Description

Toxoplasmosis is caused by Toxoplasma gondii, an obligate intracellular protozoan parasite with a complex life cycle, which can cause a wide range of clinical symptoms depending on individual strain virulence and the host immune system.

• Primary infection is often asymptomatic and may result in fever, lymphadenopathy, and eye disease.
• Congenital infection classically presents with triad of chorioretinitis, hydrocephalus, and brain calcifications.
• Reactivation of disease may develop after either primary or congenital infection and most commonly presents as chorioretinitis.
• Patients with immune deficiency can develop brain abscesses, encephalitis, fever of unknown origin, or pneumonia.

Epidemiology

• Toxoplasmosis infects about a third of the world’s population.
• Toxoplasmosis is the leading cause of death due to foodborne illness in the United States.
• T. gondii is found worldwide and can infect most warm-blooded animals.
• Cats are the definitive hosts, and the parasite replicates sexually in the feline small intestine.
• Vertical transmission is more common with primary infection during pregnancy or within 3 months prior to conception. Treatment of primary maternal infection can decrease fetal transmission rate by half from 50–60% to 25–30%.

Risk Factors

• Main risk factors for T. gondii infection are eating raw or rare meat, consuming local cured or smoked meat, working with meat, drinking unpasteurized goat milk, or having more than three kittens.
• Untreated or contaminated water is also a risk factor and has been responsible for outbreaks of toxoplasmosis.
• Immunocompromised individuals are at increased risk for toxoplasmosis, including reactivation of chronic disease.

General Prevention

Pregnant women should be counseled to avoid cat feces exposure including gardening, landscaping, and changing litter boxes and to avoid consuming undercooked meat.

Pathophysiology

• Cats shed oocysts in feces, which then sporulate and become infectious.
• Humans are infected by eating raw or undercooked meat infested with oocytes; accidental ingestion of contaminated soil, food, or water; contaminated blood transfusion or organ donation; or via transplacental transmission from mother to fetus.
• In the human host, tissue cysts are formed in skeletal muscle, myocardium, brain, and eyes.
• Tissue cysts persist for the life of the host.
• Reactivation can occur when the immune system is compromised particularly due to T-cell deficiency.

Commonly Associated Conditions

• Reactivation of disease may develop after either primary or congenital infection and most commonly presents as chorioretinitis.
• Patients with immune deficiency can develop brain abscesses, encephalitis, fever of unknown origin, or pneumonia.