- Anthrax is an ‘urgent’ notifiable condition that must be notified immediately to the department by medical practitioners and pathology services.
- Anthrax is an acute bacterial disease that affects the skin in 95 per cent of cases. Rarely, it can infect the lungs after inhalation or the intestinal tract after ingestion.
- Anthrax infection is primarily zoonotic.
- Cutaneous anthrax is treatable, but the pulmonary and intestinal forms are more severe with a case-fatality rate approaching 100 per cent.
- An anthrax vaccine is available, but not for civilian use in Australia.
Notification requirement for anthrax
Anthrax infection is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days.
This is a Victorian statutory requirement.
Primary school and children’s services centre exclusion for anthrax
School exclusion is not required.
Infectious agent of anthrax
Bacillus anthracis is a Gram-positive, aerobic, rod-shaped bacterium that is encapsulated, spore-forming and non-motile. Its spore-forming capacity renders it an extremely durable and persisting environmental agent.
Identification of anthrax
Anthrax is an acute bacterial disease that usually affects the skin. It may rarely involve the lungs after inhalation or the intestinal tract after ingestion.
This form accounts for more than 95 per cent of anthrax cases worldwide. Lesions usually occur on exposed skin and often commence with itchiness. They pass through several stages:
- papular stage
- vesicular stage with a blister that often becomes haemorrhagic, sometimes surrounded by secondary vesicles
- eschar stage that appears after 2–6 days to become a depressed black scab (malignant pustule), which may have surrounding redness and extensive oedema (swelling).
Anthrax lesions are usually painless, but pain may result due to surrounding oedema or secondary infection. Untreated lesions can progress to involve regional lymph nodes. An overwhelming septicaemia or meningitis can occur in severe cases.
Untreated cutaneous anthrax has a case-fatality rate of 5–20 per cent, but death is rare with early appropriate treatment.
Pulmonary (inhalational) anthrax
This is very rare and often presents with mild and non-specific symptoms, including fever, malaise and mild cough or chest pain (upper respiratory tract symptoms are rare). Early symptoms may be confused with a flu-like illness.
This is followed within 3–6 days by rapid onset of respiratory distress, including stridor, severe dyspnoea, hypoxia, shock and cyanosis, with radiological evidence of mediastinal widening. Death follows shortly thereafter.
The mortality rate approaches 100 per cent with delayed or no treatment. Commencement of appropriate antibiotic therapy and supportive care before the onset of respiratory symptoms significantly decreases the mortality rate.
These are very rare forms of anthrax in developed countries but may occur in large outbreaks in developing countries following ingestion of meat from infected animals.
In intestinal anthrax, gastrointestinal symptoms may be followed by fever, septicaemia and death. Case-fatality rates of 25–75 per cent have been reported.
In oropharyngeal anthrax, fever, neck swelling due to lymphadenopathy, throat pain, oral ulcers and dysphagia may be followed by severe local ulcers and swelling, septicaemia and death. Case-fatality rates are similar to those for the intestinal form.
Laboratory confirmation of anthrax is by demonstrating the presence of B. anthracis in blood, lesions or discharges by direct staining of smears using Gram or other special stains, or by the isolation of the organism by culture or animal inoculation. Nucleic acid testing of B. anthracis targets BA1, BA2 and BA3 is in use at the Microbiological Diagnostic Unit but remains under development.
Incubation period of Bacillus anthracis
The incubation period is typically 1 day for cutaneous anthrax and 1–7 days for pulmonary anthrax. Evidence from mass exposures indicates that incubation periods up to 60 days are possible for pulmonary anthrax (related to the delayed activation of inhaled spores). The incubation is typically 3–7 days for the gastrointestinal form.
Public health significance and occurrence of anthrax
Anthrax is primarily a disease of herbivores. Humans usually become infected when they come into contact with infected animals or their products.
Anthrax is primarily an occupational hazard for handlers of processed hides, goat hair, bone products, wool and infected wildlife. It can also be contracted by contact with infected meat, for example in abattoir workers.
New areas of infection in livestock may develop through the introduction of animal feed containing bone meal. Cutaneous outbreaks sometimes occur in knackery workers and those handling pet meat. Anthrax spores can persist for years in the soil of certain tracts of land, such as areas where the carcasses of animals that died of anthrax are buried.
Anthrax can also be used as a biowarfare or bioterrorism agent, most likely spread as an aerosol. Any new case should be assessed with this possibility in mind, particularly but not exclusively in cases of pulmonary anthrax and in geographical areas where anthrax has historically not been known.
Reservoir of Bacillus anthracis
Spores may remain viable in contaminated soil for many years. Dried or processed skins and hides of infected animals may also harbour spores for years.
Mode of transmission of Bacillus anthracis
Cutaneous anthrax is usually introduced through a skin injury. It can occur:
- by contact with tissues of animals such as cattle, horses, pigs and others dying of the disease, or in processing after death
- by contact with contaminated hair, wool, hides, bone material or products made from them (hide porter’s disease)
- by contact with soil associated with infected animals and contaminated bone meal used in some gardening products
- possibly by biting flies that have fed on infected animals in some parts of the world (not seen in Australia).
Pulmonary anthrax (woolsorter’s disease) can occur:
- by inhalation of aerosolised spores in industries that inadvertently deal with contaminated tissues or products (such as industries tanning hides or processing wool or bone products), or by accident in laboratory workers
- by intentional release of spores using a variety of aerosol devices, including mailed items.
Intestinal or oropharyngeal anthrax is caused by ingestion of anthrax-contaminated undercooked meat. There is no evidence of transmission through the milk of an infected animal.
The deliberate release of anthrax spores through contaminated letters in the United States in October 2001 resulted in 22 cases of anthrax, of which half were cutaneous and half were pulmonary anthrax.
Period of communicability of anthrax
There is no evidence of direct spread from person to person. Articles and soil contaminated with spores may remain infective for years.
Susceptibility and resistance to anthrax
Recovery is usually followed by prolonged immunity.
Control measures for anthrax
Preventative measures include:
- At present, anthrax vaccine is not available for civilian use in Australia. Subject to the availability of a vaccine in the future, it will only be provided under the Special Access Scheme administered by the Therapeutic Goods Administration for those groups at highest risk of infection with B. anthracis (that is, laboratory staff working with cultures of the organism).
- Educate employees who are handlers of potentially infected articles in the proper care of skin abrasions.
- Ensure proper ventilation in hazardous industries and the use of protective clothing.
- Sterilise hair, wool or hides, bone meal or other feed of animal origin before processing.
- Affected properties are quarantined. Potentially exposed stock are vaccinated, dead animals are burned and contaminated sites are disinfected. The quarantine is not released until occurrences of anthrax cases have ceased and at least 6 weeks has elapsed since the last round of vaccination on the property.
Control of case
The following treatment advice is to be used as a guide only. Always consult the current version of Therapeutic guidelines: antibiotic) and seek expert advice from an infectious diseases physician.
Pulmonary, gastrointestinal and meningeal anthrax
The keys to successful management appear to be the early institution of antibiotics and aggressive supportive care. Chest tube drainage of the recurrent pleural effusions, which are typically haemorrhagic, may lead to dramatic clinical improvement.
Control of contacts
Although there is no person-to-person transmission, the department will trace and follow up anyone who may have been exposed to the same source as the case, and it may be recommended that such people take antibiotics (post-exposure prophylaxis).
Control of environment
If an animal anthrax case is suspected, it should be reported to the Department of Primary Industries (DPI). Movement of animals and animal products from the farm is suspended. Appropriate rapid testing (immunochromatographic test or ICT) is conducted in the field on cattle and sheep carcasses, and blood samples for confirmatory testing are submitted to the DPI’s Attwood laboratory. If the case occurs on a dairy farm, the dairy factory is advised to suspend the collection of milk until the case is investigated and Dairy Food Safety Victoria is advised.
If an animal anthrax case is confirmed, the affected property is quarantined, potentially exposed stock are vaccinated, dead animals are buried and contaminated sites are disinfected. The quarantine is not released until occurrences of anthrax cases have ceased and at least 6 weeks has elapsed since the last round of vaccinations on the property. DPI staff will liaise with knackeries, local veterinary practitioners, the dairy industry, health authorities, local government and regional emergency services staff.
Decontamination of environments contaminated after a deliberate release of anthrax spores requires full HAZMAT decontamination by appropriately protected trained personnel using strong chlorine-based disinfectants. The risk of secondary aerosolisation is generally thought to be very low, although spores produced for bioterrorism may be deliberately prepared to increase this risk. Although the risk of anthrax can be significantly reduced by environmental decontamination measures, evidence from deliberate releases of anthrax spores in other countries suggests that complete environmental decontamination of anthrax spores is extremely difficult.
Outbreak measures for anthrax
A single case of anthrax should be considered an outbreak and should be managed with great urgency. If one or more people seem to have been infected in an unusual way, such as in cases where there is no evidence of exposure to infected animals or their products, a deliberate release of anthrax organisms must be considered.
If a credible threat is received or an anthrax release is confirmed, the appropriate response code will be declared by the Australian Government Chief Medical Officer through the Australian Health Protection Principal Committee and the Department of Health’s National Incident Room will be activated.
If a focus of infection is identified or a deliberate release of organisms is suspected, outbreak control measures include:
- coordination with appropriate emergency services, including the police force, as required
- active case finding
- alerts for postal facilities, medical practitioners and healthcare facilities
- the release of appropriate public information
- environmental control measures
- control of contacts (those potentially exposed), including field workers involved in environmental control measures.
Reviewed 18 September 2023