Farm and Home Biosecurity
Consumer/General Public
Tularemia: Questions and Answers
What is tularemia?
Tularemia, or rabbit fever, is a zoonotic bacterial disease. The causative
agent of Tularemia, Francisella tularensis , is one of the most infectious
pathogen bacteria known, requiring inoculation of inhalation of as few as 10
organisms to cause disease. Although many wild and domestic animals can be
infected, the rabbit is most often involved in disease outbreaks.
Who gets tularemia?
The disease occurs throughout the United States in all months of the year.
Most cases occur in June through September, when arthropod-borne (ticks, flies,
mosquitoes) transmission is most common. Cases in winter usually occur among
hunters and trappers who handle infected animal carcasses. The incidence,
however, is higher for adults in early winter during rabbit hunting season and
for children during the summer when ticks and deer flies are abundant.
How is tularemia spread?
Many routes of human exposure to the tularemia bacteria are known to exist.
The common routes include inoculation of the skin or mucous membranes with blood
or tissue while handling infected animals, the bite of an infected tick, contact
with fluids from infected deer flies or ticks, or handling or eating
insufficiently cooked rabbit meat. Less common means of spread are drinking
contaminated water, inhaling dust from contaminated soil or handling
contaminated pelts or paws of animals. Tularemia is not spread from person to
person.
A variety of small mammals, including voles, mice, water rats, squirrels,
rabbits, and hares, are natural reservoirs of infection. They acquire infection
through bites by ticks, flies, and mosquitoes, and by contact with contaminated
environments.
What are the symptoms of tularemia?
Symptoms vary, depending on the route of introduction. In those cases where a
person becomes infected from handling an animal carcass, symptoms can include a
slow-growing ulcer at the site where the bacteria entered the skin (usually on
the hand) and swollen lymph nodes. If the bacteria is inhaled, a pneumonia-like
illness can follow. Those who ingest the bacteria may report a sore throat,
abdominal pain, diarrhea and vomiting. The major target organs are the lymph
nodes, lungs and pleura, spleen, liver, and kidney.
The onset of tularemia is usually abrupt, with fever, headache, chills and
rigors, generalized body aches, coryza, and sore throat. Symptoms can appear
between one and 14 days after exposure, but usually do so after three to five
days.
What is the treatment for tularemia?
The drug of choice for treating tularemia is streptomycin or gentamicin,
although other antibiotics also are effective. The overall mortality rate for
severe Type A strains has been 5-15% without antibiotics treatment. With
treatment, the most recent mortality rates in the US have been 2%.
How is tularemia diagnosed?
Francisella tularensis may be identified by direct examination of secretions,
exudates, or biopsy specimens using direct fluorescent antibody or
immunohistochemical stains. Growth of F tularensis in culture is the definitive
means of confirming the diagnosis of tularemia.
Is there a vaccine?
In the United States, a live-attenuated vaccine derived from the avirulent
Live Vaccine Strain (LVS) has been used to protect laboratory personnel
routinely working with F. tularensis. Given the short incubation period of
tularemia and incomplete protection of current vaccines against inhalational
tularemia, vaccination is not recommended for post-exposure prophylaxis.
Long-term immunity usually follows recovery from tularemia. However,
reinfection has been reported.
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