Introduction

Infection with Toxoplasma gondii in the immunocompetent individual has generally been regarded as being of little significance. This is probably because many clinicians are influenced by the normally favourable outcome of toxoplasmic lymphadenopathy, the most characteristic clinical presentation. However, toxoplasma infection has a world-wide distribution and since the vast majority of infections are usually not diagnosed (Ho-Yen 1992), the true importance of toxoplasma in the immunocompetent individual is unknown.

A vast amount of information is now available on toxoplasma infection, and the possible outcomes in the immunocompetent individual are shown in Figure 4.1. In those who have not been infected with toxoplasma, significant exposure to the organism usually results in a primary infection. However, there is some evidence that in a few immune individuals and where there is significant strain variation, a second infection is possible (Abdul-Fattah et al. 1992). Reactivated infections are probably more common than second infections, especially in individuals with immune dysfunction that may result from concomitant viral infections, for example human immunodeficiency virus (HIV) or immunosuppressive therapy. Acute toxoplasma infections can be primary, reactivated or second infections (Figure 4.1) and have a wide variety of clinical presentations. In the 1970s, it was generally regarded that acquired toxoplasmosis in the immunocompetent individual resulted in infection rather than disease (Feldman 1974). Now, this belief is being questioned.