How common is toxoplasmosis?

How many people are infected?

The figure usually quoted is that roughly a third of the world’s population carries Toxoplasma gondii². It is a reasonable headline number, but it conceals an enormous range. Seroprevalence, the proportion of people with antibodies showing past infection, varies from under 10% in some countries to over 60% in others¹. Almost nobody lives in a place where the average applies.

One thing the number does mean is that infection is normal and usually harmless. If a third of humanity carried something dangerous, it would be obvious. The reason toxoplasmosis matters is not how common it is but the three specific situations in which it causes harm, covered on the overview page.

Why the numbers vary so much

Three things drive the differences, and none of them is the number of cats.

• How meat is prepared. Populations that traditionally eat raw or rare meat, or cured and salted products that have not been cooked or frozen, have higher rates. This is the single biggest factor, and it is why France historically reported high seroprevalence.
• Climate and soil. The oocysts shed by cats survive far longer in warm, humid soil than in cold or arid conditions, so hot wet regions tend to have more environmental contamination.
• Water and sanitation. Where drinking water is untreated, waterborne oocysts add a route of infection that is largely absent in countries with filtered municipal supplies.

Cat ownership itself is a surprisingly weak predictor, which people find counter-intuitive. The reasons are set out on the cats page, and the food and environmental routes on the meat, water and soil page.

Seroprevalence is falling in rich countries

In the United States and much of Western Europe the proportion of people carrying the parasite has declined over recent decades. The usual explanation is a combination of changes in how livestock are raised, with more indoor production and less exposure of animals to contaminated soil, together with freezing in the meat supply chain, which kills tissue cysts¹.

There is a sting in that good news. A population with fewer infected adults is a population with more seronegative women entering pregnancy without immunity, which is exactly the group at risk of a first infection while pregnant. Falling prevalence does not automatically mean fewer congenital cases, and it is one argument for the prenatal screening programmes that some countries run and others do not¹. What a first infection in pregnancy actually does is covered on the congenital toxoplasmosis page.

Does a high local rate mean you are in danger?

Not in the way people usually assume. Seroprevalence measures how many people have already been infected, which is mostly a statement about the past. For a healthy non-pregnant adult the practical significance of a first infection is small in any case: most people never notice it.

Where local figures do matter is in pregnancy and in immunosuppression, and there the relevant question is not the national average but your own antibody status, which a blood test answers directly. There is also a strain dimension that prevalence figures hide completely: the parasite genotypes circulating in South America differ from those in Europe and North America and cause more severe disease, so two regions with the same seroprevalence can carry different risks. That is explained on the strains page.

Sources

1. Pappas G, Roussos N, Falagas ME. Toxoplasmosis snapshots: global status of Toxoplasma gondii seroprevalence and implications for pregnancy and congenital toxoplasmosis. Int J Parasitol 2009;39:1385-94. PubMed · DOI
2. Montoya JG, Liesenfeld O. Toxoplasmosis. Lancet 2004;363:1965-76. PubMed · DOI
3. Centers for Disease Control and Prevention. Toxoplasmosis. Accessed 15 October 2026.