Human Helminth Infections: A Primer

Abstract

Parasitism is the commonest lifestyle of animals. Parasitic helminths in the phyla Nematoda and Platyhelminthes have co-evolved with humans at least since we began to live in sufficiently large groups. Once essentially ubiquitous in human populations, parasitic helminths now are found almost entirely in resource-limited regions of the tropics, where sanitation and health infrastructure are inadequate to prevent their transmission. Between one and two billion people remain infected with at least one of these pathogens. Helminth infections are chronic and, although now rarely acutely lethal, have impacts on child development and growth, reflected in cognitive and physical impairment. Overt pathology is most notable in those who bear large numbers of parasites and are frequently re-infected, but detrimental effects are likely to be present even in less severely infected individuals. Control campaigns, now mostly based on mass drug administration, have made impressive gains in many areas and for some parasites, but much remains to be done. The complex milieu of helminth parasites, malnutrition, and co-infection with other pathogens underlies the cycle of poverty. Elimination and eventual eradication of these parasites will help to break this cycle and must be sustained and augmented by economic development for improved sanitation and healthcare delivery.