Trypanosoma evansi in Indonesian buffaloes: evaluation of simple models ofnatural immunity to infection

Deterministic models were employed to investigate the biology of Trypanosom a evansi infection in the Indonesian buffalo. Models were fitted to two age -structured data sets of infection. The Susceptible-Infected-Susceptible (S IS) model was the best supported description of this infection, although th e results of the analysis depended on the serological test used: the Tr7 Ag -ELISA was judged the most reliable indicator of infection. Estimated force s of infection increase with age from 1.2 to 2.0 acquisitions per buffalo p er year. The buffaloes would clear infection in an estimated mean time peri od of 16.8 months (95 % CIs: 12.5-25.9 months) since acquisition? either by drug treatment by owners or self-cure. A general discussion on the role of immunity in protozoan infections includes consideration that the fitted SI S model would be consistent with strain-specific immunity. The model may be come a useful tool for the evaluation of control programmes.