Toxoplasmosis is a widespread parasitic infection caused by the single-celled organism Toxoplasma gondii. This parasite can infect most warm-blooded animals, including humans, and typically causes no symptoms in individuals with healthy immune systems. Despite often being asymptomatic, it is a common infection globally, with significant implications for certain vulnerable populations.
Global and Regional Prevalence
Toxoplasmosis, caused by Toxoplasma gondii, is estimated to infect approximately one-third of the world’s population. The average global seroprevalence, indicating past or present infection, is about 25.7%, though this figure varies widely from 0.5% to 87.7% across different populations.
Prevalence is notably higher in certain regions. African countries report the highest average seroprevalence at 61.4%, followed by Oceania (38.5%), South America (31.2%), and Europe (29.6%). Regions like USA/Canada (17.5%) and Asia (16.4%) exhibit lower average rates. These differences often correlate with local climate, traditional dietary practices, and sanitation standards. Hot, humid climates and lower altitudes are associated with higher infection rates because the parasite survives better in these environments.
Main Sources of Infection
Humans primarily contract toxoplasmosis through several common routes, largely involving the accidental ingestion of the parasite. A frequent source is the consumption of raw or undercooked meat, such as pork, lamb, or venison, which can contain dormant tissue cysts. Thoroughly cooking meat to recommended temperatures effectively inactivates the parasite and reduces this risk.
Another mode of transmission involves contact with contaminated cat feces. Domestic and wild cats are the definitive hosts where Toxoplasma gondii reproduces, shedding microscopic oocysts in their feces. These oocysts become infective one to five days after being passed and and can persist in soil, water, and on unwashed produce for many months. Accidental ingestion can occur from activities like gardening, cleaning a cat’s litter box without proper hand hygiene, or consuming unwashed fruits and vegetables grown in contaminated soil.
Mother-to-child transmission, known as congenital toxoplasmosis, occurs when a newly infected pregnant individual passes the parasite through the placenta to their unborn child. Transmission can also happen through organ transplantation or blood transfusions, though these instances are rare.
Factors Influencing Risk
Certain individuals face a higher risk of acquiring toxoplasmosis or developing severe complications. Pregnant individuals are particularly vulnerable, as a new infection during pregnancy can lead to congenital toxoplasmosis in the fetus, potentially causing miscarriage, stillbirth, or severe health problems for the child. The risk of transmission to the baby generally increases with the gestational age at which the mother becomes infected.
Immunocompromised individuals, such as those with HIV/AIDS, cancer patients undergoing chemotherapy, or organ transplant recipients, are also at increased risk. For them, a new infection can cause severe disease, and a previously acquired latent infection can reactivate, leading to serious complications affecting the brain, eyes, or lungs, and potentially resulting in death.
People living in regions with high environmental parasite prevalence, often linked to local climate and food preparation habits, have an elevated chance of exposure. Individuals who frequently engage in activities that bring them into contact with soil or cat feces, such as gardeners or those cleaning cat litter boxes, are also at increased risk of ingesting the parasite. This includes children who play in outdoor sandboxes that may be contaminated with cat feces.