Anthrax is an infection that is caused by the bacteria Bacillus anthracis. These bacteria form spores that are hard-shelled, dormant versions of the bacteria. When the spores get inside of the body, they can become "activated" and cause symptoms of infection. These spores can survive in the soil for many decades.
Anthrax most commonly occurs in animals such as pigs, cattle, horses, and goats, but it can also infect people. Infections in people are caused by contact with the spores through a cut or scratch in the skin (known as cutaneous anthrax), by inhaling the spores (known as inhaled or pulmonary anthrax), or by eating meat that contains the spores (known as intestinal anthrax).
In biological warfare, anthrax can be transmitted intentionally through the air or by contact with an object that has the bacteria on it. Anthrax cannot be passed from one person to another (i.e., it is not contagious).
It is very rare that people get anthrax infection through natural causes. However, anthrax can be produced in laboratories and may be used as an agent of biological warfare. Anthrax is used in this manner because of the serious disease that results when the anthrax spores are inhaled. Pulmonary anthrax often causes death if it's not treated in the early stages, which is why it is very important to recognize the symptoms of this infection (see "Symptoms and Complications").
The most common type of anthrax infection is cutaneous (on the skin) anthrax. In fact, this accounts for over 95% of naturally-occurring anthrax infections. Cutaneous anthrax infection may take place when someone handles animals or animal products (wool or other woven materials) that are contaminated with anthrax, or if someone handles materials that have been intentionally contaminated with anthrax.
It is quite rare for meat to be contaminated with the bacteria that causes anthrax in North America. Therefore, intestinal anthrax is very rare on this continent.
Symptoms and Complications
Pulmonary anthrax is by far the most dangerous form of this infection, but also the rarest. It causes symptoms that start out like the flu. These symptoms include fever, chest discomfort, malaise, tiredness, and dry cough. Symptoms usually appear a week after infection, but may take up to 2 months to show up.
If the symptoms are not treated quickly, the infection can rapidly turn into a severe infection similar to pneumonia (inflammation of the lungs). Shortness of breath, high fever, fast heart rate, and heavy sweating then develop. Meningitis (swelling of the brain) and pain in the abdomen follow. Few survive more than a few days beyond the development of these types of symptoms. Fortunately, the risk of death for patients given early and aggressive treatment decreases to around 45%.
Cutaneous anthrax is much less dangerous than the inhaled form of anthrax. When infection occurs in this manner, the skin develops a raised, sometimes itchy bump that looks and feels like an insect or spider bite.
Symptoms of cutaneous anthrax usually appear around 1 to 7 days after infection. Within a day or 2, sores develop that usually turn black in the centre. Usually, people with cutaneous anthrax feel only mildly ill. Early antibiotic treatment is almost always successful in curing this type of anthrax. It may take several weeks to heal.
If cutaneous anthrax is not treated, the bacteria may get into the bloodstream and cause more serious symptoms. Signs of spreading infection include fever, chills, and swollen lymph glands close to the area of the sore.
Intestinal anthrax symptoms include severe abdominal pain, nausea, vomiting, severe diarrhea, fever, and bleeding from the gastrointestinal tract (stomach and intestines). The severity of these symptoms range from mild (or none) to fatal. Symptoms of intestinal anthrax appear in about 1 to 7 days.
It is important to remember that anthrax is not passed from person to person. It is very rare for a person to develop anthrax unless the spores get below the surface of the skin or the lining of the stomach or intestines. The inhaled form of anthrax develops only after thousands of spores are inhaled all the way down to the lungs.
Making the Diagnosis
Anthrax is diagnosed by taking samples from blood, respiratory secretion, or from any skin sores. The samples are sent to a laboratory to determine if they contain the bacteria that cause anthrax. The results are usually available about 2 days after the sample is taken.
Blood tests can determine if a person has come in contact with the bacteria that cause anthrax. Antibodies (proteins that fight off substances the body sees as foreign) to the bacteria will have been produced by the body's immune system, and they can be detected by a laboratory test.
People can be exposed to the bacteria that cause anthrax without becoming sick. Your doctor will evaluate your risk of exposure. However, if a test comes back positive, that person should be treated for anthrax in case the infection is in the early stages, before symptoms are evident.
Treatment and Prevention
Anthrax is prevented with immunization and antibiotic treatment for those people who have been exposed to anthrax. Pre-exposure immunization is not recommended for the general population, but may be given to those with higher occupational risk (e.g., veterinarians or military personnel). Although it is still considered investigational, subcutaneous (under the skin) vaccinations are usually given as soon as exposure is detected, again 2 weeks later, and then another 2 weeks after that. Treatment with antibiotics continues for at least 4 weeks (until all the vaccination injections have been given) and generally up to 60 days.
Cutaneous anthrax is usually treated with either fluoroquinolone antibiotics (e.g., ciprofloxacin*, moxifloxacin, levofloxacin), or doxycycline for 7 to 10 days for naturally-acquired infections. Treatment may be extended to 60 days if there is a risk of inhalation exposure, or if the infection is suspected to be associated with an act of biological warfare. In young children, ciprofloxacin may cause bone development problems, and doxycycline may cause discolouration of teeth and slowing bone growth. The risks involved for children and adolescents younger than 18 years of age using these antibiotics should be weighed against the benefits of treatment for anthrax.
Pulmonary anthrax is usually treated with a dual combination of injected (intravenous) antibiotics: either ciprofloxacin with clindamycin, or ciprofloxacin with linezolid. In very specific cases, these can be switched out for other antibiotics, such as rifampin, meropenem, ampicillin, or levofloxacin. After 2 weeks, or once the individual is clinically stable (whichever is longer), these antibiotics are instead taken by mouth, for a total period of 60 days. Pregnant women receive the same treatment. Pulmonary anthrax can also be treated with a combination of antibiotics alongside injections of intravenous anthrax immunoglobin monoclonal antibodies, such as obiltoxaximab.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.
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