Understanding Anthrax

by National Institute of Health

About Anthrax and Bioterror

Anthrax, notorious for its role in the fall 2001 bioterror attacks, is a disease caused by a microbe known as Bacillus anthracis. In the fall of 2001, lethal anthrax bacteria were spread deliberately through the U.S. mail. Twenty-two people became ill, and five died. The perpetrator has not been caught.

Even before this bioterror attack, public health officials were concerned about the potential for such an event. In 1999, the Centers for Disease Control and Prevention (CDC) created A, B, and C lists of biological agents that terrorists could use to harm civilians. An expert panel of doctors and scientists classified Bacillus anthracis as a Category A bioterror agent. The CDC bioterror lists represent the biological agents that pose the greatest threats to national security due to their ease of transmission, high rate of death or serious illness, potential for causing public panic, and special public health measures an epidemic would require.

Since the creation of the CDC lists, public health officials and researchers have worked to plan and prepare for a possible bioterror attack. Following the 2001 anthrax attacks, federal funding for these efforts increased dramatically.

About The Disease

Anthrax infects livestock far more often than people, but it can cause three forms of human disease: cutaneous (affecting the skin), inhalational (in the lungs), and gastrointestinal (in the digestive tract).

Cutaneous anthrax

Cutaneous anthrax is the most common form of the disease. People with cuts or open sores can get cutaneous anthrax if they come in direct contact with the bacteria or its spores, usually through contaminated animal products. The skin will redden and swell, much like an insect bite, and then develop a painless blackened lesion or ulcer that may form a brown scab. Cutaneous anthrax responds well to antibiotics but may spread throughout the body if untreated. People who work with certain animals or animal carcasses are at risk of getting this form of the disease. Cutaneous anthrax is rare in the United States. According CDC, there are only one to two U.S. cases per year.

Inhalational anthrax

When spores of B. anthracis are inhaled, they germinate and the bacterial cells infect the lungs and then spread to the lymph nodes in the chest. As the bacteria grow, they produce two kinds of deadly toxins. Symptoms usually appear 1 to 7 days after exposure, but they may first appear more than a month later. Fever, nausea, vomiting, aches, and fatigue are among the early symptoms of inhalational anthrax; it progresses to labored breathing, shock, and often death. Historically, the mortality rate for naturally occurring inhalational anthrax has been high-about 75 percent. But inhalational anthrax is also rare. Prior to 2001, the last known U.S. case was in 1976 when a California craftsman died after getting the infection from imported yarn contaminated with anthrax spores.

Gastrointestinal anthrax

People can acquire gastrointestinal anthrax from eating meat contaminated with anthrax bacteria or their spores. Symptoms are stomach pain, loss of appetite, diarrhea, and fever. Antibiotic treatment can cure this form of anthrax, but untreated, it may kill half of those who get it. It occurs naturally in warm and tropical regions of Asia, Africa, and the Middle East. There have been no confirmed cases of gastrointestinal anthrax in the United States, although a Minnesota farm family may have experienced symptoms of the disease in 2000 after eating meat from a steer that had anthrax.

About The Microbe

Bacillus anthracis is a bacterium that lives in soil and has developed a survival tactic that allows it to endure for decades under the harshest conditions. An anthrax bacterial cell can transform itself into a spore, a very hardy resting phase, to withstand extreme heat, cold, and drought, without nutrients or air. When environmental conditions are favorable, the spores will germinate into thriving colonies of bacteria. For example, a grazing animal may ingest spores that begin to grow, spread, and eventually kill the animal. The bacteria will form spores in the carcass and then return to the soil to infect other animals in the future.

While its spore form allows the bacteria to survive in any environment, the ability to produce toxins is what makes the bacteria such a potent killer. Together, the hardiness and toxicity of B. anthracis make it a formidable bioterror agent. Its toxin is made of three proteins: protective antigen, edema factor, and lethal factor.

Protective antigen binds to select cells of an infected person or animal and forms a channel that permits edema factor and lethal factor to enter those cells.

Once inside the cell, edema factor causes fluid to accumulate at the site of infection. Edema factor can contribute to a fatal build-up of fluid in the cavity surrounding the lungs. It also can inhibit some of the body's immune functions.

Lethal factor also works inside the cell, disrupting a key molecular switch that regulates the cell's functions. Lethal factor can kill infected cells or prevent them from working properly.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.