Another tick disease to watch for: Tularemia

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Farm Forum

There was a time when I had my finger on the pulse of tick populations in southeastern South Dakota.

That time would be my years in mixed-animal vet practice. My measuring stick was the farm dogs coming into the clinic for their yearly spring vaccinations. Unless my patients had been treated with one of the good tick-repelling products we now have, I could easily detect the beginning, peak, and end of the tick season in our area simply by the number of dogs with ticks and how infested they were.

My tick barometer is now more limited: to the one dog in my household, and she doesn’t get out in the grass near as much as most of my former patients did. Still, that first tick detection is my reminder that late April and early May is the start of tick season.

To most of my clients, the “ick” factor is the worst part of finding ticks on an animal (or themselves for that matter). However, some ticks in some areas are good at spreading diseases to the animals or people that they feed on. One of those diseases, present in South Dakota, is tularemia. Even though most people have not heard of this disease, South Dakota has tularemia cases every year in people – and usually animals as well.

Tularemia is a bacterial disease, caused by the germ Francisella tularensis. Many different animal species can be affected with tularemia. Around here, cottontail rabbits and rodents are important hosts for the bacteria. This germ spends a lot of time in the bloodstream of affected animals, so ticks (and other biting insects) can pick up the bacteria from a carrier animal and transmit it to a new animal. Tularemia seems to be “endemic,” or particularly established, in certain areas of South Dakota, such as southwestern and central South Dakota, and north of the Black Hills. However, several tularemia cases have been found in animals in Sioux Falls throughout the years as well.

Animals typically become infected with tularemia when they eat infected rabbits or rodents or from tick or fly bites. Cats are one of the more common domestic animals to be affected with tularemia, probably due to their rodent-hunting tendencies. Dogs are more resistant to clinical disease. Tularemia can affect lambs, calves, and foals typically through tick infestations, so most of those cases coincide with spring and summer, when ticks are active. The signs of infection are not always obvious. In cats, tularemia can show up as anything from a mild fever with swollen neck glands to severe overwhelming infection and death. In wild animals such as rabbits, the disease makes them lethargic and sluggish before death, making them easy prey for cats and other predators.

People become infected with tularemia through bites from ticks or other insects, and sometimes from bites or scratches from an infected animal. Occasionally rabbit hunters can become exposed to the disease when they handle or dress an affected rabbit. It can take as few as 10 to 50 bacteria to infect a person or an animal. The most common signs in people, along with fever, tiredness, and stiffness, are a sore at the point of entry and swelling in the lymph nodes around the area. A severe — but fortunately rare — form is the pulmonic form, where inhalation of the bacteria results in severe pneumonia. Treatment for people and animals involves appropriate antibiotics and supportive care, but in animals, tularemia is often severe enough that treatment is not always effective.

Is tularemia the first condition that should come to mind when you find a sick cat or are ill yourself? Probably not— thankfully, tularemia is not a common occurrence. But it is out there and we can expect that cases in animals and people will occur sometime and somewhere in South Dakota this season. Make sure that your pets and other animals are closely observed for illness, and as always, seek veterinary care when necessary. Your veterinarian can also advise you of the best ways to keep ticks and other insects off your pets and livestock (Important note: Many insect repellants labeled for dogs are toxic to cats!), and take precautions yourself against ticks and biting insects.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at russell.daly@sdstate.edu or at 605-688-5171.