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Toxoplasmosis

Definition

Toxoplasmosis is an infection with the protozoan intracellular parasite Toxoplasma gondii.

Causes

Toxoplasmosis is found in humans worldwide, and in many species of animals and birds. Cats are the definitive host of the parasite.

Human infection results from ingestion of contaminated soil, careless handling of cat litter, ingestion of raw or undercooked meat (lamb, pork, and beef), transmission from a mother to a fetus through the placenta (congenital infection), or by blood transfusion or solid organ transplantation.

Over 80-90% of primary infections produce no symptoms. The incubation period for symptoms is 1 to 2 weeks.

Congenital toxoplasmosis is caused by infection with Toxoplasma gondii in a pregnant woman, with up to 50% of such infections transmitted to the fetus. Signs of congenital infection may be present at birth or develop over the first few months of life.

Infants may show signs of central nervous system disorders, enlargement of the liver and spleen, blindness, and mental retardation. Toxoplasmosis also affects people who are immunosuppressed

Symptoms

In non-immunosuppressed people:

• mild illness with fever, resembling mononucleosis
• enlarged lymph nodes in the head and neck
• headache
• sore throat
• muscle pain

In congenital infection:

• central nervous system disorders
• enlarged liver or spleen
• rash, fever, jaundice, anemia
• inflammation of the retina of the eye
• psychomotor and learning disorders (may not appear until later)

In an immunosuppressed person:

• brain lesions are associated with fever, headache, confusion, seizures, and abnormal neurological findings
• retinal inflammation causing blurred vision

Exams and Tests

Tests to determine infection or presence of cysts:

• serologic titers for toxoplasmosis
• MRI of head
• cranial CT scan
• brain biopsy
• slit lamp examination reveals characteristic retinal lesions

Treatment

No treatment is recommended for people without symptoms, except children, to prevent retinal inflammation. Treatment of women in pregnancy is controversial because of the toxicity of the medications, but treatment is still advocated.

Medications to treat the infection include: pyrimethamine, sulfonamide drugs, folinic acid, clindamycin, and trimethoprim-sulfamethoxazole. Treatment in AIDS patients is continued as long as the immune system is weak, to prevent reactivation of the disease.

Outlook (Prognosis)

Acute infection in children may cause retinochoroiditis (inflammation of the retina). Toxoplasmosis in adults has a good prognosis (probable outcome) if the immune system is healthy. Chronic infection without any symptoms is usually benign (harmless).

Possible Complications

• spread of the infection in immunocompromised hosts (can be fatal)
• permanent disability in infants (blindness, learning disorders, and so on)
• recurrence of the disease

When to Contact a Medical Professional

Call for an appointment with your health care provider if symptoms of toxoplasmosis occur. Urgent or emergency conditions exist if the disorder occurs in an immunosuppressed person or in a baby, or if confusion, seizures, or other severe symptoms develop.

Prevention

Avoid undercooked meats, or freeze meat to -20 degrees Celsius for 2 days. Protect children's play areas from cat and dog feces. Wash the hands thoroughly after contact with soil that may be contaminated with animal feces.

Pregnant women should have their blood examined for Toxoplasma antibody -- and those with negative results should take measures to prevent infection by avoiding exposure to cat feces (including not cleaning litter boxes), cooking meat thoroughly, and washing hands thoroughly after handling raw meat.

Patients with HIV disease should have toxoplasma antibody titers checked. If the results of the blood test are positive and if the CD4 count is less than 100, patients should be given prophylactic antibiotics (trimethoprim-sulfamethoxazole is the medication of choice) with antiretroviral therapy until the CD4 cell count has risen.

Cohen J, Powderly WG. Infectious Diseases. 2nd ed. New York, NY: Elsevier; 2004.

Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. 6th ed. London: Churchill Livingstone; 2005.