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Identification F. tularensis is a small Gram-negative aerobic bacillus with two main serotypes: Jellison Type A and Type B. Type A is the more virulent form. The causative agent of the disease was named after Dr. Edward Francis and the location where the organism was discovered, Tulare County, California. Tularemia is frequently spread by direct contact with rabbits, leading to the term "rabbit fever." However, the disease can also be spread by other animals, typically rodents, and by arthropods. It is a primarily rural disease that is found in all 50 states, except Hawaii. Pathogenesis Historical commentaries reference the virulence of the disease, indicating that people have been aware of pathogenicity of Francisella for thousands of years. However, there is still much to be learned about this extremely virulent organism. The disease can be contracted by ingestion, inhalation, or by direct skin contact. Tularemia occurs in six different forms: typhoidal, pneumonic, oculoglandular, oropharyngeal, ulceroglandular, and glandular. Clinical diagnosis can be difficult since the disease mimics a slough of other illnesses. Pathogenesis varies greatly depending on mode of infection. Manifestations The incubation period is about 3-5 days but it can take as long as two weeks for symptoms to appear. Symptoms vary based on mode of infection, but generally include fever, chills, joint and muscle pain, headache, weakness, and sometimes pneumonia. People who develop pneumonic tularemia experience chest pain, bloody sputum, and difficultly breathing. The disease is easily cured by antibiotic treatment. Treatment If infection is suspected, diagnosis can be made based on serological assays since F. tularensis is difficult to culture on standard media. Agglutination titers can be performed following the first week of infection and reach a peak during the 4-8 weeks. Infected individuals are normally placed on a regimen of streptomycin or gentamycin for 10-14 days. Beta-lactams are generally ineffective due to beta-lactamase activity. Prevention The disease is usually contracted by
handling infected animal carcasses, consuming contaminated food or water,
or by inhaling the bacteria. Standard precautions should be observed when
infection is suspected. Wear waterproof gloves when handling animals and
thoroughly cook the meat of rabbits and rodents. There is no evidence of
person-to-person transmission. A live, attenuated vaccine is currently
under review by the USFDA and may be available soon in the United States.
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