Anthrax is a potentially fatal infection with Bacillus anthracis, which may affect the skin, the lungs, or, rarely, the digestive (gastrointestinal) tract.
Anthrax can occur in wild and domestic animals that graze, such as cattle, sheep, and goats. Anthrax bacteria produce spores that can live for years in soil. Grazing animals become infected when they have contact with or consume the spores. Usually, anthrax is transmitted to people when they have contact with infected animals or animal products (such as wool, hides, and hair). Spores may remain in animal products 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 eating contaminated, undercooked meat. Anthrax cannot spread from person to person.
Anthrax is a potential biological weapon because anthrax spores can be spread through the air and inhaled.
Anthrax bacteria produce several toxins, which cause many of the symptoms.
Symptoms vary depending on how the infection is acquired: through the skin, through inhalation, or through the gastrointestinal tract.
More than 95% of cases involve the skin. A painless, itchy, red-brown bump appears 1 to 12 days after exposure. The bump forms a blister, which eventually breaks open and forms a black scab (eschar), with swelling around it. Nearby lymph nodes may swell, and people may feel ill—sometimes with muscle aches, headache, fever, nausea, and vomiting. About 20% of untreated people die, but with treatment, death is rare.
Inhalation Anthrax (Woolsorter's Disease):
This form is the most serious. It results from inhaling anthrax spores. Spores may stay in the lungs for weeks but eventually enter white blood cells, where they germinate, and the resulting bacteria multiply and spread to lymph nodes in the chest. The bacteria produce toxins that make the lymph nodes swell, break down, and bleed, spreading the infection to nearby structures. Infected fluid accumulates in the space between the lungs and the chest wall.
Symptoms develop 1 to 43 days after exposure. Initially, they are vague and similar to those of influenza, with mild muscle aches, a low fever, chest discomfort, and a dry cough. After a few days, breathing suddenly becomes very difficult, and people have chest pain and a high fever with sweating. Blood pressure rapidly becomes dangerously low (causing shock), followed by coma. These severe symptoms probably result from a massive release of toxins. Infection of the brain and the fluid around the meninges (an infection called meningoencephalitis) frequently develops. Many people die 24 to 36 hours after severe symptoms start, even with early treatment. Without treatment, all people with inhalation anthrax die. In the 2001 outbreak in the United States, 5 of the 11 people treated for inhalation anthrax died.
Gastrointestinal anthrax is rare. When people eat contaminated meat, the bacteria grow in the mouth, throat, or intestine and release toxins that cause extensive bleeding and tissue death. People have a fever, a sore throat, a swollen neck, abdominal pain, and bloody diarrhea. They also vomit blood. At least half of untreated people with gastrointestinal anthrax die. With treatment, about half of people die.
Doctors suspect skin anthrax based on its typical appearance. Knowing that people have had contact with animals or animal products or were in an area where other people developed anthrax supports the diagnosis. If inhalation anthrax is suspected, chest x-ray and computed tomography (CT) are done.
Samples from infected skin, fluids around the lungs, or stool are removed and examined with a microscope or cultured (enabling bacteria, if present, to multiply). Anthrax bacteria, if present, can be readily identified. If people have inhalation anthrax, doctors may also take samples of the sputum or blood or do a spinal tap (lumbar puncture) to obtain a sample of the fluid that surrounds the brain and spinal cord (cerebrospinal fluid). The samples are examined and analyzed. Blood tests may be done to check for fragments of the bacteria's genetic material or antibodies to the toxins produced by the bacteria.
Prevention and Treatment
A vaccine against anthrax can be given to people at high risk of infection. Because of anthrax's potential as a biological weapon, most members of the armed forces have been vaccinated. To be effective, the vaccine must be given in six doses. Despite widely publicized anxiety, over 1.25 million people have received the anthrax vaccine without having serious adverse reactions.
People who are exposed to anthrax may be given an antibiotic by mouth, usually ciprofloxacin or doxycycline or, if they cannot take these antibiotics, amoxicillin. The antibiotic is continued for 60 days to prevent the infection from developing. People may not need to take the antibiotic as long if they are also given several doses of anthrax vaccine.
The longer treatment is delayed, the greater the risk of death. Thus, treatment is usually started as soon as anthrax is first suspected:
Last full review/revision September 2008 by Matthew E. Levison, MD