Introduction

In patients infected with human immunodeficiency virus (HIV) the most frequent manifestation of toxoplasmosis is encephalitis. Toxoplasmic encephalitis is, in fact, the most common cause of focal central nervous system infections in people with acquired immunodeficiency syndrome (AIDS). In addition, toxoplasma infection and disease may occur in other organ systems. The mechanism of disease in the overwhelming majority of patients is reactivation of latent toxoplasma infection subsequent to severe immune suppression. This chapter will consider the epidemiology, clinical presentation, diagnosis, treatment and prognosis of toxoplasma infection in the setting of HIV infection.

Epidemiology

Human infection with Toxoplasma gondii occurs primarily from consumption of undercooked meats, particularly lamb and pork (containing tissue cysts) (Weinman & Chandler 1956; Masur et al. 1978; Dubey 1986) or ingestion of food, water or inadvertently of soil or sand contaminated with oocysts (Teutsch et al. 1979; Benenson et al. 1983). The overwhelming majority (>95%) of cases of toxoplasmosis in patients with AIDS occur as a consequence of reactivation of a dormant (latent) infection (Luft & Remington 1988). Latent infection can easily be identified by serological testing. The incidence of toxoplasmic encephalitis is directly proportional to the prevalence of latent toxoplasma infection in any given population. Serological surveys in humans demonstrate that the prevalence of antibodies to T. gondii increases with increasing age (Feldman & Miller 1965). There is no significant difference between the sexes.