Molecular characterization of trypanosomes in small ruminants and pigs from western Kenya
Ng'ayo, Musa Otieno
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Trypanosomosis a disease caused by protozoan parasites of the genus Trypanosoma. It is mainly transmitted by tsetse flies Glossina (Glossinidae; Diptera) in Africa. The disease causes over 40,000 deaths in human population and is also a major impediment to livestock production and economic development in many countries in sub Saharan Africa, where it is endemic. The role of small ruminants and pigs as reservoir of trypanosomosis is not well elaborated especially in Western Kenya. This study was designed to investigate trypanosomosis in small ruminants and pigs from Western Kenya, which is the only known active focus of sleeping sickness in Kenya. Microscopic and Polymerase Chain Reaction (PCR) based methods were used to determine diversity of trypanosomes infecting these livestock. Aneamia as a consequence of the disease in these livestock was assessed and expressed as packed cell volume (PCV). Further, isolates of T. brucei were and analyzed for the presence of Serum Resistant Associated (SRA) gene and genotyped using five microsatellites. Tsetse flies density and identity by species were also determined to assess their involvement in disease transmission. A total of 402 animals (255 goats, 95 sheep and 52 pigs) were sampled. Twenty one percent infections were detected by PCR, while 1.2% were detected by microscopy. PCR detection showed that 24% of the sheep, 21% pigs and 19.3% goats were infected. The main trypanosome species detected were T. vivax 6%, T. sindae 5.5 %, T. congolense 5.2 %, T. brucei 4.7 % and 17% of T. brucei stocks had the SRA gene. Glossina fuscipes fuscipes and G. pallidipes were caught together with stomoxys and tabanids. The results of genetic analysis revealed a diverse heterogeneity of genotypes. All microsatellite loci analyzed showed a high degree of size polymorphism. In particular one specific pattern clearly segregates the human pathogen T. b. rhodesiense. This study showed that PCR is a sensitive and reliable method of identifying infections, including those with no patent parasitaemia by microscopic methods. It was concluded that small ruminants and pigs in the area were infected and harbor various species of trypanosomes, including the human infective forms. Further, some of these livestock are infected with multiple genotypes of T. brucei, which may have implication on gene flow, and the transfer of genes that confer important traits, such as human infectivity.