These organisms can be encountered outside of a bioterrorism event and produce human disease. It's important to be familiar with the geographic areas where these organisms naturally occur and the how disease is transmitted.
Bacillus anthracis: Bacillus species inhabit the soil, water, and airborne dust. Anthrax is the disease produced, which is transmitted to humans via direct contact with infected herbivorous animals. This is where the disease is primarily encountered. Anthrax is controlled in animals in the United States, so the disease is rare. In humans, most cases are cutaneous infections found in people that handle animals and animal products, including veterinarians and agricultural workers. Anthrax is consistently present in the animal population of some geographical regions, such as Iran and Pakistan, but only small numbers of animals experience the disease at any given time.
Yersinia pestis: Y. pestis is found primarily in rodents, but can also be found in several animal species, such as cats, rabbits, camels, squirrels. Animal to human transmission most commonly occurs via a flea bite, causing the most common form of the disease known as the bubonic plague. Human-to-human transmission occurs by either flea bite or respiratory droplets. This causes an overwhelming disease known as pneumonic plague, which is the most likely form that would be implicated in the event of a bioterrorist attack. Human cases of the plague continue to occur in many countries, including Africa, the southwestern United States, parts of Asia, and the former Soviet Union.
Francisella tularensis: Many animals, including rodents, rabbits, deer, and raccoons act as host for this organism. Humans and domesticated animals, such as horses, cattle, cats, and dogs can become infected. The infection is transmitted to domesticated animals by ticks and biting flies. Humans are most commonly infected from the bite of an infected tick or fly. Other means of infection include direct contact with the blood of infected animals when skinning game, eating contaminated meat, drinking contaminated water, or inhaling the organisms produced by aerosols. F. tularensis carries a high risk of laboratory acquired infection and documented cases of infection have occurred. Most cases of tularemia are reported in the southern and south-central United States.