Anthrax: Public health response plan for Australia

Background

Page last updated: 05 December 2012

2. Background


Infectious agent
Epidemiology
Australian situation
Potential for anthrax as a biological weapon
Surveillance for deliberate releases of anthrax

Infectious agent

Bacillus anthracis is a Gram positive, aerobic spore-forming bacterium, approximately 1ým wide and 2–10ým long. It is easily cultured in the laboratory on simple media, and vegetative forms grow in chains. It sporulates readily, and the spores are heat resistant and persist for long periods in the environment. Virulent strains produce a toxic complex of three factors: oedema factor, protective antigen factor and lethal factor. Virulence genes can be readily detected by reference laboratories using PCR methods.

Epidemiology

The organism is generally regarded as an obligatory pathogen, whose persistence in the environment is dependent on replication in a susceptible host, in addition to the relative resistance of the spores to desiccation, heat and ultraviolet light. The disease is a zoonosis which can be contracted naturally from a number of species including cattle, sheep, goats, pigs, dogs, cats and horses, and their products such as hides and meat. Natural anthrax infection is rarely contracted through drinking milk from an infected animal.
The vegetative form of B. anthracis is relatively fragile and will not survive in this form in the environment. However, on release from an infected animal and exposure to air, vegetative cells sporulate and may remain viable and infectious in this form for many years in some soils. Spores are highly resistant to desiccation and much more heat resistant than the vegetative form. Animals may contract anthrax though exposure to grass and other feeds contaminated with spores of B. anthracis.

Human-to-human transmission of anthrax is exceedingly rare. One report of possible community transmission of cutaneous anthrax has been published. This article, published in 1975, suggests a possible link for spread of subclinical disease via communal loofahs [1]. Standard infection control precautions are adequate to prevent transmission.

Australian situation

Anthrax occurs sporadically in herbivorous animals such as cattle, sheep and goats in Australia. Only cutaneous anthrax has ever been recorded in humans in Australia. For this reason alone, a single case of either inhalational or gastrointestinal anthrax should be viewed with a high index of suspicion of deliberate release of B. anthracis.

In the 1920s, cutaneous cases were associated with infected shaving brush bristles. In the early 1960s a farm worker died, after he refused early medical treatment, from the complications of cutaneous anthrax contracted after conducting post mortems on sheep. Only eleven human cases were reported from 1977 to 2010. Anthrax has been nationally notifiable since 1 January 2001.

Potential for anthrax as a biological weapon

B. anthracis has major potential as a biological weapons agent because:
  • it can be isolated and cultured in large quantities with relatively simple equipment and culture media;
  • it produces large quantities of spores which can remain viable in the environment for many years; and
  • inhalational and possibly gastrointestinal forms have a high case fatality rate.
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Successful delivery of spores to produce the inhalational form of the disease requires that the agent be dispersed in an aerosolised form. Producing a powdered form with the appropriate particle size and physical properties, and which will remain suspended for sufficient periods of time to be effective, is technologically difficult. Lower grade material may be effective in causing large numbers of infections if dispersed in sufficient quantities. Foods adulterated with anthrax spores may be an effective vehicle for causing an outbreak of intestinal anthrax. Foods that are eaten cold are most likely to be amenable to deliberate contamination.

An anthrax release is likely to be first suspected based on the following:
  • any case of inhalational or gastrointestinal anthrax
  • one or more human cases of anthrax where there is no identified occupational or other epidemiological link to B. anthracis;
  • claim of release of anthrax into the environment by an individual or group; or
  • analysis of ‘suspicious unidentified substances’.

Strains of B. anthracis isolated from the environment are generally sensitive to a number of antibiotics, including penicillins, tetracyclines, macrolides, chloramphenicol and quinolones. B. anthracis strains may have constitutive and inducible beta-lactamases. B. anthracis is resistant to cephalosporins. Because of potential for laboratory genetic manipulation of B. anthracis, all clinical isolates should be tested for antibiotic susceptibility by validated test methods.

Surveillance for deliberate releases of anthrax

Anthrax is an exceedingly rare disease in Australia. Only eleven cases of cutaneous anthrax have been reported since 1977, and inhalational and intestinal anthrax have never been reported in this country. A high index of suspicion of a deliberate release of anthrax should be entertained if even one case of inhalational or intestinal anthrax is diagnosed.

A deliberate release of anthrax should be considered in the event of one or more cases of human anthrax where there is no plausible occupational or other relevant contact history, or advice from State or Australian Government animal health authorities of an outbreak of anthrax in animals.

The occurrence of multiple cases of cutaneous anthrax should be interpreted in the light of the patients’ histories (e.g. exposure to livestock or livestock products). If such a history exists, agricultural authorities should be consulted as part of the assessment of the likelihood of a deliberate exposure.

All cases of suspected and confirmed human anthrax should be reported immediately to the local public health unit, together with all available clinical and epidemiological information. The State/Territory health authority will advise the Communicable Diseases Network of Australia (CDNA) Secretariat of confirmed cases who will advise other State/Territory jurisdictions and the Australian Government Department of Agriculture, Fisheries and Forestry (DAFF). State/Territory health authorities should also advise their respective departments of agriculture. Each agency should also advise their respective media response teams. A coordinated media response plan will be activated by the respective jurisdictions.

If a deliberate release of B. anthracis is suspected, national security agencies, including the Attorney-General’s Department Crisis Coordination Centre, Australian Federal Police (AFP) and State/Territory police will also be notified.top of page