Insights into Trypanosomiasis Transmission: Age, Infection Rates and Bloodmeal Analysis of Glossina fuscipes fuscipes in N.W. Uganda

Background: Tsetse flies (Glossina) transmit species of Trypanosoma which cause human African trypanosomiasis (HAT) and animal African trypanosomiasis (AAT). Measuring the infection status of wild-caught tsetse is an important part of operations to control HAT. In north-west Uganda, we conducted field studies over a 15-month period to compare classical, microscope-based, and PCR-based methods of detecting trypanosomes in tsetse. We also quantified the age structure and host preferences of tsetse. Methods: Using Pyramidal traps placed along the Kochi River, in Koboko district, 12512 G. fuscipes fuscipes were caught. A subset of females (n= 5051) and males (n= 1221) underwent dissection wherein mouthparts, midguts and salivary glands were screened for trypanosomes. Additionally, the age of the females was estimated using ovarian ageing and the trypanosome-positive status of 1931 females and 438 males was investigated by ITS PCR. Further the bloodmeal sources of 131 tsetse were identified using vertebrate cytochrome b PCR. Results: Infection rates estimated were significantly greater (1.9-9.3 times) using the PCR-based method compared to the classical dissection-based method. Positive rates for T. brucei sl, T. congolense and T. vivax were 1.6% (1.32-2.24), 2.4% (1.83-3.11and 2.0% (1.46-2.63), respectively by PCR. The abundance and age structure of tsetse populations were relatively stable and the slight seasonal four-fold variation in abundance appeared to be correlated with rainfall. Analyses of age structure suggests a low natural daily mortality of 1.75% (1.62-1.88). The majority of bloodmeals were identified as cattle (39%, 30.5-47.8) and human (37% of meals, 28.4-45.6). Conclusion: PCR provides a more sensitive and specific method of estimating the infection rates of all pathogenic species of trypanosome circulating in Koboko. The seasonally stable abundance, low mortality rate and high proportion of bloodmeals from humans may explain, in part, why this district has historically been a focus of sleeping sickness. ### Competing Interest Statement The authors have declared no competing interest.