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Anthrax
Replaces Farmnote No 55/94
- REVIEWED AND UPDATED 09/08/06 by Richard Norris
Anthrax was diagnosed on three cattle properties in an isolated area at Walpole, about 100 km west of Albany in March 1994. Prior to that date anthrax had not been reported in Western Australia.
A total of 29 cattle died in this outbreak from January to April 1994. The source of the infection was not identified. All remaining cattle on each property were vaccinated annually for five years. All properties were quarantined for six weeks from the time of the last death to minimise the risk of further outbreaks of disease.
Anthrax is a notifiable disease under the Stock Diseases (Regulations) Act. If anthrax is suspected, then it is a legal requirement to notify the Department of Agriculture and Food as quickly as possible.
Cause
Anthrax is caused by a bacterium, Bacillus anthracis. This organism forms spores which can remain viable in the soil for up to 50 years. The organism may infect many species of domestic and wild animals, as well as people.
Clinical signs in animals
Sheep, goats and cattle infected with anthrax generally die suddenly. Sick animals are rarely seen as death usually occurs within 1 to 2 hours of these signs. Affected animals may be weak and staggery, be fevered and have laboured breathing. Affected milking cows may stop producing milk, and their milk and urine may be stained with blood. Temperatures of 39.5C to 41.7C have been recorded in affected cattle as the earliest and only clinical signs. In an outbreak one or two animals may die initially, followed about a week later by many other deaths. Prompt action will avoid further losses.
Death is less sudden in pigs and dogs; therefore sick animals may be seen. They may be drowsy and have a characteristic large swelling of the throat. This swelling interferes with breathing and can choke the animal to death.
Horses may have colic or diarrhoea, and also may have doughy swellings under the throat, chest, abdomen or on the legs.
Method of spread in animals
Generally, animals pick up the infection through contaminated food or water. Sources of contaminated food include pasture, carcasses or ingestion of soil containing anthrax spores. Inhalation of spores is not considered a significant method of spread of infection in animals. Direct contact with infected animals will not spread the disease.
Outbreaks often occur after soil disturbance or a major weather change such as heavy rain after a prolonged drought and when the daily temperature is more than 15C.
Signs and method of spread in people
People can be infected by handling carcasses, skins or wool of animals which have died from anthrax. The infection may cause a severe generalised illness, commonly starting as a localised skin sore usually as a result of cuts and abrasions on the hands and arms where contact has been made with an infected animal or its products.
The sore begins 2 to 3 days after contact as a simple, usually itchy, pimple. It rapidly becomes a small, boil-like blister with clear fluid which later becomes blood stained. In 2 to 6 days the sore grows in size and develops a central black swollen scab with swelling. Sometimes more blisters surround it. If anthrax is suspected, early medical diagnosis is vital to avoid serious illness or death.
Treatment
The sudden nature of the disease in cattle, sheep and goats means treatment is rarely possible. However, if sick animals are identified they can show a dramatic response to high doses of penicillin administered under veterinary supervision.
Vaccination is very effective in preventing disease from occurring in other animals on a property experiencing an outbreak. Full immunity takes 10 to 14 days to develop. Antibiotics must not be used at the same time as vaccines are given, since they interfere with the development of immunity.
Persistence of the bacteria
Anthrax can persist in the soil for many years because highly resistant spores form when the bacteria are exposed to air. They are spread by transfer of material from infected carcasses or contaminated soil. Spores germinate when eaten by grazing stock. They then multiply quickly, invading the bloodstream in large numbers; this causes fever and rapid death.
Spores need oxygen to form. Anthrax bacteria in discharges from a dead animal react with oxygen to form the spores which can survive for many years and contaminate the area. Anthrax bacteria inside an unopened carcass are destroyed when the carcass decomposes.
Disposal of carcasses
Carcases infected with anthrax should be burnt. However, sometimes this is not practical, and the alternative is to bury them. If infected carcasses are left intact and are buried, the anthrax bacteria do not form spores and the bacteria survive for only a relatively short period.
Formation of spores is minimised by not opening or skinning a suspect anthrax carcass and burning or burying under at least 2 metres of soil. Hydrated lime should be spread over the soil on top of the carcass to help decontaminate the area.
When to suspect anthrax
Be suspicious if animals die suddenly, especially if they have a blood stained or tarry discharge from the nose, mouth or anus, or if blood continues to ooze from sites of predation by crows (e.g. eyes, anus or udder). Apart from these symptoms, there are no characteristic signs. Anthrax is diagnosed in the laboratory.
Should you suspect that an animal may have died from anthrax, contact the local office of the Department of Agriculture and Food immediately. It is preferable to have a false alarm than to allow deaths to go unreported, thereby placing both present and future generations of livestock and producers at risk.
Page last Reviewed : September 2006
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