Host-pathogen evolution: Implications for the prevention and treatment of malaria, myocardial infarction and AIDS.

Humans have evolved complex immune systems to protect against infection by pathogens. However, pathogens possess a remarkable genetic versatility that allows them to gain new vigour and so escape such population immunity. Conflicting pathogen-host objectives, therefore, lead to the evolutionary equivalent of an "arms race". Typically, in this struggle, pathogens attempt to deplete their host of specific nutrients that are essential for immune system function. After infection, the resulting deficiency of nutrient(s) may cause many of the disease symptoms and sequela. In malaria, Plasmodium falciparum, for example, depletes its host of Vitamin A, possibly resulting in blindness in some cases. However, 200,000 International Units of Vitamin A, given to children every three months can reduce significantly their susceptibility to malaria. This would seem to be a minimum child dosage for the treatment of the disease. In contrast, the Coxsackie B virus causes a selenium deficiency that may result in myocardial infarction or Keshan disease. However, table salt fortified with 15ppm anhydrous sodium selenite can cause dramatic drops in the incidence of Keshan disease, while selenium supplementation also reduces re-infarction rates. HIV-1 depletes its host of four nutrients: selenium, cysteine, glutamine and tryptophan, resulting in symptoms known as AIDS. Open and closed clinical trials in South Africa, Zambia and Uganda, involving daily adult doses of 600mcg l-selenomethione, and some 500mg l-glutamine, hydroxytryptophan and N-acetyl cysteine, however, have shown that such supplementation can reverse the symptoms of AIDS and prevent HIV-1 infected patients declining into this disease. It is obvious, therefore, that supplementation of diet with specific nutrients can reduce infection by particular pathogens. In addition, if infection still occurs, their use as a treatment may prevent many of the symptoms and sequela commonly associated with diseases such as malaria, myocardial infarction and AIDS.