Anthrax bacteria occur worldwide. The organisms known as Bacillus anthracis may ordinarily produce disease in domesticated as well as wild animals such as goats, sheep, cattle, horses, and swine. Humans become infected by contact with infected animals or contaminated animal products. Infection occurs mainly through the skin and rarely by breathing spores or swallowing them. Spores exist in the soil and become active when the organisms in the carcass are exposed to air.
Apart from biological warfare, anthrax in humans is rare. In the United States, only 127 cases of anthrax appeared in the early years of the 20th century and dropped to about 1 per year during the 1990s.
Signs and symptoms
Skin anthrax (cutaneous): Infection begins when the spores enter the skin through small cuts or abrasions. Spores then become active in the host (human or animal) and produce poisonous toxins. Swelling, bleeding, and tissue death may occur at the site of infection.
- More than 95% of the cases of anthrax involve the skin. After a person is exposed, the disease first appears in 1-5 days as a small pimple-looking sore that progresses over the next 1-2 days to contain fluid filled with many organisms. The sore is usually painless and it may have swelling around it. Sometimes the swelling affects a person’s entire face or limb.
- Victims may have fever, feel tired, and have a headache. Once the sore opens, it forms a black area of tissue. The black appearance of the tissue injury gives anthrax its name from the Greek word anthrakos meaning coal. After a period of 2-3 weeks, the black tissue separates, often leaving a scar. With adequate treatment, less than 1% of people infected with skin anthrax die.
Inhalation anthrax: In inhalation anthrax, the spores are inhaled into the lungs where they become active and multiply. There they produce massive bleeding and swelling inside the chest cavity. The germs then can spread to the blood, leading to shock and blood poisoning, which may lead to death.
- Historically known as woolsorter’s disease (because it affected people who work around sheep), inhalation anthrax can appear anywhere within 1-6 days, or as long as 60 days after exposure. Initial symptoms are general and can include headache, tiredness, body aches, and fever. The victim may have a nonproductive cough and mild chest pain. These symptoms usually last for 2-3 days.
- Some people show a short period of improvement. This is followed by the sudden onset of increased trouble breathing, shortness of breath, bluish skin color, increased chest pain, and sweating. Swelling of the chest and neck may also occur. Shock and death may follow within 24-36 hours in most people with this type of infection.
- Anthrax is not spread from person to person. Inhalation anthrax is the most likely form of disease to follow a military or terrorist attack. Such an attack likely will involve the aerosolized delivery of anthrax spores.
Mouth, throat, GI tract (oropharyngeal and gastrointestinal): These cases result when someone eats infected meat that has not been cooked sufficiently. After an incubation period of 2-5 days, victims with oropharyngeal disease develop a severe sore throat or sores in the mouth or on a tonsil. Fever and neck swelling may occur. The victim may have trouble breathing. GI anthrax begins with nonspecific symptoms of nausea, vomiting, and fever. These are followed in most victims by severe abdominal pain. The victim may also vomit blood and have diarrhea.
Doctors will perform various tests, especially if anthrax is suspected.
- With skin anthrax, a biopsy is taken of the sore (lesion), and lab tests are performed to look at the organism under a microscope and confirm the diagnosis of anthrax.
- The diagnosis of inhalation anthrax is difficult to make. A chest x-ray may show certain signs in the chest cavity. Cultures (growing the bacteria in a lab and then examining them under a microscope) are minimally helpful in making the diagnosis. Blood tests may also be performed.
- GI anthrax also is difficult to diagnose because the disease is rare and symptoms are not always obvious. Diagnosis usually is confirmed only if the victim has a history of eating contaminated meat in the setting of an outbreak. Once again, cultures generally are not helpful in making the diagnosis.
- Meningitis (brain swelling) from anthrax is difficult to distinguish from meningitis due to other causes. A spinal tap may be performed to look at the person’s spinal fluid in identifying the organism.
The most useful microbiologic test is the standard blood culture, which is almost always positive in victims with anthrax throughout their bodies. Blood cultures should show growth in 6-24 hours and if the laboratory has been alerted to the possibility of anthrax, biochemical testing should provide a preliminary diagnosis 12-24 hours later. However, if the laboratory has not been alerted to the possibility of anthrax, there is the chance that the organism may not be identified correctly.
Rapid diagnostic tests for anthrax and its proteins include polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and direct fluorescent antibody (DFA) testing. Currently, these tests are only available at national reference laboratories.
- Inhalation anthrax: As previously stated because inhalation anthrax moves quickly throughout the body, doctors will begin antibiotic treatment right away even before a firm diagnosis is made through lab testing.
- Ciprofloxacin (Cipro), doxycycline (Vibramycin), and penicillin are FDA-approved antibiotics for treatment of anthrax. Experts currently recommend ciprofloxacin or other drugs in the same class for adults who are assumed to have inhalation anthrax infection. Penicillin and doxycycline may be used once organism culture sensitivities are known.
- Traditionally, ciprofloxacin and other antibiotics in that class are not recommended for use in children younger than 16-18 years because of a weak theoretical link to permanent joint disorders. Balancing these small risks against the risk of death and the possibility of infection with a resistant strain of anthrax, experts recommend that ciprofloxacin nonetheless be given to children in appropriate doses.
- Because there is a risk the infection will recur, victims are treated with antibiotics for at least 60 days.
- Skin anthrax: Treatment of skin anthrax with antibiotics generally prevents the disease from progressing to the entire body although the black tissue and scar continue to form. Although previous guidelines have suggested treating skin anthrax with 7-10 days of therapy, recent recommendations suggest treatment for 60 days in the setting of bioterrorism, thus assuming the person may also have been exposed to inhalational anthrax.
- In pregnant women, experts recommend that ciprofloxacin be given after exposure as a preventive medication following exposure to an anthrax attack.
After exposure, the antibiotics ciprofloxacin, or doxycycline may be prescribed by a doctor and the medications are usually taken for 60 days. A vaccination series to protect against anthrax consists of 6 injections given over a period of 18 months, followed by booster shots every year.
If a biological warfare attack is expected or may have occurred, people who have not had the vaccine may be given ciprofloxacin or doxycycline for at least 4 weeks.