Anthrax

Bacillus anthracis - (a large, square-ended, rod-shaped, capsulated, spore-forming bacillus).

Anthrax occurs in Australia, most commonly in New South Wales, in what is known as the 'anthrax belt' (extending the length of Central New South Wales, into Victoria, and into southern Queensland). The organism is fastidious and only survives in high calcium, alkaline soils in the rainfall belt of 200-500 mm of rain per year on average.

Repeated incidents have occurred in Queensland near St George-Dirranbandi. Isolated incidents have also occurred on the Marlborough peninsula, and near Wandoan.

Clinical signs in animals

The signs of anthrax are:

• single or multiple animals found dead
• weakness, staggering and laboured breathing
• very high rectal temperature – 41-42°C
• sudden death in grazing animals
• blood-stained discharges after death, usually seen at all external orifices, and rapidly decaying carcass.

Clinical signs in humans

The cutaneous form is the common human disease (malignant pustule) after contact with contaminated animal products and soil. Infection can also occur by ingesting or inhaling anthrax spores (i.e. wool-sorters disease). If the disease is not treated promptly with antibiotics, death may occur.

Depending on the severity of the outbreak, impacts to businesses include:

• animal deaths
• movement restrictions
• increased labour due to intense animal observation
• treatment and vaccination costs
• decontamination and disposal costs of carcasses
• marketing restrictions
• abattoir rejection
• consumer rejection of animal product
• human health risks.

These impacts can be very costly for livestock producers. If your property is at risk of anthrax due to being in southern Queensland, or having received livestock from a high-risk area, you should consider preventative measures (see below).

Environment

The carcass of an animal that has died from anthrax releases bacteria. This bacteria may form spores that contaminate the environment for more than 50 years. In soil, these spores are highly resistant.

However, due to exposure to sunlight, microbial activity and desiccation, spores on the surface rarely survive more than four years. The main risk is the exposure of old cattle or sheep graves by road works, cultivation or runoff following heavy rain.

Under the right conditions, anthrax spores may multiply vegetatively in the soil. Soil disturbance increases the risk of disease.

Run-off from infected soil, and carcasses can contaminate water.

The organism can be spread by pigs, dogs, wild birds, in flowing water, and through contamination by infected animals.

Grazing abrasive forage in denuded pasture, especially in ‘melon hole country’ and around water points increases the disease incidence when spores are present.

Animals

Animals become infected with anthrax from eating contaminated feedstuffs or grazing on contaminated land. Infected animals often die suddenly, with only a brief illness (1-2 hours) preceding death.

The incubation period (time from exposure to bacteria until clinical signs appear) is 2-14 days. Animals may be infected by grazing and show no clinical signs for this period. If these animals are moved during the incubation period to a new location, the subsequent death of these infected animals will create a new source of infection

Pigs may become infected after eating contaminated blood and meat from carcasses. Cattle have been infected after chewing on old bones or carcases from infected animals containing spores. Large outbreaks have resulted from contaminated feed additives such as bone flour and peanut meal. Inhalation is of minor importance in animals, but contaminated dust can be a source. Wound contamination occasionally occurs.

Humans

People are most likely to become infected when handling infected animals or breathing in anthrax spores from infected animal products (e.g. hides and wool). There are 3 forms of anthrax disease in people:

• lung (inhalation)
• skin (cutaneous)
• intestinal.

Read about anthrax infections in people on the Queensland Health website.

Outbreaks from contaminated soil typically occur after a major climate change (i.e. rain following drought), and in warm weather when the temperature is over 15°C. Earthworks may increase risk.

In an uncontrolled outbreak, an initial case may be followed by secondary cases becoming infected from contamination by the initial case.

Call Biosecurity Queensland immediately if you suspect anthrax.

Do not open the carcass. This prevents people, other animals and the land from becoming contaminated.

If you suspect that a person has been exposed to anthrax, seek medical advice and contact a Queensland public health unit.

Control of anthrax in domestic livestock is important for preventing its spread to people, animals and land. Control measures are to restrict movements of potentially infected animals and animal products, and to vaccinate all animals at risk of exposure to infection. Biosecurity Queensland will provide advice on measures, that are consistent with the national guidelines, that can be taken to control the disease. Carcasses must be disposed of by deep burial or by burning to ash, to minimise long-term soil contamination.

In rare cases, valuable individual animals can be treated with large doses of antibiotic. Treatment must be started quickly. It is more effective in pigs, dogs, and humans than in ruminants. Treatment with antibiotics will render vaccination ineffective, as the vaccine is live and will be killed by antibiotics. Early treatment with antibiotics for people infected with anthrax can prevent severe disease.

Rendering plants and factories processing wool and hides must adhere to workplace health and safety regulations.

Restrictions

If anthrax is confirmed or suspected, movements of animals and animal products from the property will be restricted. All cattle and sheep retained on the infected property, and possibly those on neighbouring properties, must be vaccinated to prevent further cases occurring.

Prevention

Livestock should be excluded from areas that have previously been contaminated by anthrax.

Livestock may be protected from the impacts of anthrax by vaccination. Supply and use of anthrax vaccine requires authorisation by the Chief Veterinary Officer. Refer to your veterinarian for further information on vaccination.

Keep livestock away from soil disturbances caused by earthworks or flooding.

Monitor stock health, and investigate incidents of ill-health, especially rapid deaths.

Maintain secure boundary fences to prevent stock straying. Control feral animals to reduce soil disturbance, the risk of animals becoming infected and the risk of spreading infection to new areas.

Livestock producers, especially in southern Queensland, should consider anthrax in their farm biosecurity plans. Consult your local veterinary practitioner to decide what preventative measures to take to protect your property and health.