Bacterial Agents Used for Bioterrorism

Jan K. Horn

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Tularemia

Tularemia is a disease of the northern hemispheres caused by Francisella tularensis, an aerobic gram-negative coccobacillus.[11] In the United States, most cases are associated with rabbits or hares in the winter and with ticks in the summer. About 200 cases/year are reported in the United States, mostly in the south-central and western states as a consequence of tick bites. The infectious inoculum is quite low (one to ten organisms by aerosol or intradermal route). There is no evidence for person-to-person transmission.

A number of clinical forms of the disease can occur depending on the type of exposure. Ulceroglandular infection is typified by cutaneous ulceration at the site of the tick bite with regional lymphadenopathy. Glandular infection is manifested by adenopathy without the skin lesion. The oculoglandular form is associated with a painful purulent conjunctivitis and adenopathy, presumably from wiping eyes after contact with an open ulcer. Typhoidal infection, believed to be a possible presentation for infections resulting from bioterrorism, is the most severe form, accompanied by bacteremia and rarely adenopathy. Pneumonic infection, as a consequence of aerosol transmission, is also a bioterrorist threat that can follow secondarily the glandular forms of the disease.

Pneumonic tularemia has an incubation period of three to five days (range one to 21 days) followed by the abrupt onset of fever, chills, headaches, myalgia, and a nonproductive cough. Chest x-ray displays segmental lobar infiltrates, hilar adenopathy, and effusions. Mortality approaches 30% if untreated and is <10% if treated. Treatment should include streptomycin, gentamycin or a tetracycline. Prophylaxis for febrile cases should consist of doxycycline or tetracycline; however, a seven-day fever watch preceding treatment is preferable. At this point, vaccines are investigational and not available for general use. The role of vaccination against tularemic primary infection or postexposure prophylaxis is unknown.

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