Modelling the transmission dynamics of Echinococcus granulosus in sheep and cattle in Kazakhstan

Cystic echinococcosis, caused by Echinococcus granulosus, is an emerging disease in many parts of the world and, in particular, in eastern Europe and the former Soviet Union. This paper examines the abundance and prevalence of infection of E. granulosus in cattle and sheep in Kazakhstan. Observed data are fitted to a mathematical model in order to determine if the parasite population is partly regulated by intermediate host immunity and to define parameters in the model. Such data would be useful to develop simulation models for the control of this disease. Maximum likelihood techniques were used to define the parameters and their confidence limits in the model and the negative binomial distribution was used to define the error variance in the observed data. The results indicated that there are significant variations in the infection pressure to sheep depending on their location. In particular sheep from Almaty Oblast and from central and northern Kazakhstan appeared to have a greater exposure than sheep from Jambyl or South Kazakhstan Oblasts. The infection pressure to cattle was somewhat lower in comparison. In common with other similar studies, there was no evidence of parasite-induced immunity in sheep or cattle in Kazakhstan due to natural infection. The highest abundance and prevalence were seen in the oldest age classes of animals.