Anthrax (Splenic fever, Siberian ulcer, Charbon, Milzbrand)
Anthrax is mainly a disease of sheep, horses, cattle, and other herbivorous animals. Historically, the disease in humans has been restricted mainly to people who work with animals, or animal products. However recent episodes have brought attention to the causative agent of anthrax, Bacillus anthracis. This pathogenic organism produces spores when environmentally stressed. These spores, which contain the genetic material of the bacteria, encased in a tough coat, are highly resistant to harsh environmental conditions such as drying, heat, starvation, etc. There are reports of anthrax spores remaining viable for over 50 years in soil. Spores can germinate and form the vegetative, disease-producing form when environmental conditions are favorable. The spore-forming characteristic, and the fact that the bacteria, unlike most spore-forming pathogenic bacteria, can readily grow in the presence of oxygen, has made Bacillus anthracis one of the top choices as a biological warfare agent. Anthrax is a zoonotic disease caused by the sporeforming bacterium Bacillus anthracis
Anthrax is most common in wild and domestic herbivores (eg, cattle, sheep, goats, camels, antelopes) but can also be seen in humans exposed to tissue from infected animals, contaminated animal products or directly to B anthracis spores under certain conditions. Depending on the route of infection, host factors, and potentially strain-specific factors, anthrax can have several different clinical presentations. In herbivores, anthrax commonly presents as an acute septicemia with a high fatality rate, often accompanied by hemorrhagic lymphadenitis; in dogs, humans, horses, and pigs, it is usually less acute. B anthracis spores can remain infective in soil for many years. During this time, they are a potential source of infection for grazing livestock, but generally do not represent a direct infection risk for humans. Grazing animals may become infected when they ingest sufficient quantities of these spores from the soil. In addition to direct transmission, biting flies may mechanically transmit B anthracis spores from one animal to another. The relative importance of this mode of transmission during epizootics or epidemics has yet to be quantified but is frequently suspected. Feed contaminated with bone or other meal from infected animals can serve as a source of infection for livestock, as can hay that is heavily contaminated with infected soil. Raw or poorly cooked contaminated meat is a source of infection for carnivores and omnivores; anthrax resulting from contaminated meat consumption has been reported in pigs, dogs, cats, mink, wild carnivores, and humans.