Tularemia is a disease of animals and humans caused by the bacterium Francisella tularensis. Rabbits, hares, and rodents are especially susceptible and often die in large numbers during outbreaks. Humans can become infected through several routes, including:

Tick and deer fly bites
Skin contact with infected animals
Ingestion of contaminated water
Inhalation of contaminated aerosols or agricultural dusts
Laboratory exposure
In addition, humans could be exposed as a result of bioterrorism.
Symptoms vary depending on the route of infection. Although tularemia can be life-threatening, most infections can be treated successfully with antibiotics. 

The bacterium that causes tularemia is highly infectious and can enter the human body through the skin, eyes, mouth, or lungs. Symptoms of infection vary depending on the route of entry. Usual sources of infection are described below. Transmission of tularemia from person to person has not been reported.

Tick or deer fly bites
In the United States, ticks that transmit tularemia to humans include the dog tick (Dermacentor variabilis), the wood tick (Dermacentor andersoni), and the lone star tick (Amblyomma americanum). Deer flies (Chrysops spp.) have been shown to transmit tularemia in the western United States. Infections due to tick and deer fly bites usually take the form of ulceroglandular or glandular tularemia.

Handling infected animals
lone star tick
Lone star tick (Amblyomma americanum)

F. tularensis bacteria can be transmitted to humans via the skin when handling infected animal tissue. Inw particular, this can occur when hunting or skinning infected rabbits, muskrats, prairie dogs and other rodents. Many other animals have also been known to become ill with tularemia. Domestic cats are very susceptible to tularemia and have been known to transmit the bacteria to humans. Care should be taken when handling any sick or dead animal. Outbreaks of tularemia have occurred among hamsters purchased from pet stores. At least one child in the U.S. has developed tularemia after being bitten by a pet hamster. Infection due to handling animals can result in glandular, ulceroglandular and oculoglandular tularemia. Oropharyngeal tularemia can result from eating under-cooked meat of infected animals.

Other exposures
Humans can acquire tularemia by inhaling dust or aerosols contaminated with F. tularensis bacteria. This can occur during farming or landscaping activities, especially when machinery (e.g. tractors or mowers) runs over infected animals or carcasses. Although rare, this type of exposure can result in pneumonic tularemia, one of the most severe forms of the disease. Water can also become contaminated with the bacteria through contact with infected animals. Humans who drink contaminated water that has not been treated may contract oropharyngeal tularemia. This mode of transmission appears to be much more common in Europe than the U.S.

The signs and symptoms of tularemia vary depending on how the bacteria enter the body. Illness ranges from mild to life-threatening. All forms are accompanied by fever, which can be as high as 104 °F. Main forms of this disease are listed below:

Ulceroglandular This is the most common form of tularemia and usually occurs following a tick or deer fly bite or after handing of an infected animal. A skin ulcer appears at the site where the bacteria entered the body. The ulcer is accompanied by swelling of regional lymph glands, usually in the armpit or groin.
Glandular Similar to ulceroglandular tularemia but without an ulcer. Also generally acquired through the bite of an infected tick or deer fly or from handling sick or dead animals.
Oculoglandular This form occurs when the bacteria enter through the eye. This can occur when a person is butchering an infected animal and touches his or her eyes. Symptoms include irritation and inflammation of the eye and swelling of lymph glands in front of the ear.
Oropharyngeal This form results from eating or drinking contaminated food or water. Patients with orophyangeal tularemia may have sore throat, mouth ulcers, tonsillitis, and swelling of lymph glands in the neck.
Pneumonic This is the most serious form of tularemia. Symptoms include cough, chest pain, and difficulty breathing. This form results from breathing dusts or aerosols containing the organism. It can also occur when other forms of tularemia (e.g. ulceroglandular) are left untreated and the bacteria spread through the bloodstream to the lungs.
Typhoidal This form is characterized by any combination of the general symptoms (without the localizing symptoms of other syndromes)

Tularemia can be difficult to diagnose. It is a rare disease, and the symptoms can be mistaken for other, more common, illnesses. For this reason, it is important to share with your health care provider any likely exposures, such as tick and deer fly bites, or contact with sick or dead animals. 

Blood tests and cultures can help confirm the diagnosis. Antibiotics used to treat tularemia include streptomycin, gentamicin, doxycycline, and ciprofloxacin. Treatment usually lasts 10 to 21 days depending on the stage of illness and the medication used. Although symptoms may last for several weeks, most patients completely recover.

Use of insect repellent
Wearing gloves when handling sick or dead animals
Avoiding mowing over dead animals
In the United States, naturally occurring infections have been reported from all states except Hawaii.
When hiking, camping or working outdoors:
Use insect repellents containing 20% to 30% DEET (N,N-diethyl-meta-toluamide), picaridin or IR3535. EPA provides information on the proper use of repellents.
Wear long pants, long sleeves, and long socks to keep ticks and deer flies off your skin.
Remove attached ticks promptly with fine-tipped tweezers.
Don’t drink untreated surface water.
When mowing or landscaping:
Don’t mow over sick or dead animals. When possible, check the area for carcasses prior to mowing.
Use of masks during mowing and other landscaping activities may reduce your risk of inhaling the bacteria, but this has not been studied.
If you hunt, trap or skin animals:
Use gloves when handling animals, especially rabbits, muskrats, prairie dogs, and other rodents.
Cook game meat thoroughly before eating.
Until recently, a vaccine has been available to protect laboratorians routinely working with Francisella tularensis. This vaccine is currently under review by the US Food and Drug Administration (FDA) and is not generally available in the United States.

Content source: Centers for Disease Control and Prevention
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
Division of Vector-Borne Diseases (DVBD)

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