Abstract / Summary
Background. Gambian human African trypanosomiasis (gHAT) is a neglected tropical disease caused by Trypanosoma brucei gambiense transmitted by tsetse flies (Glossina). Humans are the major host and mass screening and treatment of the human population has contributed to the elimination of gHAT as a public health problem in many countries, including Uganda. There is some evidence that animals may act as hosts for T. b. gambiense which may undermine efforts to eliminate transmission. We undertook a study to determine whether cattle and pigs were harbouring T. b. gambiense in a region of north-western Uganda where efforts to eliminate transmission of gHAT were ongoing. Methodology Blood was collected from 2,775 cattle and 531 pigs and examined for the presence of trypanosomes by the haematocrit centrifugation technique (HCT). In addition, polymerase chain reaction (PCR) was used to amplify the trypanosomal internal transcribed spacer (ITS1). Those whose ITS-1 results indicated the Trypanozoon group (T. brucei) were further tested by sub-species specific PCRs for T. b. gambiense and T. b. rhodesiense. The results were analysed by species of infecting parasite, geographic location and presence or absence of vector control activities in the area. Principal Findings. Among the cattle samples, 2.2% were positive by HCT (95% CI = 1.7% - 2.8%), while 5% were positive by PCR (95% CI = 4.2% - 5.9%), but this varied depending on location with up to 26.5% positive in one village. Among pigs, 3 samples (0.6%; 95% CI 0.2% - 1.6%) were positive by HCT and none were positive by PCR. No samples were found positive for potentially human infective trypanosomes. There was no significant association between trypanosome species and vector control activities (p > 0.05). Based on these results it was concluded with 95% confidence that human infective trypanosomes are not circulating in livestock at a prevalence greater than 1/1000, and when this is augmented with results of previous surveys potentially human infective parasites are not circulating at a prevalence greater than 1/2848. At the level of the trypanosome species, there is no significant difference in the prevalence of species in vector controlled versus non-vector controlled areas (p > 0.05). Conclusions. These results support the evidence base that livestock are unlikely to be an important reservoir for potentially human infective parasites and therefore not a threat to the elimination of Gambian human African trypanosomiasis in Uganda.