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

There is no doubt that at high intensity of infection, intestinal parasites can cause severe illness and the death of their hosts. Even with the high prevalence of these infections, however, such severe cases are rare and the norm is for low to moderate numbers of parasites which cause few if any overt symptoms. Nevertheless, it has been argued that by causing subtle reductions in appetite, absorption, digestion and acute-phase status and increasing intestinal nutrient losses, these low-level but long-term infections could be responsible for the persistent, poor nutritional status of so many children in Third World communities. Although geographically, high parasite prevalence occurs in conjunction with high levels of protein-energy malnutrition, attempts to establish a cause and effect relationship have had very limited success with many investigators being unable to demonstrate any detrimental consequence of infection. The unimpressive results might be explained to some extent by the unusual features of helminth infections such as rapid reinfection, the overdisperse distribution pattern and the uncertainty of a host inflammatory response, but they also suggest that A. lumbricoides (on which most studies have concentrated) may be of little nutritional importance. It seems likely that the more invasive parasites, e.g. the hookworms, S. stercoralis, T. trichiura and perhaps G. lamblia may have a greater impact and clearly more studies are required here. Safe, cheap and effective anthelmintics are now available and, on the grounds of disease prevention, there is a case for their nationwide use. However, from the available evidence, it would be unwise to expect that such programmes would make a significant impact on the nutritional status of children in Third World communities.