Mice suppress malaria infection by sampling a ‘bitter’ chemotherapy agent

Abstract

Rodents have evolved a variety of feeding strategies for maintaining physiological homeostasis. We examined the possibility that mice possess behavioural mechanisms for counteracting parasite-related diseases. We used an inbred strain of laboratory mouse (BALB/c), a murine-specific malaria parasite (Plasmodium berghei berghei), and a ‘bitter’ chemotherapy agent (chloroquine) as our model system. We asked whether the infected mice would ingest an unpalatable chloroquine solution, and, if so, whether they would benefit from doing so. Seven days after infecting the experimental mice with the parasites, we provided them with a choice between two water bottles; one contained water and the other a 1mM chloroquine solution. We monitored their daily consumption from both bottles, and progression of the malaria infection by tracking changes in the percentage of parasitemia of red blood cells and mortality. We had two control groups: one had access to chloroquine but were not infected (no-malaria mice), and the other was infected but did not have access to chloroquine (no-chloroquine mice). The experimental mice showed significantly less parasitemia and mortality than the no-chloroquine mice. The ability of the experimental mice to contain the malaria infection was determined by the fact that they took approximately 20% of their fluid from the chloroquine solution. We found, however, that this chloroquine consumption was not caused by the malaria infection because the no-malaria mice ingested statistically similar amounts of the chloroquine solution. Upon examining the literature, we discovered many other examples of apparently healthy mammals sampling a diverse range of ‘bitter’ substances. We conclude that the tendency to sample different ‘bitter’ substances is widespread among mammals, and may constitute a feedforward mechanism for chemoprophylaxis against parasitic infections and other illnesses.