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Toxoplasmosis

Toxoplasmosis is caused by an intracellular parasite called Toxoplasma gondii that can infect a variety of mammals and birds.  Wild and domestic cats are the definitive host, excreting infective eggs (oocysts) in their feces, which persist in the environment.  The oocysts become infective one to five days after exposure to oxygen and can survive extreme temperature and humidity conditions for up to 18 months.  Domestic animals most commonly infected include cats, sheep, goats and swine.  Dogs and horses are infrequently infected, and cattle are relatively resistant.  Wild game such as deer, rabbits and wild fowl can also be infected with toxoplasmosis.  Animals other than cats do not shed oocysts in their feces, but develop infective cysts in their muscles and other organs.

Sources of Toxoplasma gondii Infection in Humans

People typically become infected in one of three ways.  The most common source of infection is foodborne through eating undercooked, contaminated meat (especially pork, lamb and venison); accidental ingestion of undercooked, contaminated meat after handling it and not washing hands thoroughly (Toxoplasma cannot be absorbed through intact skin); eating food that was contaminated by knives, utensils, cutting boards or other foods that had contact with raw, contaminated meat; or eating unwashed fruits and vegetables from a garden where the soil has been contaminated with oocysts.  People can also become infected through accidental ingestion of oocysts when cleaning a cat litter box or working in soil (such as gardening) that has been contaminated with oocysts, or drinking contaminated water.  Toxoplasmosis can also pass from an infected mother to her fetus.

Human infections are usually asymptomatic in healthy individuals.  About twenty percent of persons develop mild flu-like symptoms (fever, malaise, swollen lymph nodes, rash and muscle aches) that may take months to resolve.  More severe infections are associated with immunocompromised individuals and manifest as inflammation of the heart, eye or brain that can be fatal.  Exposure during pregnancy can lead to severe congenital effects in the infant including mental retardation and loss of vision.  Abortions and stillbirths may be seen, particularly when infection occurs during the first trimester.


Animals associated with toxoplasmosis include:

  • Cats:  Cats can be infected with Toxoplasma parasites and shed the oocysts in their feces.  After maturing, the oocysts can then infect humans and other animals.
  • Livestock:  Goats, sheep and swine are among the domestic animals commonly infected with Toxoplasma parasites.  Cattle are relatively resistant to infection with Toxoplasma.  Infected livestock do not shed oocysts in their feces, but develop infective cysts in their muscles and other organs.

Steps to reduce your risk of toxoplasmosis:

  • Cook food to safe temperatures.  A food thermometer should be used to measure the internal temperature of cooked meat.  Do not sample meat until it is cooked.
    • For whole cuts of meat (excluding poultry): Cook to at least 145°F (63°C) as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest for three minutes once it reaches the final temperature before carving or consuming.
    • For ground meat (excluding poultry): Cook to at least 160°F (71°C); ground meats do not require a rest time.
    • For all poultry (whole cuts and ground): Cook to at least 165°F (74°C), and for whole poultry, allow the meat to rest for three minutes before carving or consuming.
  • Freeze meat for several days at sub-zero (0°F) temperatures before cooking to greatly reduce chance of infection.
  • Peel or wash fruits and vegetables thoroughly before eating.
  • Wash cutting boards, dishes, counters, utensils and hands with hot soapy water after contact with raw meat, poultry, seafood or unwashed fruits and vegetables.
  • Avoid drinking untreated drinking water.
  • Wear gloves when gardening and during any contact with soil or sand because it might be contaminated with cat feces that contain Toxoplasma.  Wash hands with soap and warm water after gardening or contact with soil or sand.
  • Teach children the importance of washing hands to prevent infection.
  • Keep outdoor sandboxes covered.
  • Feed cats only canned or dried commercial food or well-cooked table food, not raw or undercooked meats.
  • Change the litter box daily if you own a cat.  The Toxoplasma parasite does not become infectious until one to five days after it is shed in a cat's feces.

If you are pregnant or immunocompromised:

  • Avoid changing cat litter if possible.  If no one else can perform the task, wear disposable gloves and wash your hands with soap and warm water afterwards.
  • Keep cats indoors.
  • Do not adopt or handle stray cats, especially kittens.  Do not get a new cat while you are pregnant.

Toxoplasmosis resources:

 

Last updated:  01/23/2015

Zoonotic Disease Program