Paradoxical helminthiasis and giardiasis in Cape Town, South Africa: epidemiology and control

Vera J Adams, Miles B Markus, Joanita FA Adams, Esme Jordaan, Bronwyn Curtis, Muhammad A Dhansay, Charlie C Obihara, John E Fincham

Abstract

Background. South Africa has endorsed a World Health Assembly (WHA) resolution calling for control of soil-transmitted helminths (STHs). In Cape Town, services and housing that exist in old-established suburbs should minimise the prevalence of intestinal parasitic infections, even when residents are poor. Where families live in shacks in densely-populated areas without effective sanitation, more than 90% of children can be infected by STHs. The humoral immune response to worms theoretically favours infection by Mycobacterium tuberculosis and HIV.

Objectives. Obtain estimates of gender-, age-, school-related and overall prevalence of helminthiasis and giardiasis in a low-income but well-serviced community. Assess possible sources of infection. Alert health services to the need for control measures and the threat from protozoal pathogens. Warn that the immune response to intestinal parasites may favour tuberculosis (TB) and HIV/AIDS.

Methods. A cross-sectional study of the prevalence of helminthiasis and giardiasis was carried out in a large, non-selective sample of children attending nine schools. Gender, school and age effects were related to non-medical preventive services, sewage disposal practices and possible sources of infection.

Results. The overall STH infestation rate was 55.8%. Prevalence was influenced by school and age but not by gender. Eggs and cysts were seen at the following prevalences: Ascaris 24.8%; Trichuris 50.6%; Hymenolepis nana 2.2%; Enterobius 0.6%; Giardia 17.3%; hookworm 0.08%; and Trichostrongylus 0.1%. Approximately 60% of sewage sludge is used in a form that will contain viable eggs and cysts.

Conclusions. Prevalence trends in this old community in Cape Town could indicate infection by swallowing eggs or cysts on food or in water, more than by exposure to polluted soil. Sewage sludge and effluent might be sources of infection. In adjacent, under-serviced, newer communities, promiscuous defaecation occurs. Probable vectors are discussed. The immune response to intestinal parasites might be a risk factor for HIV/AIDS and TB.

Key words: Ascaris, Enterobius, HIV/AIDS, hookworm, IgE, Trichuris, tuberculosis