Group mean Schistosoma mansoni
reinfection patterns are presented for 2 years
after treatment with
oxamniquine in 1981 of over 100 9- to 16-year-old Kenyan schoolchildren, and for one year after
retreatment in 1983 with either
oxamniquine or
praziquantel when most (nearly 700) infected people in the whole community were treated. Quality control confirmed comparable Kato egg counts throughout the study. Continuing transmission after 1981 raised prevalence to nearly its original level within 6 months, but intensity remained suppressed throughout the 2 year follow-up and very few children reacquired heavy
infections (greater than 400 eggs/g). Age and sex had significant effects:
reinfection diminished with age, especially among boys--a pattern not apparently attributable to differential water contact. Children with heavy pretreatment
infections tended to develop heavy
reinfections but this trend was not statistically significant on a group basis, nor were similar trends during the period of less pronounced transmission following the 1983 community treatment.
Oxamniquine was equally effective in children receiving it in both 1981 and 1983, and the efficacy of
praziquantel resembled that of
oxamniquine. In this area of Kenya, repeated
chemotherapy will be needed to contain transmission, probably annually or biennially, unless supplemented with other, effective control measures. These findings confirm the beneficial effects of treating even a limited segment of a community at intervals of a year or more without necessarily stopping transmission. They are also compatible with recent findings on potential immune mechanisms in man.