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.

Transmission

Tularemia may be acquired through the following routes:

• 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

Person-to-person transmission of Francisella tularensis has never been documented.

Incubation period

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.

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. 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 - the most serious, but least common forms of the disease. Symptoms 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

Treatment and prevention

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.

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. There is no vaccine available in the UK.

Epidemiology

Tularemia does not occur naturally in animals within the UK.

F. tularensis infects more than 100 species of wild mammals, birds and insects worldwide. 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.

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.