Anthrax

• Anthrax is a noncontagious zoonotic disease caused by the spore-forming bacterium Bacillus anthracis.
• Anthrax is most common in wild and domestic herbivores such as cattle, sheep, goats, camels, and antelopes, but can also be seen in humans exposed to tissue from infected animals, to contaminated animal products, or under certain conditions, directly to B anthracis spores.
• Depending on the route of infection, host factors, and potentially strain-specific factors, anthrax can have different clinical manifestations.
• In herbivores, anthrax commonly causes acute septicemia with a high fatality rate, often accompanied by hemorrhagic lymphadenitis.
• In dogs, humans, horses, and pigs, disease is usually less acute but still potentially fatal.
• Spores of B anthracis can remain viable in soil for many years and are a potential source of infection for grazing animals; however, they generally do not represent a direct risk of infection for people.
• Grazing animals may become infected when they ingest sufficient quantities of spores from the soil.
• Bacillus anthracis, the causative agent of anthrax, is a large, gram-positive, aerobic, spore-forming bacillus.
• After wound inoculation, ingestion, or inhalation, anthrax 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.
• 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.
• Anthrax has been reported on nearly every continent and is most common in agricultural regions with neutral or alkaline, calcareous soils.
• In these regions, anthrax epizootics periodically emerge among susceptible domesticated and wild animals.
• These epizootics are usually associated with drought, flooding, or soil disturbance, and many years may pass between outbreaks.
• Four clinical forms of anthrax are seen in humans: natural transmission, gastrointestinal anthrax, inhalational anthrax, and cutaneous anthrax.
• In cases of natural transmission, people exhibit primarily cutaneous anthrax.
• Gastrointestinal anthrax may be seen among human populations after consumption of contaminated raw or undercooked meat.
• Under certain artificial conditions, humans may develop a highly fatal form of disease known as inhalational anthrax or wool sorter’s disease.
• This form manifests as acute hemorrhagic lymphadenitis of the mediastinal lymph nodes, often accompanied by hemorrhagic pleural effusions, severe septicemia, and meningitis.
• Vaccination is the main method of prevention and control of anthrax in production animals.
• The clinical course of injection anthrax ranges from peracute to chronic.
• Dark blood may ooze from the mouth, nostrils, and anus, with marked bloating and rapid body decomposition in postmortem lesions of injection anthrax.
• There may be bloody discharges from the natural body openings in acute anthrax of cattle and sheep.
• In acute anthrax of cattle and sheep, there is an abrupt onset of fever and a period of excitement followed by lethargy, stupor, respiratory or cardiac distress, staggering, seizures, and death.
• The blood is dark and thickened and fails to clot readily in postmortem lesions of injection anthrax.
• The nonencapsulated Sterne-strain vaccine is used almost universally for production animal vaccination.
• Some infections of cattle, sheep, and goats are characterized by localized, subcutaneous edema, and swelling can be quite extensive.
• Antimicrobial therapy is used in the treatment of anthrax in production animals.
• Hemorrhages of various sizes are common on the serosal surfaces of the abdomen and thorax as well as on the epicardium and endocardium in postmortem lesions of injection anthrax.
• In the peracute form of injection anthrax, which is common in cattle, sheep, and goats, staggering, dyspnea, trembling, collapse, a few convulsive movements, and death occur after a brief period of illness.
• Rigor mortis is frequently absent or incomplete in postmortem lesions of injection anthrax.
• An uncommon fourth form of the disease, injection anthrax results from the subcutaneous inoculation of B anthracis spores.
• Areas most frequently involved in injection anthrax are the ventral aspect of the neck, thorax, and shoulders.
• In production animals, anthrax can be controlled largely by annual vaccination of all grazing animals in the endemic area and by implementation of control measures during epizootics.
• Management of anthrax-infected carcasses is a crucial aspect of control and prevention.