Tsetse distribution, trypanosome infection rates, and small-holder livestock producers' capacity enhancement for sustainable tsetse and trypanosomiasis control in Busia, Kenya

Trypanosoma Congolense Resistant to Trypanocidal Drugs Homidium and Diminazene and their Molecular Characterization in Lambwe, Kenya

PURPOSE

African animal trypanosomiasis (AAT) is a disease affecting livestock in sub-Saharan Africa. The use of trypanocidal agents is common practice to control AAT. This study aimed to identify drug-resistant Trypanosoma congolense in Lambwe, Kenya, and assess if molecular test backed with mice tests is reliable in detecting drug sensitivity.

METHODS

Blood samples were collected from cattle, in Lambwe, subjected to buffy coat extraction and Trypanosoma spp. detected under a microscope. Field and archived isolates were subjected to molecular characterization. Species-specific T. congolense and TcoAde2 genes were amplified using PCR to detect polymorphisms. Phylogenetic analysis were performed. Four T. congolense isolates were evaluated individually in 24 test mice per isolate. Test mice were then grouped (n=6) per treatement with diminazene, homidium, isometamidium, and controls. Mice were subsequently assessed for packed cell volume (PCV) and relapses using microscopy.

RESULTS

Of 454 samples, microscopy detected 11 T. congolense spp, eight had TcoAde2 gene, six showed polymorphisms in molecular assay. Phylogenetic analysis grouped isolates into five. Two archived isolates were homidium resistant, one was also diminazene resistant in mice. Two additional isolates were sensitive to all the drugs. Interestingly, one sensitive isolate lacked polymorphisms, while the second lacked TcoAde2, indicating the gene is not involved in drug sensitivity. Decline in PCV was pronounced in relapsed isolates.

CONCLUSION

T. congolense associated with homidium and diminazene resistance exist in Lambwe. The impact can be their spread and AAT increase. Polymorphisms are present in Lambwe strains. TcoAde2 is unlikely involved in drug sensitivity. Molecular combined with mice tests is reliable drug sensitivity test and can be applied to other genes. Decline in PCV in infected-treated host could suggest drug resistance.

Spatial Distribution of Tsetse Flies and Trypanosome Infection Status in a Vector Genetic Transition Zone in Northern Uganda

Background

Tsetse flies are vectors of the genus Trypanosoma that cause African trypanosomiasis, a serious parasitic disease of people and animals. Reliable data on the vector distribution and the trypanosome species they carry is pertinent for planning sustainable control strategies. This study was carried out to estimate the spatial distribution, apparent density, and trypanosome infection rates of tsetse flies in two districts that fall within a vector genetic transition zone in northern Uganda.

Materials and Methods

Capturing of tsetse flies was done using biconical traps deployed in eight villages in Oyam and Otuke, two districts that fall within the vector genetic transition zone in northern Uganda. Trapped tsetse flies were sexed and morphologically identified to species level and subsequently analyzed for detection of trypanosome DNA. Trypanosome DNA was detected using a nested PCR protocol based on primers amplifying the internal transcribed spacer (ITS) region of ribosomal DNA.

Results

A total of 717 flies (406 females; 311 males) were caught, all belonging to the Glossina fuscipes fuscipes species. The overall average flies/trap/day (FTD) was 2.20 ± 0.3527 (mean ± SE). Out of the 477 (201 male; 276 females) flies analyzed, 7.13% (34/477) were positive for one or more trypanosome species. Three species of bovine trypanosomes were detected, namely, Trypanosoma vivax, 61.76% (21/34), T. congolense, 26.47% (9/34), and T. brucei brucei, 5.88% (2/34), and two cases of mixed infection of T. congolense and T. brucei brucei, 5.88% (2/34). The infection rate was not significantly associated with the sex of the fly (generalized linear model (GLM), χ² = 0.051, p = 0.821, df = 1, n = 477) and district of origin (χ² = 0.611, p = 0.434, df = 1, n = 477). However, trypanosome infection was highly significantly associated with the fly's age based on wing fray category (χ² = 7.56, p = 0.006, df = 1, n = 477), being higher among the very old than the young.

Conclusion

The relatively high tsetse density and trypanosome infection rate indicate that the transition zone is a high-risk area for perpetuating animal trypanosomiasis. Therefore, appropriate mitigation measures should be instituted targeting tsetse and other biting flies that may play a role as disease vectors, given the predominance of T. vivax in the tsetse samples.