Abstract

A field study was carried out to determine the patterns of transmission of Theileria parvainfection (expressed as entomological inoculation rate (EIR)) between cattle and T. parvainfected Rhipicephalus appendiculatus ticks in three different farming systems in Rwanda. The EIR was measured for a given period of time as a product of the tick burden feeding on an animal and the proportion of them that are T. parva infected. A total of 750, 600 and 150 questing ticks were collected in restricted, free-range and fenced farming systems, respectively. A PCR-RFLP method was used to discriminate between T. parva and Theileria taurotragi species co-infecting R. appendiculatus. Data on tick numbers infecting animals were obtained from a survey carried out in the three farming systems in similar conditions in the previous year. The results showed higher EIR (9 infected ticks/animal/week) in the restricted farming system as a result of higher tick numbers (233 ticks/animal) and high infection rate in ticks (3.98%) than in the fenced (high infection rate (4.37%) but acaricide suppressed tick burden (28 ticks per animal)) and in the free grazing (high tick number (292 ticks/animal) but low infection rate (0.17%)) suggesting an epidemiologically critical situation in animals kept under restricted conditions. The study showed clearly that tick load is not the only epidemiological determinant in ECF, differential managerial methods applied lead to variable epidemiological situations in a given ecological area.

Key words: Theileria parva, tick numbers, infection rate, EIR, farming system.