Intestinal helminthic infections in the southern Rift Valley of Ethiopia with special reference to schistosomiasis.

Nineteen communities located in the southern part of the Ethiopian Rift Valley were surveyed for S. mansoni infection and other helminth parasites of man. S. mansoni infected individuals were recorded in 11 communities and human prevalence reached more than 10% in 4 of them. The snail intermediate hosts were Biomphalaria pfeifferi in the lower Omo River basin and B. sudanica in the Rift Valley lakes. Other parasites encountered included A. lumbricoides (11.2%), T. trichiura (10.3%), hookworms (25.3%), Taenia sp. (8.1%), Strongyloides sp. (2.9%), H. nana (0.8%), Trichostrongylus sp (0.3%) F. hepatica (0.1%) and E. vermicularis (0.1%). In some communities the prevalence of hookworms, A. lumbricoides and T. trichiura reached 70%, 66.6% and 60%, respectively. A strong association (r = 0.9) was observed between altitude and parasite prevalence and burden. In nine communities located below 1200 metres, infected individuals harboured nearly two or less the number of parasite species while in 10 communities located at altitude above 1200 metres, multiple infection with three or more parasites reached as high as 53.2%. Similarly, the average parasite species per infected person ranged from 0 to 1.4 in the nine communities located at lower altitudes and from 1% to 2.6% in the 10 communities located at higher altitudes. By ages, both prevalence and multiparasitism are significantly in favour of those below 20 years of age (P < 0.005) although hookworms are prevalent in a wider age range. The widespread occurrence of intestinal schistosomiasis in the southern Rift Valley and the epidemiological pattern of other intestinal helminth parasites of man in this section of the Valley are discussed.