Anthrax is an acute infectious disease caused by the bacteria Bacillus anthracis and is highly lethal in its most virulent form. Anthrax most commonly occurs in wild and domestic herbivores, but it can also occur in humans when they are exposed to infected animals, tissue from infected animals, or high concentrations of anthrax spores.
Anthrax infection is rare but not remarkable in herbivores such as cattle, sheep, goats, camels, and antelopes. Anthrax can be found globally. It is more common in developing countries or countries without veterinary public health programs. Certain regions of the world (South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East) report more anthrax in animals than others.
When anthrax affects humans, it is usually due to an occupational exposure to infected animals or their products (such as skin and meat). Workers who are exposed to dead animals and animal products from other countries where anthrax is more common may become infected with B. anthracis. Anthrax in wild livestock has occurred in the United States. Although many such workers are routinely exposed to significant levels of anthrax spores, most are not sufficiently exposed to develop symptoms.
Means of infection
Anthrax can enter the human body through the intestines, lungs (inhalation), or skin (cutaneous). Anthrax is non-contagious, and is unlikely to spread from person to person.
Pulmonary (pneumonic, respiratory, inhalation) anthrax infection initially presents with cold or flu-like symptoms for several days, followed by severe (and often fatal) respiratory problems. If not treated soon after exposure, inhalation infection is the most deadly, with a nearly 100% mortality rate. A lethal case of anthrax is reported to result from inhaling 10,000-20,000 spores. This form of the disease has also been known as Woolsorters' Disease.
Gastrointestinal (gastroenteric) anthrax infection often presents with serious gastrointestinal difficulty, vomiting of blood, and severe diarrhea. Untreated, intestinal infection results in a 25-60% death rate.
Cutaneous (skin) anthrax infection presents with a large necrotic ulcer (a irritating and itchy skin lesion or blister which is dark in color, usually concentrated as a black dot, somewhat resembling bread mold) at the site of infection, forming about a week or two after exposure. Unlike bruises or most other lesions, cutaneous anthrax does not cause pain. Cutaneous infection is the least deadly; without treatment, approximately 20% of all skin infection cases are fatal. Treated cutaneous anthrax is rarely fatal.
Treatment and Prevention
Treatment for anthrax infections includes large doses of intravenous and oral antibiotics, such as penicillin, ciprofloxacin, erythromycin and vancomycin. For inhalation cases, antibiotic treatment is not very effective if initiated more than 24 hours after infection, after symptoms appear. Antibiotic prophylaxis is crucial in cases of pulmonary anthrax to save lives. Some antibiotic restistant strains are known.
A vaccine, produced from one component of the toxin of a non-virulent strand, is also available. The vaccine must be given at least four weeks before exposure to Anthrax; annual booster injections are required to maintain immunity.
The spores can be trapped with a simple HEPA or P100 filter. Anthrax as an airborne threat can be prevented with a full-face mask. Unbroken skin is decontaminated simply with soap and water.
Description of the Bacterium
Bacillus anthracis is a rod-size gram-positive bacterium of size about 1 by 6 microns. It was the first bacterium ever to be shown to cause disease, by Robert Koch in 1877. The bacteria normally rest in spore form in the soil, and can survive for decades in this state. Once taken in by a herbivore, the bacteria start multiplying inside the animal and eventually kill it, then continue to reproduce in the carcass. Once they run out of nutrients there, they revert back to the dormant spore state.
The infection of herbivores (and humans) proceeds as follows: the spore is located and engulfed by scavenger cells of the immune system specialized to deal with invaders. Inside the scavenger cell, the spore turns into a bacillus, multiplies, and eventually bursts the cell, releasing bacilli into the bloodstream. There they release a protein toxin which has macrophages as its principal target. The toxin has two components: edema factor and lethal factor. Edema factor inactivates macrophages so that they cannot participate in the fight against the infection; lethal factor causes the macrophage to make TNF-alpha and interleukin-1-beta, both normal components of the immune system used to induce an inflammatory reaction. The excessive inflammation throughout the body ultimately leads to septic shock and death.
The virulence of a strain of anthrax is dependent on its enclosing capsule and its toxin; both are determined by different genes.
Spores of this bacteria can be used in biological warfare. US Army personnel are now routinely vaccinated prior to active service in places where biological attacks are considered a threat. The vaccine, produced by BioPort Corporation, contains no live bacteria, and is approximately 93% effective in preventing infection. Anthrax vaccination is one of many factors suspected of causing Gulf War Syndrome.
The simplest method of obtaining an anthrax sample would be to get it from a animal killed by anthrax; this source is rare in developed countries but common in underdeveloped countries.
Cultivating anthrax spores takes minimal equipment and about a first-year collegiate microbiological education. However, to make an aerosol form of anthrax suitable for biological warfare requires extensive training and highly developed equipment. The major problem is to prevent the spores from forming clumps too large for effective infection.
- University of Wisconsin-Madison Department of Bacteriology, Bacteriology 330 Lecture Topics: Anthrax, http://www.bact.wisc.edu/Bact330/lectureanthrax
- CDC Division of Bacterial and Mycotic Diseases, Anthrax Disease Information, http://www.cdc.gov/ncidod/dbmd/diseaseinfo/anthrax_g.htm
- Sheldon Campbell, Anthrax in a BioWar environment, http://www.emergency.com/anthrax.htm
- Anthrax: pre-publication and special Issue, Nature, http://www.nature.com/nature/anthrax/