Diseases From Animals: A Primer
A is for animals, Z is for zoonoses.
They come from giant Gambian rats and fuzzy bunnies. They come
from puppies and pythons. Whether the animal is friend or food or foe, it can
carry dangerous diseases.
There are at least 39 important diseases people catch directly
from animals. There are at least 48 important diseases people get from the bite
of bugs that bit an infected animal. And there are at least 42 important
diseases that people get by ingesting or handling food or water contaminated
with animal feces.
Some are as old as memory: rabies, bubonic plague, food poisoning.
Others have only recently emerged: monkeypox, West Nile encephalitis, Legionnaires' disease. And some, such as highly lethal
bird flu, we fear even though they haven't -- yet -- spread in humans.
People have lived with animals for eons. There's a reason for
that. They don't just make us feel better. They actually contribute to our
health. People who keep pets tend to have lower cholesterol levels and lower blood
pressure. They tend to get more exercise and to feel less lonely.
On the other hand, pets and other animals can get sick. And
some of these illnesses can be quite dangerous. This article offers an overview
of these diseases -- and how to avoid them.
Why Animal-Borne Diseases Matter
Diseases passed to humans from animals are called zoonoses.
What makes one of these diseases important? Two things, says zoonosis expert
Lawrence T. Glickman, VMD, DrPH, professor of veterinary epidemiology and
environmental health at Purdue University School of Veterinary Medicine, West
"If you ask Americans in general what is the most important
zoonosis, most would say rabies," Glickman tells WebMD. "It is
something they fear, it is in the news. But in terms of risk, there are only
zero to two human cases a year in the U.S. It's one of those zoonoses that are
important because of their seriousness, but not their frequency: rabies,
tularemia, plague, monkeypox, listeria, anthrax. These are diseases that are
very serious if one gets them but which are relatively uncommon."
On the flip side, Glickman notes, are animal-borne diseases
that are important because they are fairly common even if not often fatal.
Cat-scratch fever, for example, infects as many as 20,000 Americans a year. And
an estimated 4%-20% of U.S. kids get roundworm from dogs and cats.
"Even these diseases can be quite serious," Glickman
says. Here's a roundup of a few important 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."