Effects of p-aminobenzoic acid, methionine, threonine and protein levels on susceptibility of mice to Plasmodium berghei

The effects of dietary p-aminobenzoic acid (PABA), protein, methionine and threonine on Plasmodium berghei infection in mice were investigated. Animals were fed diets containing 12 or 20% casein supplemented with PABA (0 or 2 mg/kg diet), methionine (0 or 15 mg/g casein) and threonine (0, 7.5, 27.5 or 47.5 mg/g casein). Percent mortality was lower in rats fed diets without PABA than in those fed diets containing PABA. All further experiments were conducted without supplemental PABA. While the mean day of death was greater in the groups fed 12% casein, percent mortality in these groups was nearly twofold higher than in the groups fed 20% casein. The presence or absence of 15 mg methionine per gram casein had no effect on percent mortality, mean day of death, or percent parasitemia, regardless of dietary casein level. Supplementation of threonine at any level to the 12% casein diet with supplemental methionine resulted in mortality rates similar to those from animals fed the 20% casein diets, but percent mortality was not altered by threonine in the absence of supplemental methionine. The mean day of death of animals fed 20% casein increased with increments of added threonine. Methionine had no influence on this phenomenon. It is concluded that the quantity of dietary protein and the quality of its amino acid composition can have profound effects on the susceptibility of mice to malaria.