Anthrax
Anthrax is infection with the gram-positive bacterium Bacillus anthracis that typically involves the skin, lungs, or digestive tract.
Anthrax is a potentially fatal disease that usually spreads to people from animals, especially cows, goats, and sheep. Dormant bacteria (spores) can live in soil and in animal products (such as wool) for decades and are not easily killed by cold or heat. Even minimal contact is likely to result in infection. Although infection in people usually occurs through the skin, it can also result from inhaling spores or from eating contaminated, poorly cooked meat. Infection cannot spread from person to person.
Because anthrax is highly lethal when inhaled, it has been considered and used by some countries and terrorists as an agent of biological warfare (see Section 17, Chapter 188). Anthrax bacilli produce several toxins, which are responsible for many of the symptoms.
Symptoms and Diagnosis
Anthrax skin infection begins as a painless, red-brown bump that appears 1 to 5 days after infection. The bump forms a blister, which hardens and eventually breaks open to form a black scab (eschar). Lymph nodes in the affected area may swell, and the person may feel ill--sometimes experiencing muscle aches, headache, fever, nausea, and vomiting. One in five untreated people dies.
Pulmonary anthrax (woolsorter's disease) results from inhaling the spores of the anthrax bacterium. The spores multiply in the lymph nodes near the lungs. Toxins produced by the bacteria cause the lymph nodes to swell, break down, and bleed, spreading the infection to nearby structures in the chest. Infected fluid builds up in the lungs and in the space between the lungs and the chest wall. Symptoms develop in two stages. For the first 2 to 3 days, the symptoms are vague and similar to those of influenza, with mild aches, fever, and dry cough. The person then suddenly develops severe difficulty breathing, high fever, and sweating, rapidly followed by shock and coma. This second stage is probably the result of a massive release of toxins. Infection of the brain and meninges (meningoencephalitis) may also occur. Many people die 24 to 36 hours after severe symptoms start, even with early treatment.
Anthrax of the digestive tract (gastrointestinal anthrax) is rare. When a person eats contaminated meat, the bacteria grow in the mouth, throat, or intestines and release toxins that cause extensive bleeding and tissue death. Sore throat, neck swelling, abdominal pain, vomiting, and bloody diarrhea also develop. At least half of the untreated people die.
Anthrax skin sores are diagnosed by their typical appearance. Knowing that a person had contact with animals or was in an area where other people developed anthrax also helps a doctor make the diagnosis. Anthrax bacteria are easily recognized under a microscope in samples from skin or body fluids. Also, the bacteria may be grown in culture. Blood tests can be used to detect fragments of bacterial DNA or antibodies to one of the bacterial toxins. In a person with pulmonary anthrax, the bacteria are sometimes, but not always, present in the sputum. In serious infections, the person may die before any test results are complete, so treatment is usually started when anthrax is first suspected.
Prevention and Treatment
People at high risk of contracting anthrax--such as veterinarians, laboratory technicians, and employees of textile mills that process animal hair--can be vaccinated. Because of anthrax's potential as a biological weapon, most members of the armed forces are also vaccinated. Despite widely publicized anxiety, well over 1.25 million people have received anthrax vaccine without serious adverse reactions. People exposed to anthrax may be given preventive treatment using either oral ciprofloxacin or doxycycline if the bacteria's susceptibility to penicillin is unknown. If susceptibility to penicillin is documented, children should be given preventive treatment with oral amoxicillin.
Anthrax infection is treated with a combination of antibiotics, including intravenous ciprofloxacin or doxycycline, plus clindamycin, rifampin, or penicillin. Corticosteroids may also be used to reduce any swelling in the throat. The longer treatment is delayed, the greater the risk of death.
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