Splenic fever, Siberian ulcer, Charbon, Milzbrand
Overview
- 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 people exposed to tissue from infected animals, to 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, people, horses, and pigs, it is usually less acute although still potentially fatal.
- B anthracis spores can remain viable 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 risk of infection for people. Grazing animals may become infected when they ingest sufficient quantities of these spores from the soil.
Pathogenesis
- After wound inoculation, ingestion, or inhalation, spores infect macrophages, germinate, and proliferate. In cutaneous and GI infection, proliferation can occur at the site of infection and in the lymph nodes draining the site of infection. Lethal toxin and edema toxin are produced by B anthracis and respectively cause local necrosis and extensive edema, which are frequent characteristics of the disease. As the bacteria multiply in the lymph nodes, toxemia progresses and bacteremia may ensue. With the increase in toxin production, the potential for disseminated tissue destruction and organ failure increases. After vegetative bacilli are discharged from an animal after death (by carcass bloating, scavengers, or postmortem examination), the oxygen content of air induces sporulation. Spores are relatively resistant to extremes of temperature, chemical disinfection, and dessication. Necropsy is discouraged because of the potential for blood spillage and vegetative cells to be exposed to air, resulting in large numbers of spores being produced. Because of the rapid pH change after death and decomposition, vegetative cells in an unopened carcass quickly die without sporulating.
Clinical signs
- In acute anthrax of cattle and sheep, there is an abrupt fever and a period of excitement followed by depression, stupor, respiratory or cardiac distress, staggering, convulsions, and death. Often, the course of disease is so rapid that illness is not observed and animals are found dead. Body temperature may reach 107°F (41.5°C), rumination ceases, milk production is materially reduced, and pregnant animals may abort. There may be bloody discharges from the natural body openings. Some infections are characterized by localized, subcutaneous, edematous swelling that can be quite extensive. Areas most frequently involved are the ventral neck, thorax, and shoulders.