BackgroundAfrican animal trypanosomosis is becoming prevalent beyond its traditionally defined geographical boundaries and is a threat to animals beyond the tsetse belts in and outside Africa. However, knowledge of infections with clinically important trypanosome species and their diversity among field-collected hematophagous biting flies and domestic animals is limited mainly to tsetse and their mammalian hosts in tsetse-infested areas. This study aimed to examine the presence of trypanosomes in both biting flies and domestic animals outside the tsetse belt in northern Kenya, potential mechanical vector species, and their host-feeding profiles.MethodsWe screened for pathogenic African trypanosomes in blood samples from domestic animals and field-trapped flies by microscopy and sequencing of internal transcribed spacer (ITS1) gene PCR products. We sequenced kinetoplast maxicircle genes to confirm Trypanosoma brucei detection and the RoTat 1.2 and kinetoplast minicircle genes to differentiate type-A and type-B Trypanosoma evansi, respectively. Further, we identified the hosts that field-trapped flies fed on by PCR-HRM and sequencing of 16S rRNA genes.ResultsHippobosca camelina, Stomoxys calcitrans, Tabanus spp., and Pangonia rueppellii are potential vectors of trypanosomes outside the tsetse belt in Marsabit County, northern Kenya. We identified Trypanosoma spp., including Trypanosoma vivax, T. evansi, T. brucei, and T. congolense in these biting flies as well as in camels (Camelus dromedarius). Trypanosomes detected varied from single up to three trypanosome species in H. camelina and camels in areas where no tsetse flies were trapped. Similar trypanosomes were detected in Glossina pallidipes collected from a tsetse-infested area in Shimba Hills, coastal Kenya, showing the wide geographic distribution of trypanosomes. Furthermore, we show that these biting flies acquired blood meals from camels, cattle, goats, and sheep. Phylogenetic analysis revealed diverse Trypanosoma spp. associated with variations in virulence and epidemiology in camels, which suggests that camel trypanosomosis may be due to mixed trypanosome infections rather than only surra (T. evansi), as previously thought.

Trypanosomes are important global livestock and human pathogens of public health importance. Elucidating the chemical mechanisms of trypanosome-relevant host interactions can enhance the design and development of a novel, next-generation trypanosomosis diagnostics. However, it is unknown how trypanosome infection affects livestock volatile odors. Here, we show that Trypanosoma congolense and Trypanosoma vivax infections induced dihydro-β- ionone and junenol, while abundance of dihydro-α-ionone, phenolics, p-cresol, and 3-propylphenol significantly elevated in cow urine. These biomarkers of trypanosome infection are conserved in cow breath and the urine metabolites of naturally infected cows, regardless of population, diet, or environment differences. Furthermore, treating trypanosome-infected cows reduced the levels of these indicators back to the pre-infection levels. Finally, we demonstrated that the potential of some specific biomarkers of phenolic origin may be used to detect active trypanosome infections, including low-level infections that are not detectable by microscopy. The sensitivity and specificity of biomarkers detection are suited for rapid, robust, and non-invasive trypanosomosis diagnosis under field conditions.

The sources of animal odours are highly diverse, yet their ecological importance, in host–vector communication, remains unexplored. Here, using the camel (host)–Stomoxys calcitrans (vector) interaction, we collected and analyzed the Volatile Organic Compounds (VOCs) of camels from four of its different odour sources: breath, body (skin), urine, and dung. On non-metric model multivariate analyses of VOCs we show that substantial chemo-diversity exists between metabolic products associated with an individual camel. VOCs from the four metabolic products were distinct and widely segregated. Next, we show electrophysiologically, that VOCs shared between metabolic products activated more Olfactory Sensory Neurons (OSNs) and elicited strong behavioural attractive responses from S. calcitrans under field conditions independent of geography. In our extended studies on house flies, the behavioural response to these VOCs appears to be conserved. Overall, our results establish that VOCs from a range of metabolic products determine host–vector ecological interactions and may provide a more rigorous approach for discovery of unique and more potent attractants.

African animal trypanosomosis (nagana) is becoming prevalent beyond its traditionally defined geographical boundaries in African tsetse belts. However, knowledge of clinically important trypanosomes and infection rate in non-tsetse hematophagous flies and domestic animals are limited. This study characterized the potential mechanical vectors, their host feeding patterns, and trypanosome infection in them and domestic animals outside the tsetse belt in northern Kenya. Field-trapped flies and blood from camels, cattle, donkeys, goats, and sheep were screened for trypanosome infection by microscopy and polymerase chain reaction (PCR) of the internal transcribed spacer 1 region. Blood-fed specimens were analysed using PCR-HRM and/or sequencing of 16S rRNA gene to identify vertebrate blood-meal host sources. Hippobosca camelina, Stomoxys calcitrans, Tabanus spp., and Pangonia rueppellii were identified as potential vectors of trypanosomes outside the tsetse belt in Marsabit County. The trypanosome species, Trypanosoma vivax, T. evansi, T. brucei, and T. congolense were recovered in biting flies as well as in camels (Camelus dromedarius). The diversity of parasites in the biting flies was similar to that detected in the tsetse fly Glossina pallidipes collected from the tsetse-infested Shimba Hills, in coastal Kenya, suggesting a wide geographic distribution of the trypanosomes in Kenya. The biting flies fed on camels, cattle, goats, and sheep. Furthermore, we identified diverse clinical outcomes based on PCV (anemia), heamorrhagia) associated with infection with disparate Trypanosoma species. Thus, infection of flies and camels by diverse Trypanosoma species could contribute to the complex epidemiology of observed trypanosomosis in camels.