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Anthrax

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Reporting Obligations

Confirmed and suspected cases should be reported immediately by phone to the local Health Unit. One case is deemed a public health emergency.

Epidemiology

Aetiologic Agent

The aetiological agent of anthrax is the bacterium Bacillus anthracis (B. anthracis), an aerobic, Gram-positive, encapsulated, spore forming, nonmotile rod. Anthrax can result from natural infection or secondary to a bioterror event.

Clinical Presentation

Depending on the route of transmission, anthrax infection can result in four clinical syndromes: cutaneous, inhalation, gastrointestinal, and injection.

Cutaneous anthrax is characterized by initial itching of the exposed skin surface; an initial vesicle at the site of inoculation develops into a painless black eschar; fever, malaise and headache may be present.

Inhalational anthrax is the most lethal form of disease. Initial presentation includes fever, malaise, mild cough, dyspnea, nausea or vomiting, and this is followed by acute onset of respiratory distress and shock; there is also radiological evidence of mediastinal widening and pleural effusion present.

Gastrointestinal anthrax cases present with acute nausea, vomiting, abdominal distension, pain, fever, gastrointestinal (GI) bleeding and peritonitis.

Injection anthrax cases, associated with heroin use, have emerged in recent years and have been seen in heroin-injecting drug users in northern Europe. This type of infection has never been reported in Canada. Patients with injection anthrax have not presented with typical symptoms associated with the preceding three classical forms of anthrax. Most patients have serious localized soft tissue infections accompanied by significant soft tissue edema. Fever is not a prominent feature and pain is less severe than with other serious soft tissue infections. Not all cases have localized injection-related lesions; some cases have presented with symptoms more typical of systemic anthrax infections. Injection anthrax can spread throughout the body faster and be harder to recognize and treat. Many other more common bacteria can cause skin and injection site infections, so a skin or injection site infection in a drug user does not necessarily mean the person has anthrax.

Systemic illness can result from hematogenous and lymphatic dissemination with any form of anthrax. Anthrax meningitis can occur in any patient with systemic illness and in patients without other apparent clinical presentations. Anthrax meningitis begins with hypotension, quickly followed by delirium or coma; refractory seizures, cranial nerve palsies, and myoclonus have been reported. Case fatality rate for meningitis exceeds 90%.

Modes of Transmission

Transmission occurs by inoculation through open skin via contact with infected animal tissue, other animal products (especially animal skins), and contaminated soil; by ingestion of undercooked, contaminated or raw meat; and following injection of drugs (e.g. heroin) that have been contaminated with anthrax spores. Inhalational anthrax results from the inhalation of anthrax spores, particularly in risky industrial settings such as animal skin processing facilities, or as a result of a bioterrorist incident.

Incubation Period

From 1–7 days, although incubation periods of up to 60 days are possible.

Period of Communicability

Person to person transmission is rare. Articles and soil contaminated with spores may remain infective for years.

Risk Factors/Susceptibility

There is some evidence of inapparent infection among individuals in frequent contact with the infectious agent. Post-infective immunity may be incomplete, and subsequent reinfections may occur, though reports of such second attacks are rare.

Diagnosis and Laboratory Testing

Laboratory demonstration of B. anthracis obtained from blood, CSF, pleural fluid, ascitic fluid, vesicular fluid or lesion exudates.

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Treatment and Case Management

Treatment of the case should be under the direction of an infectious diseases specialist. Refer to the reference below for more information on treatment.

Public Health staff will be involved to obtain specific information to determine the source of infection and whether other cases may have been exposed.

Note: Given the potential for the appearance of anthrax cases to signal a bioterrorism incident, investigation and follow-up may involve the activation of the emergency management system in place in the province.

For hospitalized persons routine practices are recommended. Persons who may have been exposed to anthrax are not contagious, so quarantine is not appropriate.

Persons with open and/or draining lesions should be cared for using contact precautions. Dressings with drainage from the lesions should be incinerated, autoclaved, or otherwise disposed of as biohazard waste.

Patient Information

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Additional Resources

Ministry of Health and Long-Term Care. “Health Care Professionals, Diseases: Anthrax”.

Heymann, D.L. Control of Communicable Disease Manual (Twentieth Edition). Washington, American Public Health Association, 2015.

References

Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2019.