Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects both humans and other animals. Effective vaccines against anthrax are now available, and some forms of the disease respond well to antibiotic treatment.
Like many other members of the genus Bacillus, B. anthracis can form dormant endospores (often referred to as “spores” for short, but not to be confused with fungal spores) that are able to survive in harsh conditions for decades or even centuries. Such spores can be found on all continents, even Antarctica. When spores are inhaled, ingested, or come into contact with a skin lesion on a host, they may become reactivated and multiply rapidly.
Anthrax commonly infects wild and domesticated herbivorous mammals that ingest or inhale the spores while grazing. Ingestion is thought to be the most common route by which herbivores contract anthrax. Carnivores living in the same environment may become infected by consuming infected animals. Diseased animals can spread anthrax to humans, either by direct contact (e.g., inoculation of infected blood to broken skin) or by consumption of a diseased animal’s flesh.
Anthrax does not spread directly from one infected animal or person to another; it is spread by spores. These spores can be transported by clothing or shoes. The body of an animal that had active anthrax at the time of death can also be a source of anthrax spores. Owing to the hardiness of anthrax spores, and their ease of production in vitro, they are extraordinarily well suited to use (in powdered and aerosol form) as biological weapons. Such weaponization has been accomplished in the past by at least five state bioweapons programs — those of the United Kingdom, Japan, the United States, Russia, and Iraq — and has been attempted by several others.
Until the 20th century, anthrax infections killed hundreds of thousands of animals and people worldwide each year. French scientist Louis Pasteur developed the first effective vaccine for anthrax in 1881. As a result of over a century of animal vaccination programs, sterilization of raw animal waste materials, and anthrax eradication programs in United States, Canada, Russia, Eastern Europe, Oceania, and parts of Africa and Asia, anthrax infection is now relatively rare in domestic animals. Anthrax is especially rare in dogs and cats, as is evidenced by a single reported case in the United States in 2001.
Anthrax typically does not cause disease in carnivores and scavengers, even when these animals consume anthrax-infected carcasses, but can occur in this manner. Anthrax outbreaks do occur in some wild animal populations with some regularity. The disease is more common in countries without widespread veterinary or human public health programs. In the 21st century, anthrax is still a problem in less developed countries. An outbreak of anthrax in humans who had eaten meat from a dead carabao was reported in Cagayan Province in the Philippines in early 2010, with over 400 cases of illness and at least two fatalities.
B. anthracis bacterial spores are soil-borne. Because of their long lifespan, spores are present globally and remain at the burial sites of animals killed by anthrax for many decades. Disturbed grave sites of infected animals have caused reinfection over 70 years after the animal’s interment.