ACQUIRED TOXOPLASMOSIS: INFECTION VERSUS DISEASE *

Although recognized as a common infection of man the world over, toxoplasmosis is considered uncommon as a disease entity. The lack of appreciation of the true incidence of the disease undoubtedly results from the lack of readily available serological tests for toxoplasmosis in most laboratories in the United States. The inability to confirm that toxoplasmosis is the cause contributes to the failure on the part of physicians to consider toxoplasmosis in cases of encephalitis, myocarditis, lymphadenopathy, and other diseases. In addition, both the high prevalence of antitoxoplasma serological titers among normal human populations and the wide spectrum of clinical manifestations caused by toxoplasma that mimic many other disease states complicate interpretation of serological test results. Similarly, persistence of high antibody titers and of toxoplasma cysts in most organs and tissues of asymptomatic human beings for years following acute infection complicates interpretation of successful isolation attempts. The persistence of dormant toxoplasma infection among large populations and the potential for its reactivation have become a problem in the increasing numbers of patients whose immunologic defense mechanisms are Compromised by their underlying disease and/or therapy.' Since acute toxoplasmosis in these patients is often fulminant, and since specific therapy is available, definitive diagnosis of acute infection in such individuals is essential. It is, thus, unfortunate that, in the absence of demonstration of rising serological test titers, the definite serological diagnosis of acute acquired infection or reactivation of latent infection is so difficult. A greater appreciation of the more common clinical manifestations of toxoplasmosis would very likely lead to recognition of a larger number of cases, some of which might benefit from treatment. During the past seven years we have studied a number of cases of laboratory-acquired toxoplasmosis, disseminated toxoplasmosis in immunologically comprised patients, and lymphadenopathy and chorioretinitis probably due to toxoplasma. The purpose of this presentation will be to highlight certain clinical manifestations of these acquired cases, to describe problems encountered in establishing the diagnosis, and to suggest methods of distinguishing active disease from past infection. Our group has previously published suggestions for the diagnosis of congenital toxoplasmosis in the early postnatal period.2