Toxoplasmosis: Causes and How It Spreads

Causes

The Toxoplasma gondii protozoan parasite causes toxoplasmosis.

Approximately 11 percent of the US population 6 years and older have had a Toxoplasma infection. In various places throughout the world, research shows that more than 60 percent of some populations have had Toxoplasma infection.

How it spreads

Areas with hot, humid climates and lower altitudes often have the highest rates of infection. This is because the parasite survives better in these types of environments.

Toxoplasmosis is not passed from person-to-person, except in instances of mother-to-child (congenital) transmission (mother passing an infection to her baby during pregnancy or at birth) and blood transfusion or organ transplantation.

Toxoplasmosis can spread in the following ways:

Foodborne transmission

Food can transmit the tissue form of the parasite to humans. People can become infected by:

• Eating contaminated undercooked meat (e.g., pork, lamb, venison) or shellfish (e.g., oysters, clams, or mussels)
• Accidentally consuming contaminated undercooked meat or shellfish after handling the foods and not washing your hands thoroughly (Intact skin does not absorb Toxoplasma)
• Eating food contaminated by knives, utensils, cutting boards, and other foods that were in contact with raw contaminated meat or shellfish
• Drinking water contaminated with Toxoplasma gondii
• Drinking unpasteurized goat's milk

Animal-to-human (zoonotic) transmission

Cats play an important role in the spread of toxoplasmosis. Cats can become infected by eating infected rodents, birds, or other small animals. The parasite is then passed in the cat's feces (poop) in a microscopic (very small and often not able to see with the naked eye) form.

• Kittens and cats can shed millions of parasites in their feces for as long as 3 weeks after infection.
• Mature cats previously infected with toxoplasmosis are less likely to shed Toxoplasma.
• Infected cats shed the parasite in their feces and can contaminate their litter box, or if the cat is outside, contaminate the soil or water.

People can accidentally consume the parasite through contact with cat feces that contain Toxoplasma through the following:

• Accidentally consuming the parasite after cleaning an infected cat's litter box, where the cat has shed Toxoplasma, and not washing your hands
• Consuming anything that has come into contact with cat feces containing Toxoplasma
• Accidentally consuming soil containing the parasite (e.g., not washing your hands after gardening or eating unwashed fruits or vegetables from a garden)
• Drinking water contaminated with Toxoplasma parasites

Mother-to-child (congenital) transmission

Women who are newly infected with Toxoplasma during or just before pregnancy can pass the infection to their unborn child. Although the mother may not have symptoms, the unborn child can have severe health issues.

Rare instances transmission

Organ transplant recipients can become infected when receiving an organ from a Toxoplasma-positive donor. Though rare, people can also become infected when receiving infected blood via transfusion. Laboratory workers who handle blood can also become infected through accidental contamination.