The epidemiology of Schistosoma haematobium and S. mansoni infections in the Egypt-49 project area. 2. Prevalence of bilharziasis in relation to personal attributes and habits.

The over-all uncorrected prevalence rates of bilharziasis determined in this survey were-Control Division, 59.5%; Rural and Reclamation Divisions, 35.9%; Urban Division, 21.0%. There are significant differences in rates of infection between sections within a division, between adjacent villages and even between different parts of one village. Prevalence increases rapidly with age up to about the age of 14 years, declines somewhat up to the age of 40 years and then remains fairly constant at a rate of about 30%; the age-group 0-8 years should provide the most sensitive group for the assessment of control measures. S. mansoni infection is acquired more slowly than S. haematobium infection during childhood and is more persistent among adults.Except for the youngest age-group, bilharziasis rates are higher in males than in females, but more detailed analysis shows that this is true only for farmers and farm labourers and for those who swim. In respect of occupational categories, farmers and farm labourers, with prevalence rates of 50.6% and 41.6%, respectivelx, bear the brunt of the infection, since they constitute 48% of the population, although fishermen (60.4%) and boatmen (52.0%) have higher infection rates.Differences in bilharziasis rates can also be related to differences in religion, educational attainment and domestic habits (swimming, washing clothes, utensils and cattle) according to the opportunity provided for contact with polluted water. Swimming, because of the thorough exposure to possible schistosome infection that it provides, is one of the most important activities involved in the transmission of bilharziasis.

The epidemiology of Schistosoma haematobium and S. mansoni infections in the Egypt-49 project area. 3. Prevalence of bilharziasis in relation to certain environmental factors.

The influence of the size and location of communities in relation to the different types of watercourse, the availability of a protected water supply, types of housing and the presence of other sanitary facilities on the prevalence of bilharziasis in the Egypt-49 project area has been studied. There is no direct relationship between the size of village and the prevalence of bilharziasis. Main drains and distributaries are potent sources of infection and, in terms of the total population exposed, distributaries play the most significant role in the transmission of infection. Of the other factors, the availability of a protected water supply seems to have the greatest effect on the prevalence. Although the presence of a latrine in the dwelling does not of itself influence the extent of schistosome infection, which is caught from polluted water, the installation of latrines assists in the cultivation of healthy habits, thereby lessening the prevalence not only of bilharziasis but also of certain other infections.

The behavioural pattern of social and religious water-contact activities in the Egypt-49 bilharziasis project area.

Social and religious water-contact activities have been recorded over a period of one year in four villages situated on different types of watercourse in the Egypt-49 project area. Females have more frequent water contacts than males; females under 25 years old have more frequent contacts than older ones. Males are more active contaminators than females, among whom girls under 5 years old are the chief polluters. Summer is the period of most frequent, prolonged and extensive body-surface contact. One-quarter of all exposures take place between noon and 3 p.m., the period of maximum cercarial load. The most frequent activities during this critical period are washing of utensils, bathing and playing, and wadu (ritual washing). Peak exposures therefore coincide with the peak seasonal and diurnal cycle of infectivity of watercourses in the area.It is suggested that an index might be established that would take into account the frequency and duration of exposure and the amount of body-surface exposed and that could be related to the periodic variations of cercarial densities in the watercourses.