Introduction

Parasitic worms do not usually interest doctors because, although worms can cause severe clinical disease, they usually have insidious effects on growth and development that rarely cause attendance at health centres. Yet it is precisely these chronic effects, affecting more than two billion people with lifelong infections, that have forced the public health community to reassess the importance of these infections. And recognition of the simplicity, safety, low cost, and efficacy of treatment has now resulted in major global initiatives to achieve control.

Methods

Information for this review came from Medline and hand searches of published literature, correspondence with experts in the subject, and the personal experiences of the authors.

Size of the problem

Parasitic worms may be the commonest cause of chronic infection in humans. In many low income countries it is more common to be infected than not. Indeed, a child growing up in an endemic community can expect be infected soon after weaning, and to be infected and constantly reinfected for the rest of her or his life.

There are about 20 major helminth infections of humans, and all have some public health significance,1 but among the commonest of all human infections are the geohelminthiases. Recent global estimates indicate that more than a quarter of the world's population are infected with one or more of the most common of these parasites–the roundworm, Ascaris lumbricoides; the hookworms, Necator americanus and Ancylostoma duodenale; and the whipworm, Trichuris trichiura.2 About 85% of the 200 million people with schistosomiasis live on the African continent,3 70 million people have haematuria associated with Schistosoma haematobium infection, and the two commonest species together contribute to the deaths of more than a quarter of a million people a year from complicated nephrosis and portal hypertension.4 Hookworm infection is the leading cause of pathological …