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Toxoplasmosis…What You Need to Know

What is Toxoplasmosis?

Toxoplasmosis is a disease caused by Toxoplasma gondii, a microscopic intracellular parasite that is found in many species of animals, including humans. It's one of the most prolific parasites found in domestic cats worldwide. Although many different animals can carry toxoplasmosis, only cats are capable of transmitting it in their feces. Many cats (especially outdoor cats) and up to 1/3 to 1/2 of adult humans have antibodies for, or have been exposed to, the parasite.

How do cats and humans become infected?

Cats become infected by ingesting a form of the parasite that is contained in raw meat or tissues (by hunting or being fed raw meat). They then shed the oocysts, or eggs, in their feces a few days after ingestion. These oocysts can infect humans by direct ingestion and from mother to unborn child. Humans can also become exposed and infected through other means (see below).

Who should be concerned?

Toxoplasmosis infection poses a higher risk in pregnant women (and their unborn children) and immunodeficient individuals. Thankfully, the incidence of infection in infants has dropped over recent years. However, with the AIDS epidemic, the incidence of the disease in immunodeficient persons is still considerable. Although many people have been exposed, it's these groups that are susceptible to serious effects of Toxoplasma. These include fever, lethargy, blindness, mental retardation, seizures, coma, and even death. Many infants show no signs at birth but develop problems later in life. Although uncommon, cats can also suffer serious symptoms such as neurologic signs, decreased appetite, and weight loss. Treatment for all groups can be successful but depends on early diagnosis and the immunocompetence of the individual.

What other ways can humans be exposed to Toxoplasma?

Exposure to cats is not the only way that humans can be exposed to the parasite. In fact, it is not the most common way. In the U.S., ingestion of infected meat sources is the most common method people come in contact with the parasite. Although it is thought to be very rare, it is possible that some people are exposed through inhalation of dust contaminated with Toxoplasma oocysts.

The good news…how can infection be prevented?

Part of prevention in humans involves understanding how and when there is a high probability of exposure. As stated above, cats shed the oocysts in their feces. These oocysts do not become infectious until 1 to 2 days after they are shed. Because cats are fastidious groomers, it is unlikely that a person would be exposed from feces left on the hair coat of cats. Because cats do not act sick while shedding oocysts, it is important for all at-risk people to take preventative measures when in contact with cats. As long as these measures are taken, it is completely safe to have a cat at home and is generally not necessary to have it screened before an at-risk individual comes into contact with it. The fact that a cat has been exposed to the Toxoplasma does not mean that it is actively shedding oocytes.

Follow these steps to ensure adequate prevention of Toxoplasma exposure:

  • Always cook meat thoroughly (to medium-well or an internal temperature of 152 degrees F). Be sure to thoroughly wash hands, knives, cutting boards, and other tools used after cutting or handling uncooked meat.
  • Avoid drinking water from streams, etc. without boiling first. The infectious oocysts can remain viable in water after it has been contaminated with feces.
  • Wear gloves or wash hands thoroughly after gardening or working in soil. Even if there is no longer evidence of cat feces in or on the ground, the oocysts can remain there for some time.
  • Wash all homegrown vegetables well before consuming them.
  • Changing the cat litter daily will virtually eliminate exposure to the infectious form of the oocysts. Make sure to dispose of litter in a sealed container (zip-lock bag, etc.). Pregnant women and immunocompromised persons should have a family member or friend change the litter each day.
  • Do not allow cats to hunt birds or rodents. Don't feed cats raw meat scraps.

Although toxoplasmosis is a potentially serious disease for certain individuals, a few easy precautions can be taken to sharply decrease exposure and allow you to feel confident that you are doing everything you can to steer clear of this disease. Even though cats are notoriously associated with toxoplasmosis, pregnant women and other at-risk persons who prevent a possible exposure situation with their cat are in fact more likely to be exposed to the disease by other means. Therefore, there is no reason that cats and these individuals cannot share a safe and healthy environment.