ildlife Matters

 

WILDLIFE DISEASES:

There are many diseases of wildlife, but I am only going to cover a few that are especially important to people. They are not strictly diseases of wildlife as domestic animals can become infected too; and both can infect people. Some of them can be deadly if not treated, but you really don’t want to get any of them.

RABIES

Rabies is probably known to nearly everyone as it is usually the first one mentioned in any discussion of wildlife diseases. Rabies has been known to be transmitted by animal bites for over 2,000 years. It can infect any mammal and occurs on every continent except Antarctica. Many countries do not have accurate information on rabies deaths, but it has been suggested that it could be 15,000 per year world-wide. Some authorities estimate it at 10,000 deaths per year just in India.

The primary species transmitting the disease varies greatly around the world. I found it interesting that in tropical areas various species of mongoose were the main vectors. In North America the main vectors are striped skunk, fox, raccoon, and bats. The disease is spread by contact with saliva of an infected animal. Usually this is a bite wound but can also be a scratch or existing open wound. Infection from inhalation of the virus is rare, but has been known to occur in bat caves.

An animal can only transmit the virus after the onset of clinical signs. Early signs include behavioral changes such as appearing anxious, aggressive, or more friendly than usual. As disease progresses, the animal may become extremely sensitive to light or sound, have seizures, or become very vicious. Final stage: paralysis of nerves to head and throat, extreme salivation, inability to swallow, respiratory failure, then death.

In the U.S. there is an average of 2 human cases and 400 to 500 domestic pet cases per year. As of 2016, only 14 people have survived rabies after showing symptoms. Minnesota had 32 confirmed positive cases of rabies in 2018: 27 bats, 3 skunks, 1 dog, and 1 cat. Bats made up the largest percentage of animals tested, but only 3 to 4% of those tested were positive for rabies. About 45% of skunks and 6% of cattle tested from 2003 to 2018 in Minnesota were positive for rabies. Vaccination of dogs and cats against rabies has saved many lives of both people and pets.

TULEREMIA

This bacterial disease was once commonly known as rabbit fever, but sometimes as deer fly fever. It is most often infects rabbits, hares, and rodents such as beaver, muskrat, squirrels, and prairie dogs. These species often suffer large die-offs during outbreaks. An infected beaver may result in most, or all, beavers for several miles downstream also dying. We have had tularemia outbreaks in this area so people should keep that in mind. Beaver and muskrat trappers are often advised to wear rubber gloves. It can also infect many other species, including humans, dogs, and cats (cats are especially susceptible). Normal cooking temperatures will kill the bacteria in the meat, but meat from animals that died of tularemia should not be eaten. Most people discard the entire rabbit or hare carcass if they find skin ulcers or boils on the animal.

The bacteria can be transmitted to people by bites of dog ticks (and a few other ticks not found here) and deer flies (which we have in abundance); also by bites from infected animals, skin contact with infected animals, drinking contaminated water (usually because an infected beaver or muskrat died in that water body), and a very serious infection by inhaling the bacteria in dust (such as when cutting brush or when a tractor or mower runs over an infected animal or carcass). The bacteria can survive in water, mud, and carcasses for weeks. Humans can also be infected by the saliva or claws of an infected pet dog or cat. At least one child became infected after being bitten by a pet hamster.

Typical signs of tularemia infection are skin ulcers, swollen or painful lymph glands, inflamed eyes, sore throat, mouth sores, diarrhea, and pneumonia. Treatment usually involves antibiotics for 10 to 21 days. Most people completely recover and become immune, but some become infected more than once. The bad news is that some infections may result in very serious complications such as meningitis, hepatitis, endocarditis, sepsis, or osteomyelitis. However, in U.S. less than 2% of tularemia infections are fatal.

HYDATID DISEASE

The adult stage of this parasite is a small (less than ¼ inch long) tapeworm in the small intestines of canids (including domestic dogs). The tape worm sheds eggs which are excreted with the feces.

When a suitable intermediate host ingests these eggs (by eating contaminated vegetation or berries, by drinking contaminated water, or from soil contaminated by feces), they hatch in the small intestine into a larval form which penetrates the intestinal wall, migrates to various places in the body and forms a thick-walled cyst. In the cyst, that larval form multiplies into numerous individuals of yet another larval form.

Intermediate hosts include humans, all ruminants (both wild and domestic), many rodents, one paper listed horses, and one paper listed hogs (but did not specify if hogs got the tapeworm or the cysts). Interestingly, none of the papers I’ve read mentioned bears. Canids (including dogs) become infected with the tapeworm by eating the cysts in the intermediate host which they killed or by scavenging vehicle kills or gut piles.

The cysts are most often found in the lungs and liver of the intermediate hosts, but sometimes in the heart, spleen, kidneys, eyes, muscles, bones, and the central nervous system (including the brain). The ones I have found in deer and moose lungs ranged in size from that of a pea to almost 2 inches in diameter. However, the cysts continue to grow for years and can become 8 to 12 inches in diameter according to a number of papers.

Numerous large cysts in the lungs of wildlife can make the animal more vulnerable to predation by reducing how far, or fast, it can run during pursuit. However, heavy infections and/or large cysts can be detrimental to the well-being of any animal (including people). Eventually they cause discomfort, pain, nausea, and vomiting; they can be life-threatening if not treated. Treatment may involve anti-infective drugs, PAIR technique (Puncture, Aspirate, Injection, Re-aspirate), or surgery. Severe untreated infections have a high mortality rate.

Humans usually become infected by ingesting the eggs after handling infected animals or their hides which have been contaminated by the feces. The hair of pet dogs can be contaminated with the eggs if the pet has become infected as a result of being permitted to run free and scavenge. The best way to prevent infection is something wives and mothers have been telling their husbands and children for decades — “Wash your hands before you eat”.