Anthrax is a serious infectious disease caused by the spore-forming bacterium Bacillus anthracis. The bacteria can be found naturally in soil, are resistant to drying and disinfection, and can remain alive in contaminated soil for decades. Anthrax commonly affects domestic and wild animals around the world. It is primarily a disease of plant-eating (herbivorous) animals such as cattle, sheep, goats, camels and horses. Disturbed grave sites of infected animals have been known to cause infection after 70 years. The introduction of veterinary vaccines has been effective in controlling the disease in animals.
People generally get sick with anthrax if they come in contact with infected animals or contaminated animal products. The disease is primarily an occupational hazard of veterinarians, agriculture and wildlife workers, or workers who butcher animals or process meat, hides, hair and wool. In fact, anthrax was historically called ‘woolsorter’s disease’ because it was so common among workers in the wool, hides and tanning industries. Anthrax is not contagious, which means you can’t catch it like the cold or flu. Although it is rare in the U.S., it continues to be a critical public health concern because the spores have been used as a weapon of biological warfare.
The type of illness a person develops depends on how anthrax enters the body. All types of anthrax can eventually spread throughout the body and cause death if they are not treated with antibiotics.
Infection can occur in four forms:
Cutaneous: caused by the bacterium entering a cut or scrape on the skin.
This is the most common form of infection with anthrax, accounting for more than 95% of naturally occurring human cases. Infection usually develops within 1 to 7 days after exposure with sores most commonly found on either the face, neck, arms or hands. Cutaneous anthrax begins as a raised itchy bump that looks like an insect bite but within 1 to 2 days becomes a painless sore, usually 1 to 3 cm in diameter, with a typical black area in the center. Lymph glands near the infected area may swell. Deaths from cutaneous anthrax are rare because the illness can be cured with appropriate antibiotics. Without treatment up to 20% of cutaneous anthrax cases may result in death.
Inhalation: caused by breathing in anthrax bacteria or spores. The spores are too small to be seen by the naked eye and have no special color, smell or taste.
This is considered the deadliest form of anthrax and the form most often associated with bioterrorism. Infection usually develops within a week after exposure, but it can take up to 2 months. Inhalation anthrax begins with mild cold or flu-like symptoms which include: fever, chills, malaise, mild cough or chest pain. Symptoms progress to respiratory distress with stridor (vibrating noise when breathing), hypoxemia and cyanosis (bluish coloring of the skin due to low oxygen). Death from inhalation anthrax can be greater than 85% if left untreated. However, early diagnosis and aggressive treatment can increase survival rates.
Gastrointestinal: caused by eating raw or undercooked meat from an animal infected with anthrax.
Gastrointestinal anthrax is the rarest form, difficult to recognize and has rarely been reported in the U.S. Infection usually develops from 1 to 7 days after exposure. Gastrointestinal anthrax is characterized by an acute inflammation of the intestinal tract. Initial signs of nausea, loss of appetite, vomiting, and fever are followed by abdominal pain, vomiting of blood, and severe diarrhea. Lesions have been found in the intestines and in the mouth and throat. Without treatment, more than half of patients with gastrointestinal anthrax die. However, with proper treatment, 60% of patients survive.
In 2009 to 2010, another type of anthrax infection was identified in heroin-injecting drug users in northern Europe. This type of infection has never been reported in the U.S. Symptoms may be similar to those of cutaneous anthrax, but there may be infection deep under the skin or in the muscle where the drug was injected. Symptoms can include: fever, chills, itchy bumps where the drugs were injected, and a painless sore with a black center. Some people presented with symptoms that were not typical of other common forms of anthrax infection such as meningitis and multiorgan failure. Injection anthrax can spread throughout the body faster and be harder to recognize and treat. About 30% of people with injection anthrax have died.
Domestic and wild animals such as cattle, sheep, goats, antelope, and deer can carry the disease. Humans can become infected with anthrax by handling products from infected animals, by breathing in anthrax spores from contaminated animal products or by eating raw or undercooked meat from infected animals. Anthrax cannot be spread from person to person.
People at highest risk of getting the disease are workers who handle animal products, agricultural and wildlife workers, and veterinarians who handle infected animals.
Humans can also be infected deliberately by terrorists using anthrax as a weapon.
Infections with anthrax are diagnosed by testing directly for the bacteria in blood, skin lesions, spinal fluid, or respiratory secretions. Rapid detection methods include polymerase chain reaction (PCR) and direct fluorescent antibody test. Because it may be difficult to find bacteria once treatment has started, infection can be confirmed by measuring antibodies or toxin in the blood.
If inhalation anthrax is suspected, chest X-rays or CT scans can be used for confirmation.
People suspected of being exposed to anthrax bacteria or spores should be decontaminated and treated. Effective decontamination of people can be accomplished by a thorough wash-down with antimicrobial soap and water. Waste water should be treated with bleach or other antimicrobial agent. Effective decontamination of articles can be accomplished by boiling them in water for 30 minutes or longer. Chlorine bleach is ineffective in destroying spores and vegetative cells on surfaces, though formaldehyde is effective. Burning clothing is very effective in destroying spores. Infection can be prevented in people exposed to anthrax with doctor prescribed antibiotic treatment for 60 days.
Doctors have several options for treating patients with anthrax, including antibiotics and antitoxin. Patients with serious cases of anthrax will need to be hospitalized. They may require aggressive treatment, such as continuous fluid drainage and help breathing through mechanical ventilation. For symptomatic gastrointestinal anthrax and inhalation anthrax, large doses of intravenous (IV) antibiotics are needed immediately. Early antibiotic treatment of anthrax is essential—any delay lessens chances for survival.
Reinfection following recovery from a prior infection has rarely been reported.
It is very uncommon for people in the United States to get infected with anthrax. The last fatal case of natural inhalational anthrax in the United States occurred in California in 1976, when a home weaver died after working with infected wool imported from Pakistan.
Anthrax is classified as a Category A Bioterrorism Agent. Humans can be infected deliberately by terrorists using anthrax as a weapon, as seen in the United States in 2001. In 2001, powdered anthrax spores were deliberately put into letters that were mailed through the U.S. postal system. Twenty-two people, including 12 mail handlers, got anthrax, and five of these 22 people died. We do not know if or when another anthrax attack might occur. An anthrax attack could take many forms. For example, it could be placed in letters and mailed, as was done in 2001, or it could be put into food or water. Anthrax also could be released into the air from a truck, building, or plane.
While there is a vaccine licensed to prevent anthrax, it is not typically available for the general public. Anthrax vaccine is routinely used in three groups of adults 18 to 65 years of age who may be at risk of coming in contact with anthrax because of their job:
- Certain laboratory workers who work with anthrax
- Some people who handle animals or animal products, such as some veterinarians
- Some members of the United States military
To build up protection against anthrax, these groups should get 5 shots of anthrax vaccine over 18 months. To stay protected, they should get annual boosters. The shots are injected into the muscle (intramuscular).
Prevention of naturally acquired human anthrax begins with prevention and control in animals. Effective control centers around vaccinating livestock, treatment of symptomatic animals and proper disposal of carcasses. In addition, educate employees who handle potentially contaminated animal products about the signs and symptoms of anthrax infection. Use extreme caution when handling dead animals that may be infected with anthrax. Other prevention methods include controlling dust and providing good air circulation when working with animal hides, fur, hair, or wool. In addition, have workers wear protective clothing and provide a place to shower and change clothes after work.
Last reviewed July 2019