Tularemia: Hunting Dogs Are an Overlooked Source of Human Infection

Tularemia, a fatal bacterial disease in wild rodents and lagomorphs, can also infect humans and dogs. While contact with contaminated blood or meat makes hunters a group particularly at risk for the disease, the prevalence of infection in hunting dogs has been poorly documented. However, according to an initial serological study conducted by the University of Veterinary Medicine in Vienna, the bacteria Francisella tularensis were isolated from the blood of nearly 7% of the hunting dogs tested. This prevalence confirms the existence of an additional risk of infection for humans via dogs, which, moreover, often remain asymptomatic. Tularemia, caused by the bacteria Francisella tularensis, primarily affects rodents, rabbits, and hares. In these wild species, this infectious, contagious, and inoculable disease takes the form of septicemia, which rapidly leads to death. It is also a major zoonosis, affecting in particular certain high-risk professions such as hunters, breeders, veterinarians, farmers, etc. Like animals, humans become infected through the skin and mucous membranes (contact with carcasses or contaminated materials, cat scratches or bites), through the digestive tract (consumption of contaminated water or undercooked meat), through the respiratory tract (inhalation while handling animals or contaminated products), or through exposure to tick bites. The pathogenic bacteria also infects cats, horses, sheep, pigs, etc. In dogs, the infection often remains asymptomatic or goes unnoticed. Blood tests conducted by Austrian researchers confirmed the prevalence of infection with the bacteria Francisella tularensis in hunting dogs in Austria, with the bacteria isolated in 5 of the 80 animals tested. The dogs came from rural areas where tularemia is endemic. The blood samples were tested using two different agglutination tests to detect agglutinating antibodies. In cases of suspected tularemia, the tests were repeated due to possible cross-reactions with other pathogenic bacteria, which could complicate the interpretation of the results. However, a definitive serological diagnosis was established for the five positive dogs in the study. According to the authors, the seroprevalence of 6.25% demonstrates that hunting dogs can be regularly infected, even without apparent symptoms. As carriers of the disease, they must also be considered potential vectors, posing a potential source of infection for humans. Like hunters, dogs come into direct contact with infected animals (for example, when retrieving killed game). However, the prevalence of the disease in these animals remains to be determined. Until now, given their high natural resistance to infection, they have been largely overlooked in scientific studies on the modes of tularemia transmission. However, according to the findings of the Austrian study, dogs may act as intermediate hosts or even serve as a reservoir for the disease. In this context, further studies are needed to confirm whether dogs indeed pose a major risk to human health.