Anthrax
Basic Information 
Epidemiology
Contagion and Zoonosis
• The zoonotic risk of B. anthracis cannot be minimized, and the occupational risk of infection of veterinarians is very high compared with the risk of intentional human-to-human transmission. Personal protection when handling anthrax-suspected animals should be complete, including gloves, boots, protective suits, and respiratory and eye protection. This protection must be maintained throughout all environmental and equipment decontamination processes. Complete bathing is recommended after handling any tissues or animals.
• In some situations, prophylactic antibiotic therapy is recommended if exposure is thought to be high or inadvertent through improper attention to personal protection. Animal hide, hair, and wool can contain spores, and people at occupational risk should seek immediate medical attention if skin or respiratory signs occur.
Geography and Seasonality
• Climatic stressors allow reliable prediction of anthrax outbreaks. With climatic change, outbreaks of anthrax occur in infection cycles. A harbinger of infection or primary infection cycle occurs with the sudden death of one or two animals that have been recently introduced into an area. These infected carcasses contaminate the soil with B. anthracis. The secondary infection cycle involves multiple animals that develop anthrax after exposure to contaminated soil or carcasses from the primary infection cycle.
• Anthrax in local cattle is usually observed within the same time period.
Clinical Presentation
Physical Exam Findings
• Although not as frequently diagnosed with B. anthracis infection as cattle, horses do develop disease and die from anthrax. After an incubation period of about 3 to 7 days (can be as short as 1 day or as long as 7 days), horses usually develop the acute form of anthrax, although sudden death may occur. Initial clinical signs frequently include colic with presenting signs that may resemble those of acute enteritis. These horses rapidly progress to high fever with dyspnea. Subcutaneous edema of the ventral neck, thorax, and abdomen may be seen, especially with mediastinal involvement. Ventral edema involving the prepuce and mammary gland is postulated to be secondary to local transmission from insects.
• If an animal dies of disease consistent with anthrax in an endemic area, it is best not to open the carcass. Not only is this important for human safety, but it is also exceptionally important for long-term control by minimizing environmental contamination. Collection of blood in a closed system or a splenic aspirate obtained percutaneously is recommended to facilitate confirmation of the diagnosis. Blood clots poorly in affected animals, so a sample may be obtained for an extended time after death.
• Postmortem analysis is not recommended. The pathologic hallmark of anthrax is the absence of rigor mortis, with passage of blood from body orifices. Petechiae and ecchymoses are widespread, with large quantities of blood-stained serous fluid within body cavities. Severe mediastinal edema, enteritis, and splenomegaly are common. In particular, the spleen has a “blackberry jam” appearance.
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