Biological Weapons -- Tularemia

The bacteria that causes tularemia is one of the most infectious pathogenic bacteria known, requiring inoculation or inhalation of as few as 10 organisms to cause disease. Humans become infected through diverse environmental exposures which can develop severe, and sometimes fatal, illnesses, but do not transmit infection to others. F tularensis could be a dangerous potential biological weapon because of its extreme infectivity, ease of dissemination, and substantial capacity to cause illness and death. In the US, human cases have been reported in every state except Hawaii. Tularemia is almost entirely a rural disease. F tularensis is found in widely diverse animal hosts and habitats and can be recovered from contaminated water, soil, and vegetation. In the U.S., reported cases have dropped sharply from several thousand per year prior to 1950 to less than 200 per year in the 1990s. In 1969, a WHO committee estimated that an aerosol dispersal of 110 pounds of virulent F tularensis over a metropolitan area with 5 million inhabitants would result in 250,000 incapacitating casualties, including 19,000 deaths. Illness would be expected to last for several weeks and disease relapses to occur during the ensuing weeks or months. . Symptoms A skin ulcer shows up in approximately 60% of patients and is the most common sign of tularemia. Ulcers are generally single lesions with heaped up borders 0.4-3 cm (1-3/4") in diameter. Incubation is 1 - 21 days (generally 3 - 5 days). The onset of tularemia is usually abrupt, with fever, headache, chills and shivering, generalized body aches (especially in the low back), cold symptoms, and sore throat and unexpected severe respiratory illness in otherwise healthy people. Nausea, vomiting, and diarrhea sometimes occur. Sweats, fever and chills, progressive weakness, malaise, loss of appetite, and weight loss are to be expected. A weapon using airborne tularemia would likely result in an outbreak of acute illness three to five days later. If untreated, tularemia symptoms often last several weeks, sometimes, for months, usually with progressive muscle weakness. Any form of tularemia may be complicated by secondary pleuropneumonia, sepsis, and, rarely, meningitis. Tularemia can infect humans through the skin, mucous membranes, gastrointestinal tract, and lungs. The major target organs are the lymph nodes, lungs and pleura, spleen, liver, and kidney. How does it spread? Ticks Humans can become infected by various modes, including bites by infected insects, handling infectious animal tissues or fluids, direct contact with or ingestion of contaminated water, food, or soil, and inhalation of infective aerosols. Although F tularensis is highly infectious and pathogenic, its transmission from person to person has not been proven. The organisms may also be transmitted by aerosol as a BW agent release, or by contamination of food or water supplies. Studies of volunteers have shown that tularemia aerosol exposures can incapacitate some persons in the first day or two of illness, and significant impairment in performing tasks can continue for days after antibiotic treatment is begun. F. tularensis can remain viable for weeks in water, soil, carcasses, hides, and for years in frozen rabbit meat. It is resistant for months to temperatures of freezing and below. It is easily killed by heat and disinfectants. Diagnosis Physical findings are usually non-specific. Chest x-ray may reveal a pneumonia. Routine culture is possible but difficult. The diagnosis can be established retrospectively by serology.Identification and diagnosis of tularemia using routine lab procedures could take several weeks. Treatment Supportive care may include respiratory support and hydration. Open lesions should be covered and topical antibiotics applied. Prompt treatment with antibiotics is recommended with one of the following: • streptomycin 7.5 to 10 mg/kg IM every 12 hours for 10 to 14 days. • gentamicin 3 to 5 mg/kg IV daily for 10 to 14 days. • ciprofloxacin 400 mg IV every 12 hours, switch to oral ciprofloxacin (500 mg every 12 hours) after the patient is clinically improved; continue for completion of a 10- to 14-day course of therapy. • ciprofloxacin 750 mg orally every 12 hours for 10 to 14 days. Isolation is not recommended, since it doesn't seem to be contagious. All food must be thoroughly heated before consumption to kill any organisms. Water must be thoroughly disinfected before consumption. Vaccine Given the short incubation period and incomplete protection of current vaccines, vaccination is not recommended for post-exposure prevention. A live, attenuated vaccine is available as an investigational new drug. It's administered once by scarification. A two week course of tetracycline is effective as prophylaxis when given after exposure. Mortality Prior to antibiotics, the overall mortality from infections was 5% - 15% and as high as 30% - 60% for untreated pneumonic and severe systemic forms of disease. Now, the overall fatality rate of reported cases in the U.S. is less than 2%. The less severe strains of the disease are rarely fatal. Without treatment, the clinical course could progress to respiratory failure, shock, and death. Sources: USAMRIID's Medical Management of Biological Casualties Handbood; Fourth Edition February 2001; pages 9-10; http://usamriid.detrick.army.mil/education/bluebook/bluebook.pdf Federation of American Scientists; http://www.fas.org/nuke/intro/bw/agent.htm Virtual Naval Hospital: Treatment of Biological Warfare Agent Casualties; http://www.vnh.org/FM8284/index.html CBS Bioterrorism Interactive; http://cbsnews.cbs.com/

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