Communicable Disease or Not

Photo by Dane County Humane Society

I often see animals with diseases and infections that sound scary. Owners ask if a cat diagnosed with feline AIDS is contagious to them or if a dog’s warts can infect their child. Here are the answers to those questions and more.

Feline Immunodeficiency Virus

Better known as FIV or feline AIDS, feline immunodeficiency virus is not communicable to people and is species specific. It’s a serious cat disease that’s most commonly spread by deep bite wounds, particularly when outdoor cats fight. But like HIV, it can also be spread sexually, from infected mother to baby, and through blood transfusions. Casual contact, like shared water and food bowls or cats snuggling, is unlikely to transmit the virus. FIV-positive cats don’t necessarily need to be isolated from other cats unless they fight with them. There’s currently no vaccine or treatment.


Rarely communicable to people, heartworms can infect both dogs and cats. They’re parasites transmitted by female mosquitoes taking a blood meal from your pet. It’s very serious, which is why you should keep your pet (even inside cats) on year-round heartworm prevention. Heartworms in humans most frequently cause asymptomatic lung disease, but can be found in the brain, eye, and testicle, though this is uncommon. According to the CDC, there were only 81 cases in people reported between 1941 and 2005.

Ear Mites

While very contagious between cats and dogs, they’re rarely communicable to people. These eight-legged, almost-microscopic mites feed on ear wax, are very itchy, and most frequently affect young kittens. In very rare instances, people have developed an itchy rash from them, but unless you’re putting them in your ears, it’s unlikely you’ll have issues. They’re easy to diagnose by seeing the mite in ear gunk (yes, that’s a scientific term) under a microscope, and treatment is very effective.

Sarcoptic Mange

Sometimes communicable to people, sarcoptic mange is caused by a different mite species than ear mites, and also causes an itchy rash on dogs, foxes, and coyotes. The mite is species specific, but humans can develop an itchy rash from close contact with an infected dog. It can be difficult to find mites, but oral flea and tick preventatives make treatment very easy.

Photograph provided by Dane County Humane Society

Demodectic Mange

Found in dogs or cats, but not communicable to people. Every mammalian species has its own Demodex mites that live in hair follicles. Most people are carriers of human Demodex mites, particularly in their eyelashes and other face- and neck-hair follicles. Unless you’re immune suppressed, they don’t cause problems. Demodex mites are rarely communicable between dogs, but are contagious between cats. Newer flea and tick preventatives have been found very effective in treating dogs and cats.


Communicable to humans, leptospirosis is a bacterial disease spread through the urine of infected animals. The bacteria gets into water or soil, and can survive for weeks or months. Infected dogs and humans often develop a fever, are lethargic, drink excessively, don’t want to eat, and become jaundiced. And while it’s easily treatable, it’s not easy to diagnose because the signs can be mistaken for other diseases. Without treatment, it can lead to kidney damage, liver failure, and even death. Yearly vaccinations offer the best protection, although there are at least 10 serovars (subtypes) of leptospirosis that infect dogs, and most vaccines only contain 4.


Not communicable to humans, the inflammation of the eye can cause redness and discharge. In dogs, this is generally due to pollen, smoke, or other irritants and allergens in the environment. In cats, it can be due to chlamydia, which is very rarely communicable to humans.


A fungal infection causing a lesion on the skin with a ring of crusts around the outside, ringworm is very contagious to people, although the spores can only infect skin that’s abraded or cut. Kittens are a common source of ringworm, but most children become infected from spores found in soil when playing outside. Athlete’s-foot cream usually clears up infections in people, and most kittens are treated with oral medication or an all-body dip. If your pet is diagnosed with ringworm, cleaning the house to remove spores is very important to prevent reinfection.


Common in cats, but not communicable to people. All mammals have their own herpes virus that can cause an infection, but they aren’t spread between species. Herpes in cats causes watery eyes, sneezing, and congestion. Herpes in humans causes cold sores. Herpes in adult dogs may only cause a mild upper respiratory infection, but if the dog is pregnant, it can cause an abortion, stillbirth, or death of a very young puppy.

Photograph provided by Dane County Humane Society


Not directly communicable to humans or other pets, the life cycle of a tapeworm requires an intermediate host to eat it (dog, cat, human, etc.) in order for the tapeworm to become infective. Most tapeworms in dogs and cats come from eating infected fleas, but another tapeworm species comes from eating undercooked meat (rodents, pork, beef, lamb, rabbits, etc.). If you see something that looks like flat rice or sesame seeds around your pet’s back end, collect and take some to your vet, who can often tell you where the pet picked up the parasite and provide treatment.


This is a serious disease in young dogs that causes diarrhea, vomiting, dehydration, and possibly death. All mammals can be infected by parvo, but each virus is species specific, so the dog parvo virus can’t infect humans. The human parvo virus causes fifth disease, mainly affecting young children, and leaves a rash on the cheeks. Vaccinating puppies is very important to protect dogs.

Kennel Cough

Inflammation of the trachea and bronchi in the lungs that leads to a hacking cough in dogs, kennel cough is caused by a number of different viruses and bacteria, none of which are contagious to humans but are very contagious to other dogs! If your dog has been exposed to other dogs and is then coughing, it may have kennel cough and shouldn’t be around other dogs until the coughing has stopped. Sometimes kennel cough is self-limiting and goes away on its own after a couple weeks, but it can progress to pneumonia and require antibiotics.


Communicable to humans through infective eggs in the soil, it takes 30 days for eggs to become infectious, so pick up your pet’s poop frequently! Most puppies and kittens are born with roundworms, so regular deworming and stool checks by your vet are important to treat them. Roundworms in puppies and kittens can cause vomiting, diarrhea, unthriftiness, or even an intestinal obstruction. In people, roundworm larvae will move through the body affecting various organs and, if they get in the eye, potentially causing blindness. Be sure you and your children wash your hands after playing outside or with pets.

There are many other scary-sounding diseases and infections that dogs, cats, and other animals can get. Please don’t wait to take a sick pet to the doctor—you should feel comfortable talking with your vet if you have questions or are concerned about a diagnosis.

Photograph by Brenda Eckhardt

Lori Scarlett, DVM, is the owner and veterinarian at Four Lakes Veterinary Clinic. For more information, visit .