Zoonotic Disease — From People to Pets to People

While you might quarantine a child with chicken pox to prevent her from infecting other children, you wouldn't expect her to pass that illness along to the family pet. That’s because when it comes to diseases, most stay firmly within one host species. But zoonotic diseases, which can be passed between people and animals, are different. They’re everywhere, and they demand attention. And in the summer months, when you head outside with your pets, you must be even more vigilant. Fortunately, a few simple facts can help you avoid zoonotic diseases and their scary effects throughout the year.

From A to Zoonotic

Everyone is vulnerable to zoonotic diseases, but for people with weakened immune systems, zoonotic diseases are particularly dangerous. A variety of things can compromise the human immune system, including cancer treatment, chronic diseases like diabetes and kidney disease, conditions like AIDS, or even age (the very old and very young are more at risk). And considering that more than 40 percent of immunosuppressed people are pet owners, knowledge about zoonotic disease transmission is vital.

They may sound exotic, but you’re probably already familiar with many zoonotic diseases. A classic we all know (and fear) is rabies, which is an ongoing problem worldwide and claims more than 50,000 human lives every year. Vaccines protect pets against rabies, but unvaccinated wildlife and pets are a conduit for transmitting rabies to people.

Zoonotic diseases also make up the vast majority of new public health challenges. Avian flu and anthrax are just two in an ever-increasing parade of animal-to-human diseases. In fact, the Centers for Disease Control categorizes more than 75 percent of newly identified infectious diseases as being zoonotic.

Zoonotic diseases also can damage the bond between a family and its pet. When people don’t understand zoonotic diseases and how they’re transmitted, cats and dogs often are held responsible for infections. In reality, very few zoonotic diseases are directly transmissible from your pet, and only a few of the many parasitic diseases seen in people come from cats and dogs. So people shouldn’t shun pets to avoid catching a zoonotic disease; however, controlling or eliminating common pet parasites that cause or carry zoonotic diseases is a good place to start.

How Are Zoonotic Diseases Transmitted?

Parasitic diseases are among the most frequently occurring zoonotic diseases in pets, and they’re the most likely to infect average suburban Americans. The most common intestinal parasite in dogs and cats, the roundworm (Toxocara spp.), can pose a threat to children. Infected dogs and cats shed Toxocara eggs in their feces. People can be infected by accidentally consuming the eggs. Kids playing in dirt or sand might ingest Toxocara eggs, so pay special attention to sandboxes and make sure they are covered when not in use. Once in the body, roundworms in the larval stage migrate through tissues and organs, including the eyes. Roundworms can cause injury, even blindness.

People also get infected with zoonotic diseases through skin contact with parasites. For example, a larval-stage hookworm (Ancylostoma spp.), a common intestinal parasite of cats and dogs, can bore through skin and cause an itchy rash. Cat Scratch disease organisms (Bartonella henselae) are found in flea feces, and when those feces get into the body through scratches, bites or wounds, the organism can cause full-blown illness, including fevers and swollen glands. (Kittens are most frequently associated with transmission of this disease, so effective flea control at an early age is essential.)

Another way zoonotic diseases are passed is when people are exposed to infectious agents by eating contaminated food or undercooked meat and thus accidentally ingesting materials like feces-contaminated dust, dirt or even water. It’s alarmingly easy to consume parasite eggs. The eggs are very tiny and can easily become airborne during any activity that exposes fecal material, such as digging in the soil. These airborne particles can land on the mouth or be present in dirt that gets rubbed across the face and then swallowed. No one willingly eats animal poop, but statistics show about 15 percent of Americans have been exposed to roundworms — meaning they accidentally ate parasite eggs.

Zoonotic diseases also can occur through “bug” bites, such as when a tick carrying the infectious agent that causes Lyme disease bites you or your dog. This method of transmission — tick as delivery service — is the hallmark of what’s called a vector-borne disease. You cannot get Lyme disease from pets; instead, pets can increase exposure to infected ticks by carrying “hitchhiker” ticks into the home. These ticks may introduce the Lyme disease organism to your family. Ticks and fleas carry many potentially harmful organisms, and when they bite, they’re often leaving more than just an unpleasant presence.

Decreasing the Fear Factor

Take these precautions during warm-weather activities and throughout the year to help keep your family safe from zoonotic diseases.

• Schedule annual or biannual veterinary visits for your pet, which should include fecal examinations.
• Keep your pet on year-round monthly parasite prevention, as recommended by your veterinarian.
• Keep pets indoors or supervised to discourage hunting, and do not feed pets raw or undercooked meats.
• Wash your hands frequently, especially after handling animals and working outdoors. Be sure your children wash their hands after playing outside.
• Wash wounds, even small cuts, promptly and thoroughly.
• Wear gloves when gardening.
• Clean cats’ litterboxes daily, wearing gloves, and always wash your hands immediately afterward.
• Cover children’s sandboxes.
• Avoid approaching, touching or handling stray animals.
• Protect against ticks by wearing long-sleeved shirts, long pants and hats. Check for ticks after hiking, playing or working in tick-infested environments. Also consider using repellants.

Pregnant? Don’t Be Spooked By Your Cat

Pregnant women are especially at risk for a zoonotic disease called toxoplasmosis, which is caused by a cat parasite, Toxoplasma gondii. This parasite can infect people if they accidentally consume either undercooked meat from infected animals or contaminated cat feces. If a pregnant woman is infected, there’s a risk to her unborn baby.

Pregnant women or those who may become pregnant should wear gloves when handling cat feces or avoid them entirely — what a great excuse to delegate that daily litterbox cleaning — and always wear gloves when gardening or working outdoors to avoid accidental exposure to cat feces. It’s also important for pregnant women to eat meat that is fully cooked and fruits and vegetables that are thoroughly washed. But unless your cat hunts and eats prey, it’s unlikely that its feces will harbor the parasite. And if a cat is exposed, it will usually only be potentially infectious to people for a short period of time. Pregnant women can safely own cats — they should simply take precautions.

Minimizing the Risk

Millions of Americans are infected with a zoonotic disease every year, and treating their illnesses costs billions of dollars. Infected and exposed people may require direct medical care or ongoing treatment for what can become a chronic illness, such as Lyme disease. There is an extreme variation in the prevalence and severity of zoonotic diseases. Some are relatively rare; others are more common. Some can be fatal, while others are simple, treatable skin infections.

Even in the face of these frightening facts, there are fairly simple ways to increase your odds of staving off zoonotic diseases. The best way is to use parasite control for your dogs and cats. All pets (even indoor cats) should be on year-round monthly parasite-control programs. When our pets are healthy, they don’t pose a health risk to us. Problems usually arise only when a pet’s care is disrupted or parasite-control regimens are ignored.

Veterinary wellness exams every six months to a year are imperative. Your veterinarian will examine your pet and discuss which parasite preventives are right for your pet. The doctor also may recommend additional treatments — such as deworming — based on your pet’s age, lifestyle and health status.

And remember simple prevention measures like daily disposal of pet feces and thorough hand washing. With a little knowledge and effort, you can reduce your family’s risk of and exposure to zoonotic diseases — and enjoy a long, healthy relationship with your pet.