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Sera from 273 wild mammals from Missouri and Kansas (USA), collected between December 1974 and December 1987, were tested for the presence of antibodies to Toxoplasma gondii using the Sabin-Feldman dye test. Sixty-five (24%) had antibodies at titers ofor = 1:8, including 38 (66%) of 58 carnivores, 14 (15%) of 94 omnivores, 13 (11%) of 117 herbivores, and none of four insectivores. The prevalence of antibodies in mice (Mus musculus and Peromyscus spp.) and rats (Rattus norvegicus and Sigmodon hispidus) was low (3%), while medium sized herbivores such as squirrels (Sciurus spp.), rabbits (Sylvilagus floridanus), and muskrats (Ondatra zibethicus) had prevalences of about 18%. Red foxes (Vulpes fulva) and mink (Mustela vison) had the highest prevalence of antibodies with frequencies of 90 and 66%, respectively. In 32 attempts to isolate Toxoplasma gondii from wild mammals with positive (or = 1:4) titers, only six (19%) were successful: a gray squirrel (Sciurus carolinensis), a beaver (Castor canadensis), an opossum (Didelphis marsupialis), a red fox and two mink. These findings are consistent with the hypothesis that the probability of infection with Toxoplasma gondii, and therefore prevalence of antibodies in wildlife, is greatest in carnivores.

The role of the cat (Felis domestica) as a definitive host for Sarcocystis cuniculi of European rabbits (Oryctolagus cuniculus) was confirmed. It was shown that after dosing with sporocysts from cats, rabbits developed sarcocysts and these became infective for cats at not less than 93 days post-infection (p.i.). The earliest infection detected was at 142 days p.i. Infected muscle from an experimental rabbit did not transmit Sarcocystis when fed to other rabbits. Microscopically, sarcocysts in European rabbits (O. cuniculus) were morphologically indistinguishable from those in cottontail rabbits (Sylvilagus floridanus).