Seasonal Monitoring of Glossina Species Occurrence, Infection Rates, and Trypanosoma Species Infections in Pigs in West Nile Region, Uganda

Abstract

Human African trypanosomiasis (HAT) is caused by the Trypanosoma sub species (ssp.), T. brucei rhodesiense and T. brucei gambiense. It is exclusively associated with Glossina species (tsetse fly) habitats, and therefore restricted to sub-Saharan Africa. Animals, including pigs, have shown to be able to carry human-pathogenic T. brucei ssp. and are therefore important in disease transmission. Determining the Trypanosoma prevalence in pigs and tsetse flies in the Northwestern region of Uganda, a historical HAT hotspot, was suggested in consultation with Coordinating Office for Control of Trypanosomiasis in Uganda (COCTU). Between February and June 2019, tsetse flies and pigs were sampled in six government intervention sites and six control sites in Arua and Maracha districts. Pigs were screened for infection with Trypanosoma and tsetse traps were deployed to monitor vector occurrence, followed by dissection and microscopy to establish infection rates with Trypanosoma spp. Deoxyribonucleic acid (DNA) was extracted from pig blood samples and blood meals of tsetse flies for further classification of Trypanosoma species using Internal transcribed spacer (ITS)-Polymerase chain reaction (PCR) and to establish the host preference of the vectors.The results showed that 7/1262 (0.56 %) of the sampled pigs were Trypanosoma positive under the microscope, all of these were from the intervention villages. 223/341 (65.4%) of the PCR analyzed pig samples were positive, 60% from intervention sites and 40% from control sites, and all were T. vivax infections.There were 583 tsetse flies collected and 360 of them were dissected. Thirteen of the 360 dissected tsetse flies (3.8%) were shown to be positive for Trypanosoma under the microscope.In addition, 59 of the dissected flies (16.4%) had bloodmeals present. The difference in captured tsetse flies in the government intervention sites in comparison to the control sites was significant (p<0.05), with a tsetse fly density of 0.68 tsetse/trap/day in the intervention sites, and 1.24 tsetse/trap/day in control site. Seasonality did not play a substantial role in the tsetse fly density (p>0.05).This project illustrated that pigs can carry the causative agent for African Animal Trypanosomiasis (AAT), Trypanosoma vivax, even though considered resistant to Trypanosoma vivax infection. The low vector abundance in a historical HAT hotspot in Uganda was also exemplified.