Tularemia in Animals in
Russ Daly, DVM
Dale Miskimins,
Veterinary Science Department
Tularemia is a rare but potentially severe disease that can develop in many species of wild and domestic animals, but especially rabbits, rodents, cats, and humans. During the most recent fiscal period of July 2006 through June 2007, a total of five cases of tularemia have been diagnosed in animals submitted to the Animal Disease Research and Diagnostic Laboratory (ADRDL) at South Dakota State University (SDSU). Diagnoses of tularemia at SDSU are made in most years; single cases were seen in FY 2006 and 2005, two in 2004, and one in 2003.
Tularemia is caused
by a gram-negative bacterium called Francisella tularensis. The organism is named for Edward Francis, a
US Public Health surgeon who dedicated his life to researching the organism;
and for
Of the domestic animals, cats and dogs are the most commonly affected species, although clinical signs are more common in cats. There is evidence in endemic areas that many dogs seroconvert to F. tularemia, but clinical reports of illness are rare. In livestock, sheep are the most commonly affected species, but horses and calves have also been affected. In these species, young animals—lambs, foals, and calves—seem to be more frequently affected.
Francisella tularensis is highly infective. As few as 10 to 50 organisms inhaled or otherwise introduced into the body can cause illness in humans. The organism, besides surviving in its maintenance hosts and vectors (insects), can survive for long periods of time (weeks to months) in water, soil, and dead animal carcasses. Dogs and cats often become infected through the bite of an insect carrier or from eating or contacting infected prey, and livestock usually are infected through bites from the carrier insects. As such, conditions that promote tularemia in an area can often be related to an increase in rabbit or rodent populations (or a decrease in their predators), along with environmental conditions that promote survival of the vectors.
People become
infected usually by contact with the vectors (ticks, deerflies, and possibly
mosquitoes) or through contact (bite, or scratch) with an infected animal. Cats can infect people without showing clinical
signs themselves. People have also been
infected after mowing over dead rabbits with lawn mowers and inhaling the
agent! Because it is so highly
infectious, F. tularensis classified
as a Category A agent of bioterrorism.
In
Many different types of clinical signs may result from infection with tularemia in people and animals. Tularemia in cats can result in symptoms ranging from non clinical infection to mild illness with swollen lymph nodes and fever to severe overwhelming infection and death. In sheep and other livestock, general, non-specific signs are commonly noted. These include: fever, sluggishness, stiffness, and decreased appetite. Clinical signs in rabbits and rodents are lethargy and sluggishness, making these animals easy prey for cats and other predators.
Tularemia
in humans results in any one of six syndromes, the most common of which is the
“ulceroglandular” form, where a sore develops at the point of entry of the
bacteria, accompanied by swelling in the local lymph nodes. The most severe form is the primary pneumonic
(lung infection) form, but is relatively rare.
Tularemia is diagnosed yearly in people in
Treatment of tularemia in animals centers on use of an appropriate antibiotic, along with supportive care.
Examples of recent animal cases seen at SDSU’s ADRDL:
1.
Cat from west-central
Pathologic findings included: abscesses in lungs, swollen lymph nodes in jaw area and in abdomen, and areas of necrosis (dead tissue) in the spleen. Microscopically, there was inflammation in the lungs, liver, spleen, lymph nodes, and intestine. The tissues were positive by culture and PCR (polymerase chain reaction: a very sensitive method of bacterial detection) for F. tularensis.
Later, a dead cottontail was submitted from the same locale. Lesions included enlarged spleen and white pinpoint spots on the liver. Inflammation of the liver, intestine, and lung were found microscopically. F. tularensis was isolated from lung, liver, kidney, and spleen.
2. Cat from
southern
3.
Cat from central
Tularemia is a relatively rare but serious disease that has potential to cause disease in people through their contact with infected animals or insect vectors. Animal owners--cat owners especially--should, as always, observe their animals closely for signs of illness and contact their veterinarian as soon as possible when unusual signs develop. Proper use of tick and insect repellants on pets and livestock is another good practice to prevent transmission of this and other vector-borne diseases. Cat owners should use caution, and consult their veterinarian, when using many of the insect repellants that are available. Many products that are labeled for use on dogs oftentimes will be toxic for cats. People themselves should also use insect repellants when outside with their animals and take proper precautions when disposing of dead animals that are found (wearing gloves, double-bagging).
Resources:
1. Feldman KA. Tularemia. J Am Vet Med Assoc 2003; 222: 725-730.
2. SD Department of
Health. December 2006
June 14, 2007