Tularemia
(Rabbit Fever)
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:
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 (photo above). In the southwestern and western United States, the incidence of tularemia is highest during summer months due to tick bites (photo below).
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. Webmaster's
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