The impact of gastrointestinal parasites on protein-energy malnutrition in man

Human intestinal parasites occur throughout the world but it is in the wet tropics and sub-tropics where they are found in their greatest numbers.A basic requirement for the continued survival of these organisms is an inadequate and unhygienic method of disposal of faecal material.For transmission to take place, eggs, larvae or cysts passed in the faeces of an infected individual must be brought back into close contact with a potential host.For some species, infection occurs orally, i.e. by ingestion of Ascaris lumbricoides or Trichuris trichiura eggs or Giardia fambfia cysts from contaminated food, water, hands or utensils.Others such as the hookworms and Strongyloides stercoralis only require that the skin of the host comes into contact with infective larvae which are able to enter the body by skin penetration.Thus, infection with these worms usually occurs through the feet when walking barefoot on faecally contaminated earth.Many parasites have essential developmental stages in the soil, e.g. to be infective, eggs of A .lumbricoides and T. trichiura need an incubation period to allow embryonation whereas those of the hookworms and S. stercoralis hatch producing larvae which must pass through several stages before becoming infective.These processes are accelerated in warm damp soil, thus the earth floor which is the norm in most houses in developing countries is an ideal vehicle for promoting parasitic illness.The whole process of transmission is exacerbated by overcrowding and a general lack of hygiene both in terms of facilities such as running water and proper sanitation but also by poor health and hygiene education.Consequently, intestinal parasites reach their highest prevalence and intensity in impoverished parts of the developing world, that is in the same areas where malnutrition, particularly of children, remains a major problem.This inevitably raises the question of whether these parasites might be responsible, at least in part, for the poor growth and nutritional status of such children (Chagas & Keusch, 1986; Crompton, 1986; Stephenson, 1987).Estimates of the prevalence of intestinal parasites is certainly in keeping with this premise.Cases of ascariasis, caused by the roundworm A .lumbricoides, number