Introduction

Toxoplasma gondii is a classic example of an organism that has re-emerged as a threat to human health due in main to two external factors – the advent of HIV infection (discussed in Chapter 5) and advances in medical techniques and treatment such as transplantation and chemotherapy for malignancy – and the intrinsic ability of the protozoan to produce a persistent but latent infection via tissue cysts.

Toxoplasma gondii infection in an immunocompetent person is usually a trivial event which is normally asymptomatic; severe life-threatening disease is very rare. However, this is not the case in immunosuppressed patients (Table 6.1), in whom toxoplasma infection can result in significant morbidity and mortality. Clinically the situation can be complicated since the symptoms and signs of toxoplasma infection can mimic, confound or compound the presentation of the underlying disease and the possibility of infection may not even be considered. Diagnosis of infection is not always straightforward since the immune response in these patients may be atypical; clinical awareness of the possibility of infection must, therefore, be paramount.

Toxoplasma infection can be acute, chronic, latent or reactivated. Though naturally acquired acute infection can and does occur in immunosuppressed patients, it is not a common occurrence and reactivation of a previously latent infection is the usual scenario. The risk of infection in the individual patient depends on two factors – the prevalence of toxoplasma infection in that particular patient's community and the degree and nature of immunosuppression.