DELAYED REINFECTION OF SCHISTOSOMA-MANSONI IN THE BLUE NILE VALLEY OFWESTERN ETHIOPIA 10 YEARS AFTER MASS CHEMOTHERAPY

In the Blue Nile Valley of western Ethiopia a successful control progr amme against Schistosomiasis mansoni starting from 1985 was in 1989 in terrupted by local guerrilla warfare. The control was based on human m ass chemotherapy campaigns during the rainy season of 1985 and 1986 an d a limited annual, focal molluscicidal activity where re-infection wa s demonstrated. In 1995 the area was revisited and selected schools in previously hyperinfected villages were examined for reinfection. The results were compared to re-calculated figures for the 5-19 year age g roup from previous pre-, per- and post-control surveys in the same loc alities. In 1995 prevalence rates in the 5-19 year age group had risen to 68% (Salba-Korka) and 63% (Sirba), which are very close to the 198 5-1986 pre-control prevalences. Infection intensities, however, had no t risen to the same degree. In Salba-Korka the 1986 pre-control geomet ric mean S. mansoni eggs per gram of faeces in the 5-19 year age group was 73, after mass treatment until 1989 it was close to 0, whereas in 1995 it was still only 27. In Sirba the result was similar. This migh t indicate a slower transmission rate after the control period than pr eviously. The reported seasonality of transmission and the local use o f the molluscicidal bark of the 'Bitza' tree might possibly have had s ome delaying effect. (C) 1998 Published by Elsevier Science B.V. All r ights reserved.