Schistosomiasis control based on repeated chemotherapy in a rural village of the sugar-cane zone in northeast Brazil.

A schedule of repeated chemotherapy with oxamniquine, consisting of biannual treatment of school-aged (7-13 years) children and annual treatment of all other age groups, was used in a representative rural village from a highly endemic area of schistosomiasis in Pernambuco. Significant reductions in infection were obtained only after two cycles of treatment, as the overall prevalence decreased from 72.6% to 41.7% and the geometric mean egg counts per gram of faeces among positives fell from 188.4 to 76. In a school-aged cohort (n = 29) three treatments at six-month intervals were necessary to significantly reduce the proportion of positives (from 75.9% to 51.7%). In a cohort of children under 7 years of age (n = 20) the proportion of positives actually increased (from 30% to 45%) despite two annual treatments. Water contact was intense and host snail density was relatively high. As there is no short-term perspective of improved sanitation, auxiliary measures such as focal mollusciciding are needed for an adequate control of schistosomiasis in this and alike areas.

Schistosomiasis in a low prevalence area: incomplete urbanization increasing risk of infection in Paracambi, RJ, Brazil.

The risk of schistosomiasis infection and heavy infection in the locality of Sabugo was evaluated in relation to housing in areas with different urbanization development and to residential supply with snail-infested water. Critical sanitary conditions were found in areas of incomplete urbanization, where healthy water supply sources were scarce, and draining of sewage, without previous treatment, was made directly to the water-bodies used for domestic and leisure activities, despite being Biomphalaria tenagophila snail breeding-places. Stool examinations (Kato-Katz and Lutz methods) showed prevalence of 2.9% mean intensity of 79 eggs per gram of stool and 47% of positive cases presenting intense infection. The use of snail-contaminated water for domestic purposes was considered a risk factor for infection. It is concluded that incomplete urbanization would facilitate transmission, probably enhancing the intensity of infection and that a low prevalence could hide a highly focal transmission. The relevance of these facts upon the efficiency of epidemiologic study methods and disease control planning are then discussed.

Fate of chloroalkylene-9-14C in carrots, sugar beets, and soil under outdoor conditions.

Immediately after application of chloroalkylene-9-14C to soil (1.32 ppm, based on dry weight of soil in the upper layer of 0 to 10 cm) under outdoor conditions, carrots were sown; in the following year, sugar beets were grown. About 80% of the radioactivity applied volatilized within one vegetation period. Most of the remaining radioactivity was still in the upper soil layer; 0.8% had dispersed to a depth of 40 cm, and 3.3% was taken up by the carrot plants. In the second year, no more decreases of soil residues was observed; uptake by sugar beets was 0.1% of the applied radioactivity. In the first year, the residues in the upper soil layer consisted of 41% unchanged chloroalkylene-9, 19% soluble metabolites, and 40% unextractable residues; the amount of unextractable residues rose to 68% in the second year. The following conversion products were characterized in the soil extracts: a monohydroxylated dichlorobiphenyl, a monomethoxylated dichlorobiphenyl, and two isomeric monohydroxylated, monoisopropylated dichlorobiphenyls; in carrot roots, a monomethoxylated dichlorobiphenyl was detected. Conjugates occurring in the soil yielded, after acid hydrolysis, a monohydroxylated dichlorobiphenyl among other compounds.