An experimental host-parasite association involving BALB/c male mice infected with Plasmodium chabaudi chabaudi was used in order to investigate the influence of the parasite on the sexual physiology and behavior of infected hosts. Infected males displayed complete courtship behavior leading to ejaculation and sired litters on several occasions. A weekly assay of testosterone and corticosterone plasma concentrations revealed a twofold decrease in the testosterone level at 4 and 5 weeks post-injection, during recrudescence. This imbalance was accompanied by a decrease in the overall duration of the social investigation contacts occurring during courtship and by a reduction in the fertilization rate of the infected animals. These physiological perturbations can be regarded as an adaptive response of the host to the recrudescing parasites, which illustrates the rodents’ capacity for regulating the testosterone profiles needed to balance the competing demands of immunity and reproduction.
