Water contact and Schistosoma haematobium infection: a case study from an upper Egyptian village.

The quantitative relationship between water contact and Schistosoma haematobium infection was studied in a cohort of male school children aged 6-17 in El Ayaisha village, Upper Egypt, during a two-year study. An exposure index (total body minutes, TBM) was used to identify the activities responsible for exposure to cercariae-infested water and to examine the relationship between water contact and infection. Results show that 65% of all contacts and 86% of all TBM were due to swimming in the Nile and canals and that swimming was the most important exposure and contamination activity. Using multivariate analysis, several sites, study periods, residence groups and mostly canal contacts were significantly correlated with egg-counts. Positive relationships could also be identified using egg-counts with water contact data from preceding study periods, indicating the influence of pre-existing infections, prepatency and seasonality of water contact and transmission. TBM were usually more significantly correlated with egg-counts than frequency and duration of contact. The relevance of the findings for control programmes and the use of school children and the exposure index for water contact studies are discussed.

Enzyme- and 125I-labeled anti-immunoglobulin assays in the immunodiagnosis of schistosomiasis.

An enzyme-linked immunosorbent assay (ELISA), and radioimmunoassays using antigen bound to plastic tubes or microcrystalline particles, were adapted for the indirect serological measurement of anti-schistosome antibodies. These alkaline phosphatase and 125I-labeled anti-immunoglobulin techniques were found to be highly quantitative and adaptable. Comparison showed them to be considerably more sensitive than the indirect hemagglutination and indirect fluorescent antibody techniques. Using adult S. mansoni freeze-thaw antigen, anti-schistosome antibodies were detected in sera from patients infected with Schistosoma mansoni and S. haematobium. However, results in patients with schistosomiasis haematobium were generally intermediate between those of patients with schistosomiasis mansoni and normal, uninfected controls.

A longitudinal study of Schistosoma haematobium infection in Qena governorate, Upper Egypt. 1. Initial epidemiological findings.

An epidemiological study was conducted as an initial phase of a longitudinal study on the immunology of Schistosoma haematobium in Upper Egypt. The study area was confined to three villages in Qena governorate, a region endemic solely for S. haematobium. In a cross-sectional survey in two of these villages, the overall prevalence of infection was 28.7% (29.9% at Khozam and 26.9% at El Ayaisha) based on urine examination of the family members in every third household. S. haematobium infection was found in all age groups including infants below 1 year of age. The age distribution of those infected showed the classical rise in the percent infected, reaching a peak of 57-63% in the 11- to 15-year age group followed by a rapid decline and stable low prevalence below 28% in adult years. Males consistently had higher prevalence rates than females at all ages with the profiles of the age prevalence curves strikingly similar. In the two villages, significantly (P less than 0.05) higher infection rates were found in farmers compared to those in other occupations. The overall prevalence of infection in school children (5-16 years old) in the three villages was 61.1% based on the examination of one urine sample. Almost 10% greater prevalence was found when four consecutive daily urines were examined compared to one in the same study group sampled 1 month apart. There was a rapid increase in prevalence with age, reaching a maximum at age 10 with relatively little fluctuation to age 16 years. When comparing the age prevalence data with the intensity of infection expressed as either mean or median age excretion per milliliter urine, it was found that both were parallel and rose sharply from age 5-10 years, but the latter significantly declined several years prior to any perceptible diminution in prevalence.