Genetic diversity of trypanosomes pathogenic to livestock in tsetse flies from the Nech Sar National Park in Ethiopia: A concern for tsetse suppressed area in Southern Rift Valley?

摘要

In Ethiopia, home to the largest African herd of cattle, animal trypanosomiasis is a major constraint to the efforts made for food self-sufficiency. We searched for trypanosomes in tsetse flies caught in the Nech Sar National Park (NSNP), Southern Rifty Valley, Ethiopia, at the district of Arba Minch where intensive tsetse control is successfully improving cattle productivity. Despite narrow geographical and temporal scales of our survey, we found a remarkable diversity of trypanosomes using the sensitive and discriminative method of fluorescent fragment length barcoding. We also found a high density of Glossina pallidipes (47.8 flies/trap/day) showing relevant cytochrome oxidase I gene variability. The identification of blood meal sources through cytochrome b gene sequences revealed cattle and warthog as preferential ungulate hosts of tsetse flies in the study area. Our survey identified trypanosomes in 38% of the 287 flies examined (42% of proboscises and 32% of guts), and the following infection rates for each species: Trypanosoma vivax 23%, T. simiae 23%, T. congolense 22%, T. theileri 19.9%, T. (Trypanozoon) spp. 10.5%, T. godfreyi 9.4%, T. simiae Tsavo 6.3%, and mixed infections in proboscises (30%) and guts (61%). Phylogenetic analysis revealed T. vivax of the "West African-South American" genotype, T. congolense of Savannah (16.7%), Kilifi (3.5%) and Forest (2.1%) lineages, and new genotypes of T. simiae. To our knowledge, this is the first survey of trypanosomes in the NSNP, and the most comprehensive molecular characterisation of trypanosomes in tsetse flies of Ethiopia, including the comparison with samples from West and other East African countries. Our results support the diversification of T. vivax in East Africa, and the dispersion of the genotype herein identified in Ethiopia across West Africa and then in South America. Altogether, tsetse density and infection rate, repertoire of trypanosomes and feeding behavior indicate a high risk of transmission of trypanosomes pathogenic to ungulates by tsetse flies from the NSNP, a hotspot of tsetse infestation and trypanosome diversity. Our findings reinforce the need for constant surveillance, and the reliance on community efforts to prevent reinvasion of tsetse and animal trypanosomiasis in suppressed areas of Southern Rift Valley.