Research Links Tularemia to Hunting Dogs

Tularemia, also known as rabbit fever or deer-fly fever, is an infectious bacterial disease caused by the gram-negative intracellular pathogen Francisella tularensis. Known to be life-threatening in rodents, rabbits, and hares, tularemia can also infect humans and dogs.

Infection with the bacterium can be spread through tick and deer fly bites, ingestion of contaminated water, and contact with infected animals. It is the latter that puts hunters—and their dogs—who come into contact with the blood or raw meat of diseased animals at increased risk for infection.

Even though hunting dogs are considered to be at risk, the frequency of canine infection has not been studied extensively. This is attributed to the fact that without secondary disease, dogs usually exhibit few or no clinical signs. They also tend to have a high natural resistance to low levels of the bacteria.

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However, there are theories that dogs may act as interim hosts and a further source of infection. This has led researchers to investigate the prevalence of infection among the group.

Research Linking Tularemia to Dogs

Scientists from the Research Institute of Wildlife Ecology at Vetmeduni Vienna in Austria analyzed blood samples taken from Austrian hunting dogs from rural areas known to be endemic to tularemia. The 80 blood samples were examined using 2 agglutination tests to detect antigens on the surface of the bacteria or antibodies produced by the immune system.

“Agglutination works by specifically clumping these proteins to make them visible under the microscope. In the case of suspected tularemia, more than one of these tests is necessary due to the possibility of cross-reactivity with other pathogens. If all tests are positive, the disease can be confirmed without a doubt,” explained Annika Posautz, DVM, the study’s lead author.

Following 2 independent analyses of the samples, about 7% (5) of the hunting dogs tested positive.

“The frequency of about 7% shows that hunting dogs can also become infected regularly,” said Dr. Posautz. “As vectors of the disease, even without symptoms, the animals must also be considered unexpected carriers.”

Looking Ahead

Tularemia was first identified in 1912 following reports of a plague-like illness in ground squirrels in Tulare County, California. The bacterium has high zoonotic potential and, according to the Centers for Disease Control and Prevention, naturally occurring infections in humans have been reported in all states except Hawaii but are most common in the south-central United States, the Pacific Northwest, and parts of Massachusetts. Human tularemia incidence in the United States peaked in 1939 with 2291 reported cases; the incidence has since decreased to 100 to 200 cases annually.

The study’s authors said that future research should address whether dogs should be considered a potential source of infection for humans and whether other factors, such as the age of a dog, increase the likelihood of infection.