Abstract

INTRODUCTION

Schistosomiasis is one of the most widespread parasitic infections in man, second only to malaria in terms of socioeconomic and public health importance in many tropical and subtropical areas. It is particularly common in the rural areas of developing countries, with an estimated 200 million people infected globally, and 600 million exposed to infection The prevalence of infection varies from under 10% in some areas to over 80% in others (Mahmoud 1977; Pitchford 1986).

It is caused by blood flukes (schistosoma), which invade the vascular system. The infection is transmitted by specific snails whose distribution determines the prevalence of the three different species of schistosome responsible for most disease in man: Schistosoma haematobium, S. mansoni, and S. japonicum (Table 1). S. haematobium is found mainly in Africa. S. mansoni has a similar distribution but in addition is endemic to South America, Japan and South-east Asia (Bird 1964; Warren 1986;