Jeroen Saeij

Toxoplasmosis

Meat, water, soil and shellfish: infection beyond cats

If you want to know where people actually catch this parasite, follow the food. Meat that was not cooked enough, and oocysts that reach us through water, soil and produce, account for nearly everything.

By Jeroen Saeij · Updated 17 September 2026

The short answer

There are two forms of the parasite that can infect you: cysts in the meat of infected animals, and oocysts shed by cats into soil and water. Cooking meat through, or freezing it for a few days, kills the cysts. Washing produce, avoiding untreated water and raw shellfish, and washing your hands after contact with soil deals with the oocysts. Curing, drying and smoking cannot be relied on.

Two routes into the body

Toxoplasma has two infectious stages that matter to people. Tissue cysts sit in the muscle of infected animals, so any meat can carry them. Oocysts are shed by cats and contaminate soil, water and anything that touches them12. The balance between the two differs from place to place. In six European cities, undercooked or cured meat explained 30 to 63 percent of infections in pregnant women and soil contact 6 to 17 percent3. In North America the balance tilts the other way: a test that distinguishes oocyst infections from meat infections found that 78 percent of mothers of congenitally infected babies had been infected by oocysts, and half of them could not name any risk they had taken4.

Meat

Which meats carry the parasite depends on how the animals live. Pork, lamb and game are the traditional culprits, and free-range animals, which spend time outdoors where cats have been, are more likely to be infected than animals raised indoors2. In the American study of recently infected adults, the foods that stood out were rare lamb, raw ground beef, and locally produced cured, dried or smoked meat5.

Two things reliably kill the cysts. Heat: in laboratory work on infected pork, cysts survived 52 °C for almost ten minutes but were destroyed within four minutes at 61 °C and above6. Public-health cooking temperatures build in a margin: 63 °C (145 °F) with a three-minute rest for whole cuts, 71 °C (160 °F) for ground meat, and 74 °C (165 °F) for poultry, checked with a thermometer7. Cold works too: cysts in pork were rendered non-infectious by freezing at about −12 °C, whereas at −4 °C they survived for weeks8. A household freezer at −18 °C (0 °F) for several days is the standard advice7.

What does not reliably work: curing, salting, drying and smoking. Commercially produced products are usually safe because of controlled processes and frozen ingredients, but home-made and artisanal products are a documented source of infection53. Neither microwaving nor searing the outside of a piece of meat guarantees that the center reached a safe temperature.

Water

Oocysts are among the hardiest things a parasite has ever produced. They shrug off the chlorine levels used in drinking water, and they survive for months in cool, damp conditions. Two large outbreaks show what that means. In Victoria, British Columbia, in 1995, at least a hundred people fell ill, nineteen of them with eye disease, and the source was a municipal system that used unfiltered surface water9. In Brazil, an outbreak was traced to a contaminated water supply, and the parasite was isolated from the water itself10. Filtration and boiling are what remove oocysts; chlorine alone does not.

My own lab recently identified part of what makes oocysts so tough: a cluster of genes for proteins that protect the parasite inside the oocyst against drying, freezing and salt11. It is an elegant piece of biology and a serious nuisance for water engineers.

Soil, produce and shellfish

Soil is where oocysts wait, and gardening without gloves, unwashed vegetables and children’s sandboxes are the ways they reach a mouth37. Rain washes them into rivers and coastal water, where filter-feeding shellfish concentrate them. Eating raw oysters, clams or mussels was a risk factor in the American study5, and the same run-off explains why sea otters along the California coast die of toxoplasmosis12. Unpasteurized goat’s milk is a further, less common route5.

In the kitchen and the garden

The whole of prevention fits on an index card7:

These habits protect against a good deal more than Toxoplasma. Most of them are the same ones that keep Salmonella, E. coli and Listeria out of your food.

Sources

  1. Centers for Disease Control and Prevention. About Toxoplasmosis. Accessed 17 September 2026.
  2. Jones JL, Dubey JP. Foodborne toxoplasmosis. Clin Infect Dis 2012;55:845-51. PubMed · DOI
  3. Cook AJ, Gilbert RE, Buffolano W et al. Sources of toxoplasma infection in pregnant women: European multicentre case-control study. European Research Network on Congenital Toxoplasmosis. BMJ 2000;321:142-7. PubMed · DOI
  4. Boyer K, Hill D, Mui E et al. Unrecognized ingestion of Toxoplasma gondii oocysts leads to congenital toxoplasmosis and causes epidemics in North America. Clin Infect Dis 2011;53:1081-9. PubMed · DOI
  5. Jones JL, Dargelas V, Roberts J et al. Risk factors for Toxoplasma gondii infection in the United States. Clin Infect Dis 2009;49:878-84. PubMed · DOI
  6. Dubey JP, Kotula AW, Sharar A et al. Effect of high temperature on infectivity of Toxoplasma gondii tissue cysts in pork. J Parasitol 1990;76:201-4. PubMed
  7. Centers for Disease Control and Prevention. Preventing Toxoplasmosis. Accessed 17 September 2026.
  8. Kotula AW, Dubey JP, Sharar AK et al. Effect of Freezing on Infectivity of Toxoplasma Gondii Tissue Cysts in Pork. J Food Prot 1991;54:687-690. PubMed · DOI
  9. Bowie WR, King AS, Werker DH et al. Outbreak of toxoplasmosis associated with municipal drinking water. The BC Toxoplasma Investigation Team. Lancet 1997;350:173-7. PubMed · DOI
  10. de Moura L, Bahia-Oliveira LM, Wada MY et al. Waterborne toxoplasmosis, Brazil, from field to gene. Emerg Infect Dis 2006;12:326-9. PubMed · DOI
  11. Arranz-Solís D, Warschkau D, Fabian BT et al. Late Embryogenesis Abundant Proteins Contribute to the Resistance of Toxoplasma gondii Oocysts against Environmental Stresses. mBio 2023;14:e0286822. PubMed · DOI
  12. Shapiro K, VanWormer E, Packham A et al. Type X strains of Toxoplasma gondii are virulent for southern sea otters (Enhydra lutris nereis) and present in felids from nearby watersheds. Proc Biol Sci 2019;286:20191334. PubMed · DOI