Animals play a critical role in the epidemiology of infection in humans, and virtually all cases of human anthrax can be directly or indirectly linked to an infected animal. Specific people at risk include anyone working outdoors in an incubator region, veterinarians, abattoir workers, animal herders and those who work processing animal products. Humans can be infected via:

• direct contact with infected animals (e.g., farmers, abattoir workers, veterinarians)
• occupational exposure with contaminated animal products (e.g., those working with sheep and goat hides = "wool sorter's disease")
• ingestion of meat from infected animals (Milk can also contain the organism in the end stages of disease, but milk is rarely considered a significant risk factor for human infection because, at this point, the animals appear so sick that most people would not consider drinking the milk)
• contact with soils that were contaminated by an infected animal

Clinical forms of anthrax in humans:

• Cutaneous anthrax:
  • lesions are unique, beginning as a pruritic papule, progressing through an ulcer stage with surrounding vesicles, and ultimately resulting in a black, necrotic "eschar."
    • There may also be fever, lymphadenopathy and malaise along with the cutaneous lesions.
    • The case fatality rate, even with cutaneous anthrax, is 20% without antibiotic therapy (typically penicillins or ciprofloxacin).
• Inhalational anthrax:
  • a flu-like presentation initially, followed by acute respiratory distress and hypotension >>> shock and death.
    • Anthrax is NOT very contagious from person-to-person via aerosols.
    • Massive mediastinal lymphadenopathy, mediastinal hemorrhage and radiographic evidence of mediastinal widening are classic findings in humans with inhalational anthrax (not true pneumonia).
    • highly fatal
• Gastrointestinal anthrax:
  • oropharyngeal edema (ulcerative lesions of the oropharyngeal mucosa and tonsils, cervical lymphadenopathy)
  • hematemesis (gastric ulcers)
  • bloody diarrhea (ulceration in the intestines [ileum and cecum])
  • hemorrhagic mesenteric lymphadenitis
  • ascites
  • shock and death
    • highly fatal

There is currently only one human anthrax vaccine licensed in the U.S., anthrax vaccine adsorbed (AVA). This is a mixture of B. anthracis proteins, but the PA protein is thought to be the most important immunogen. Newer vaccines are under development.

Examples of recent outbreaks of anthrax in humans include:

• Perhaps the most famous outbreak of anthrax took place in Sverdlovsk, Russia in April-May 1979. This outbreak, involving both people and cattle, has been traced to the release of spores into the air surrounding a biological weapons factory. (See the article in Science and the book, Anthrax, The Investigation of a Deadly Outbreak, by Jeanne Guillemin, for fascinating accounts of microbiological "who done it.")
• Direct contact with infected cattle accounted for 10,000 cases of human anthrax in Zimbabwe from 1979-1985 and 716 cases in Chad in 1988. Outbreaks occurred again in Zimbabwe (linked to consumption of meat from 2 cows found dead) and Zambia (70 people and over 200 cows) in 1997, and again in Zimbabwe in 2000 and 2001.
• In 1996, 3 people developed cutaneous anthrax from an infected cow at an abattoir in Russia and there have been additional cases in The Republic of Georgia and Azerrbaijan.
• In 1997, human cases occurred in Thailand following consumption of meat from the head of an infected cow (12 cases), and one abattoir worker in Australia was infected during what became a large scale outbreak among cattle in Victoria. In 1998, 3 people contracted anthrax in Thailand again following consumption of the meat from cows that had died.
• In 1998, outbreaks in the Central Asian republics of Buryatia, Kazakhstan and Tajikistan affected over 300 people.
• Also in 1998, B. anthracis was discovered during the repair of walls in King's Cross railroad station in London. The bacteria were present in horse hairs used to strengthen the wall plaster when the station was built in the 1800s!
• In 1999, at least 20 dairy cattle were infected in Thailand, purportedly following the smuggling of infected cattle into the country from Burma. Owners were infected when they consumed meat from their infected cattle.
• A farmer in the Russian Republic of Buryatia died and at least 10 other people became infected in 1999 after consuming contaminated meat from infected cattle. Bacillus anthracis was also isolated from slaughtered pigs in the Seversky district in the Krasnodar region of the country.
• The bioterrorist-related cases of anthrax in the United States in 2001.

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