anthrax

Overview

Anthrax is rare in humans though occasionally occurs in ruminants, such as cattle, sheep, goats, camels, and antelopes. The disease is more common in developing countries without veterinary public health programs while developed regions of the world (North America, Western and Northern Europe, and Australia) report fewer cases of anthrax in animals. There are 89 known strains of anthrax. The most widely recognized strain is the virulent Ames strain used in the 2001 anthrax attacks in the United States.

The infection of ruminants (and humans) proceeds as follows: the spore is located and engulfed by phagocytes of the immune system specialized to deal with invaders.

The anthrax toxin has two components: edema factor and lethal factor. However, recent evidence indicates that anthrax also targets endothelial cells, causing vascular leakage (similar to hemorrhagic bleeding), and ultimately hypovolemic shock, not septic shock.

The virulence of a strain of anthrax is dependent on multiple factors, primarily the poly-D-glutamic acid capsule that protects the bacterium from phagocytocis by host neutrophils and its toxins, edema toxin and lethal toxin.

Exposure

Occupational exposure to infected animals or their products (such as skin and meat) is the usual pathway of exposure for humans. Workers who are exposed to dead animals and animal products are at the highest risk, especially in countries where anthrax is more common. Anthrax in wild livestock occurs in the United States. Many workers are routinely exposed to significant levels of anthrax spores but most are not sufficiently exposed to develop symptoms.

In July 2006 an artist who worked with untreated animal skins became the first person in more than 30 years to die in the United Kingdom from anthrax.

Mode of infection

Anthrax can enter the human body through the intestines (ingestion), lungs (inhalation), or skin (cutaneous). Anthrax is non-contagious and is unlikely to spread from person to person.

Pulmonary (pneumonic, respiratory, or inhalation) anthrax

Respiratory infection initially presents with cold or flu-like symptoms for several days, followed by severe (and often fatal) respiratory collapse. If not treated soon after exposure, before symptoms appear, inhalational anthrax is highly fatal, with near 100% mortality. A lethal dose of anthrax is reported to result from inhalation of 10,000-20,000 spores.

Gastrointestinal (gastroenteric) anthrax

Gastrointestinal infection often presents with serious gastrointestinal difficulty, vomiting of blood, severe diarrhea, acute inflammation of the intestinal tract, and loss of appetite.

Cutaneous (skin) anthrax

Cutaneous infection often presents with large, painless necrotic ulcers (beginning as an irritating and itchy skin lesion or blister that is dark and usually concentrated as a black dot, somewhat resembling bread mold) at the site of infection. Unlike bruises or most other lesions, cutaneous anthrax infections do not cause pain. Treated cutaneous anthrax is rarely fatal.

Treatment and prevention

Treatment for anthrax infection and other bacterial infections includes large doses of intravenous and oral antibiotics, such as penicillin, ciprofloxacin, doxycycline, erythromycin, and vancomycin. Antibiotic-resistant strains of anthrax are known.

An FDA-licensed vaccine, produced from one non-virulent strain of the anthrax bacterium, is manufactured by BioPort Corporation, subsidiary of Emergent BioSolutions. The trade name is BioThrax, although it is commonly called Anthrax Vaccine Adsorbed (AVA). Inhalation of anthrax spores can be prevented with a full-face mask using appropriate filtration.

In recent years there have been many attempts to develop new drugs against anthrax.

Site cleanup

Anthrax spores can survive for long periods of time in the environment after release. Methods for cleaning anthrax contaminated sites commonly use oxidizing agents such as peroxides.

Using the catalyst method, a complete destruction of all anthrax spores takes 30 minutes.

History

Discovery

Robert Koch, a German physician and scientist, first identified the bacteria which caused the anthrax disease in the 1870s. His experiments not only helped create an understanding of anthrax, but also helped elucidate the role of microbes in causing illness at a time when debates were still held over spontaneous generation versus cell theory. Thirty days after the first injection, both groups were injected with a culture of live anthrax bacteria.

Biological warfare

Anthrax spores can and have been used in biological warfare. The Rhodesian government used anthrax on cattle and humans in the period 1978-1979 during its war with black nationalists. The anthrax vaccine, produced by BioPort Corporation, contains non-living bacteria, and is approximately 93% effective in preventing infection. Anthrax vaccination is one of many factors suspected of causing Gulf War syndrome. Bush administrations authorized the sale to Iraq of numerous "dual-use" items that have both military and civilian applications, such as poisonous chemicals and deadly biological pathogens, including anthrax and bubonic plague.

Weaponized stocks of anthrax in the US were reportedly destroyed in 1969 after President Nixon ordered the dismantling of US biowarfare programs.

British bioweapons trials in 1942 severely contaminated Gruinard Island in Scotland with anthrax spores of the Vollum/14578 strain, thereby rendering it uninhabitable for the following 48 years. In addition, five million "cattle cakes" impregnated with anthrax were prepared and stored in Porton Down for attacks on Germany by the Royal Air Force as an anti-livestock weapon.

During the Cold War the USAF was displeased with the operational characteristics of the M114 four-pound bomblet charged with porcine brucellosis (agent US), and embarked on a crash program (St. Jo) for the E61 half-pound dumbbell bomblet with N (anthrax). This St. Jo program indicated the median infective dose for anthrax at 8,000 spores per person when inhaled from animal studies in monkeys. Prior to St. Jo, anthrax was considered a low priority biological due to its low potency in comparison with other biologicals.

An accidental release of anthrax in a research lab at Fort Detrick in Frederick, Maryland in the United States led to the permanent sealing of a building with plastics and glues.

Cultivating anthrax spores can take minimal equipment and a first-year collegiate microbiological education. However, to make an aerosol form of anthrax suitable for biological warfare (the process of "weaponizing" the spores), requires extensive training and highly advanced equipment. Bentonite is one of the few substances identified publicly that helps reduce the static charge of anthrax spores (causing them to disperse more easily).

High quality weaponized anthrax spores were used for bioterrorism in the 2001 anthrax attacks, delivered by mailing postal letters containing the spores. A scientific experiment performed by a high school student (later published in The Journal of Medical Toxicology) suggested that a common electric iron adjusted to the hottest setting (at least 400 degrees Fahrenheit) and used for at least 5 minutes should destroy all anthrax spores in a common envelope contaminated with anthrax.