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50+: Live Better, Longer

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Diseases From Animals: A Primer

A is for animals, Z is for zoonoses.


Cats allowed to roam outdoors often pick up a parasite known as Toxoplasma gondii. Most of the time, the cat will fight off the infection before it becomes contagious. However, sometimes cats shed egg-like forms of the parasite in their feces. That's why pregnant women, small children, people with damaged immune systems, and people on cancer chemotherapy should avoid cleaning cat litter boxes.

Usually, a person who gets toxoplasmosis gets very few symptoms. But when a person does get the disease, it causes a flu-like illness and/or muscle aches and pains lasting for a month or even longer. "A very sizeable proportion of humans -- 30%-40% -- have been infected with toxoplasmosis, usually by eating undercooked meat," Glickman says. "Most people never had a symptom or had very mild disease. But in people [with weakened immune systems] it can be fatal. And the worst infections may be in pregnant women. The organism can go to the fetus and, if the baby doesn't die, cause lifetime illness."

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.

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