Francisella tularensis is the causative agent of tularemia, primarily transmitted through ticks and contact with infected rodents. This gram-negative bacillus is difficult to culture due to its fastidious growth requirements, and tularemia can manifest in various forms, including fever and respiratory symptoms. An attenuated vaccine is available for high-risk individuals, while diagnosis is confirmed through culture or serological tests.

1. Francisella

2. FRANCISELLA TULARENSIS
• The genus Francisella, consisting of F. tularensis, is named after
Francis for his pioneering studies on tularemia, caused by this bacillus.
• This is the causative agent of tularemia, a disease of rabbits and other
rodents, originally described in Tulare County, California.
• Infection is transmitted by ticks and several other arthropod vectors.
Human infection may occur by direct contact with infected rodents
such as rabbits or through tick bites.
• It can also be acquired by ingestion of contaminated meat or water
and inhalation of infective aerosols.

3. Morphology
• It is a minute, capsulated, non-motile, Gram-negative bacillus, about
0.3- 0. 7 x 0.2 µm in size.
• It resembles mycoplasma in being filterable and in multiplying by
filament formation and budding, besides binary fission.
• In infected animals, it acts as an intracellular parasite, being found in
large masses inside liver and spleen cells.
• It has fastidious growth requirements, and special media such as
Francis' blood dextrose cystine agar have to be employed for its
isolation.
• Minute transparent colonies appear after incubation for 3-5 days.

4. Classification
• Strains of S.tularensis have been subdivided into biotypes based on
their virulence and epidemiological behaviour.
• Highly virulent strains are found only in North America, while strains
of low virulence are seen in Europe and Asia as well.
• In human beings, tularemia may present as local ulceration with
lymphadenitis, a typhoid-like fever with glandular enlargement or an
influenza-like respiratory infection

5. Diagnosis
• The disease may also be water-borne, as a result of water pollution by
the excreta of infected rodents.
• The bacillus is highly infectious and laboratory infection has been
quite common.
• Diagnosis may be made by culture or by inoculation into guinea pigs
or mice.
• Agglutinating antibodies may be demonstrated in sera from patients.
An attenuated vaccine is available which can be administered by
scarification to persons who are subject to high risk of infection.

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