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Diseases From Animals: A Primer

A is for animals, Z is for zoonoses.

Diseases From Cats and Dogs

By far they're our best friends. And that means cats and dogs are common sources of disease.

Cats often carry a germ called Bartonella henselae. Some 40% of cats are infected at least once in their lives -- usually when they're kittens -- but they don't look sick. Humans get infected only when they are bitten or scratched by an infected animal -- cat-scratch fever

Other bacterial infections humans can get from cats and dogs include:

  • Plague. Rodents carry the plague bacteria. Very rarely, cats get fleas from infected rodents and pass the disease to humans.

  • Q fever. People are much more likely to get Q fever from barnyard animals than from cats. But it does happen. Half of infected people get symptoms that include fever, headache, chest or stomach pain, diarrhea, and/or vomiting. It can also cause temporary swelling of the heart -- a dangerous event for people who already have heart disease.

  • Campylobacter infection. Found in animal feces, this germ causes gastrointestinal symptoms. It's usually not dangerous, but can cause severe illness in people with weakened immune systems.

  • Leptospira infection. Humans get infected via contact with water, food, or soil containing urine from infected animals. Left untreated, leptospirosis can be quite serious. It can lead to liver failure, trouble breathing, kidney damage, brain and spinal cord infection, and, rarely, death. Symptoms vary widely but can include high fever, severe headache, chills, muscle aches, and vomiting. There may also be yellow skin and eyes, red eyes, abdominal pain, diarrhea, or a rash.

  • Salmonella infection. People get this often-severe gastrointestinal infection via contact with animal feces. It can cause severe kidney damage to young children.

Both cats and dogs sometimes get parasites that infect humans. One of the most common is roundworm. Left untreated, nearly all puppies and kittens pick up this parasite. Its egg-like form -- the oocyst -- can survive for years in soil.

When humans ingest oocysts, tiny worms hatch in the gut and move through the body. Symptoms include fever, coughing, asthma, and/or pneumonia. Once in a while, the tiny worms enter the eye and scar the retina. This results in permanent partial vision loss. "Some 750 to 1,500 kids go blind each year with roundworm infection [of the eyes] passed from dogs through feces to children, " Glickman says.

Other parasites of cats and dogs:

  • Toxoplasmosis. See above.
  • Tapeworm. A person gets infected by swallowing an infected flea -- a relatively rare event, but it happens.
  • Hookworm. Hookworms are common in tropical and subtropical areas. They infest soil contaminated by animal feces. Humans get infected by direct contact, usually by walking on contaminated soil. Heavy infections can be serious.
  • Cryptosporidiosis. This parasite cause mild to severe intestinal symptoms like diarrhea. It's not usually a dangerous infection, except to people with weakened immune systems.

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