Soil-Transmitted Helminths and Water

Abstract

The number of species of soil-transmitted helminths (STHs) infecting humans in the tropical and subtropical parts of the world may be up to a dozen or more. However, the most common STHs include the large roundworm, Ascaris lumbricoides, the whipworm, Trichuris trichiura, and two species of hookworm, Necator americanus and Ancylostoma duodenale. Besides, three other helminths, Enterobius vermicularis, Strongyloides stercoralis and Oesophagostomum bifurcum, show considerable morbidity of disease though at a smaller scale than the four common STHs. In addition to their health effects in the form of iron deficiency anaemia, rectal prolapse and chronic dysentery, helminth infections also impair physical and mental growth in childhood, impede educational advancement and hinder economic development. The greatest numbers of soil-transmitted helminth infections occur in Asia, especially the sub-Saharan Africa, India, China, and Southeast Asia. Periodic deworming launched by government and non-government organizations has shown to improve growth, micronutrient status (iron and vitamin A) and motor and language development in preschool children. The present chapter describes and summarizes, through a systematic review of the published literature and notifications of World Health Organization (WHO), the prevalence and intensity of infection caused by the common STHs, the morbidity caused by them, the risk factors and the methods of intervention.