Voss: Zoonotic diseases, part 1

Before I decided to become a veterinarian, I spent years researching careers in infectious disease, particularly zoonotic diseases, or infections that can pass between animals and people. I eventually pursued a master’s degree focused on infectious and zoonotic diseases before deciding that I wanted to practice veterinary medicine. But my fascination with the intersection of human and animal health never went away.

More than half of the infectious diseases that affect people are considered zoonotic, which is a remarkable statistic when you stop to think about it. Some infections spread through direct contact, others indirectly through contaminated environments, food or water. Others rely on vectors such as mosquitos, fleas and ticks.

That overlap between veterinary and human medicine is why I frequently hear the same questions in the exam room: “Am I going to catch this from Fido?” or “Should I keep him away from the kids until he’s better?”

The answer is sometimes yes, but with a few important caveats. There are several zoonotic diseases we encounter in dogs and cats, and understanding them can help keep everyone safe, both two-legged and four-legged. Because infectious disease risk varies considerably by geography, we’ll focus on some of the infections pet owners in the Roaring Fork Valley should know about.

We’ll start with some of the most common gastrointestinal parasites: roundworms, hookworms and Giardia. These are frequent findings in veterinary hospitals and depending on the organism involved, can also infect people.

For most people, infection results in gastrointestinal upset such as diarrhea, abdominal cramping or vomiting. More rarely, however, roundworms can cause a serious condition called visceral larva migrans. In this situation, immature parasites leave the gastrointestinal tract and migrate through the body. They can travel to organs and trigger significant inflammation. In some cases, they can also migrate to the eye, a condition known as ocular larva migrans, which can cause permanent vision loss. 

Hookworms have their own unpleasant little trick. When exposed, humans can develop a condition called cutaneous larva migrans after contact with contaminated soil or sand. The microscopic larvae can penetrate exposed skin, particularly bare feet, and migrate just beneath the surface. The result is an intensely itchy, winding red track that follows the parasite’s path.

Fortunately, prevention of all of these is straightforward and common sense. Wash your hands after handling pet waste, especially before eating or preparing food. Pick up after your dog, even when on a hiking trail or other outdoor area to help keep the community clean. Regular fecal testing and following your veterinarian’s recommendations for parasite prevention and deworming can also reduce the number of parasites your pet is carrying and shedding in the environment. 

Another common question I get in the clinic involves bacterial skin infections, or pyoderma. Dogs and humans have different communities of bacteria living on their skin. One of the most common causes of canine pyoderma is Staphylococcus pseudintermedius, a bacterium that normally lives on dogs but is not a typical resident of healthy human skin. Although transmission to people can occur, human infection is uncommon. S. pseudintermidius is considered an opportunistic pathogen, meaning it is more likely to cause trouble when a person has an increased susceptibility to infection or when the normal skin barrier has been broken. That risk can be particularly relevant with bites, scratches, open wounds or surgical incisions.

A related concern is MRSP, or methicillin-resistant Staphylococcus pseudintermedius. As the name suggests, this bacterium is resistant to many commonly used antibiotics, making infections more challenging to treat. Fortunately, the risk of transmission to humans is no different than with other skin infections, but if transmitted to humans can be similarly difficult to treat. 

If your dog has an infected wound, rash or skin lesion, you don’t need to quarantine him from the family or entirely stop giving him affection. Instead, use some common sense. Avoid allowing him to lick open wounds, keep direct contact with infected lesions to a minimum and wash your hands after handling infected areas. These precautions are particularly important for people who are immunocompromised. This will also help your pet heal as well, because additional contact with the lesions can introduce your skin’s bacteria into the lesion which could potentially complicate or prolong healing.

Most importantly, follow your veterinarian’s treatment plan and give antibiotics exactly as prescribed. Stopping antibiotics early or inconsistent dosing can contribute to treatment failure or antibiotic resistance.  

What about ear infections? Fortunately, the answer is similar to most skin infections, as the flora inside dog and cat ears is largely the same as the remainder of their skin. Most canine and feline ear infections are caused by bacteria or yeast that are not a significant threat to humans. So, while I wouldn’t recommend using your finger as a Q-tip for your dog, the likelihood of catching your pet’s ear infection is extremely low. 

Good hygiene, appropriate veterinary care and a little common sense go a long way toward protecting both pets and people. There are plenty of other interesting zoonotic diseases worth knowing about, so next week we’ll get into those! 

Dr. Kelly Voss is a veterinarian at Aspen Animal Hospital, where she practices small animal medicine and surgery. She has a background in emergency and critical care and is passionate about bringing high-quality veterinary care to the mountains. Have a question for the column? Email her at dr.kellyvoss@gmail.com.