ABSTRACT

Humans are remarkably susceptible to infections with parasites and harbour over 30 species of protozoa and over 60 species of helminths but, fortunately, only a few of these are common and even fewer normally cause serious disease. However, in recent years there have been increasing numbers of reports of new and hitherto relatively harmless parasitic infections that have become life-threatening in individuals infected with HIV or undergoing immunosuppressive therapy. It is beyond the scope of this chapter to discuss all the important parasitic infections and coverage will be restricted to what are known as the ‘six diseases’ identified by the World Health Organization in the 1970s as the most important infections in its Tropical Diseases Research Programme. Of these, leishmaniasis, African and South American trypanosomiasis, malaria, schistosomiasis and filariasis are caused by parasites, the sixth being leprosy. Table 4.1 lists the parasites covered in this chapter, diseases caused and prevalence. These parasitic diseases are the ones that have received most attention and about which most is known, but this does not mean that other parasites do not present serious problems or that parasites are not important outside the tropics and the reader is referred to standard textbooks of parasitology and tropical medicine listed in the bibliography

for further information. In addition to their effects on humans, parasites present a continual threat to domesticated animals all over the world and the losses caused in terms of loss of productivity and premature mortality run into many millions of pounds every year.