Foxes are among the urban wildlife in Denver that carry diseases capable of being passed to humans.
Foxes are among the urban wildlife in Denver that carry diseases capable of being passed to humans.

Denver Urban Wildlife Guide With Dr. Kevin Fitzgerald: Diseases and Dangers

Editor's note: Dr. Kevin Fitzgerald, a veterinarian at Alameda East Veterinary Hospital as well as a star of two past Animal Planet programs, Emergency Vets and E-Vet Interns, and a regular on the Denver standup comedy scene, recently told us about rattlesnake facts and myths. This is the second post in a new series about urban wildlife in Denver. Click to read our first offering, "Denver Urban Wildlife Guide With Dr. Kevin Fitzgerald: Meet Your Neighbors."

Dr. Kevin Fitzgerald doesn't want anyone to think he sees undomesticated critters who venture into city settings from only a negative perspective. As he told us in his introduction to Denver urban wildlife, "These animals enrich our lives."

However, he added, "we need to be vigilant, too, because urban wildlife can pass on diseases to pets — and to us."

Below, Fitzgerald explains zoonosis (the transfer of diseases from animals to humans) and the maladies that are most common among the wildlife that regularly ventures into Denver and other urban areas in Colorado — "mice and rats, pigeons, raccoons and squirrels, coyotes, bats, skunks, foxes, rabbits, prairie dogs, rattlesnakes, and I include deer."

Note that we've linked to Wikipedia pages for each of the diseases Fitzgerald mentions, so you can access additional information about them.

Why Animal-Human Disease Transfer Is Growing More Common

"There are about 150 known zoonotic diseases, but really only about thirty that we see with any frequency. Still, wildlife can serve as a reservoir for a variety of these diseases, which are emerging because of urbanization, climate change, deforestation, the alteration and destruction of the wildlife's natural habitat, land-use changes, human population growth, the increasing movement of people into cities and the increasing population of food animals.

"Where we used to have land for deer and other wildlife near cities, we now have cattle, and they're really destructive, eating down further than the wildlife can get. So having food animals in urban areas really changes things for wildlife."

Dr. Kevin Fitzgerald has lived a wild life.
Dr. Kevin Fitzgerald has lived a wild life.

Where Human Health Meets Animal Health

"How do you get these diseases? Direct contact with animal products, including contact with their urine or feces. It could be in the water you drink in a stream. Fecal to oral — that's probably the most common. Also bites and scratches. And many of these guys have active parasites like ticks and flees. We can also get diseases from undercooked meat or infected milk.

"In Colorado, fleas on prairie dogs carry the bacteria for plague, and we see that in areas where we kill too many rattlesnakes. The population of prairie dogs blooms and we see plague. And we also see it where we kill off other predators.

"We see hantavirus in field mice, and we can get it from ticks. There are different tick-borne diseases. We can also breathe in hantavirus in closed areas like a barn. And we also see tularemia, one of the rabbit diseases."

Bats and Diseases

"I go to a cigar place on Sixth and Washington, and right around sundown, people will say, 'Look at those weird birds and how they're flying." Well, those aren't birds. They're bats. On Sixth Avenue from east to west, we've got bats under the eaves of buildings. They use human habitations and they're all over the place. People come from all over the U.S. to study bats in Colorado.

"There are 45 species of bats in the United States and 1,000 species worldwide. And there are only 4,000 mammals altogether, so almost a quarter of mammals are bats. All bats are insectivores, and they're the only mammal that can fly.

"The primary zoonotic disease for bats is rabies. For some reason, bats can tolerate rabies longer than any species and not show the symptoms — not right away. The sign of rabies in bats is unusual behavior. They can have neurological symptoms, and there's one form of rabies where they become agitated. But if a bat's on the ground, they're sick — which is why you should never approach a bat on the ground.

"Bats can also carry salmonella, plague and external parasites — different mites that can give you cat-scratch disease — and histoplasmosis, which can be carried in bird or bat droppings, although it's more of a Midwestern thing because of the moisture. It's not humid enough here for it to be a big problem. Most of the cases are sub-clinical, where people get a little cough, but then they get better without treatment. But bats are also a reservoir for the SARS virus."

Here's an example of how not to handle a bat.
Here's an example of how not to handle a bat.

The Rabies Test

"Any mammal can get rabies, but we don't always see it in smaller animals, usually because they've been mauled and don't survive. Like last year — we had a positive test on a squirrel, which was very unusual, because usually they die right away from their injuries. But these diseases are still out there — still morphing and evolving — and we had positive tests on quite a few different types of animals.

"Last year, we had an alpaca test positive for rabies. We also had two horses, six bats, four raccoons, three cats, two foxes, the one squirrel and eight skunks. We get rabid skunks along the Aurora border every year.

"In humans infected with rabies, we see flu-like symptoms, and then symptoms of cerebral dysfunction, followed by respiratory failure and death. It's one of the few zoonotic diseases that's routinely fatal if it goes on too long. We've got good treatments if we get them early, but once the clinical signs are revealed, the disease is fatal."

Skunks and Diseases

"Skunks are a diverse carnivore that are found in North America, and we see them a lot when they come up from creeks or know there's a garbage can behind a restaurant.

"They can have rabies, canine distemper, tularemia, giardia, which can cause diarrhea, roundworms, ringworms and also leptospirosis, which is also called swamp fever and Weil's disease. It's a contamination of the water by infected animals. The agent is a bacteria, and there are high incidences of it in moist environments: rivers, creeks, marshes, streams, lakes. We see it in Colorado.

"Sub-clinical hosts of lepto when they're not sick are rats, raccoons, possums, reptiles, beavers, skunks, squirrels, foxes, humans, dogs, horses, cattle, sheep. After you've ingested it, you get vomiting and fever and diarrhea and red eyes and renal failure. But we've got a good vaccine for dogs.

"Nobody thinks about this, but skunks will attack people and domestic pets. They can be aggressive. They'll take a dog on. So you've got to make sure your dog is vaccinated for rabies and distemper, at least."

Raccoons about to figure out how to open a trash can.
Raccoons about to figure out how to open a trash can.

Raccoons and Diseases

"Raccoons are nocturnal, dexterous and intelligent — and when they're in an urban environment, they can learn. There was a study out of Iowa State University involving raccoons and three of the most typical types of garbage cans. They found that 30 percent of urban raccoons could open them, but 0 percent of rural raccoons were successful. So the urban raccoons learned to open garbage cans.

"They can carry lepto, rabies, canine distemper, infectious canine hepatitis, toxoplasmosis, giardia — and the big one we worry about is baylisascaris roundworm. If you ingest feces with them in it, the infected eggs from these guys will get into your intestines and migrate around and cause a lot of damage from their migration. They can even get into the eyes and the brain.

"They're like skunks when it comes to how aggressive they are. As a vet, you frequently see raccoons attack people or pets."

Foxes and Diseases

"The red fox is the most widespread carnivore on earth. They're found in habitats throughout almost the entire northern hemisphere. I was doing research in the Arctic Circle, and we found places where the red foxes were displacing the arctic fox. With global warming, they're going up further and further.

"Foxes can carry distemper, lepto, rabies, toxoplasmosis, sarcoptic mange, tularemia, giardia. And we definitely see bites to humans and domestic pets.

"There have been times where people thought they'd found evidence of ritualistic cat mutilations that were actually just the way foxes kill cats. People will think, 'These are copycat killers.' But no, no, no: It's the way a fox kills a cat. They can pull a cat off a porch, easy."

Coyotes and Diseases

"Coyotes are amazingly resilient and adaptive. They used to be found mainly in the southwestern U.S., but they're now in all 48 states in the continental U.S. Studies over the past five years have counted 2,000 coyotes in Chicago, 500,000 coyotes in California, 20,000 coyotes in New York state.

"They can carry canine distemper and rabies, parvovirus that dogs can get, tularemia, giardia, infectious canine hepatitis.

"With these guys, we definitely see attacks on people and domestic pets. We just had two of those at the hospital. And they used to only be nocturnal in the Boulder area, but now you see them in the day. You can see them other places in the daytime, too. I saw two of them running right down University. They live right in the city, and they're destructive and tough — and they'll kill foxes that they see as their competitors."

Rabbits in Colorado frequently carry tularemia.
Rabbits in Colorado frequently carry tularemia.

Rabbits and Diseases

"Rabbits can be found throughout North America, but we don't usually see ones with rabies; if they get mauled, they don't usually live. But they often have cheyletiella, a walking dandruff or mange mite, salmonella, E. coli and tularemia, which is also called deer-fly fever or Francisella disease, after the bacteria Francisella tularensis. It's a bacteria that a lot of animals are susceptible to — beaver, squirrels, moles, sheep and cats. And humans are really susceptible to it, too — especially people who eat rabbits and handle infected carcasses.

"When humans get it, they get a fever or pneumonia. Dogs and horses get a fever, too. We diagnose it with a drug test or biopsy and then we culture it. Antibiotic treatment is the mainstay, but most animals die before it starts. The prognosis for rabbit fever depends on how long it's been going before it's diagnosed.

"By the way, hares are different from rabbits — but they can get tularemia and a kind of pneumonic plague."

Squirrels and Diseases

"There are a lot of different kinds of squirrels: the eastern gray squirrel, the western gray squirrel, the fox squirrel. And what they can give you is lepto; tularemia; dermatophytes, which is a skin-loving fungus; plus rabies and plague, which is a big one for them, too.

"We don't want to scare people about these things. But we need to make them familiar with urban wildlife in their area and help them be well-versed in the diseases they can harbor so we can all stay safe."

Coming next: Things you can do to protect yourself and your pet from the risks associated with urban wildlife.

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