Anthrax is a sometimes deadly infection caused by the bacterium Bacillus anthracis. This bacterium is housed in a spore — a cell that's dormant, but may become active in the right conditions. Anthrax usually affects livestock, but it also infects humans. Humans can become infected when handling products of infected animals, or if exposed to anthrax that's used as a biological weapon — such as when anthrax spores were deliberately spread in powder-containing envelopes through the U.S. postal system in 2001.
Anthrax infection can occur through a wound in the skin, by ingesting it or by inhaling it. Symptoms depend on which way you're infected and range from a sore on the skin to nausea and vomiting to shock. Early treatment with antibiotics can cure most anthrax infections spread through the skin and many of those spread by ingestion. Inhaled anthrax is the most difficult to treat and is often fatal.Signs and symptoms
Anthrax occurs in three forms, each with different signs and symptoms. Signs and symptoms usually occur within seven days of exposure to the bacterium, but with inhalation anthrax, they can take up to 43 days to appear.
Cutaneous anthrax. This form of anthrax infects the skin. It's contracted by direct contact with the bacterium, when anthrax spores enter a cut, blister or abrasion on your skin. The infection begins as a raised, sometimes itchy bump resembling an insect or spider bite. But within a day or two, the bump develops into an open, usually painless sore with a black center. Cutaneous anthrax is the most common form of the disease, accounting for 95 percent of cases, and it's also the mildest form of the disease. With treatment, cutaneous anthrax is fatal in less than 1 percent of cases. However, there is a slight danger that the infection may spread to other parts of your body. Signs of spreading include fever, chills and swollen, infected lymph glands above the area of the sore.
Gastrointestinal anthrax. It's possible to contract this form of anthrax by eating undercooked meat from an infected animal. Gastrointestinal anthrax causes inflammation of your intestines, and then sores (ulcers) form within your intestines — much like the sores that appear on the skin in the cutaneous form. Initial signs and symptoms include nausea, vomiting, loss of appetite and fever, followed by abdominal pain, vomiting of blood and severe, bloody diarrhea. It's fatal in 25 percent to 60 percent of cases.
Inhalation (pulmonary) anthrax. It's possible to contract this form of anthrax by inhaling anthrax spores. Initial signs and symptoms of inhalation anthrax resemble those of the flu — sore throat, mild fever, fatigue, muscle aches and mild chest discomfort. These first signs and symptoms may last for a few hours or a few days, and they may appear to subside briefly. However, soon afterwards, the disease progresses, producing a high fever, breathing problems and shock. The disease affects lymph nodes inside the chest, may destroy lung tissue, and may spread to the blood or to the brain, causing meningitis. Researchers believe that inhalation anthrax is fatal in approximately 75 percent of cases, even with appropriate treatment. However, of the 11 people infected with inhalation anthrax in the United States in 2001, six survived.
Causes
Anthrax disease is caused by a rod-shaped bacterium, Bacillus anthracis, which normally resides as a spore in the soil. These spores are extremely hardy and have been known to survive in soil for many years. Anthrax spores remain dormant until they find their way into a host — an animal or a human.
Anthrax primarily affects wild and domestic livestock — such as sheep, cattle, horses, goats and camels — that contract intestinal anthrax by eating spores from the soil. Anthrax once was common in most areas where livestock are raised. But in modern times, animal vaccination programs have greatly reduced the natural occurrence of the disease among both animals and humans in much of the world.
Outbreaks of animal anthrax still occur in places that don't have widespread livestock immunization programs, such as Iran, Iraq, Turkey, Pakistan and sub-Saharan Africa. Although rare, they occasionally occur in the United States, as well.
Historically, most human cases of anthrax have occurred as a result of exposure to infected animals or their meat or hides. In fact, anthrax used to be known as woolsorter's disease because people who worked with wool in the 18th century often contracted inhalation anthrax from handling spore-contaminated wool in enclosed factories.
Anthrax as a biological weapon
Before 2001, numerous nations are believed to have experimented with anthrax as a biological weapon, including the United States. The worst documented outbreak of inhalation anthrax in humans occurred in Russia in 1979, when anthrax spores were accidentally released from a military biological weapons facility near the town of Sverdlovsk, killing at least 66 people.
But most people weren't aware of this weapon until the fall of 2001, when letters containing anthrax spores sent via the U.S. Postal Service resulted in 22 cases of anthrax infection. Eleven people were infected with cutaneous anthrax. Eleven others were infected with inhalation anthrax, resulting in five deaths.
These cases heightened concern about the possibility of a large-scale anthrax attack by terrorist groups. The Centers for Disease Control and Prevention has classified anthrax as a Category A bioterrorism agent — which is considered the biggest threat to national security. Unlike some other Category A agents, anthrax doesn't spread person to person, thus limiting the risk to those directly exposed in an attack.
Risk factors
Anthrax isn't contagious. People who get inhalation anthrax don't exhale spores. There are no reports of the disease spreading from one person to another.
To contract anthrax, you must come in direct contact with anthrax spores. However, you can be exposed to anthrax spores and not become infected.
When to seek medical advice
If you believe that you're at risk of anthrax exposure — for example, you work in an environment where anthrax has been detected — immediately notify authorities for testing and see a doctor for evaluation and care. If you develop signs and symptoms of the disorder after exposure to animals or animal products in parts of the world where anthrax exists, seek prompt medical attention. Early diagnosis and treatment is crucial.
Screening and diagnosis
In the United States, the Laboratory Response Network (LRN) — a partnership linking 100 state and local public health laboratories — has been established to quickly diagnose and stop the spread of anthrax.
If authorities suspect exposure to anthrax, environmental sampling can help determine whether a substance contains anthrax spores or whether an area — such as a mailroom, desk, ventilation system or animal source — may be contaminated.
In addition, various tests can help doctors determine if a person has the disease.
Environmental sampling
If you find a suspicious powder that you think may contain anthrax, immediately contact local law enforcement authorities. They can decide to bring in a hazardous-material team trained to test for materials such as anthrax. The team collects samples of the substance and samples from surfaces that may have been contaminated. The samples are then checked in a lab for signs of Bacillus anthracis bacteria.
If anthrax is found in the environment, the contaminated areas — such as a mailroom, desk or ventilation system — are sterilized with special washes.
Human tests
In addition to examining you and inquiring about your health status and where you work, your doctor can administer tests that may determine if you have the disease. However, there's no screening test that can show if you've been exposed to anthrax.
Your doctor will want to rule out other, much more common conditions that may be causing your signs and symptoms, such as flu (influenza) or pneumonia. You may have a rapid flu test to quickly diagnose a case of influenza.
Tests to detect and diagnose anthrax include:
Skin biopsy. A sample of a suspicious lesion on your skin can be sent to a lab to check for microscopic evidence of cutaneous anthrax.
Sputum testing. To diagnose inhalation anthrax, respiratory secretions can be cultured to check for the presence of anthrax bacteria.
Blood tests. If you have signs and symptoms of any form of anthrax, your doctor can take a blood sample and send it to a lab, where it can be checked for the presence of anthrax bacteria. The bacteria should grow in cultures within six to 24 hours, but a laboratory in the LRN must confirm any diagnosis.
Chest X-ray or computerized tomography (CT) scan. Your doctor may request a chest X-ray or CT scan to help diagnose inhalation anthrax. Since this form of anthrax infects both the lungs and lymph nodes in your chest, there's often a very characteristic appearance on the chest X-ray.
Endoscopy and stool samples. To diagnose intestinal anthrax, your doctor may examine your throat or intestines with the aid of an endoscope — a thin, flexible tube with a video camera at its tip that can be inserted into your throat or intestines to check for anthrax lesions. Stool samples can be tested for the presence of anthrax bacteria.
Spinal tap. Sometimes your doctor may need a sample of spinal fluid to confirm a diagnosis of anthrax meningitis. This involves inserting a needle into your spinal canal and drawing out fluid for testing.
If a case of anthrax is suspected or confirmed, doctors have been advised to contact local and state health officials immediately. This helps alert government and health leaders — and the public — of a possible outbreak.
Treatment
Treatment for all three forms of anthrax depends on oral or intravenous (IV) antibiotics. Treatment is most effective when started as early as possible.
Some strains of anthrax may be more responsive to one type of antibiotic than to another. Ciprofloxacin (Cipro), doxycycline and penicillin are approved by the Food and Drug Administration (FDA) for treatment of anthrax in adults and children. However, your doctor may prescribe other antibiotics or a combination of antibiotics.
These medications work by killing the anthrax bacteria. However, antibiotics may fail in inhalation anthrax once symptoms become severe because the bacteria may already have released large amounts of toxin that aren't affected by antibiotics. Scientists are working to develop an anthrax antitoxin that could neutralize the toxin produced by anthrax bacteria.
If you've been exposed to anthrax, your doctor will likely prescribe a long course — 60 days or more — of antibiotics. If you have inhalation anthrax, you'll likely be hospitalized and treated with intravenous antibiotics.
Anthrax isn't spread person to person. So a person with anthrax doesn't have to be quarantined or isolated. If you were in contact with someone with anthrax, you'll need to be treated only if you were exposed to a source of anthrax infection.
Prevention
In addition to treating anthrax, antibiotics are recommended to prevent infection in anyone exposed to anthrax. Ciprofloxacin and doxycycline are FDA-approved for post-exposure prevention of anthrax in adults and children. Levofloxacin is approved for adults who've been exposed.
Anthrax vaccine
The FDA approved a human vaccine in 1970, which has mostly been used by military personnel. Vaccination consists of three shots given two weeks apart followed by three additional shots given at six, 12, and 18 months. Annual booster shots are recommended to maintain immunity.
The human anthrax vaccine doesn't contain live anthrax bacteria, so it can't cause the infection. Side effects may include soreness at the injection site, a flu-like reaction and possibly more-serious allergic reactions. The anthrax vaccine isn't recommended for children, pregnant women or older adults. It's an effective, but not a 100 percent protective vaccine.
The vaccine isn't available to the public. Instead, the vaccine is reserved for:
Active-duty U.S. military personnel who are deployed to areas with high risk of exposure to anthrax
People who work with anthrax in a laboratory setting
People who handle potentially infected animal products in areas of the world where anthrax is a threat to livestock
People who work with imported animal hides or furs from areas with a high incidence of anthrax
Scientists are working to produce a new anthrax vaccine. The new vaccine may require fewer doses and be available in large quantities.
Avoiding contact with infected animals
In countries where anthrax is common and vaccination levels of animal herds are low, it's wise to avoid contact with livestock and animal products and to avoid eating meat that hasn't been properly slaughtered and cooked.
Other preventive measures include carefully handling dead animals suspected of having the disease and providing good protection when processing hides, fur, wool or hair.
Coping skills
When it comes preparing for a possible anthrax attack, the most prudent course of action is to keep a healthy perspective and to stay aware of current events. Here are some things you can do and not do to protect yourself and your family from anthrax:
Should you call your doctor and ask to be vaccinated against anthrax? No. The anthrax vaccine isn't available to the public at this time.
Should you call your doctor and ask for a prescription for antibiotics? No. Only people who have been exposed to anthrax should take the antibiotics, and health officials must determine who has been exposed. In addition, there's no way to know which antibiotic is appropriate to take until exposure or an outbreak occurs. Ciprofloxacin and other antibiotics should be used only when there's a medical need as determined by a doctor.
The anthrax attacks in the United States after Sept. 11, 2001, increased public awareness of the risk of anthrax and other bioterrorism agents. U.S. government and health officials are on alert for outbreaks of anthrax and have plans in place to address potential large-scale outbreaks.
To reduce your exposure to anthrax used as a biological weapon, report any suspicious substance to local authorities. If you come in contact with a clearly suspicious substance, don't sniff, touch, taste or look closely at it. Don't try to clean it up. Move away from the substance. Alert others in the area about the substance. Leave the area, close any doors and take actions to prevent others from entering the area. If possible, shut off the area's ventilation system. Those exposed to the substance should wash their hands with soap and water. Then report the substance to local law enforcement authorities. Seek additional instructions for exposed or potentially exposed people.
By Mayo Clinic Staff
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