What is Tularemia?
Tularemia (also known as rabbit fever or deerfly fever) is an infectious disease in ticks and rabbits that is caused by a bacterium (Francisella tularensis). The disease was first described in Japan in 1837. Its name relates to the description in 1911 of a plague-like illness in ground squirrels in Tulare county, California (hence the name tularemia) and the subsequent work done by Dr. Edward Francis. Tularemia occurs throughout North America and in many parts of Europe and Asia. Francisella tularensis is found worldwide in over a hundred species of wild animals, birds and insects. Some examples of animals, other than rabbits, that carry tularemia are meadow mice, ground hogs (woodchucks), ground squirrels, tree squirrels, beavers, coyotes, muskrats, opossums, sheep, and various game birds.
There are two common ways that humans can contract tularemia:
- From the bite of an infected tick, deerfly (Chrysops discalis), or mosquito. When transmitted to humans by insects, exposed body surfaces are bitten, and the on set of pain and fever is sudden.
- When broken skin (cuts, abrasions) comes into direct contact with an infected rabbit carcass (namely rabbit species of the genus Sylvilagus which are the cottontails).
Less common means of spreading the disease are drinking contaminated water, inhaling dust from contaminated soil, or handling contaminated pelts or paws of animals. Human-to-human transmission of tularemia is uncommon.
What are the clinical features or symptoms of tularemia?
In humans, tularemia may appear in two forms depending on how a patient contracted the disease. The most common form is usually acquired through the bite of an infected tick (especially deer ticks and dog ticks) or from contact with infected rabbits. (Please take note that dog ticks are also called wood ticks and that deer ticks are the primary cause for a very serious disease called Lyme Disease.) Patients will develop an ulcer at the site of infection (photo at left) and lymph glands become inflamed and swollen. Severe fever and flu-like symptoms may accompany the ulcer or lesion. Symptoms start to show within 1-14 days after contracting the disease, with 3-5 days being most common. The fever generally lasts for 3 to 6 weeks if no type of antibiotic therapy is used to combat the bacteria. Patients with the less common form of tularemia, which occurs mainly after inhalation of bacteria, typically experience sudden chills, fever, weight loss, abdominal pains, tiredness, and headaches. Patients with this form of tularemia may develop an unusual pneumonia that can be fatal.
Symptoms of the disease in a rabbit are a white spotted liver, swollen spleen, and an ulcerated or raw area about ¼ inch in diameter which is where the animal was bitten by a tick or deer fly and thus infected.
How is tularemia transmitted to humans through wild game?
Reports of tularemia outbreaks indicate two primary modes of disease transmission. An increase in the number of reported cases in the eastern and midwestern United States during fall and winter coincides with hunting season when hunters are skinning rabbits. In the southwestern and western United States, the incidence of tularemia is highest during summer months due to tick bites .
The risk of contracting tularemia from rabbits is greatest when handling rabbits after the hunt during the cleaning process. Hunters skinning rabbits are advised to wear protective rubber gloves to reduce the risk of contracting the bacteria that cause tularemia when broken skin (cuts, scratches, open wounds, abrasions) comes into contact with an infected carcass or a live, infected rabbit.
Cook all rabbit meat thoroughly before eating. This doesn't mean you have to over cook the meat, simply make sure it is not bloody in the middle which is a sign that the meat is still raw or uncooked. Bacteria that cause tularemia can live for weeks in water, soil, carcasses, and hides, and for years in frozen rabbit meat.
Other than hunters, who else may be at risk for illness from tularemia?
Approximately 150-300 tularemia cases are reported in the United States annually, with a majority of those from Alaska, Arkansas, Illinois, Oklahoma, Missouri, Tennessee, Texas, Utah, and Virginia. The frequency of tularemia has dropped markedly over the last 50 years and there has been a shift from winter disease (usually from rabbits) to summer disease (more likely from ticks). The bacteria F. tularensis is a hazard to laboratory staff that work closely with rabbits. Matter of fact, nearly all cases reported each year are by people that receive the bacterial disease from a tick bite rather than from cleaning rabbits. Note: as few as 5-10 bacteria can result in disease. Others at risk may include timber industry personnel, outdoor enthusiasts, as well as those who work, play, or live in tick-infested regions during summer months.
As recently as 1984, 20 people from the Crow Creek and Lower Brule Indian reservations in west-central South Dakota were diagnosed with tularemia. Tularemia was spread through these two reservations by dog ticks (Dermacentor variabilis) that carried the bacteria.
Treatment of tularemia
Doctors recommend a preventative vaccine for people at high risk of contracting tularemia. Untreated, tularemia (Type B) carries a mortality rate of 5-15%, even higher to about 35% with the typhoidal form (Type A). Appropriate antibiotics lower both mortality rates to about 1%. If you suspect that you have been infected with tularemia, seek care from a medical professional immediately. Antibiotics such as streptomycin, gentamicin, and tobramycin are effective in the treatment to eliminate this infectious bacteria. Long-term immunity will follow recovery from tularemia. However, reinfection has been occasionally reported in laboratory workers that had not received the Tularemia vaccine.
Contacting your health care physician
Diagnosis of tularemia is difficult because symptoms of tularemia are also common in other diseases. However, Tularemia can be positively diagnosed by an antibody test, but your doctor may not conduct the test unless you tell him you are a rabbit hunter, or that you are an outdoors type person that has been exposed to ticks. Patients who provide their physician with a recent history of activities could assist in the diagnosis of tularemia. Information provided in this document should NOT be used as a substitute for seeking professional treatment from your local health care provider if symptoms develop after receiving a tick bite or being exposed to the flesh of a wild animal.
How can tularemia be prevented?
Rubber, plastic, or latex gloves should be worn while skinning or handling rabbits, especially if you have open cuts or abrasions. Wild rabbit and rodent meat should be cooked thoroughly before eating. Once again, this doesn't mean you have to over cook the meat, simply make sure it is not bloody in the middle which is a sign that the meat is still raw or uncooked. When outdoors, avoid bites of deer flies and ticks by wearing insect repellents that contain DEET (for skin) and/or repellents containing Permethrin (for clothing only). Also, conduct "tick checks" every two to three hours if spending a lot of time outdoors where ticks are plentiful. All ticks attached to the body should be removed immediately. Using a pair of tweezers, slowly pull the tick straight out, no twisting, then wash hands thoroughly after removal (click here for tick removal photo). Avoid drinking, bathing, swimming or working in untreated (nonchlorinated) water. It is wisely suggested that you not pick up wild dead rabbits found in the outdoors. Also, be suspicious of rabbits that appear to be seriously ill or are easily caught by your Beagles.
I have been a rabbit hunter for more than 30 years and I have never seen a rabbit with a contaminated, spotted liver. I am also unaware of any friends that are hunters or outdoors persons that have ever contracted the disease. Remember, out of several million people that frequent the outdoors, work with laboratory rodents, and rabbit hunt only 150-300 cases are diagnosed throughout the entire US on a yearly basis. Also, remember this disease has been on a sharp decline for the past 50 years. The sole purpose of this article is to educate you on the disease tularemia, but in no way is this article intended to exaggerate its minimal risk factor. Just beware that the disease does exist, use the proper precautions, and enjoy rabbit hunting and eating rabbit meat.