EPIDEMIOLOGY, IMMUNOLOGY AND CHEMOTHERAPY OF SCHISTOSOMA-MANSONI INFECTIONS IN A RECENTLY EXPOSED COMMUNITY IN SENEGAL

Schistosoma mansoni was introduced in the Richard Toll area (Senegal) around 1988, probably due to man made ecological changes in the Senega l river basin. Since 1991, we investigate the community of Ndombo, clo se to Richard Toll, Four random population samples of approximately 40 0 subjects are surveyed, starting at 8 months intervals. Each cohort i s examined parasitologically (Kato Katz, clinically, serologically (ci rculating antigen and antibody profiles); treated with praziquantel 40 mg/kg; and followed up 6-12 weeks, 1 and 2 years after treatment, Wat er contact patterns and snail densities are longitudinally surveyed, I n the first cohort, prevalence of infection was 91%, with 41% excretin g over 1000 eggs per gram (epg); the mean egg count was 646 epg, indiv idual counts up to 24,000 epg, Prevalences remained almost 100%, but e gg counts declined strongly in adults, in spite of continued exposure and the supposed lack of acquired immunity, Antigen detection in serum and urine confirmed that the egg counts genuinely reflect variations of worm burdens, Serum, circulating anodic antigen (CAA) provided intr iguing epidemiological information on worm burdens, while circulating cathodic antigen (CCA) showed promise for non-invasive diagnosis and s creening, So far, similar epidemiological results were found in subseq uent cohorts, although some variations were observed, possibly due to seasonal transmission fluctuations. IgE levels increased with age, whi le IgG4 peaked in the age group 10-19 years. IgE and IgG4-levels again st adult worm antigen (AWA) and soluble egg antigen (SEA) increased be tween cohort 1 and cohort 3 in almost all age groups. In all 3 cohorts examined so far a strong correlation between IgG4 and pre-treatment e gg-load was observed, Further follow up anti. analysis, and comparison with chronically infected populations will provide insight in the dev elopment of acquired immunity. Abdominal discomfort was reported by 61 % and diarrhoea by 33% of the subjects in the first cohort; mild hepat omegaly was found in 16%, splenomegaly in 0.5%, There was no correlati on between frequency of symptoms and egg counts. This low morbidity, i n spite of intense infections, was confirmed by ultrasound, and may be due to the recent nature of the focus, In the first cohort, 82% of tr eated subjects still excreted eggs 12 weeks after treatment, though eg g counts declined strongly, Antigen detection confirmed these results, Parasitological negativation rates in subsequent cohorts, followed up sooner after treatment, improved but remained remarkably low, The low drug efficacy may be due to very rapid reinfection (though further re infection after one year was limited), and/or to the lack of immunity in the population. Reduced susceptibility of the local schistosome str ain can not be excluded, however, Praziquantel treatment provoked impr essive but transient side effects (colics, vomiting, urticaria, oedema ), the frequency of which correlated with intensity of infection,