Host genetics: a key factor in regulating the distribution of parasites in natural host populations.

The immune response that expels the tapeworm Hymenolepis citelli from the small intestine of its host the white-footed deer mouse is genetically controlled. Patent infections with this tapeworm occur only in individuals that are homozygous for a recessive allele expressed at a single gene locus. By studying this natural host-parasite system in the laboratory it was shown that host genetics contributes to parasite overdispersion in a host population in the absence of all other ecological variables. Thus, the substantive influence of the proportions of resistant and susceptible genotypes in the host population must be considered when developing parasite population models of transmission or control measures.