Modelling the prevalence of Echinococcus and Taenia species in small ruminants of different ages in northern Jordan

A base-line survey of Echinococcus granulosus, Taenia hydatigena and T. ovis were undertaken in order to investigate the transmission dynamics of these parasites in northern Jordan. Intensity of E. granulosus infection, in sheep, increased with age in a linear fashion whilst the asymptotic prevalence was one. This implied that E. granulosus is in an endemic steady state with no evidence of protective immunity in the intermediate host. The mean number of cysts increased by 1.66 per year with approximately 0.320 infections per year, each infection consisting of 598 eggs to produce 5.2 cysts. The basic reproduction ratio (R-0) was estimated to be 1.5-1.8. A similar pattern was suggested with E. granulosus in goats but the infection pressure appeared to be lower with only 0.128 cysts per year. Although infection in goats appeared to be endemic there was some evidence of departure from the model which might indicate that the model needs adjusting for this species. In the case of T. hydatigena the host age-intensity helminth distribution indicated that this parasite was hyperendemic in both sheep and goats, implying regulation by intermediate host immunity. Consequently, R-0 was determined from asymptotic prevalence curves for T. hydatigena and was calculated to be 4.0 and 3.1 in sheep and goats, respectively. The lower R-0 in goats, together with the higher asymptotic age-intensity and age-prevalences, indicates that goats acquire immunity more slowly to T. hydatigena in comparison to sheep. Taenia ovis was not detected in any animals. (C) 1998 Elsevier Science B.V. All rights reserved.