What is tularemia?
Also known as rabbit fever or deer fly fever, tularemia is a rare infection caused by Francisella tularensis bacteria found in the Northern Hemisphere. It is of particular importance because it is a zoonotic disease, which means it can be it can spread to people. It also has the potential to be used as a biological weapon.
The bacteria can survive for long periods in the environment, particularly in warm, moist conditions. It is an intracellular bacteria, predominantly living within the macrophages (a type of white blood cell).
How is tularemia transmitted?
Tularemia can infect more than 100 species of mammal and is widespread through the rabbit, hare, and rodent population. Infection can also occur in birds, amphibians, fish, and reptiles. Cats (and humans) can pick up the disease in the following ways:
- Oral transmission: Eating infected animals, usually rabbits or rodents or drinking contaminated water
- Aerosol: Inhaling the bacteria in contaminated soil or via infected animals
- Vector-borne: Tick, biting-fly, flea or mosquito bite, intermediate hosts feed on an infected animal, during which time they ingest the bacteria, the next time the insect feeds, the bacteria enter the new host
The bacteria can survive for weeks or months in the environment. In the United States, the most common tick vectors include the Lone Star Tick, American Dog Tick and the Rocky Mountain Wood Tick. Tularemia is most prevalent in the warmer months, between April and September. Kittens are usually sicker than healthy adults.
The disease occurs in the Northern Hemisphere which includes the United States, Europe, and Asia.
There are three strains of this bacteria. A, B and C.
- Type A (F. tularensis tularensis) – The most virulent strain, can be found in North America and has recently been found in arthropods in Northern Europe. This strain typically infects wild and domesticated mammals.
- Type B (F. tularensis holarctica) – Produces milder symptoms. Can be found in the Northern Hemisphere, including Continental Europe, North America and parts of Asia. It occurs in water animals.
- Type C (F. novicida) – Has low virulence and is much less common than A and B.
What does tularemia do to infected cats?
- Ulceroglandular tularemia: The prevalent form of the disease and is acquired by direct contact with an infected animal or vector-borne.
- Glandular tularemia: Similar to ulceroglandular tularemia, however, there is no ulcer present.
- Oculoglandular tularemia: This is a form of ulceroglandular tularemia, only the conjunctiva is affected.
- Oropharyngeal tularemia: Eating or drinking contaminated food or water or inhaling the organism can cause this form of tularemia.
- Typhoidal tularemia: The systemic form of tularemia without an obvious route of exposure. Micro-abrasions on the skin or via inhalation could explain how the exposure occurred.
- Pneumonic tularemia (respiratory): This form is rare, but the most severe and is acquired via inhaling the organism or when the pathogen spreads from other infected sites within the cat’s body.
What are the symptoms of tularemia in cats?
The incubation period of tularemia is between 1-10 days. The severity of the disease varies according to the route of exposure and the strain. Some infected cats will remain subclinical.
- Respiratory infection
- Loss of appetite
Also, symptoms can vary depending on the type of tularemia the cat has.
- Ulceroglandular tularemia: An inflamed papule develops at the site of exposure, over time this ulcerates, lymph nodes close to the site become swollen and painful.
- Glandular tularemia: Swollen lymph nodes close to the site of inoculation.
- Oculoglandular tularemia: Purulent conjunctivitis, most often in one eye, ocular pain, redness, sensitivity to light, enlarged lymph nodes.
- Oropharyngeal tularemia: Ulcers on the tonsils, stomatitis (inflamed and sore mouth), swelling of localised lymph nodes, vomiting, and diarrhea.
- Typhoidal tularemia: Symptoms of typhoidal tularemia can be a combination of generalised symptoms such as fever, anorexia, and lethargy.
- Pneumonic (respiratory) tularemia: Coughing, difficulty breathing.
As the disease progresses, septicemia, jaundice, enlarged liver and spleen. Possible complications include kidney failure, meningitis, sepsis, hepatitis, disseminated intravascular coagulation and acute respiratory distress.
How is tularemia diagnosed?
Your veterinarian will perform a physical examination of your cat and obtain a medical history from you.
- Baseline tests: Biochemical profile and complete blood count may reveal elevated liver enzymes if there is liver involvement.
- Culture and sensitivity: Tissue samples such as lymph nodes, liver or spleen, blood, exudates from ulcers are sent to a laboratory where cultured on a medium (agar) which promotes the growth of bacteria. Once the bacteria or fungi have been cultured, discs made from filter paper that have been impregnated with antimicrobial drugs are placed on the bacterial or fungal lawn. When bacteria or fungi are sensitive to a particular antimicrobial, a plaque or zone of inhibition will form around the disc, where the bacteria or fungus have been killed. This helps to determine which antimicrobials are most effective.
- Antibody test: A blood test to look for the presence of antibodies in the blood serum. The result may be negative if the cat is tested too early as it can take some time for antibodies to develop.
- Polymerase chain reaction: PCR can detect minute amounts of DNA or RNA which can identify the bacteria when the above tests are inconclusive.
Depending on local regulations, it may be mandatory to report tularemia to the appropriate authorities.
How is tularemia treated?
Antibiotics for 14 days as well as supportive care which may include fluids to correct dehydration and nutritional support. Draining abscesses will be surgically removed.
Due to the infectious nature of tularemia and the zoonotic risk, the cat will be isolated during treatment and hospital staff must wear personal protective gear.
How do cats transmit tularemia to people?
Transmission can occur via exposure to respiratory secretions, bites, and scratches, infected cats can also indirectly pass on the disease via a tick, flea or mosquito bite.
At the moment there is no vaccine for tularemia; therefore prevention is better than cure. Avoid letting cats outdoors in high-risk areas and try to eliminate hunting. As tularemia is vector-borne, always use a flea and tick preventative. Take care when handling dead or dying animals. If a dead animal needs to be disposed of, use a long-handled shovel and apply insect repellant. Wash hands and clothing immediately afterwards.