Immunity in toxoplasmosis.

Asymptomatic Toxoplasma infection of both man and animals is common in the Americas. This is shown by the high prevalence of Toxoplasma antibody, commonly found in 50-60% of human subjects 20-30 years old, in the absence of apparent clinical disease (I). Similarly, serologic surveys have found antibody in normal animals (2). Clinical illness also occurs, however, such as the illness that led to Splendore’s discovery of Toxoplasma in a spontaneously diseased rabbit at the Portuguese Hospital in Sao Paulo (3). In this vein, postmortem examination of babies and adults was instrumental in recognizing neonatal and adult toxoplasmosis in Latin America (4, 60). What immunologic insights can be drawn from the simultaneous presence of asymptomatic, clinical, and even fatal infections in animals and man? (It seems appropriate to start with a brief general discussion of toxoplasmosis immunology, because that is basic to an understanding of clinical toxoplasmosis, its diagnosis, and its optimal treatment.) Regarding man, Table 1 compares diverse human immunologic responses to Toxoplasma infection, grouping these