Epidemiology of and diagnostic strategies for toxoplasmosis

Abstract

The apicomplexan parasite Toxoplasma gondii was discovered a little over 100 years ago, but knowledge of its biological life cycle and its medical importance has grown in the last 40 years. This obligate intracellular parasite was identified early as a pathogen responsible for congenital infection, but its clinical expression and the importance of reactivations of infections in immunocompromised patients were recognized later, in the era of organ transplantation and HIV infection. Recent knowledge of host cell-parasite interactions and of parasite virulence has brought new insights into the comprehension of the pathophysiology of infection. In this review, we focus on epidemiological and diagnostic aspects, putting them in perspective with current knowledge of parasite genotypes. In particular, we provide critical information on diagnostic methods according to the patient's background and discuss the implementation of screening tools for congenital toxoplasmosis according to health policies.

Fig 1

Biologic stages of Toxoplasma gondii. Shown are microscopic examinations of tachyzoites in a bronchoalveolar lavage fluid sample stained with Giemsa (A) (magnification, ×500), a cyst in the brain of an infected mouse (B) (magnification, ×500), and unsporulated (C) and sporulated (D) oocysts (magnification, ×1,000).

Fig 2

Life cycle of Toxoplasma gondii. Shown are the biology, infection, and replication of the three infective stages of the parasites in their respective hosts.

Fig 3

Sources of T. gondii infection in humans. The various sources of food-borne and environmental contamination of humans are represented.

Fig 4

Kinetics of the antibody (Ab) response. The average kinetics of the different isotypes are represented, but they may differ among patients and according to the serologic technique used. IgM can be detected for years after infection.

Fig 5

Interpretation of T. gondii serology in pregnant women.

Fig 6

Management of pregnancy with confirmed or highly suspected pergestational toxoplasmosis. WG, weeks of gestation.