TRANSMISSION DYNAMICS OF ECHINOCOCCUS-GRANULOSUS, TAENIA-HYDATIGENA AND TAENIA-OVIS IN SHEEP IN URUGUAY

A base-line survey was carried out on the transmission dynamics of Ech inococcus granulosus, Taenia hydatigena and Taenia ovis in sheep in th e Department of Florida, Uruguay. Mean life expectancy at birth of the sheep population in this Department was estimated at 3.5 and 4.8 year s for male and female sheep, respectively. Both intensity and prevalen ce of E. granulosus infection increased with age providing no evidence that immunity was acquired in the population. This revealed that E. g ranulosus was only relatively stable and in an equilibrium endemic ste ady state with an estimate of the basic reproduction ratio (R(0)) of a bout 1.2. The mature larval population in sheep was over-dispersed wit h parameter k, from fitting a negative binomial, being 0.199 and 0.556 in 42- and 54-month-old sheep, respectively. The mean number of cysts increased by 1.05 cysts per year and the infection pressure was calcu lated as 0.174 infections per year, implying that each infection consi sted of 693.6 eggs to produce 6.03 cysts. Neither intensity nor preval ence of infection with T. hydatigena or T. ovis increased with age. Th is indicated that immunity was acquired to reinfection by both parasit es and they were in an equilibrium hyperendemic steady state with an e stimated R(0) of 4.2-5.8. Viability and fertility of E. granulosus, an d viability of T. hydatigena cysts in the older age groups were low. T he effects of the different transmission levels of the parasites on po tential control strategies are discussed.