Tularemia or Rabbit Fever: Definition, Causes, Treatment and Prevention

Definition

Tularemia is a rare infectious disease that typically attacks the skin, eyes, lymph nodes and lungs. Tularemia also called rabbit fever or deer fly fever is caused by the bacterium Francisella tularensis. The disease mainly affects mammals, especially rodents, rabbits and hares, although it can also infect birds, sheep, and domestic animals, such as dogs, cats and hamsters. It spreads to humans through several routes, including insect bites and direct exposure to an infected animal. Highly contagious and potentially fatal, tularemia usually can be treated effectively with specific antibiotics if diagnosed early.

Tularemia lesion 

History

Ancient

F. tularensis has been identified as the cause of human outbreaks in ancient Canaan in about 1715 BC and in 1075 BC. A long-lasting epidemic that plagued the eastern Mediterranean in the 14th century BC was also traced back to a focus in Canaan along the Arwad-Euphrates trading route. According to Siro I. Trevisanato, this epidemic contaminated an area stretching from Cyprus to Iraq, and from Palestine to Syria, sparing Egypt (due to a quarantine) and Anatolia (owing to effective political boundaries). Subsequently, wars are believed to have spread the same disease into central Anatolia, from whence it was deliberately introduced into western Anatolia, in acts constituting the first known record of biological warfare. Finally, Aegean soldiers fighting in western Anatolia returned home to their Greek islands, further spreading the same epidemic.

Modern

The tularemia bacterium was first isolated by G.W. McCoy of the U.S. Public Health Service plague lab and reported in 1912. Scientists determined tularemia could be dangerous to humans; a human being may catch the infection after contacting an infected animal. The ailment soon became associated with hunters, cooks and agricultural workers.

Epidemiology

Tularemia occurs throughout the Northern Hemisphere, except for in the United Kingdom. Cases have been reported in the United States, the former Soviet Union, Japan, Canada, Mexico, and Europe. It has not been reported in Africa and South America.

Types of Tularemia

There are several types of tularemia.

Ulceroglandular

This type is the most common. Painful open sores develop where the bacteria entered the skin: through a break in the skin, usually on the hands and fingers, or a tick bite, usually in the groin, armpit, or trunk. The bacteria travel to nearby lymph nodes, making them swollen and painful. Occasionally, the skin around the lymph nodes breaks down, and pus may drain from them.

Ulceroglandular tularemia

Glandular

The lymph nodes become swollen and painful, but sores do not form.

Glandular tularemia

Oculoglandular

An eye becomes painful, swollen, and red, and pus often oozes from it. Nearby lymph nodes become swollen and painful. Oculoglandular tularemia probably results from touching the eye with a contaminated finger or from having infected fluid splashed into the eye.

Oculoglandular tularemia

Oropharyngeal

The throat (pharynx) is sore, and lymph nodes in the neck are swollen. Some people also have abdominal pain, nausea, vomiting, and diarrhea. Oropharyngeal tularemia is usually caused by eating undercooked contaminated meat.

Typhoidal

Chills, high fever, and abdominal pain develop, but no sores form and lymph nodes do not swell. Typhoidal tularemia develops when the bloodstream is infected. Sometimes the source of infection is unknown.

Pneumonic

The lungs are infected. People may have a dry cough, be short of breath, and have chest pain. Pneumonic tularemia is caused by inhaling the bacteria or spread of the bacteria through the bloodstream to the lungs. This type develops in 10 to 15% of people with ulceroglandular tularemia and in 50% of people with typhoidal tularemia.

 

Pneumonic tularemia

Septicemic

This rare type is the most serious. It is a bodywide illness that develops when bacteria spread through the bloodstream and cause many organs to malfunction. Blood pressure is low, the lungs fill with fluid, and clotting factors in blood are used up, causing bleeding (disseminated intravascular coagulation).

Risk factors of Tularemia

Animals carry the bacteria that causes tularemia. You’re at increased risk of getting the disease if you have frequent contact with animals.

People at an increased risk for tularemia include:

• Those who work closely with animals, such as veterinarians, zookeepers, and park rangers
• Those who live in heavily forested areas
• Those who work with animal carcasses, such as hunters, taxidermists, and butchers
• Those who work in gardening and landscaping

Causes

Tularemia doesn’t occur naturally in humans and isn’t known to pass from person to person. However, tularemia occurs worldwide, especially in rural areas, because many mammals, birds and insects are infected with F. tularensis. The organism can live for weeks in soil, water and dead animals.

Causes of tularemia

Unlike some infectious diseases that spread from animals to people through a single route, tularemia has several modes of transmission. How you get 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 deer flies are most likely to transmit the disease to humans. Tick bites cause a large percentage 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 an infected animal.

Airborne bacteria: Bacteria in the soil can become airborne during gardening, construction or other activities that disturb the earth. Inhaling the bacteria can lead to pneumonic tularemia. Laboratory workers who work with tularemia also are at risk of airborne infection.

Contaminated food or water: Although uncommon, it’s possible to get tularemia from eating undercooked meat of an infected animal or drinking contaminated water. The signs include vomiting, diarrhea and other digestive problems (oropharyngeal tularemia).

Heat kills F. tularensis, so cook meat to the right temperature a minimum of 165 F (73.8 C) for ground meat and game meat to make it safe to eat.

Symptoms of Tularemia

The signs and symptoms of tularemia vary depending on how the bacteria enter the body. Illness ranges from mild to life-threatening. All forms are accompanied by fever, which can be as high as 104 °F. Main forms of this disease are listed below.

Ulceroglandular: This is the most common form of tularemia and usually occurs following a tick or deer fly bite or after handing of an infected animal. A skin ulcer appears at the site where the bacteria entered the body. The ulcer is accompanied by swelling of regional lymph glands, usually in the armpit or groin.

Glandular: Similar to ulceroglandular tularemia but without an ulcer. Also generally acquired through the bite of an infected tick or deer fly or from handling sick or dead animals.

Oculoglandular: This form occurs when the bacteria enter through the eye. This can occur when a person is butchering an infected animal and touches his or her eyes. Symptoms include irritation and inflammation of the eye and swelling of lymph glands in front of the ear.

Oropharyngeal: This form results from eating or drinking contaminated food or water. Patients with orophyangeal tularemia may have sore throat, mouth ulcers, tonsillitis, and swelling of lymph glands in the neck.

Pneumonic: This is the most serious form of tularemia. Symptoms include cough, chest pain, and difficulty breathing. This form results from breathing dusts or aerosols containing the organism. It can also occur when other forms of tularemia (e.g. ulceroglandular) are left untreated and the bacteria spread through the bloodstream to the lungs.

Typhoidal: This form is characterized by any combination of the general symptoms (without the localizing symptoms of other syndromes)

Diagnosis and test

Diagnosing tularemia isn’t easy because it can often appear like other diseases. The various possible routes of entry of the bacterium complicates the issue. Your doctor must rely heavily on a your personal and medical history to help diagnose you.

Your doctor may suspect tularemia if you’ve had recent travels, insect bites, or contact with animals. They may also suspect that you have this disease if you already have a serious medical condition that compromises your immune system, such as cancer or HIV or AIDS.

Tests for the presence of this disease include:

• A serology test for antibodies your body has created to fight the bacteria
• A pleural fluid test, which tests the fluid from the pleurae in the chest cavity
• A skin biopsy of a lesion and microscopic exam looking for the presence of tularemia
• A lymph node biopsy, which is the removal of tissue from a lymph node for examination
• A bone marrow biopsy, which is the removal of a sample of bone marrow for examination

Treatment and medications

Each case of tularemia is treated according to its form and severity. Early diagnosis allows for immediate treatment with antibiotics.

Antibiotics that may be used include:

• Ciprofloxacin
• Doxycycline (Vibramycin)
• Gentamicin, which is usually used to treat oculoglandular tularemia
• Streptomycin

Surgical intervention may be required to drain swollen lymph nodes or to cut away infected tissue from a skin ulcer. You may also be given medications for fever or headache symptoms.

Prevention of Tularemia

There’s currently no publicly available vaccine. If you work in a high-risk occupation or live in an area where tularemia is present, these measures may help reduce your chance of infection:

Protect yourself from insects: Most people in the United States get tularemia through 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 repellent with 20 to 30 percent DEET, picaridin or IR3535, but follow the manufacturer’s directions carefully. Apply insect repellant in moderation, and wash it off at the end of the day. Check yourself for ticks often and remove them immediately if you find any.

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 carefull: 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 appeared ill.

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 flea and tick protection, and don’t let them come in close contact with wild or dead animals.