Abstract:
Background: Trypanosomosis is a major impediment to livestock farming in sub-Saharan Africa
and limits the full potential of agricultural development in the 36 countries where it is endemic. In
man, sleeping sickness is fatal if untreated and causes severe morbidity. This study was undertaken
in western Kenya, an area that is endemic for both human and livestock trypanosomosis. While
trypanosomosis in livestock is present at high levels of endemicity, sleeping sickness occurs at low
levels over long periods, interspersed with epidemics, underscoring the complexity of the disease
epidemiology. In this study, we sought to investigate the prevalence of trypanosomes in small
ruminants and pigs, and the potential of these livestock as reservoirs of potentially human-infective
trypanosomes. The study was undertaken in 5 villages, to address two key questions: i) are small
ruminants and pigs important in the transmission dynamics of trypanosomosis? and ii), do they
harbour potentially human infective trypanosomes? Answers to these questions are important in
developing strategies for the control of both livestock and human trypanosomosis.
Results: Eighty-six animals, representing 21.3% of the 402 sampled in the 5 villages, were detected
as positive by PCR using a panel of primers that identify trypanosomes to the level of the species
and sub-species. These were categorised as 23 (5.7%) infections of T. vivax, 22 (5.5%) of T. simiae,
21 (5.2%) of the T. congolense clade and 20 (5.0%) of T. brucei ssp. The sheep was more susceptible
to trypanosome infection as compared to goats and pigs. The 20 T. brucei positive samples were
evaluated by PCR for the presence of the Serum Resistance Associated (SRA) gene, which has been
linked to human infectivity in T. b. rhodesiense. Three samples (one pig, one sheep and one goat)
were found to have the SRA gene. These results suggest that sheep, goats and pigs, which are kept
alongside cattle, may harbour human-infective trypanosomes.
Conclusion: We conclude that all livestock kept in this T. b. rhodesiense endemic area acquire
natural infections of trypanosomes, and are therefore important in the transmission cycle. Sheep,
goats and pigs harbour trypanosomes that are potentially infective to man. Hence, the control of
trypanosomosis in these livestock is essential to the success of any strategy to control the disease
in man and livestock.
