The nonrandom, negative binomial distribution of experimental trichinellosis in rabbits.

The distribution of parasite populations in their hosts has been the subject of a number of mathematical analyses and it has been found that these distributions are generally nonrandom and overdispersed. Data on the recovery of Trichinella spiralis in the laboratory from 371 outbred rabbits were examined. The distribution of their parasite burden was overdispersed and best fit by a negative binomial frequency distribution. The intensity of the infections was almost totally independent of the dose of inoculation, the duration of the infection, and the weight of the animals; the variations within the replicate counts were small and normally distributed about their means. These results indicate that nonrandom overdispersion may be a characteristic of even carefully controlled laboratory infections, and susceptibility factors should be considered seriously in mathematical models of parasites.