Selective primary health care: strategies for control of disease in the developing world. XII. Ascariasis and trichuriasis.

Ascariasis and trichuriasis are the most prevalent and widespread intestinal helminthiases. Transmission of disease occurs by ingestion or inhalation of Ascaris and Trichuris eggs embryonated in the soil. During the migration of Ascaris to the lungs, pneumonic symptoms may develop. The intestinal stage of the parasite can cause severe symptoms and complications when the worm burden is high. High numbers of Trichuris may cause diarrhea. The poor standard of hygiene, the biology of the parasite (which is such that a high number of very resistant eggs are produced), and the habits of the host (such as the use of night soil) are factors causing a high prevalence of infection in many countries in Asia, Africa, South America, and Europe. The mechanism of the transmission of Ascaris varies in different communities. The peak of infection is among children aged four to 14 years. Worm burden is normally low, and only a small segment of the population harbors a high proportion of the worms present in a community. Control of infections due to Ascaris and Trichuris is feasible by a combination of mass chemotherapy with the effective drugs now available, safe disposal of excreta, destruction of the eggs, and health education.