Anthrax: Zoonotic Disease Occurring as Malignant Pustule or Woolsorter's Disease in Humans

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Most herbivorous animals – including cattle, goats, horses, and sheep – are known reservoirs of the bacterium that causes anthrax, a dangerous though uncommon zoonotic disease. Primarily a disease of the animals mentioned, anthrax usually occurs as an infection of the intestinal tract. As a zoonotic disease, it is acquired by humans through contact with the contaminated hair, hides and wool of the animals.

The germ of this zoonotic disease, Bacillus anthracis, appears as spores which adhere to the hair or skin of animals, remaining potentially dangerous for a long time. People who regularly handle animals because of the nature of their work (examples, farmers, workers in the wool and hide industries, and even veterinarians) are the most susceptible to anthrax as they are always exposed to the known vectors and mode of spread of this zoonotic disease.

Anthrax may occur in humans in either of two forms: as malignant pustule or as woolsorter’s disease. In the former, the spores usually enter through a break in the person’s skin. In the latter, the spores are inhaled into the lungs or introduced into the person’s body in contaminated meat. Between these two forms of diseases, woolsorter’s disease is the more serious one, with about a fifth of all cases ending in death.

In a typical case of malignant pustule, a small, red, slightly elevated spot resembling a small boil appears within 12 to 24 hours at the site where the spores entered, usually through an abrasion or a scratch. The lesion enlarges rapidly with the surrounding area becoming hard and edematous. The person infected with malignant pustule experiences itching, although there is very little pain. If malignant pustule is treated within 24 hours from occurrence, the result is favorable. This form of anthrax in humans usually responds favorably to antibiotics.

As its name so implies, woolsorter’s disease is an occupational disease in those working in the wool industry. It was from woolsorter’s disease that Bacillus anthracis was set apart from other possible bacteria in 1877 (by the German physician Heinrich Hermann Robert Koch) and proved responsible for the anthrax in animals. If woolsorter’s disease is not immediately treated, it may lead to the local death of soft tissues (gangrene) or blood poisoning (septicemia) which can be fatal to the affected person in only about 5 to 7 days.

Vaccines are used to control this zoonotic disease in animals. For humans, control of malignant pustule or woolsorter’s disease can be accomplished in three ways: Workers in occupations where exposure to anthrax is a possibility should wear protective clothing and gloves; potentially infected hair, hides, wool, and such items made from them should be sterilized; and suspected lesions should be treated promptly. Demonstration of the bacteria in suspected lesions is a conclusive evidence of the occurrence of malignant pustule or woolsorter’s disease.

Sources:

1. “Zoonotic & Emerging Diseases”, Crossroads Veterinary Services, Large and Small Animal Medicine – http://www.crossroadsvetservices.com/index.php/large_animal/zoonoses

2. “Bacillus anthracis and anthrax”, by Kenneth Todar, Ph.D., Todar’s Online Textbook of Bacteriology – http://www.textbookofbacteriology.net/Anthrax.html

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