Nine beavers were found dead over the last few weeks in Utah. Three were tested and found to be positive for a disease called tularemia (Rabbit Fever). “The bacteria that causes this infection is known to be in the environment in many parts of Utah; however, it is unusual to see this many animals die from it at once,” Division of Wildlife Resources Veterinarian Ginger Stout said.
Tularemia is a rare disease, although we consider its prevalence to be rare based on the small number of reported cases and possibly mistaking it for another disease that manifests similar symptoms. Companion pets should be tested for it if they exhibit symptoms of the disease based on the region they live in and lifestyle.
Tularemia – also known as rabbit fever or deer fly fever – is a naturally occurring bacterial disease.
The causative bacterium, Francisella tularensis, is hardy and the resultant disease can result in fatality if it is not caught early enough. In fact, the bacterium is one of the top six “bioweapons” and so human contraction must be reported to public health authorities. The unfortunate part is that by the time we catch an outbreak, companion pets may become very ill and die because their acquisition of the disease and/or deaths only have to be reported in some jurisdictions.
Survival
Tularemia bacteria can survive for long periods of time in moist environments such as:
- Water
- Soil
- Hay, straw, leaf litter
- Feces
- Decaying carcasses
Transmission
It only takes 10-50 organisms to cause the disease, which can be transmitted via:
- Ingestion of contaminated food or water
- Handling of carcasses
- Bites from flies, ticks, fleas and mosquitoes
- Breathing
Animals
Over 250 species including mammals, birds, reptiles, and fish have been affected by the disease.
However, there are two types of hosts: reservoir (harbor the organism) and incidental (Infected by exposure).
Reservoir hosts can die from tularemia but more often they can live indefinitely after contraction, which makes them particularly potent disease transmitters:
- Rabbits
- Hares
- Beavers
- Muskrats
- Field and water voles
- Squirrels
- Lemmings
- Mice
Incidental hosts include:
- Humans
- Dogs
- Cats
- Pigs
- Horses
- Sheep
- Birds
- Fish
- Amphibians
Interestingly, cattle appear resistant to the disease.
Location
Two clinically significant subspecies of Francisella tularensis have been identified:
- Francisella tularensis tularensis (Type A)
- Francisella tularensis holarctica (Type B)
- A separate species, Francisella novicida (Type C), can also induce tularemia.
Type A is found in North America, considered the most virulent of the three and has the highest mortality rate. Type B is found in the Northern Hemisphere.
With the exception of Hawaii, 49 states have had cases of rabbit fever and the same pertains to the Canadian provinces. Recently reported cases have been in:
- Arkansas
- Kansas
- Oklahoma
- New Mexico
- Nebraska
- Colorado
- South Dakota
- Utah
- Wyoming
Type A is mainly spread by cottontail and jackrabbits and the most commonly involved insect vectors are the wood tick, lone star tick, American dog tick and deer fly. Type B is linked to a water-associated amoeba, so it is found primarily in beavers, lemmings and muskrats. Ticks, flies, fleas and mosquitoes are considered important vectors among animals for Type B. Person-to-person or other incidental animal-to-person transmission is unknown at this time.
Honestly, these are broad generalizations of the bacterium’s subspecies and indicate only the incidence researchers have found epidemiologically. Researchers agree that we have barely scratched the surface of this complicated bacterium and the associated disease, tularemia. For instance, the federal Centers for Disease Control (CDC) has a very comprehensive section on tularemia, but does not broach the differences between Type A and Type B.
Even though tularemia is a Category A bioweapon that has to be reported to public health authorities, it is believed that tularemia is often misdiagnosed based on symptoms similar to other diseases or is not reported. As you will read below, medical and veterinary professionals may inadvertently treat for another disease with the right or wrong course of antibiotics based on misdiagnosis, but may actually be treating for tularemia without knowing it.
Clinical Presentation
What is most fascinating about tularemia, is how the point of entry oftentimes exhibits the first signs of infection. Then, the symptoms will vary depending on that point and if it is caught early.
Glandular – Acquired through a vector insect or from handling sick or dead animals. You might think it is the flu because the symptoms are swollen lymph glands, fever, headache and lethargy.
- Oculoglandular – Bacteria enters through the eye and causes swelling, redness and discharge. You might think it is conjunctivitis (pink eye).
- Oropharyngeal – Eating or drinking contaminated food or water that causes what we would consider regular cold symptoms such as sore throat, mouth ulcers, tonsillitis, enlarged lymph glands. You could also think it is stomach flu due to vomiting and diarrhea.
- Pneumonic – This is caused by breathing in bacteria-laden air and can also be secondary to other forms of tularemia if they are left untreated. Symptoms include cough, chest pain, and difficulty breathing. Septic shock may ensue.
- Typhoidal – This form is the most fatal. Researchers are not too certain how this form is acquired, but believe it is through ingestion since symptoms include enlarged spleen and liver.
- Ulceroglandular – A skin ulcer appears at the site where the bacteria entered the body usually from a vector insect bite or handling contaminated carcasses. Additionally, the symptoms listed for glandular are usually also present. In humans, this is the most commonly diagnosed form of tularemia. It makes sense since it has the most obvious sign: a skin ulcer. This makes me wonder if we are occasionally missing the other clinically presentable forms that so closely mimic other diseases.
Acquisition & Prevention
While the infectious ways of contracting tularemia seem endless and mortality is possible, please remember that tularemia is a rare disease that our lifestyle choices and location can make possible. Most commonly, humans develop the ulceroglandular form from ticks or handling contaminated primary host carcasses.
Dogs and cats could contract tularemia in any number of ways like ticks, but generally they contract the oropharyngeal form because they may eat, play with or lick a decaying, infected animal carcass.
If you hear about mysterious dog illnesses or deaths, unusual rabbit or other host die-off, or have a relatively high reported tularemia occurrence in your area, take your companion dog to your veterinarian for diagnosis as incubation periods can last from 1-10 days.
Our advice:
- If you see a dead rabbit, squirrel or other animal make sure that your dog and you avoid it.
- Even though we never hear about transmission from rabbit feces, it’s best to avoid that too.
- If you have a very large yard, start walking your dog on a leash instead. Walking will be great exercise for you and your companion dog!
- Keep your indoor cat indoors.
- If a dead animal must be moved, please contact the local animal control or public health authorities. They will tell you how they want you to handle it or may come and remove it themselves.
- Bring your own water and bowl for your dog and have him avoid drinking water from creeks, ponds, and communal bowls.
Diagnosis & Treatment
Diagnosis
- Routine blood and urine tests can point to a disease but do not provide definitive diagnosis.
- Tularemia antibodies can be detected with specific blood tests, but may not appear early in the disease.
- Bacterial cultures grown in specific laboratories will provide a definitive diagnosis. However, the growth period of time is a few days.
Treatment
If caught early enough, antibiotics are the standard protocol for treatment.
Additionally, please take extra precautionary measures such as:
- Isolating your pet from other unknown animals.
- Wearing disposable gloves and using a disposable bag when picking up feces. Fence off the area where your pet most commonly defecates.
- Wear mask, gown and gloves to prevent transmission in known exposure risk areas, even though incidental host transfer is considered low.
References
Foley, Janet E., DVM. “Overview of Tularemia.” Veterinary Manual. Merck, July 2020. https://www.merckvetmanual.com/generalized-conditions/tularemia/tularemia-in-animals.
DWR Confirms Beavers Killed by Disease; Urges Public to Report Any Dead Beavers, Utah Division of Wildlife Resources, 15 Apr. 2024, https://wildlife.utah.gov/news/utah-wildlife-news/1869-dwr-confirms-beavers-killed-by-tularemia-and-urges-public-to-report-any-dead-beavers.html.
Originally Posted: February 5, 2017
Updated: April 28, 2024