Trypanosoma evansi in Northern Ethiopia: epidemiology, diversity and alternative diagnostics

Animal African trypanosomosis is a complex of parasitic diseases in various domestic and wild animal species caused by different species of trypanosomes, among which Trypanosoma (T.) evansi causes surra, affecting camel, cattle, horses, goats, sheep and buffaloes in Africa, Latin America and Asia. Due to mortality and reduced productivity of sick animals and to cost of treatment, surra is responsible for huge economic losses. Even though surra is a World Animal Health Organisation (OIE) notifiable disease, it is severely neglected in terms of awareness, control interventions and research into improved control tools.

This PhD study, conducted in Ethiopia and in Belgium, had three main aims:

1° To assess the epidemiological situation of non-tsetse transmitted animal trypanosomosis in domestic animals in Tigray and Afar regions in Northern Ethiopia;

2° To isolate and characterise trypanosome strains from these regions; and

3° To improve the molecular and serological diagnosis of surra.

In the epidemiological survey, we used a combination of state-of-the-art serological, parasitological and molecular diagnostic tests. This survey showed that T. evansi - but also T. vivax, another non-tsetse transmitted trypanosome - is a major threat to animal health in Tigray and Afar, not only in dromedary camel and cattle, but also in goats, sheep and equines. We were able to isolate 22 new parasite strains from sick camels, a selection of which were adapted to in vitro culture for in vitro drug sensitivity typing. No resistance against any of the commonly used drugs was observed in the in vitro assays, as opposed to resistance against isometamidium hydrochloride observed in vivo. Among the isolated parasite strains, we identified several that belong to the rare T. evansi type B. Infections with these type B parasites are not detected by the current OIE recommended serological diagnostic tests. Through sequencing of the F1-ATP gama subunit gene of the Ethiopian T. evansi strains and comparison with strains from other taxa and origin, mutations were revealed that may be exploitable for molecular characterisation.

This PhD study also allowed us to conduct a large scale evaluation of the Surra Sero K-SeT, recently developed by the Institute of Tropical Medicine and Coris BioConcept for serodiagnosis of T. evansi infection. The Surra Sero K-SeT displayed a considerably higher sensitivity than the OIE recommended test, CATT/T. evansi, but a somewhat lower specificity. We recommend adaptation of the Surra Sero K-SeT in order to detect T. evansi type B infections as well.