FACTORS INFLUENCING INFECTIONS IN RHIPICEPHALUS-APPENDICULATUS TICKS FED ON CATTLE INFECTED WITH THEILERIA-PARVA

A large database on the transmission of a stabilate of the Theileria p arva Muguga stock from one breed of cattle using two stocks of Rhipice phalus appendiculatus, Muguga and O1 Pejeta was developed and analysed . Factors associated with the ticks and cattle, and the infections dev eloping in cattle were studied in relation to the infection variables in the tick batches harvested daily from cattle. Generalized Linear In teractive Modelling (GLIM) was used to determine the importance of fac tors and interactions in influencing the levels of tick infection vari ables using Type I and Type III sums of squares analyses. Analysis of the 6 variables, prevalence (percentage of ticks infected), abundance (mean number of infected salivary gland acini per tick examined) and i ntensity (mean number of infected salivary gland acini per infected ti ck) in batches of 30 male and 30 female ticks showed that 24 covariate s, factors or interactions had a significant effect (P < 0.05). Certai n covariates and factors were particularly important for all 6 tick in fection variables; parasitaemia of animal on the day of tick harvest, stabilate dilution administered to animal, month in which tick batch w as harvested, minimum packed cell volume of animal over the sampling p eriod, age of animal, and the minimum leukocyte count of the animal ov er the sampling period. The GLIM analyses were found to be a useful to ol in identifying factors that influence infection levels and in devis ing methods of producing tick batches with more predictable infections .