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Tularemia is a rare infectious disease that can attack the skin, eyes and lungs. Fewer than 200 cases of tularemia are reported annually in the United States — mainly in western and south central states. Tularemia, often called rabbit fever or deerfly fever, is caused by the bacterium Francisella tularensis. The disease mainly affects animals, especially rodents, rabbits and hares, though it can also infect birds, reptiles and fish.

Tularemia spreads to humans through several routes, including insect bites and direct exposure to an infected animal. Highly contagious and potentially fatal if not treated, tularemia has been identified as a possible bioweapon. If diagnosed early, doctors can usually treat tularemia effectively with antibiotics, but the goal is to eliminate tularemia.

Most people exposed to tularemia become sick within three to five days, although it can take up to two weeks for signs and symptoms to appear. Several types of tularemia exist, each with its own set of symptoms:

• Ulceroglandular tularemia. By far the most common form of the disease, ulceroglandular tularemia begins with a skin ulcer that forms at the site of infection — usually an insect or animal bite. From there, bacteria spread to the lymph glands, which become swollen and painful. Other symptoms include fever, chills, headache and exhaustion.
• Glandular tularemia. People with glandular tularemia have all the signs and symptoms of the ulceroglandular form but don't develop skin ulcers.
• Oculoglandular tularemia. This form affects the eyes, causing pain, redness, swelling and discharge. Sometimes an ulcer may develop on the inside of the eyelid.
• Oropharyngeal tularemia. Affecting the digestive tract, oropharyngeal tularemia is marked by vomiting and diarrhea.
• Pneumonic tularemia. This causes symptoms typical of pneumonia: cough, chest pain, difficult breathing. Other forms of tularemia also can spread to the lungs.
• Typhoidal tularemia. This rare and serious form of the disease usually causes fever, extreme exhaustion and weight loss, and can affect a number of body organs, including the lungs.

Tularemia doesn't occur naturally in humans, but it does in animals — worldwide, more than 200 species of mammals, as well as birds, insects and fish, may be infected with F. tularensis. The bacteria can live for an extended time in animals, and even insects can act as reservoirs for disease. Unlike some infectious diseases that spread from animals to people through a single route, tularemia has several modes of transmission; how you contract the disease usually determines the type and severity of symptoms. In general, you can get tularemia through:

• Insect bites. Although a number of insects carry tularemia, ticks and deerflies are most likely to transmit the disease to humans. Tick bites cause a large proportion of cases of ulceroglandular tularemia.
• Exposure to sick or dead animals. Ulceroglandular tularemia can also result from handling or being bitten by an infected animal, most often a rabbit or hare. Bacteria enter the skin through small cuts and abrasions or a bite, and an ulcer forms at the wound site. The ocular form of tularemia can occur when you rub your eyes after touching a sick animal.
• Airborne bacteria. Spores of bacteria in the soil can become airborne during gardening, construction or any activity that disturbs the earth. Inhaling the spores can lead to pneumonic tularemia.
• Contaminated food or water. Although uncommon, it's possible to contract tularemia from eating the undercooked meat of an infected animal or drinking contaminated water. The signs are intestinal: vomiting, diarrhea and other digestive problems (oropharyngeal tularemia). Heat kills F. tularensis, so well-cooked meat is usually safe to eat.

Tularemia: Where, when and how much
Tularemia occurs worldwide — especially in rural areas in eastern Europe, China, Japan and Scandinavia. In the United States, most cases — with the exception of Martha's Vineyard — are clustered in the rural west and in south central states, such as Arkansas, Missouri and Oklahoma. Tick season (generally June through September) and hunting season are prime times for infection.

Tularemia is highly contagious; inhaling as few as 10 to 50 bacteria can cause disease. Yet tularemia is rare, with only a handful of cases reported each year. The bacteria are transmitted from animals to humans, not from person to person.

Although anyone of any age can develop tularemia, certain occupations or activities pose a greater risk. They include:

• Hunting and trapping. Because hunters handle wild animals, are exposed to animal blood and may eat wild meat, they have especially high rates of tularemia.
• Gardening or landscaping. Gardeners and landscapers may be especially hard-hit by tularemia. They have a higher infection rate than people in other professions and are more likely to develop pneumonic tularemia, one of the least common and most deadly forms of the disease. It's possible that gardeners inhale spores of the bacteria that are stirred up when they use mowers and weed whackers.
• Wildlife management and veterinary medicine. People who work with wildlife are at increased risk of tularemia.
• Science and medicine. A number of medical professionals working with F. tularensis have contracted pneumonic tularemia.

If you think you may have been exposed to tularemia — especially if you've been bitten by a tick or handled a wild animal in an endemic area — see a doctor as soon as possible. If you test positive for the disease, you'll need to start antibiotic treatment right away.

Doctors may check for F. tularensis in a blood or sputum sample that's cultured to encourage the growth of the bacteria. But the preferred way to diagnose tularemia is usually to identify antibodies to the bacteria in a sample of blood. You're also likely to have a chest X-ray to look for signs of pneumonia.

Most forms of tularemia can eventually spread to the lungs, leading to pneumonia and sometimes to respiratory failure — a condition in which the lungs don't take in enough oxygen, release enough carbon dioxide or both. Other possible complications include:

• Meningitis. This is a serious and sometimes life-threatening infection of the fluid and membranes (meninges) surrounding the brain and spinal cord. Signs and symptoms of bacterial meningitis include a high fever, severe headache, stiff neck and sensitivity to light. If not treated promptly, bacterial meningitis can cause brain damage and even death.
• Pericarditis. This is swelling and irritation of the pericardium, the thin membrane that surrounds the heart. Mild pericarditis often improves without treatment, but more serious cases may require antibiotic therapy.
• Bone infection (osteomyelitis). Tularemia bacteria sometimes spread to the bones, leading to pain, decreased range of motion in nearby joints, and sometimes to skin redness, tenderness or open sores in the affected areas.

Tularemia can be effectively treated with antibiotics such as streptomycin or gentamicin, which are given by injection directly into a muscle or vein. Depending on the type of tularemia being treated, doctors may prescribe oral antibiotics such as tetracycline instead. You'll also receive therapy for any complications such as meningitis or pneumonia. In general, you should be immune to tularemia after recovering from the disease, but some people may experience a recurrence or reinfection.

If you work in a high-risk occupation or live in an area where tularemia is endemic, these measures may help reduce your chance of infection:

• Protect yourself from insects. Most people contract tularemia though tick bites. If you spend time in tick-infested areas, wear long-sleeved shirts and long pants, tuck your pants into your socks, and use a broad-brimmed hat to help protect your face and neck. Even bundled up, you'll need to check your skin and clothing often for ticks. Use an insect repellant, but follow the manufacturer's directions carefully. Products containing DEET are still considered the most effective against ticks, although oil of lemon eucalyptus or natural insecticides may offer some protection. Use the lowest concentration of repellant for the circumstances, apply it in moderation, and wash it off at the end of the day. Don't use repellants containing DEET on infants younger than 2 months.
• Take care when gardening. Home gardeners and professional landscapers should consider wearing a face mask when excavating the soil, clearing weeds or brush, or mowing lawns.
• Handle animals carefully. If you hunt or handle wild rabbits or hares, wear gloves and protective goggles, and wash your hands thoroughly with soap and hot water after touching the animal. Cook all wild meat thoroughly, and avoid skinning or dressing any animal that appears ill. Better yet, don't hunt animals at all.
• Protect your pets. Livestock and pets can contract tularemia if they eat part of a diseased rabbit or are bitten by an infected tick. To help keep your pets safe, avoid letting them outside unsupervised, provide them with a flea and tick collar, and don't let them come in close contact with wild animals.