Background information

What is tularemia?

Tularemia is a zoonosis, an infection which can be spread from animals to humans. It can also be waterborne, airborne or contracted via insect bites. It is caused by the bacterium Francisella tularensis which can infect many animals, especially small rodents, rabbits and hares, and also domestic cats.

There are two types of the bacterium, both of which can infect humans. Type A infections occur naturally only in North America. Type A infects animals and ticks and can be fatal in humans. Type B causes milder symptoms than type A and does not cause fatal infections. Type B occurs in animals throughout the northern hemisphere, including North America. Neither type occurs naturally in animals or in the environment within the UK.

What is its bioterrorism potential?

There are several factors that contribute to the bioterrorism potential of this organism, including its extreme infectivity and ease of dissemination through a variety of routes. Attempts have been made to weaponise tularemia, focussing on the airborne dispersal route (which would lead to inhalation of the organism).

How do you catch tularemia?

• Through the bite of an insect, e.g. tick or mosquito, which has fed on an infected animal
• Through direct contact with the tissues/secretions of infected animals
• Through inhaling or ingesting bacteria
• Through contact with or consumption of contaminated food or water

Any of the above routes might be used in a deliberate release, but the most likely would be airborne. Person-to-person transmission of Francisella tularensis has never been documented.

How long can you have the infection before developing symptoms?

Symptoms usually develop 2-5 days after infection, but the incubation period can be as short as 1 day or as long as 3 weeks.

What are the symptoms?

Tularemia classically presents as one of six clinical syndromes (pneumonic, septicaemic, ulceroglandular, oculoglandular, oropharyngeal and typhoidal), depending on route of infection and biotype of the infecting organism. Onset of infection is usually acute and heralded by fever, chills, headache and myalgia. Following a deliberate airborne release the most likely presentations would be pneumonic or septicaemic tularemia. Natural infection can result in a variety of symptoms:

• Ulcers – these are common and occur either at the site of an infected insect bite, or sometimes on the surface of the eye following exposure to aerosolised bacteria. The ulcers may be accompanied by swollen lymph nodes, general aches and fevers.
• Sore throat, pharyngitis or tonsillitis – after consumption of contaminated food or water. Less commonly, ingestion or inhalation can lead to flu-like symptoms and a gut upset.
• Pneumonia and blood poisoning - most serious, and least common forms of the disease. These forms of disease would however be the most likely to occur following a deliberate airborne release. Symptoms would include sudden onset of high fever, chills, muscle aches, dry cough and weakness.
• Acute flu-like illness, often with diarrhoea and vomiting, can occur following inhalation or ingestion of the bacteria.

How can tularemia be treated?

Tularemia may be successfully treated with specific antibiotics. If treated, the overall mortality rate of type A tularemia is 1%. In untreated cases, the mortality rate of type A infections ranges from 4% for some of the ulcerative conditions, to 30-50% for typhoidal, septicaemic and pneumonic forms of the disease.

How can tularemia be prevented?

Prevention of naturally occurring disease depends on avoiding tick bites, careful handling of animals, and ensuring that wild animal meats are thoroughly cooked for consumption. Effective antibiotic prophylaxis is available in the event of a suspect deliberate release. There is no vaccine currently recommended in the UK.

How common is tularemia?

Tularemia does not occur naturally in animals within the UK, so tularemia is only seen as a rare imported infection acquired abroad in Europe or North America. In areas of the world where the disease is more common in animals, cases and outbreaks in humans can and do occur. For example, there have been outbreaks in Kosovo and Spain as well as in the endemic areas in northern Europe.

Last reviewed: 24 March 2010