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Toxoplasmosis: The Cat Disease Most Humans Don't Get from Cats

January 14, 2013 | 24,844 views
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By Dr. Becker

Toxoplasmosis is an infection caused by a parasite, Toxoplasma gondii or T. gondii, that lives inside cells.

Studies show that about 30 percent of U.S. cats and dogs have been exposed to the T. gondii parasite, as well as 25 to 50 percent of Americans. Animals and people living in rural areas are more likely to be exposed to toxoplasma. However, infection and clinical disease is actually quite rare.

Disease Transmission

Cats are the primary hosts for toxoplasma. The parasite completes its life cycle in a kitty’s gastrointestinal tract and winds up back in the environment in feces.

But cats are only one source of several avenues of infection. In fact, owning a cat is not a common way to acquire toxoplasmosis. In the U.S., the parasite is most often transmitted to humans through raw or undercooked meat, unwashed fruits and vegetables, and contaminated water or soil.

Animals become infected in one of three ways:

  • By eating contaminated meat
  • By ingesting contaminated feces or water
  • Through congenital infection across the placenta, meaning the babies pick up the infection from an infected mother in utero

Most cats are infected congenitally across the placenta or by nursing. Many of these kittens are stillborn or die shortly after birth. Those that do survive may have inflammation of the brain, liver, or lungs.

Toxoplasmosis infections in adult cats are rare. They are usually seen in kitties never exposed to T. gondii, those who sustain an overwhelming exposure to the parasite, or kitties who are immunosuppressed due to another infection or medication.

Symptoms of Toxoplasmosis

Toxoplasmosis can either be acute or chronic. The acute form usually comes with symptoms, but often the chronic form is a low-grade disease that is asymptomatic.

More cats than dogs show symptoms of infection. And although any dog can be infected by the parasite, it’s usually seen in young dogs with immature or compromised immune systems.

Symptoms of toxoplasmosis can include neurologic symptoms (including seizures, tremors, depression, lethargy, muscle weakness, loss of coordination, and paralysis), shortness of breath, fever, weight loss, loss of appetite, vomiting, diarrhea, jaundice (yellowing of the skin), inflammation of the tonsils, and inflammation of the retina, iris or cornea.

Diagnosis and Treatment

The best way to diagnose toxoplasmosis is to measure the existence of antibodies to the organism with the toxoplasma IgG and IgM antibody test.

Other diagnostic tests your vet may run include a complete blood count, a chemistry panel, urinalysis, fecal analysis, an eye exam, an ELISA test, chest X-rays, cerebrospinal fluid analysis, and analysis of chest or abdominal fluid.

Traditional treatments for toxoplasmosis include antibiotics, anticonvulsants (if there are seizures), supportive care of any organ systems that have been damaged, and for the debilitated patient, IV fluids.

I’ve actually seen only one case of toxoplasmosis in my veterinary career. It was in a dog who ate freshly hunted rabbit meat that had not been frozen before it was offered to the dog. The dog was brought to the emergency veterinary clinic with acute neurologic symptoms.

Fortunately, the diagnosis was made quickly, treatment was started and the dog recovered uneventfully. However, this does point out why I always recommend freezing fresh game before feeding the meat to a pet. Freezing meat for 24 hours kills toxoplasma.

The potential for toxoplasmosis is one reason vets recommend against feeding a raw food diet. However, it’s important to note that as long as the meat has been frozen for at least 24 hours, there’s absolutely no risk of toxoplasma infection.

Pregnancy, Cats and Toxoplasmosis

I’ve had a few pregnant cat owners asking me if they need to get rid of their kitties, because cats are the natural hosts of the T. gondii parasite. The only people who recommend giving up cats to avoid toxoplasmosis either don’t know what they’re talking about or haven’t kept up with the latest information on the subject.

During pregnancy, in-the-know obstetricians will simply recommend pregnant women avoid cleaning the litter box. If you have a dog and a cat, don’t allow the dog access to the litter box, as many dogs like to eat cat feces, potentially increasing the risk of transmission.

Other steps you can take to help reduce infection potential include:

  • Cover outdoor sandboxes when not in use to keep kitties from using them as litter boxes.
  • Wear gloves when gardening or doing yard work.
  • Wear disposable gloves to clean the litter box and also a face mask if you happen to be immunosuppressed.
  • Keep the litter box in pristine condition. The longer infected cat poop sits in the litter box, the higher the risk the eggs of the parasite will become infective.