Schistosomiasis mansoni in Yemeni in California: duration of infection, presence of disease, therapeutic management.

Investigations of schistosomiasis mansoni in 218 Yemeni agricultural workers in the San Joaquin Valley of California revealed a prevalence of 56%. In those infected, quantitative egg counts performed by the Kato thick smear method revealed that 57% had light infections (1-100 eggs/g), 27% moderate infections (101-400 eggs/g), and 16% heavy infections (greater than 400 eggs/g; mean--918 eggs/g). The Yemeni had been migrating to the USA for the past 20 years, a period in which the prevalence of schistosomiasis had remained constant in the Yemen. The prevalence of schistosomiasis in those who had been away from Yemen for less than 5 years was 59% with a mean egg output of 236 eggs/g, but in those away for more than 5 years (up to 20 years) it was 32% with a mean egg output of 75% eggs/g. This is in spite of the fact that 75% of the latter had returned to Yemen for short visits. Statistical analysis by the Fisher's exact probability test revealed a significantly lower egg output in those away from Yemen more than 5 years. On the basis of these findings the mean life span of the Yemen strain of Schistosoma mansoni in man was estimated to be between 5 and 10 years. The presence of disease was assessed in this population by traditional medical means without prior knowledge of the status of the infection in the individuals examined. Under these circumstances, there were no differences in symptoms such as weakness, diarrhea and abdominal pain among the uninfected proportion of the population, total infected group and a small subgroup of those most heavily infected. None of the patients had hepatomegaly and only two had splenomegaly--one lightly and the other heavily infected. Because of the toxicity of antischistosomal drugs and the lack of treatment facilities only the 22 most heavily infected (greater than 200 eggs/g) of the 122 individuals with schistosomiasis mansoni were treated with niridazole. In addition the two individuals with splenomegaly were treated with antimony dimercaptosuccinate. Side effects, though common, were not severe. Although follow-up in this migrant population was poor the nine patients examined 3 to 7 months after treatment showed a mean decrease in egg output of 97%.