What is toxoplasmosis?

Causes and Symptoms

The parasite
Toxoplasma gondii, which causes toxoplasmosis, is fairly common and can infect warm-blooded animals as well as reptiles, but the ordinary domestic cat is the only known animal that sheds the toxoplasma parasite in its feces. Humans can also be infected by coming into contact with cat feces in a litter box or by eating raw or undercooked meat from infected animals.

The parasite may be acquired or congenital. Both forms seem to have a wide variety of clinical outcomes, ranging from a mild, asymptomatic state to an infection with fatal results. Congenital infection may manifest in jaundice, fever, anemia, convulsions, inflammation of the retina (chorioretinitis), an enlarged liver or spleen, and lymphadenopathy.

Acquired toxoplasmosis infection may be mild or severe. The vast majority of people who contract the disease have no or few symptoms, while others may have swollen glands, headaches, or a sore throat. These symptoms generally appear within ten to fourteen days after infection and subside within two to twelve weeks. Severe toxoplasmosis manifests in a possible fever, rash, pneumonia, encephalitis, myocarditis, pericarditis, hepatitis, and muscle inflammation (polymyositis).

When toxoplasmosis is acquired during pregnancy, it may badly harm the fetus, even if the mother does not have any symptoms. The degree to which the infection damages the fetus depends upon the stage of pregnancy. The parasite can be passed to the fetus in 15 percent of women infected during the first trimester, in approximately 25 percent infected during the second trimester, and in up to 65 percent of those infected during the last trimester. It is possible for the pregnant woman to suffer a spontaneous abortion or a stillbirth or to deliver a premature or a full-term child in whom birth defects are present.

Toxoplasmosis can occur when the immune system is impaired. Reactivation of previously acquired toxoplasma organisms has become a serious problem for HIV-infected persons. Improved HIV treatment and prophylaxis for toxoplasmosis with trimethoprim-sulfamethoxazole have reduced the incidence of disease. Similar reactivation of toxoplasma has also occurred in immunologically suppressed solid-organ and bone-marrow transplant patients.

Treatment and Therapy

Pyrimethamine and sulfa drugs have reduced the complications from toxoplasmosis. When pyrimethamine is given to a pregnant woman during her first trimester, however, birth defects may occur. Physicians will prescribe sulfa drugs alone for infections occurring during pregnancy.

Perspective and Prospects

The protozoan Toxoplasma gondii was first isolated from an African rodent and was eventually described as a new species in 1909. In 1940, it was established as a factor for human disease.

It is possible to prevent toxoplasmosis by feeding cats only well-cooked meat or commercial cat food; keeping cats indoors, so that they cannot hunt and eat birds or mice; staying away from cats and having someone else clean the litter box during pregnancy; washing one’s hands after touching uncooked meat; and cooking meat to a minimum of 150 degrees Fahrenheit (66 degrees Celsius), or 165 degrees Fahrenheit (74 degrees Celsius) for poultry.

Bibliography

Ambroise-Thomas, Pierre, and Eskild Petersen, eds. Congenital Toxoplasmosis: Scientific Background, Clinical Management, and Control. New York: Springer, 2000.

Despommier, Dickson D., et al. Parasitic Diseases. 5th ed. New York: Apple Tree, 2006.

Joynson, David H. M., and Tim G. Wreghitt, eds. Toxoplasmosis: A Comprehensive Clinical Guide. Rev. ed. New York: Cambridge University Press, 2005.

Martin, Richard J., Avroy A. Fanaroff, and Michele C. Walsh, eds. Fanaroff and Martin’s Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 2 vols. 9th ed. Philadelphia: Mosby/Elsevier, 2011.

"Parasites—Toxoplasmosis (Toxoplasma Infection)." Centers for Disease Control and Prevention, January 10, 2013.

Parker, James N., and Philip M. Parker, eds. The Official Patient’s Sourcebook on Toxoplasmosis. San Diego, Calif.: Icon Health, 2002.

Roberts, Larry S., and John Janovy, Jr., eds. Gerald D. Schmidt and Larry S. Roberts’ Foundations of Parasitology. 8th ed. Boston: McGraw-Hill Higher Education, 2010.

Rosenblum, Laurie. "Toxoplasmosis." Health Library, November 26, 2012.

"Toxoplasmosis." Mayo Clinic, June 24, 2011.