TOXOPLASMOSIS
Infection with the intracellular
parasite Toxoplasma gondii occurs primarily through ingestion of the
infectious tissue cysts in raw or poorly cooked meat or through contact with
feces from infected cats, which contain infectious sporu-lated oocytes. The
latter may remain infectious in moist soil for more than 1 year. Only cats that hunt and kill their preyare
reservoirs for infection; those that eat prepared cat food are not. In
immunocompetent adult humans, infection ismost commonly asymptomatic and
disease is self-limited. Prior infection confers immunity, unless the
individual is immunosuppressed. Approximately 15% of reproductive-age women
have antibodies to toxoplasmosis.
Although congenital infection is
more common follow-ing maternal infection in the third trimester, the sequelae
following 1st-trimester fetal infection are more severe. Over half of infants
whose mothers are infected during the last trimester of pregnancy have
serologic evidence of infection, but three-fourths of these show no gross
evidence of infec-tion at birth. Signs of congenital infection include severe
mental retardation, chorioretinitis, blindness, epilepsy, intracranial
calcifications, and hydrocephalus.
In some regions with high
prevalence of disease (France and Central America), screening is routine in
preg-nancy. In the United States, routine screening in pregnancy is not
recommended except in the presence of maternal HIV infection. Because
identification of the organism in tissue or blood is complex and infection is
usually asympto-matic, diagnosis depends on demonstration of seroconver-sion. A
positive IgG titer indicates infection at some time. A negative IgM effectively
rules out recent infection; how-ever, IgM may persist for long periods and a
positive test is not reliable in assessing duration of disease. In addition,
false-positive IgM results are common with commercially available assays.
Confirmatory testing in pregnancy should be performed in a Toxoplasma reference laboratory prior to initiating any therapy.
Treatment of acutely infected
pregnant women with spiramycin may reduce the risk of fetal transmission but
does not prevent sequelae in the fetus if infection has oc-curred. This
medication is only available through the FDA. If fetal infection has already
been noted (through ultra-sound findings or confirmed with testing of fetal
blood or amniotic fluid), pyrimethamine and sulfadiazine therapy may decrease
the risk of congenital infection and the severity of manifestations.
Prevention of infection should be
an important part of prenatal care, including counseling regarding thoroughly
cooking all meats, careful hand washing after handling raw meats, washing of
fruits and raw vegetables before inges-tion, wearing gloves when working with
soil, and keeping cats indoors and feeding them only processed foods. If a cat
is kept outside, someone other than a pregnant woman should feed and care for
the cat and dispose of its wastes.
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