What Is Anthrax? Risk and Prevention

Anthrax is the name of a potentially deadly infection caused by the spore-forming bacterium Bacillus anthracis. The bacteria are common in soil, where they typically exist as dormant spores that can survive as long as 48 years. Under the microscope, the living bacteria are large rods. Being exposed to the bacteria is not the same as being infected by it. As with all bacteria, an infection takes time to develop, which offers a window of opportunity for disease prevention and cure. Anthrax is deadly primarily because the bacteria release toxins. Toxemia results when enough bacteria are present.

Anthrax mainly affects livestock and wild game, but it's possible for humans to contract the infection from direct or indirect contact with affected animals. It's also possible to become infected by inhaling the spores or from the bacteria directly entering the body from an injection or open wound. While person-to-person transmission of anthrax has not been confirmed, it's possible that contact with skin lesions could transmit the bacteria. Generally, however, anthrax in humans is not considered to be a contagious disease.

Routes of Anthrax Infection and Symptoms

One route of anthrax infection is from eating undercooked meat from an infected animal. — Peter Dazeley / Getty Images

There are four routes of anthrax infection. The symptoms of infection depend on the route of exposure. While symptoms from anthrax inhalation may take weeks to appear, signs and symptoms from other routes usually develop within one day to a week after exposure.

Cutaneous Anthrax

The most common way to contract anthrax is by getting the bacteria or spores into the body through a cut or open sore in the skin. This form of anthrax is rarely fatal, providing it is treated. While anthrax is found in most soil, infection tends to come from handling infected animals or their skins.

Symptoms of infection include an itchy, swollen bump that may resemble an insect or spider bite. The bump eventually becomes a painless sore that develops a black center (called an eschar). There may be swelling in the tissue surrounding the sore and in lymph nodes.

Gastrointestinal Anthrax

Gastrointestinal anthrax comes from eating undercooked meat from an infected animal. Symptoms include headache, nausea, vomiting, fever, abdominal pain, and loss of appetite. These may progress to a sore throat, swollen neck, difficulty swallowing, and bloody diarrhea. This form of anthrax is rare.

Inhalation Anthrax

Inhalation anthrax is also known as pulmonary anthrax. It is contracted by breathing anthrax spores. Of all the forms of anthrax exposure, this is the most difficult to treat and the most deadly.

Initial symptoms are flu-like, including fatigue, muscle aches, mild fever, and sore throat. As the infection progresses, symptoms can include nausea, painful swallowing, chest discomfort, high fever, difficulty breathing, coughing up blood, and meningitis.

Injection Anthrax

Injection anthrax occurs when the bacteria or spores are directly injected into the body. In Scotland, there have been cases of injection anthrax from injecting illegal drugs (heroin). Injection anthrax has not been reported in the United States.

Symptoms include redness and swelling at the injection site. The injection site may change from red to black and form an abscess. Infection can lead to organ failure, meningitis, and shock.

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Anthrax as a Bioterrorism Weapon

As a bioterrorist weapon, anthrax is spread by distributing the spores of the bacteria. — artychoke98 / Getty Images

While it's possible to catch anthrax from touching dead animals or eating undercooked meat, most people are more worried about its potential use as a biological weapon.

In 2001, 22 people became infected with anthrax when spores were sent via mail in the United States. Five of the infected individuals died from the infection. The US postal service now tests for anthrax DNA at major distribution centers.

While the United States and Soviet Union agreed to destroy their stockpiles of weaponized anthrax, it likely remains in use in other countries. The US-Soviet agreement to end bioweapon production was signed in 1972, but in 1979, over a million people in Sverdlovsk, Russia, were exposed to an accidental release of anthrax from a nearby weapons complex.

While anthrax bioterrorism remains a threat, an improved ability to detect and treat the bacteria makes the prevention of infection much more likely.

Anthrax Diagnosis and Treatment

Cultures taken from a person infected with anthrax show the rod-shaped bacteria. — Jayson Punwani / Getty Images

If you have the symptoms of anthrax exposure or have reason to think you might have been exposed to the bacteria, you should seek professional medical attention. If you know for certain you've been exposed to anthrax, an emergency room visit is in order. Otherwise, keep in mind the symptoms of anthrax exposure are similar to those of pneumonia or the flu.

To diagnose anthrax, your doctor will rule out influenza and pneumonia. If these tests are negative, the next tests depend on the type of infection and symptoms. They may include skin testing, a blood test to look for the bacteria or antibodies to it, a chest x-ray or CT scan (for inhalation anthrax), a lumbar puncture or spinal tap (for anthrax meningitis), or a stool sample (for gastrointestinal anthrax).

Even if you're exposed, an infection can usually be prevented by oral antibiotics, such as doxycycline (e.g., Monodox, Vibramycin) or ciprofloxacin (Cipro). Inhalation anthrax is not as responsive to treatment. In its advanced stages the toxins produced by the bacteria can overwhelm the body even if the bacteria are controlled. In general, treatment is most likely to be effective if it's started as soon as an infection is suspected.

The Anthrax Vaccine

There is a human vaccine for anthrax, but it isn't intended for the general public. While the vaccine doesn't contain live bacteria and can't lead to an infection, it is associated with potentially serious side effects. The main side effect is soreness at the injection site, but some people are allergic to components of the vaccine. It is considered too risky to use in children or elderly adults. The vaccine is made available to scientists who work with anthrax and other people in high-risk professions, such as military personnel. Other people who are at increased risk of infection include livestock veterinarians, people to handle game animals, and people who inject illegal drugs.

If you live in a country where anthrax is common or you travel to one, you can minimize the risk of exposure to the bacteria by avoiding contact with livestock or animal skins and making certain to cook meat to a safe temperature. No matter where you live, it's a good practice to cook meat thoroughly, use care handling any dead animal, and take care if you work with hides, wool, or fur.

Anthrax infection primarily occurs in sub-Saharan Africa, Turkey, Pakistan, Iran, Iraq, and other developing countries. It's rare in the Western Hemisphere. About 2,000 cases of anthrax are reported worldwide every year. Mortality is estimated to range between 20% and 80% without treatment, depending on the route of infection.

References and Further Reading

Types of Anthrax. CDC. July 21, 2014.
Madigan, M.; Martinko, J., eds. Brock Biology of Microorganisms (11th ed.). Prentice Hall, 2005.
"Cepheid, Northrop Grumman Enter Into Agreement for the Purchase of Anthrax Test Cartridges". Security Today. Aug. 16, 2007.
Hendricks, Katherine A., et al. “Centers for Disease Control and Prevention Expert Panel Meetings on Prevention and Treatment of Anthrax in Adults.” Emerging Infectious Diseases, vol. 20, no. 2, Centers for Disease Control and Prevention (CDC), Feb. 2014.