Pets and Germs

“Eeewh! Dog Germs!”

Lucy SCREAMED this, in the “Peanuts” comic strip, every time she got a sloppy, wet kiss from Snoopy. And it turns out, she was RIGHT! Pets and Germs: They’re a package.

Our pets are members of our families, and some of us treat them like our babies. We love that they love us to rub their bellies and scratch their ears. We love to murmur term of endearment as we hug them and cuddle them and sometimes kiss their dear little faces and let them lick our faces.

When people start kissing their dogs on the mouth, however, something lurches in my stomach. I’ve never been able to square that with seeing my dog drag some nasty black piece of dead thing with hair on it out of the bushes and chew it until I take it away, at which point he starts gobbling horse poop off of the trail.

“Dog saliva is cleaner than human saliva,” some dog owners proclaim. “It’s antiseptic, and when they lick their wounds it kills the germs.”

“That’s such a crock,” says Dr. Kenneth Harkin, Kansas State University veterinarian and infectious disease specialist, who also uses terms like “hooey” “wives tales.”

“With all the different bacteria that have been cultured from dog saliva, I would not let a dog lick a wound,” he says. “That’s just disgusting.”

“They lick their butts,” says Golden, Colorado, veterinarian Dr. Donna Valori, “and they lick their wounds, and you see some of the worst infections in dogs that continue to clean themselves. As a rule, I tell people to keep their infants away from dog mouths.”

Eggs of the worm Echinococcus Granulosis, for example, transferred by licking from an infected dog’s hind end and by more licking to an adoring master, have the potential to take root in the human liver or brain or intestines and form potentially fatal cysts, fluid-filled sacks often the size of golf balls (they’ve been seen as large as basketballs) that can rupture and release the seeds of thousands of new worms.

Dogs aren’t alone, of course. Cats,  birds, fish, amphibians, reptiles and rodent pets – medical science can trace the danger of some hideous disease to virtually  every non-human life form that we take into our homes to hold and cherish. These are among the zoonotic diseases, human diseases that originate in animals.


In defense of our pets, certainly, medical studies have also shown countless ways in which pets are a benefit to our health and happiness — and ways in which we can be dangers to our pets. Most of those dangers come from insufficient care. Some come from the environment we provide, such as the increased incidence of bladder cancer in Scottish Terriers identified as a result of exposure to herbicides used in lawn and garden. In some rare cases, we can even pass our illnesses on to them.

“For the longest time we thought bacterial and virus problems couldn’t be spread from people to dogs,” says Dr. Valori. “Dogs are often blamed for giving kids strep throat, but it’s often the other way around. We do find from throat cultures in families that keep getting Streptococcal infections of the throat, many times if the kids have it, the dogs have it.”

Ferrets are believed to catch flu from humans, and there have been large outbreaks of human flu in which dogs and cats have blood-tested positive for the virus as well. It’s not clear that even such dogs and cats with the flu virus in them actually “catch” the flu, however. With very few exceptions, disease seems to flow exclusively from pets to people and not in the other direction. Because pets, of course, are filthy.

When we take Goofy, our big loveable, bison-skullled oaf of a Yellow Labrador, for a hot-day walk on the mountain, it’s Goofy and not us that leaps into the irrigation ditches and slurps up the water. The vet has identified that activity as the probable cause when Goofy has come down with the waterborne disease Giardia, which is also identified as one of the most common diseases that people get from their pets. That throws light, perhaps, on the mystery of past bouts of “stomach flu” in our family.

The florid, itchy fungal infection known as Ringworm is another common pet affliction that people catch by contact with dogs and cats, especially kittens and puppies. As is Sarcoptic Mange, also known as “scabies,” an unpleasant itching condition caused by infestation with the Sarcoptes scabei mite.

Many of these diseases are an annoyance, but some can cause serious problems or loss of life, especially in the weaker immune systems of people with AIDS and other “immuno-compromised” diseases, in the elderly and in children.

“It’s not uncommon with parasites that dogs might have in their stools that children, especially playing in the dirt or petting the dog and not washing, can get the eggs of parasites on their hands and then from their hands to their mouths,” says Dr. Radford Davis, veterinarian and associate professor, Vet Microbiology & Preventive Medicine, at Iowa State University’s College of Veterinary Medicine. “It’s pretty common to get parasites from dogs around the world. Some can be life threatening, especially in children.”

One of these is the gastrointestinal worm Toxocara, which can be picked up not just from ground fouled by dog droppings but also simply by stroking the fur of an infected dog. Most of the time it is not life threatening; just a debilitating influence that makes people sick. Most infections are asymptomatic in adults. Children have a higher risk of clinical signs, such as blindness. But it can cause organ damage or death in the immuno-susceptible. Most common is the danger of it causing blindness, especially when contracted at a very young age.

“Go to any park, and you can probably find this parasite in 25 percent on average of the fecal samples,” says Dr. Davis. “Some areas have a higher prevalence.”

Young children are more likely to pick up Toxicara and other parasites, as they often share with pets that tendency to sample the world through their mouths. As one still shuddered by primal childhood memories of sampling those little Tootsie Rolls that magically appeared in my backyard sandbox, for example, I may be among the 60 million Americans estimated to carry the Toxoplasma parasite. Toxoplasmosis is one of the zoonotic diseases of most concern, and the completion of the parasite’s life cycle is known to take place in only one animal on the planet: the cat. When kitty goes potty in the yard, the eggs can remain a threat in the soil for a year or longer.

“Somebody who gardens a lot can pick up this parasite without owning a cat,” says Dr. Davis. “In fact, most people get it from handling soil, even when cats are not around. There have also been outbreaks associated with produce, which demonstrates that soil contaminated with cat feces can be a source of infection for people, even if they are vegetarians. The biggest concern is with pregnant women because, early on, in the first trimester, it can cause birth defects in the child.”

If someone is planning to become pregnant, a blood test is a good idea, says Dr. Davis. If she tests positive for Toxoplasma, then there is no problem because the mother will already have the antibodies to keep it in check. If she tests negative, then she is at risk. “When my wife was pregnant with our first child, she was tested and was negative, which meant I got to clean the litter box for the next nine months,” Dr. Davis says.

Nearly every pet is a possible threat. There’s “cat-scratch disease,” a Bartonella henselae bacteria infection from bites or scratches by cats, especially kittens, which usually causes only symptoms like swollen lymph nodes and fever. There’s the diarrheal disease Cryptosporidiosis, through the Cryptosporidium parasite that lives in the bowels of animals and humans. And there’s Leptospirosis, which can be contracted from dogs and result in symptoms like flu and. in extreme cases, kidney or liver failure or meningitis.

And then there’s Giardia. Dogs can get it from lapping up standing water that has been contaminated with infected urine or sometimes from direct contact with a carrier animal, according to Dr. Harkin, whose research emphasis is on Leptospirosis. “Those dogs will have in increase in urination and maybe urinate in the house,” he says. “The owner cleans that up and in the processes can get infected, maybe not washing hands afterward and rubbing eyes or putting the hand in the mouth. The organism passes through mucus membranes.”

Pet birds can convey diseases like Psittacosis, which in most humans would cause only flu like signs with pneumonia but in severe cases could cause respiratory failure or, in pregnant women, fetal death.

Not uncommon among pet fish is Mycobacterium Marinum, which would ordinarily cause no more than lesions on the hands of forearms of people reaching into fish tanks but could be serious for the immuno-compromised ill or elderly.

Many such diseases are relatively low in reported incidence, but some, like Salmonellosis, the illness caused by Salmonella bacteria, are a serious danger and the reason why pet shops no longer have those tanks of cute little turtles. Some shops do sell turtles under four inches, but it is illegal. “If you have kids under five years old, you should not have reptiles or amphibians in the home,” says Davis. “Kids die every year from this. When I was in practice in Arizona, two kids came down with Salmonella and died, and they genetically matched the Salmonella in the kids back to the reptile in the home. Day care centers  should not have reptiles or amphibians; it’s a tragedy and a lawsuit waiting to happen.”

“Rabbits are pretty safe,” he adds. “If you were going to recommend a pet for an elementary school, that would be it.” Most pets are pretty safe, in fact, and catching zoonotic diseases is a low-risk event, but not an event that its victims are likely to celebrate. The likelihood of becoming a victim can be minimzed if people would just be careful, washing hands after contact, keeping small children away from places where animals eliminate, and taking care of the pets as well.

“Most or all of the heartworm preventatives today also do a good job of controlling other worms in dogs, roundworms and hookworms,” says Dr. Harkin.  It’s very important to have a dog on a monthly preventative.” The key to preventing the passage of diseases from pets to their owners, he says, is a combination of regular visits to the vet for the animal and practicing good hygiene by the human.

And a list of good hygienic practices would probably not rank the mouth-kissing of precious doggie anywhere near the top.


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