Yes, toxoplasmosis is a zoonotic disease, meaning it spreads from animals to humans. It is caused by the parasite Toxoplasma gondii, one of the most widespread zoonotic parasites on the planet. A recent global meta-analysis found that roughly 36.6% of pregnant women worldwide test positive for past exposure, which gives a sense of just how common this infection is in the general population.
Why Cats Are Central to the Parasite’s Lifecycle
Domestic cats and their wild relatives (lions, bobcats, and other felids) are the only animals where Toxoplasma gondii can complete its full reproductive cycle. When a cat eats an infected rodent or bird, the parasite multiplies in the cat’s intestines and produces millions of microscopic egg-like structures called oocysts, which are shed in the cat’s feces for one to three weeks.
Once those oocysts hit the environment, they become the engine of transmission. In damp soil, nearly half of oocysts remain detectable after 100 days. In drier conditions they decline faster, but can still persist for months. Birds, rodents, livestock, and wild game pick up the parasite by eating contaminated soil, water, or plants. The parasite then forms dormant cysts in their muscle and brain tissue, waiting to be eaten by another animal or by a human.
How Humans Get Infected
There are three main ways people pick up this parasite, all rooted in its animal origins:
- Undercooked or raw meat. Eating meat from an infected animal is one of the most common routes. Pork, lamb, venison, and other game are frequent sources. The parasite’s tissue cysts survive in undercooked meat.
- Environmental exposure to cat feces. Gardening in contaminated soil, accidentally ingesting oocysts after cleaning a litter box, or drinking untreated water can all lead to infection. Children playing in sandboxes that outdoor cats use are also at risk.
- Mother to baby during pregnancy. A woman who becomes newly infected during or just before pregnancy can pass the parasite to her unborn child through the placenta. This is called congenital toxoplasmosis.
Raw oysters, mussels, and clams can also carry the parasite when coastal waters are contaminated with oocyst-containing runoff. Unpasteurized goat’s milk is another documented source.
Symptoms in Healthy People vs. High-Risk Groups
Most people with healthy immune systems never realize they’ve been infected. When symptoms do appear, they tend to be mild: swollen lymph nodes, muscle aches, and fatigue that can last weeks to months before resolving on their own. The parasite doesn’t leave the body, though. It settles into an inactive state in tissue cysts, potentially for life, and can reactivate if the immune system later becomes weakened.
For people with suppressed immune systems, particularly those living with HIV, the picture is very different. A new infection or reactivation of an old one can cause fever, confusion, headaches, seizures, nausea, and poor coordination. Without treatment, the infection can be life-threatening.
Ocular toxoplasmosis is another significant form. The parasite can damage the retina, causing blurred or reduced vision, eye pain (especially in bright light), redness, and tearing. These eye problems can occur in otherwise healthy people and sometimes don’t appear until years after the initial infection.
Pregnancy and Congenital Transmission
The timing of infection during pregnancy dramatically affects both the likelihood of transmission and the severity of harm. Early in pregnancy, the placenta acts as a relatively effective barrier, allowing parasites through in fewer than 10% of cases. But fetal damage at this stage tends to be severe, potentially causing miscarriage, stillbirth, or serious neurological problems. Around 3% of all congenital cases result in miscarriage or stillbirth, most of them from first or second trimester infections.
As pregnancy progresses, the placenta becomes more permeable. By the third trimester, transmission rates reach 60 to 70%, and in the final weeks they can exceed 90%. The good news is that late-pregnancy infections usually cause milder disease in the baby, or none at all at birth. The catch is that many infants who appear healthy at delivery go on to develop vision loss, intellectual disability, or seizures later in childhood. The risk of early clinical signs is highest when a mother’s infection occurs between 24 and 30 weeks of gestation, at roughly 10%. Starting at 13 weeks, the chance of transmission increases by about 12% per week.
Diagnosis
Toxoplasmosis is typically diagnosed through a blood test that looks for antibodies your immune system produces in response to the parasite. Two types of antibodies matter most. IgM antibodies appear within the first few weeks of a new infection and can persist for months. IgG antibodies develop slightly later and usually remain detectable for life, marking a past infection. Doctors use the combination of these markers, sometimes along with an avidity test that measures how tightly antibodies bind to the parasite, to determine whether an infection is recent or old. This distinction is especially important in pregnant women, where a new infection carries far greater risk than one acquired years earlier.
Treatment for Active Infection
Healthy people with mild symptoms generally don’t need treatment. For those with severe or active disease, particularly people with weakened immune systems, treatment typically involves a combination of antiparasitic and antibiotic medications taken for at least six weeks. Some cases require longer courses if the infection is extensive or slow to respond. Treatment targets the actively multiplying parasite but cannot eliminate the dormant cysts that remain in tissue, which is why reactivation remains a lifelong possibility for immunocompromised individuals.
Practical Steps to Reduce Your Risk
Because toxoplasmosis reaches humans through predictable routes, prevention comes down to food safety, hygiene, and awareness of environmental exposure.
For meat, internal temperature is the key safeguard. Cook whole cuts of beef, pork, and lamb to at least 145°F (63°C) and let them rest for three minutes. Ground meat should reach 160°F (71°C), and all poultry needs to hit 165°F (74°C). Color and texture alone are not reliable indicators. Freezing meat at sub-zero temperatures (0°F or below) for several days before cooking also greatly reduces the parasite load, though it won’t reliably kill other pathogens.
Rinse fruits and vegetables under running water, even if you plan to peel them. Wash cutting boards, knives, and countertops with hot soapy water after preparing raw meat. Avoid raw or undercooked shellfish, and skip unpasteurized goat’s milk.
If you have a cat, the risk is manageable. Indoor cats that eat only commercial cat food are far less likely to carry the parasite than outdoor cats that hunt. Change the litter box daily, since oocysts need one to five days after being shed to become infectious. Pregnant women and immunocompromised individuals should have someone else handle litter duty when possible. Wear gloves when gardening or working with soil or sand, and wash your hands thoroughly afterward.