Updated 01/18/2006 by Juliana Leite, MD

Original text 05/27/1999 Philippe Jeanty, MD, PhD & Sandra R Silva, MD

Synonyms: None.

Definition: Toxoplasmosis is caused by infection with the protozoan parasite Toxoplasma gondii. Toxoplasmosis is normally asymptomatic in immunocompetent individuals. Acute infections in pregnant women can be transmitted to the fetus and cause severe illness (mental retardation, blindness and epilepsy). The risk of maternal fetal transmission increases with gestational age at the time of exposure, whereas the incidence of severe disease decreases.

Incidence: An estimated 400-4,000 cases of congenital toxoplasmosis occur each year in the United States. Of the 750 deaths attributed to toxoplasmosis each year, 375 (50%) are believed to be caused by eating contaminated meat, making toxoplasmosis the third leading cause of food borne deaths in this country. The incidence of toxoplasmosis acquisition during pregnancy ranges from 1 to 4 per 1.0000. Half of the fetuses escape from the infection, one-third has a sub clinical infection, and only one-tenth has a severe infection.

Etiology: Infectious. Women infected with Toxoplasma before conception, with rare exceptions, do not transmit the infection to their fetuses. Women infected with Toxoplasma after conception can transmit the infection across the placenta to their fetuses. Fetal involvement results from acute infection in the mother; however, those mothers with chronic infection can transmit the disease by reactivation, which is caused by an immunological dysfunction. The rate of fetal transmission during primoinfection is 25%, 54% and 65%, in the first, second and third trimesters, respectively.

Pathogenesis: The fetus is infected hematogenously via the placenta during parasitemia in the mother. Ocular toxoplasmosis causes irreversible damage to the retina in utero. The fetus and infant mount inflammatory responses that may contribute to ocular damage (2).

Diagnosis: The classic triad of signs suggestive of congenital toxoplasmosis includes chorioretinitis, intracranial calcifications and hydrocephalus. However, most infants infected in utero are born with no obvious signs of toxoplasmosis on routine examination, but many develop learning and visual disabilities later in life. If untreated, congenital toxoplasmosis can be associated with severe and even fatal disease. Another findings include microcephaly, encephalomyelitis, seizures, mental retardation, ascites and hepatosplenomegaly. Although the diagnosis used to be made by serologic techniques and cultures, it can now be done with polymerase chain reaction detection of Toxoplasma gondii in fetal tissues.

Differential diagnosis: The other TORCH infections.

Prognosis: Approximately 75% of congenitally infected newborns are asymptomatic.

Recurrence risk: Typically none.

Management: Depending on gestational age and whether the fetus is known to be infected, pregnant women have been treated with the antibiotic spiramycin or with sulfadiazine alone or the combination of pyrimethamine and sulfadiazine. Treatment of acute infection during pregnancy has been associated with an approximately 50% reduction in fetal infection.

Prevention: Toxoplasmosis infection can be prevented in large part by cooking meat to a safe temperature, peeling or thoroughly washing fruits and vegetables before eating; pregnant women avoiding changing cat litter or, if no one else is available to change the cat litter, using gloves, then washing hands thoroughly.
 

References
1: Silveira C, Ferreira R, Muccioli C, Nussenblatt R, Belfort R Jr. Toxoplasmosis transmitted to a newborn from the mother infected 20 years earlier. Am J Ophthalmol 2003;136 (2):370-1
2: Roberts F, Mets MB, Ferguson DJ et al. Histopathological features of ocular toxoplasmosis in the fetus and infant. Arch Ophthalmol 2001;119(1):51-8
3. Lopez A, Dietz VJ, Wilson M, Navin TR, Jones JL. Preventing Congenital Toxoplasmosis. MMWR 2000;49(RR02):57-75
4. Vidigal PVT, Santos DVV, Castro FC, Couto JCF, Vitor RWA, Filho GB. Prenatal toxoplasmosis Diagnosis from amniotic fluid by PCR. Rev Soc Bras Med Trop 2002;35(1):1-6