctly identified the vertebrate host bloodmeals of two colony-reared ticks (chicken and pig) up to 1,105 days post-feeding, and identified bloodmeal hosts from 19 out of 168 field-collected soft ticks, including raccoon (78.9%), black vulture (10.5%), Texas black rattlesnake (5.3%), and human (5.3%). Our results confirm the retention of vertebrate blood DNA in soft ticks and advance the knowledge of argasid host associations in cave-dwelling O. turicata.

Tsetse blood-meal sources, endosymbionts and trypanosome-associations in the Maasai Mara National Reserve, a wildlife-human-livestock interface

African trypanosomiasis (AT) is a neglected disease of both humans and animals caused by Trypanosoma parasites, which are transmitted by obligate hematophagous tsetse flies (Glossina spp.). Knowledge on tsetse fly vertebrate hosts and the influence of tsetse endosymbionts on trypanosome presence, especially in wildlife-human-livestock interfaces, is limited. We identified tsetse species, their blood-meal sources, and correlations between endosymbionts and trypanosome presence in tsetse flies from the trypanosome-endemic Maasai Mara National Reserve (MMNR) in Kenya. Among 1167 tsetse flies (1136 Glossina pallidipes, 31 Glossina swynnertoni) collected from 10 sampling sites, 28 (2.4%) were positive by PCR for trypanosome DNA, most (17/28) being of Trypanosoma vivax species. Blood-meal analyses based on high-resolution melting analysis of vertebrate cytochrome c oxidase 1 and cytochrome b gene PCR products (n = 354) identified humans as the most common vertebrate host (37%), followed by hippopotamus (29.1%), African buffalo (26.3%), elephant (3.39%), and giraffe (0.84%). Flies positive for trypanosome DNA had fed on hippopotamus and buffalo. Tsetse flies were more likely to be positive for trypanosomes if they had the Sodalis glossinidius endosymbiont (P = 0.0002). These findings point to complex interactions of tsetse flies with trypanosomes, endosymbionts, and diverse vertebrate hosts in wildlife ecosystems such as in the MMNR, which should be considered in control programs. These interactions may contribute to the maintenance of tsetse populations and/or persistent circulation of African trypanosomes. Although the African buffalo is a key reservoir of AT, the higher proportion of hippopotamus blood-meals in flies with trypanosome DNA indicates that other wildlife species may be important in AT transmission. No trypanosomes associated with human disease were identified, but the high proportion of human blood-meals identified are indicative of human African trypanosomiasis risk. Our results add to existing data suggesting that Sodalis endosymbionts are associated with increased trypanosome presence in tsetse flies.