15.24F: Anthrax

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Anthrax is a rare, infectious disease caused by Bacillus anthracis that can spread from animals to humans.

Learning Objectives

Discuss the causes and mode of transmission for anthrax including: inhalation, ingestion and direct entry through abrasions

Key Points

Bacillus anthracis exists in the soil as spores. Spores are inactive forms of the bacteria and can survive for decades in this form.
Humans can become infected through contact with the anthrax spores from infected animals. It is not conatgious and cannot be spread from one infected person to another person.
There are three ways one can become infected with anthrax: by inhalation of anthrax spores, entrance of spores through cuts in the skin, and by eating undercooked meat containing anthrax spores.
Anthrax can be successfully treated with early antibiotic treatment. An anthrax vaccine has been approved for use in humans and is effective in protecting against an anthrax infection.

Key Terms

Bacillus anthracis: Bacillus anthracis is the etiologic agent of anthrax and the only obligate pathogen within the genus Bacillus. B. anthrais a Gram-positive, endospore-forming, rod-shaped bacterium, with a width of 1-1.2µm and a length of 3-5µm.It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions.
anthrax: An infectious bacterial disease of herbivores than can also occur in humans through contact with infected animals, tissue from infected animals, or high concentrations of anthrax spores.

Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects both humans and animals. Anthrax commonly infects wild and domesticated herbivorous mammals that ingest or inhale the spores while grazing. Carnivores living in the same environment may become infected by consuming infected animals. Humans become infected through contact with the anthrax spores from infected animals.

Bacillus anthracis is a rod-shaped, Gram-positive, aerobic bacterium about 1 by 9 micrometers in length. The bacterium normally rests in endospore form in the soil, and can survive for decades in this state. B.anthracis bacterial spores have been known to have reinfected animals over 70 years after burial sites of anthrax-infected animals were disturbed. Herbivores are often infected whilst grazing or browsing, especially when eating rough, irritant, or spiky vegetation. It has been hypothesized that the vegetation may cause wounds within the gastrointestinal tract, permitting entry of the bacterial endospores into the tissues. This has not been proven, however. Once ingested or placed in an open wound, the bacterium begins multiplying inside the animal or human and typically kills the host within a few days or weeks. The endospores germinate at the site of entry into the tissues and then spread via the circulation to the lymphatics, where the bacteria multiply.

There are three ways in which people can become infected by anthrax:

By inhaling contaminated air containing anthrax spores. This is known as inhalation anthrax or pulmonary anthrax and can cause serious, sometimes lethal respiratory disease. Symptoms are flu-like, but soon develop into nausea and severe breathing problems. Inhalation anthrax has a 97% mortality rate.
By handling infected animals and/or animal products, antrax spores can enter through cuts in the skin. This is known as cutaneous anthrax. It first appears as a boil-like lesion then eventually forms a painless ulcer with a black center. Death is rare when the appropriate antibiotics are used.
By eating undercooked meat containing anthrax spores. This is known as gastrointestinal antrax. This is rare, with only 2 cases reported in the United States. Symptoms include intestinal inflammation, nausea, loss of appetite, vomiting of blood, abdominal pain and severe diarrhea.

Anthrax can be treated with anitbiotics. The earlier the anthrax is treated, the higher the chance of survival. Treatment for anthrax infection and other bacterial infections includes large doses of intravenous and oral antibiotics, such as fluoroquinolones (like ciprofloxacin), doxycycline, erythromycin, vancomycin, or penicillin. FDA-approved agents include ciprofloxacin, doxycycline, and penicillin. In possible cases of inhalation anthrax, early antibiotic prophylaxis treatment is crucial to prevent possible death.

In the United States, the human anthrax vaccine is required for most US military units and civilian contractors assigned to homeland bioterrorism defense or deployed in Iraq, Afghanistan or South Korea.