Tularemia is an infectious disease caused by the bacteria called Francisella tularensis. There are two strains of the bacteria--Type A is found in rabbits throughout North America. This strain tends to cause more serious illness than Type B, which is found throughout the northern hemisphere in aquatic mammals and rabbits. In North America, ticks are the vector for the spread of tularemia to rabbits, rodents, our pets, and even us.
Dogs and cats are infected through tick bites, by hunting and eating infected wild animals (rabbits and rodents), drinking contaminated water, or by inhalation of the organism. Cats are particularly susceptible to infection, and the infective dose of organisms can be quite low (meaning that as few as 10 of these microscopic bacteria can cause clinical disease).
Once introduced into the body, Francisella tularensis lives inside macrophages, which are a type of white blood cell. Here, they can hide out from the body’s immune system. There is usually a localized infection at the site of exposure (a tick bite, for instance), and then as the organism travels through the body, you’ll find enlarged lymph nodes and draining abscesses. Once in the blood stream, the infective organism can travel to the body’s organs, causing widespread infection in the spleen, liver, lungs, lymph nodes and skin. What starts as microscopic abscesses turn into larger draining tracts and granuloma formations as the body attempts to wall off the disease.
Luckily for dogs, tularemia is largely self-limiting. You may see brief episodes of decreased appetite and lethargy, and if you were to take an affected dog’s temperature, you’d likely find a low grade fever before the infection is cleared from their system.
Cats aren’t so lucky, as they can get very sick when they have tularemia. Dehydration, draining abscesses, jaundice, fever, oral ulcers, and conjunctivitis are all common symptoms of tularemia, as are enlarged lymph nodes and significantly decreased appetite.
Diagnosis of tularemia can be made via blood tests looking for antibodies to the organism. Alternatively, polymerase chain reaction (PCR) can be used to find the infective organism and confirm infection.
Once found, tularemia can be treated by surgically removing draining masses (if possible) as well as also administering intravenous or oral antibiotics. Because the severity of tularemia can run the gamut from mild illness to fatal septicemia, additional supportive therapy and hospital stays may be required.
The prognosis for infected dogs is very good, as most of them are able to clear the disease with limited clinical signs of illness. Cats are treatable and carry a favorable prognosis, though rarely tularemia can be fatal despite treatment.
One rather unique aspect of tularemia is that it is zoonotic, meaning that humans can be affected, too. While it is rare in humans, most cases are acquired though tick bites or through contact with infected wild animals. Less than 2% of human cases are from interactions with domestic cats, but if your cat has been diagnosed with tularemia, an abundance of caution should be used until the organism has been cleared.