Toxoplasmosis

Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, an apicomplexan protozoan parasite. The organism exhibits a complex lifecycle in which sexual reproduction occurs exclusively within members of the cat family, while asexual replication can proceed in virtually any warm-blooded vertebrate host. Following initial infection, the parasite can establish chronic latent infection characterized by tissue cyst formation containing bradyzoite stages, primarily in muscular and neural tissues.

Acute infection in healthy adults is frequently asymptomatic, though when symptoms appear they typically manifest as a mild, influenza-like illness lasting weeks to months, characterized by muscle aches, tender lymphadenopathy, headache, fever, and fatigue. Ocular involvement may occur in a subset of patients, manifesting as chorioretinitis with potential vision impairment. In immunocompromised individuals, particularly those with advanced HIV/AIDS or transplant recipients, reactivation or severe primary infection can produce life-threatening encephalitis, seizures, poor coordination, and pulmonary disease resembling tuberculosis or Pneumocystis jirovecii pneumonia. Congenital transmission during maternal infection may result in fetal death, neurological impairment, chorioretinitis, or hydrocephalus in the offspring.

Toxoplasma gondii demonstrates an exceptionally broad host range, infecting most species of warm-blooded animals worldwide. Felids serve as the definitive hosts and primary environmental reservoir, shedding oocysts in feces that can contaminate soil, water, and vegetation. Human seroprevalence varies considerably by geographic region, dietary practices, and sanitation standards, with estimates ranging from under 20% to over 80% in different populations. The global burden of disease attributable to toxoplasmosis remains incompletely quantified due to challenges in surveillance and the often-subclinical nature of infection, though emerging evidence links chronic infection to various neuropsychiatric conditions.

Human infection occurs primarily through consumption of food or water contaminated with tissue cysts from undercooked meat, particularly pork, lamb, or venison, or with environmentally resistant oocysts from cat feces. Vertical transmission from mother to fetus represents a significant route during acute maternal infection. Rare transmission has been documented through blood transfusion, solid organ transplantation, and laboratory exposure. While the parasite is not considered directly contagious between humans under normal circumstances, scientific debate continues regarding the potential for sexual transmission based on detection of T. gondii in human semen.

Immunocompromised individuals, including persons with AIDS, organ transplant recipients, and patients receiving immunosuppressive therapies, face elevated risk of severe or life-threatening disease from reactivation of latent infection or primary acquisition. Pregnant women who acquire primary infection during gestation risk transmitting the parasite to the fetus, with severity of outcomes inversely related to gestational age at time of infection. Infants born to mothers with acute toxoplasmosis during pregnancy represent a high-risk group requiring clinical evaluation and potential therapeutic intervention.

Public health measures emphasize food safety practices, including thorough cooking of meat to internal temperatures sufficient to destroy tissue cysts and thorough washing of fruits and vegetables potentially contaminated with soil or water. Pregnant women and immunocompromised individuals should avoid handling cat litter or gardening without protective gloves, and should delegate litter box cleaning when possible. Serological screening of pregnant women in some healthcare systems enables early detection and potential intervention to reduce congenital transmission risk.

Surveillance for toxoplasmosis presents methodological challenges given the predominantly asymptomatic nature of infection in healthy populations and the reliance on serological testing for case identification. Laboratory-based reporting captures only a fraction of true infections, while congenital cases may be underdiagnosed without systematic prenatal screening protocols. Population-based seroprevalence studies provide the most reliable epidemiologic data for assessing regional burden and temporal trends. Enhanced surveillance in immunocompromised populations, particularly those with advanced HIV/AIDS, remains important for detecting reactivation disease and guiding clinical management.

1. 1 Wikidata. toxoplasmosis.
2. 2 Wikipedia. Toxoplasmosis - Wikipedia.

ICD-10

B58

ICD-11

1F54

Total cases

0

Peak month

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Coverage

0 reporting countries · —