• Francisella tularensis results tularaemia in man and certain small mammals, such as rabbits, hares, beavers and several rodent species.
• Tularaemia was originally described in Tulare county, California.
• It can be transmitted by direct contact, by biting flies, mosquitoes and ticks, by contaminated water or meat or aerosols.
• Francisella tularensis is also know as Pasteurella tularensis or Brucella tulerensis)

Morphology of Francisella tularensis:

• It is a very small, nonmotile, nonsporing, capsulate, gram-negative coccobacillus, about 0.3 to 0.7 μm × 0.2 μm in size.
• In culture it tends to be pleomorphic to and larger, even filamentous, forms are present.
• It stains poorly with methylene blue but dilute carbol fuchsin (10%) produces characteristic bipolar staining.

Cultural Characteristics of Francisella tularensis:

• F. tularensis is strictly aerobic.
• It will not grow on ordinary nutrient media but grows well on blood agar containing 2.5 percent glucose and 0.1 percent cysteine hydrochloride.
• Minute droplet-like colonies develop in 72 hours.

Biochemical characteristics of Francisella tularensis:

• Under suitable conditions acid is formed from glucose and maltose. Indole and urease tests are negative.
• Two biovars are recognized. Strains of F. tularen­sis have been subdivided into biotypes based on their virulence and epidemiological behaviour.
• Highly virulent strains are found only in N. America, while strains of low virulence are seen in Europe and Asia also.

Pathogenesis of Francisella tularensis:

• The infection, which is a typical zoonosis, is mainly spread by insects or ticks among lagomorphs and rodents.
• It is transmitted to man through handling of infected animals, e.g. rabbits or hares tick, mosquito or fly bites, inhalation of contaminated dust, ingestion of contaminated water or meat.
• Laboratory workers are at higher risk while handling infected laboratory animals or cultures of the organism.
• Man to man transmission of infection apparently does not occur.
• In human beings, tularemia may present as a local ulceration with lymphadenitis, a typhoid like fever with glandular enlargement or an influenza like respiratory infection.
• The severity of disease is much greater with type A strains and case fatality rates may exceed 5 percent.
• Disease caused by type B strains is much less severe, with very low mortality.

Laboratory Diagnosis of Francisella tularensis :

• F. tularensis is extremely dangerous to handle in the laboratory and Category 3 containment is required for all manipulations and animal work.
• Diagnosis may be made by culture or by inoculation into guinea pigs or mice. A PCR has been described, but is not widely available.
• Serology is most likely to be positive after 3 weeks.
• Rising titres of agglutinins to F. tularensis or individual titres of 160 are diagnostic.
• Serum from cases of F. tularensis may cross-react with brucellosis and vice versa, usually to relatively low titre.
• An intradermal delayed hypersensitivity test has been used in the past but the antigen is not readily available.

Treatment of Francisella tularensis:

• Streptomycin or gentamicin are the antibiotics of choice in tularaemia and are usually curative.

Prophylaxis:

• A vaccine based on the live-attenuated LVS strain confers some protection.
• It can be administered by scarification to persons who are subject to high risk of infection.
• F. tularensis has been developed as a biological warfare agent and has potential application in bioterrorism.

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