TAB C – Anthrax

Overview: Bacillus anthracis is a rod-shaped, gram-positive, sporulating organism, the spores constituting the usual infective form, which causes anthrax, a zoonotic (transmitted from animals, the usual host, to humans) disease. Cattle, sheep, and horses are the chief domestic animal hosts, but other animals may be infected. Humans may contract the disease by handling infected animals’ contaminated hair, wool, hides, flesh, blood, and excreta; from manufactured products such as bone meal; and by purposeful dissemination of spores. The disease is transmitted through skin scratches or abrasions, wounds (cutaneous), inhaling spores (inhalation), eating insufficiently cooked infected meat (gastrointestinal), or by flies (cutaneous). All human populations are susceptible. Recovery from a mild exposure to the disease may confer immunity. The spores are very stable and may remain viable for many years in soil and water.[107] However, even anthrax spores will break down by exposure to bright sunlight.[108]

Signs and Symptoms: Inhaling between 8,000 and 50,000 spores (easily inhaled in one breath) can cause inhalation anthrax, the most likely type seen on the battlefield. After a 1- to 6-day incubation period, the disease produces fever, malaise, fatigue, cough, and mild chest discomfort, followed by severe respiratory distress with dyspnea (shortness of breath), diaphoresis (sweating), stridor (high-pitched, noisy respiration), and cyanosis (dark bluish or purplish skin coloration). Shock and death can occur within 24 to 36 hours of severe symptoms. If untreated until symptoms appear, inhalation anthrax results in almost 100% fatality to those who inhale an infectious dose, which also is the lethal dose because the bacilli multiply in the blood until the toxins released during cell division cause septic shock and respiratory failure. [109,110]

Desert Shield and Desert Storm Anthrax Prophylaxis:  The Michigan Department of Public Health produced the only licensed human vaccine against anthrax. Approximately 150,000 service members received this vaccine between January 11 and February 28, 1991. Additionally, theater medical units issued soldiers ciprofloxacin (a broad-spectrum antibiotic with a long period of effectiveness against a wide range of organisms)[111] in a pill blister pack and available on order for use if exposure to anthrax was imminent. The vaccine-antibiotic combination provides the best protection against anthrax.[112]

Anthrax Vaccine Efficacy:  When using BW agents on the battlefield, aerosol delivery can cause high agent concentrations and immunization does not always guarantee complete protection. In 1996 the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) studied the efficacy of the Michigan Department of Public Health anthrax vaccine against an aerosol challenge in rhesus monkeys. The standard vaccination series for anthrax starts at Week 0 and thereafter at 2 and 4 weeks; 6, 12, and 18 months; with yearly boosters thereafter. USAMRIID administered only two doses to the monkeys at Week 0 and Week 2. The study demonstrated significant protection after the second dose. Aerosol challenges of Bacillus anthracis spores to immunized monkeys at 760 times the LD50 dose (lethal to 50% of those exposed) six weeks after the second dose did not affect the protected monkeys, whereas all the control monkeys died 3 to 5 days after exposure. After almost two years, the two vaccine doses still provided significant protection; seven of eight test monkeys survived between 239 and 535 LD50 doses.[113] The licensed US vaccine has not been clinically tested on humans to determine its efficacy against a lethal aerosol challenge,[114] but testing the vaccine on animal surrogates has provided a means to gauge the protection levels humans might achieve. For about 30 years the Michigan Department of Public Health vaccine has been used to protect persons working around animals and has been tested and approved for protection against gastrointestinal anthrax and cutaneous anthrax. Producing the anthrax vaccine uses a non-lethal (non-pathogenic) Bacillus anthracis strain to produce anthrax protective antigen (PA) protein. The protein is not toxic or contagious and cannot cause or transmit anthrax.[115]

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