When people come down with a case of diarrhea, a cough and fever, or a general feeling of laziness, they often attribute it to stomach flu, a cold, or just some bug going around.
Unknown to them, their illness could very well be the result of contact with a pet animal.
Every year, up to 10% of all diseases that occur in humans can be attributed to their pets--the estimated 48 million dogs, 25 million cats and almost 200 million birds that inhabit households nationwide.
Most of the illnesses are mild, as in the case of intestinal upset from a bacteria called salmonella, and people grin and bear the several days of discomfort. But the number and expense of treating animal-originated illnesses, and the occasional severe cases that children and the elderly contract, could be substantially reduced, in the view of a UC San Diego Medical Center pediatrician and a specialist in the field of zoonoses--diseases naturally transmitted between animal and human.
"The key is good hygiene, in making frequent hand washing a habit after handling animals, especially for children," Dr. Philip Goscienski said. "Zoonoses are largely preventable diseases and there is no need to undertake drastic life style changes, such as removing your pets.
"But there is a tendency for (the animal relationship) to be overlooked and under-reported because we emphasize human-to-human causes instead."
Goscienski said that most doctors, let alone most pet owners, are unaware of the fact that almost 200 diseases can be transmitted from animal to human. "Most have low mortality and take several weeks to diagnose in a laboratory, so you just treat them symptomatically and the patient gets better," he said. "And few doctors ask about a pet in the environment when taking the history of an illness from a patient."
Zoonoses can cause serious problems in people whose immune systems have been weakened by other diseases. The main research historically has been done on illnesses that cause widespread death, such as rabies or plague. So little is known, for example, about how many cases of viral pneumonia ("walking pneumonia") or intestinal disease might be the result of pets kept by the elderly, many of whom have an animal for companionship.
The most common diseases result from contact with cats and dogs, which generally have more contact with their owners, unlike birds which usually remain caged.
Dogs most often transmit salmonella, a bacterial infection estimated to infect 20% of all canines, and a larval parasite known as visceral larva migrans. Cats harbor ringworm, cat-scratch disease and toxplasmosis, a parasite particularly threatening to unborn children.
All result from the fact that pets have what Goscienski calls atrocious habits.
"Pets do not use soap and they do not wash their fruits and vegetables. Their unclean environment can contaminate ours."
In the case of salmonella, Goscienski advises people to wash their hands after each handling of a dog. "Obviously that is hard to do for babies, and children do not have a good record of doing so even when reminded," Goscienski said, noting that dogs are playful and protective of children, thereby ensuring frequent contact.
"So dogs should be limited inside a home when susceptive people are around, such as infants and the elderly," Goscienski said. "Do not let infants and dogs share the same play areas, and while that sounds difficult, it is not impossible."
Because dogs usually do not show symptoms of the salmonella bacteria, many pet owners do not suspect that they may be at risk when a dog licks their hand or when they handle the pet's fecal matter.
The larval parasite visceral larva migrans occurs frequently in moist, warm soils where the parasite's eggs hatch after being deposited from an infected animal's fecal matter. Goscienski estimates that between 80% and 100% of all puppies harbor the parasite, and that the eggs can be found in between 10% and 20% of the nation's parks and playgrounds.
Symptoms in humans are a fever, cough and excessive tiredness--similar to those of numerous other diseases which makes it difficult to diagnose. Goscienski recommends that dogs be kept away from children's playgrounds, and that no puppies be allowed around small children until after the dogs are wormed.
Cat-scratch disease is often a concern because it can resemble a form of cancer in children. The illness occurs in cats less than 6 months old--"it's more properly called kitten-scratch disease," Goscienski said--and is transmitted to humans through either a bite or scratch. Researchers still have not identified the specific organism that causes the disease and do not know why the cat shows no symptoms.
But two or three weeks after infection, a person's wound will not have healed completely and will show a small scar or pimple. There will be swelling of the lymph glands. Because of the resemblance to more serious diseases, a physician will sometimes have to surgically remove the lymph glands to make certain they are not cancerous.
"That obviously can be expensive, in the thousands of dollars, and can also cause a lot of worry among the parents," Goscienski said.
The parasite toxoplasmosis can harm humans when a cat, perhaps infected from a mouse or other animal, passes the oval cyst stage through its feces and the cyst is picked up through direct handling or exposure to dust from the cat's litter box. In pregnant women, the cyst can be passed on to the unborn child and cause eye and brain damage. In adults the symptoms often resemble viral infections: cough, fever, body aches.
Toxoplasmosis is almost completely preventable, however, because the cyst takes up to 48 hours to become infectious after being passed by the cat. A litter box should be changed every day and dumped in a place where the material will not be accessible to other animals or be spread as dust.
"And pregnant women should not change litter boxes at all," Goscienski said.
Goscienski said that pet owners, in addition to proper hygiene for themselves, should consider the environment of their pets. A pet should be fed well-balanced meals and provided with a clean area. Pets should not be exposed to rural outdoor areas, where they could pick up a plague and other serious diseases from wild animals. All pets should be immunized against rabies and other diseases as soon as possible and should be examined by veterinarians whenever ill.
"Don't let your children handle sick animals at all," Goscienski said. "Always avoid face-to-face contact with pets. And don't dispose of animal waste in flower areas.
"Living with a pet is like living with a sloppy roommate. You have to adjust, but in most cases it's worth it."