Congenital Toxoplasmosis

Abstract

Toxoplasmosis is caused by infection with the parasite Toxoplasma gondii. It is one of the most common parasitic infections in humans and is most typically asymptomatic. However, primary infection in a pregnant woman can cause severe and disabling disease in the developing fetus. Recent developments have included increased understanding of the role of parasite genotype in determining infectivity and disease severity. Risk factors for acquisition of infection have been better defined, and the important role of foodborne transmission has been further delineated. In addition, strategies have emerged to decrease mother-to-child transmission through prompt identification of acutely infected pregnant women followed by appropriate treatment. Refined diagnostic tools, particularly the addition of immunoglobulin G avidity testing, allow for more accurate timing of maternal infection and hence better decision making during pregnancy. Congenitally infected children can be treated, beginning in utero and continuing through the first year of life, to ameliorate the severity of disease. However, despite these many advances in our understanding of congenital toxoplasmosis prevention and treatment, significant areas of study remain: we need better drugs, well defined strategies for screening of pregnant women, improved food safety, and improved diagnostic tests.

Keywords: infant; toxoplasmosis; transmission.

Figure 1.

Lifecyle of Toxoplasma gondii.

1. (1) Unsporulated oocysts are shed in the cat's feces, although oocysts are usually only shed for 1–2 weeks, large numbers may be shed.

2. (2) Intermediate hosts in nature (including birds and rodents) become infected after ingesting soil, water, or plant material contaminated with oocysts.

3. (3) Oocysts transform into tachyzoites that localize in neural and muscle tissue and develop into tissue cyst bradyzoites.

4. (4) Cats become infected after consuming intermediate hosts harboring tissue cysts or by ingestion of sporulated oocysts.

5. (5) Animals bred for human consumption and wild game may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment.

1. Humans can become infected by any of several routes:

   1. • eating undercooked meat of animals harboring tissue cysts (6)

   2. • consuming food or water contaminated with cat feces or by contaminated environmental samples (such as fecal-contaminated soil or changing the litter box of a pet cat) (7)

   3. • blood transfusion or organ transplantation (8)

   4. • transplacentally from mother to fetus (9)

1. (10) Diagnosis is usually achieved by serology, although tissue cysts may be observed in stained biopsy specimens.

2. (11) Diagnosis of congenital infections can be achieved by detecting T gondii DNA in amniotic fluid using molecular methods such as polymerase chain reaction.