Tularemia

What is tularemia?

Tularemia is a zoonosis: an infection that lives in animals and occasionally passes to people. Francisella tularensis infects rabbits, hares, muskrats, beavers, voles and other rodents, and is carried by ticks and deer flies. As few as 10 bacteria can cause infection, which is why it is handled in special laboratories and listed as a potential bioterrorism agent.

In the US, about 100 to 200 cases are reported each year, mostly in summer, with the highest numbers in Arkansas, Missouri, Oklahoma, Kansas and South Dakota. Martha's Vineyard in Massachusetts has had outbreaks linked to lawn mowing and brush cutting. It also occurs across Europe and Asia.

How you get tularemia

• Tick bites: dog ticks, wood ticks and lone star ticks. The leading cause in the central US.
• Deer fly bites: mainly in the western US.
• Handling infected animals: skinning or dressing rabbits and hares, especially without gloves. Hunters and trappers are at high risk.
• Inhaling bacteria: from dust when mowing over a dead animal, cutting brush or farming.
• Eating or drinking: undercooked infected meat or untreated water.
• Laboratory exposure: to cultures.
• Pets: cats that hunt rabbits can occasionally pass it on through bites or scratches.

It does not spread from person to person.

Types and symptoms

All forms start suddenly with fever (often 38.5 to 40 °C, or 101 to 104 °F), chills, headache, muscle aches, tiredness and sometimes a dry cough. The rest depends on how the bacteria entered.

The swollen lymph nodes can become very large and may fill with pus and drain if treatment is delayed.

How tularemia is diagnosed

Tularemia is often suspected from the story: fever plus an ulcer or swollen glands after a tick bite, rabbit handling or mowing. Tests include:

• Blood antibody tests (serology): the most common confirmation. Antibodies take about 2 weeks to rise, so a second sample is often compared with the first.
• PCR testing of ulcer swabs, lymph node fluid or other samples.
• Culture: possible but slow, and dangerous for lab staff. Always warn the laboratory if tularemia is suspected.
• Chest X-ray if pneumonia is possible.

Doctors also consider other causes of fever with swollen glands, such as cat scratch disease, strep and staph lymphadenitis, plague in the Southwest, and other tick-borne diseases such as Rocky Mountain spotted fever and ehrlichiosis.

Treatment

Tularemia responds well to antibiotics, which are often started before test results return:

• Streptomycin or gentamicin injections for severe illness.
• Ciprofloxacin or doxycycline tablets for milder disease.
• Treatment usually lasts 10 to 21 days depending on the drug and severity.
• Large, pus-filled lymph nodes may need draining.

Penicillins and cephalosporins do not work against tularemia.

Outlook

With prompt treatment, death is rare (under 2%). Untreated pneumonic and typhoidal forms can be fatal in up to about 30% of cases. Fatigue can last weeks after recovery, and relapse can occur, especially with doxycycline. One infection usually gives long-lasting immunity. There is no licensed vaccine in the US.

Prevention

• Use insect repellent with DEET, picaridin or permethrin-treated clothing, and check for ticks after being outdoors.
• Wear gloves and eye protection when skinning or dressing rabbits and other wild game, and cook game meat thoroughly.
• Do not handle sick or dead animals with bare hands.
• Check lawns for dead animals before mowing, and consider a dust mask when mowing or brush cutting in areas with known cases.
• Do not drink untreated water.
• Keep pets from hunting wildlife and use tick prevention on them.

Frequently asked questions

How do humans get tularemia?

Most commonly from tick or deer fly bites, or from handling infected rabbits, hares or rodents, especially while skinning them. People can also get it by breathing in contaminated dust while mowing, or by drinking contaminated water or eating undercooked game. It does not spread between people.

What are the first symptoms of tularemia?

It usually starts suddenly 3 to 5 days after exposure, with high fever, chills, headache and tiredness. In the most common form, a sore or ulcer appears at the bite or cut, and nearby lymph nodes in the armpit, groin or neck become swollen and painful.

Why is tularemia called rabbit fever?

Because rabbits and hares are common sources of human infection, especially among hunters who skin and dress them. The disease was also historically linked to rabbit handling in market workers. Ticks and deer flies, which feed on rabbits and rodents, are other major sources.

Is tularemia curable?

Yes. Antibiotics such as gentamicin, streptomycin, ciprofloxacin or doxycycline cure most people, particularly when started early. Without treatment, symptoms can last weeks, and the pneumonia and typhoidal forms can be life-threatening.