Effect of Age and Sex on the Acquisition of Immunity to Toxoplasmosis in Cats*

Abstract

The effects of age and sex of the cat on oocyst shedding, multiplication of Toxoplasma gondii in tissues of cats and acquisition of immunity were investigated after oral inoculation of cats with Toxoplasma cysts. Cats (25) varying in age from 1 wk-39 mo. were killed 7-97 days after inoculation with T. gondii. Homogenates of brain, heart, mesenteric lymph nodes, retina and blood from these cats were inoculated into mice to test for Toxoplasma infectivity. Toxoplasma was isolated more frequently and in higher titers in mice receiving inocula from cats of the youngest age group (1 wk old). T. gondii was isolated from tissues of only 2 of 21 cats older than 2 mo. (at the time of inoculation), although all of the animals shed oocysts within 1 wk after ingesting the parasites. The number of oocysts shed varied among littermates of the same sex and between sexes. Generally, cats younger than 12 mo. shed more oocysts than older cats. The number of oocysts shed by older cats varied considerably; males generally shed more oocysts than the females. The number of cats examined was too small for statistical comparison. Cats older than 12 mo. probably should not be used in experiments where numbers of oocysts shed is critical.