Tularemia: Why You Shouldn’t Mow Over a Dead Rabbit

“It’s important for pet owners to be aware of this disease [tularemia] in their pets, because it is possible for a person to become infected as well."

Maria Bye, MPH, senior epidemiologist in the Zoonotic Diseases Unit, Minnesota Department of Health

“Despite concerns over its use as a bioweapon, most U.S. tularemia cases are tick-mediated and ticks are believed to be the major environmental reservoir for F. tularensis in the U.S.”

Zellner, Jason F. Huntley, PhD, “Ticks and Tularemia: Do We Know and What We Don’t Know?,” Frontiers in Cellular and Infection Microbiology, May 8, 2019

Tularemia is a zoonotic infection caused by Francisella tularensis—a bacterium most commonly found in nature in wild animals, particularly rabbits, hares, and rodents. This pathogen is usually transmitted to humans by ticks but also can be transmitted by inhaling aerosols that contain the bacterium.

On July 24, 2025, the Minnesota Department of Health issued a Health Advisory for health professionals and hospitals regarding an increase in cases of tularemia in the state. Two of the recent five cases in Minnesota were linked to tick bites. But this case triggered my post: a hapless person mowing the lawn inadvertently mowed over a dead animal (presumably a rabbit) and then developed tularemia. My decision to feature tularemia in this week’s post was made not so much to warn lawn mowers of this risk for acquiring a deadly serious infectious disease, but rather to remind everyone that it is still tick season.

What is tularemia? Tularemia, also known as “rabbit fever,” is a zoonotic infection that afflicts a wide range of animals, including reptiles, birds, fish and mammals (rabbits, rodents, and hares, as well as pet dogs and cats and humans). Cottontail rabbits are a particularly important host in North America where in the process of skinning, hunters become infected by inhaling aerosols from the dead animal—hence the moniker “rabbit fever.”

The disease and etiologic agent, a gram-negative bacterium, F. tularensis, are named after Tulare County, California where the disease was discovered in 1911 by G.W. McCoy of the U.S. Public Health Service. Between the 1970s and 2015, around 200 tularemia cases were reported in the U.S. According to the Centers for Disease Control and Prevention (CDC), in recent years the annual number of cases increased, fluctuating between 149-314. (Tularemia is generally rare in Europe although outbreaks with hundreds of cases occur every few years in Finland and Sweden.)

F. tularensis is extremely contagious (as few as 10-50 organisms can cause disease in humans, especially when inhaled), is hardy in the environment and therefore is considered a potential biological weapon. (In the 14^th century, a disease believed to be tularemia spread throughout the Hittite Empire, known as the “Hittite plague,” and its use in repelling an invasion is thought to be the first use of a biological weapon.) F. tularensis is viewed as an attractive bioterrorism agent because it’s easy to aerosolize, fast-acting, and highly incapacitating to infected people. (The Schu S4 strain was standardized as “Agent UL” for use in the U.S. M143 bursting spherical bomblet.)

Hard-shelled ticks of the Ixodidae family and deer flies are the principal vectors that transmit F. tularensis to humans. But other biting insects as well as the ingestion of contaminated food or water have been implicated in some tularemia cases. In the U.S., waterborne transmission accounts for 5-10% of cases.

Signs and symptoms of tularemia depend on the site of infection, with an ulceroglandular form being most common. In most cases, fever, lethargy, loss of appetite and skin lesions occur. Lymph node involvement is accompanied by a high fever. Without treatment, the mortality rate can be as high as 50-60%. This, however, falls to less than 2% with antibiotic (usually gentamicin or doxycycline) treatment.   

Diagnosis. The diagnosis of tularemia usually is made by culturing specimens of blood, lymph nodes, or sputum. The clinical microbiologist must be informed when tularemia is suspected not only to include special culture media but also to ensure that certain safety precautions are undertaken when culturing the specimen.

Prevention. There are no vaccines available to protect against tularemia. (Hopefully, none of us needs to worry about acquiring tularemia because of biological warfare.) Protecting yourself from contracting the disease in the first place is the best means of prevention.

Ticks are the main vector for F. tularensis infection. According to the CDC, ER visits for tick bites this summer across the U.S, are near record levels.  Therefore, everyone who is venturing into the woods needs to protect themselves against tick bites. (See, “More Reasons to Hate Ticks,” Germ Gems, May 19, 2025, providing advice regarding preventing tick bites).

While the exact frequency of contracting tularemia from mowing over a dead animal is difficult to quantify precisely, aerosol transmission is a documented, albeit rarer, route of exposure to the pathogen. So please, don’t mow over a dead rabbit when cutting your lawn. It’s an easy way to reduce your risk of potentially inhaling an aerosol containing F. tularensis.