Definition

Anthrax is an infectious disease caused by the spore-forming bacteria called Bacillus anthracis. Infection in humans most often involves the skin (cutaneous anthrax), the gastrointestinal tract, or the lungs (inhalation anthrax).

Causes, Incidence, and Risk Factors

Anthrax is caused by the bacterium Bacillus anthracis. While anthrax commonly affects hoofed animals such as sheep and goats, humans may acquire this disease as well. Humans can acquire anthrax through contact with animal hides or hair, bone products, and wool, as well as contact with infected animals. Historically, the populations most at risk for anthrax include farm workers, veterinarians, and tannery and wool workers.

Anthrax is a potential agent for use as a biological weapon or bio-terrorism. While at least 17 nations are believed to have a biological weapons program, it is unknown how many nations or groups are working with anthrax. Most bio-terrorism experts have concluded that it is technologically difficult to use anthrax effectively as a weapon on a large scale.

Cutaneous anthrax is an infection of the skin with anthrax. The disease occurs after the bacteria contact skin cuts or abrasions. Usually within two weeks, an itchy skin lesion develops (similar to an insect bite). This lesion may later blister and then break down, resulting in a black ulcer which is frequently painless. The skin lesion is usually surrounded by significant swelling. Sometimes painful lymph nodes may develop. A scab is often formed which then dries and falls off within two weeks. In 20% of untreated individuals, the infection may spread through the bloodstream and become fatal. However, in most individuals who receive appropriate treatment, death from cutaneous anthrax is extremely rare.

Inhalation anthrax develops when anthrax spores enter the lungs. A person may have spores in the nasal passages (which indicates exposure), but that doesn't mean they will get the disease. In fact, antibiotic therapy following known or suspected exposure can help prevent the disease. In order for a person to develop the actual disease, the spores must germinate -- a process which may take several days, or even up to 60 days to occur. The spores move to the lymph nodes, and once they germinate, lead to the release of several toxic substances (toxins). This results in hemorrhage, swelling, and tissue death. The main form of inhalation anthrax includes hemorrhagic infection of the lymph nodes in the chest (hemorrhagic mediastinitis). Up to half of affected individuals may also have a hemorrhagic meningitis.

There are usually two stages of inhalation anthrax -- the first stage can last from hours to a few days and is similar to a flu-like illness with fever, headache, cough, shortness of breath, and chest pain. The second stage often develops suddenly and is notable for shortness of breath, fever, and shock. This second stage is highly fatal in up to 90% of individuals because of the build-up of toxins.

The gastrointestinal form of anthrax (gastrointestinal anthrax) occurs with ingestion of contaminated meat. Disease usually develops within one week and can affect the upper portion of the gastrointestinal tract (mouth and esophagus) or the intestines and colon. Infection in both of these areas may result in spread of the infection by the bloodstream and can result in death.

Symptoms

• Cutaneous anthrax: papule, blister, ulcer with black scar with extensive surrounding swelling
• Inhalation anthrax: Initial stage -- fever, malaise, headache, cough, muscle aches, shortness of breath, and chest pain; Second stage -- fever, severe shortness of breath, and shock
• Gastrointestinal anthrax: nausea and vomiting (may include blood), anorexia, and bloody diarrhea

Signs and Tests

• The appropriate tests to diagnose anthrax depend on the type of disease suspected (cutaneous, inhalational, or gastrointestinal).
• If cutaneous anthrax is suspected, a culture of the skin lesion will be done to identify the bacteria that causes anthrax.
• If inhalation anthrax is suspected, a chest X-ray, blood cultures, sputum cultures, spinal tap for CSF culture, and gram stain may be performed. Samples may need to be sent to a special lab for more definitive testing, including PCR, immunoflourescence, and immunohistochemistry.

Treatment

The mainstay of treatment is early antibiotic therapy. Several antibiotics are effective, including penicillin, doxycycline, and ciprofloxacin (Cipro). If an outbreak of anthrax is suspected, the antibiotic of choice is ciprofloxacin, until it is known whether the anthrax strain is resistant to any of the other usual antibiotics. Because spores may take up to 60 days to germinate, the length of treatment is usually 60 days.

For inhalation anthrax, people with known or suspected exposure would be given oral antibiotics (pills). If a person develops symptoms of the disease or has a positive test for the disease (not just for exposure), antibiotics would be given intravenously (IV) for 14 days, then orally for the rest of the 60 days.

Cutaneous anthrax is treated with oral antibiotics (pills).

In the event of a bio-terrorist attack, the National Pharmaceutical Stockpile is available to supplement and help provide antibiotics should a shortage occur.

Expectations (Prognosis)

The prognosis of cutaneous anthrax treated with antibiotics is excellent. However, in the absence of antibiotics, up to 20% of individuals may die as anthrax may spread into the bloodstream.

The prognosis of inhalation anthrax once it reaches the second stage is poor, even with antibiotic therapy. Up to 90% of cases in the second stage are fatal.

The prognosis of gastrointestinal anthrax is also poor with a high proportion of individuals dying of this disease.

Complications

• Cutaneous anthrax: spread of infection into the bloodstream
• Inhalation anthrax: hemorrhagic meningitis, mediastinitis, shock, and death
• Gastrointestinal anthrax: hemorrhage, shock, and death

Call Your Health Care Provider

Notify your health care provider if you have had an exposure to anthrax and you develop signs and symptoms of cutaneous, inhalation, or gastrointestinal anthrax as described above.

Even if you are unaware of a particular exposure to anthrax, if you develop skin lesions or develop flu-like symptoms, you should contact your medical provider. While there are many illnesses with similar symptoms, you will need a medical evaluation to sort out which illness is causing your symptoms.

Prevention

There are two primary modes of prevention of anthrax.

For individuals who have been truly exposed to anthrax (but have no signs and symptoms of the disease), preventive antibiotics may be offered, such as ciprofloxacin, penicillin, or doxycycline, depending on the particular strain of anthrax.

Vaccination has also been developed and is given in a 6-dose series. This vaccine is mandated for all U.S. military personnel. It is currently not available, nor is it recommended, for use in the general public.

THERE IS NO TRANSMISSION OF ANTHRAX FROM PERSON TO PERSON. Household contacts of individuals with anthrax do not need antibiotics unless they have also been exposed to the same source of anthrax.

Additional information on anthrax is available from the Centers for Disease Control and Prevention (CDC). Advice on how to handle suspicious mail or mail-based anthrax threats is available from the United States Postal Service.