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Updated 21 May 2015

Anthrax

Anthrax is a highly infectious spore-forming bacterial disease of animals.

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Description

  • Anthrax is a highly infectious disease of animals which is rarely transmitted to people by contact with infected animals or their products. Due to its potentially lethal properties, it can be used in biological warfare - as was the case in 2001/2002 in the USA.
  • It is caused by Bacillus anthracis.
  • Humans are usually infected through the skin, but people have become infected after eating contaminated meat or inhaling the spores.
  • Inhaling spores can result in pulmonary (chest) anthrax, called woolsorter’s disease, which is often fatal.

Anthrax is a highly infectious spore-forming bacterial disease of animals, particularly grass-eating animals such as cows and sheep, which is rarely transmitted to people by contact with infected animals or their products. The disease has been around for tens of thousands of years. Spores can live in contaminated soil and animal products for decades. Transmission via the skin is the usual method of infection in humans but it can occur through eating contaminated meat or by inhaling spores. Direct person-to-person spread of anthrax is extremely unlikely to occur.

There are three main forms of anthrax affecting either the skin (cutaneous), the chest (pulmonary) or the gut (gastrointestinal). The cutaneous form is rarely fatal, but the pulmonary form usually results in death.

The antibiotics ciprofloxacin, penicillin, streptomycin, tetracycline and erythromycin can all be used in treatment.

The disease is prevented by good husbandry and abattoir controls.

The last known South African case of anthrax in animals occured about a year ago. South African vetenarians are well qualified to diagnose any unsuspecting cases in livestock.

Zimbabwe experienced a terrible epidemic of skin anthrax with more than 10 000 cases between 1979 and 1985.

Cause

Anthrax is caused by the bacterium Bacillus anthracis. This bacterium can live in tissues that contain little or no oxygen. Its spores (the size of a speck of dust) are very resistant to destruction, so it can survive in contaminated soil and animal products for decades. Animal vaccination, and the destruction of infected herds, has drastically reduced the number of infected animals. However, due to the highly resistant spores, spores are still found in soil samples from all over the world.

Humans are usually infected by inoculation through the skin, but people have become infected after eating contaminated meat. Inhaling spores can result in pulmonary (chest) anthrax, called woolsorter’s disease, which is often fatal. However, pulmonary anthrax is very uncommon since a person has to inhale several thousand spores before infection can take hold.

When anthrax spores get inside the body, they grow rapidly. The germs can cause dangerous infections. However, it is actually toxins produced by the organism which causes widespread cell damage and is resonsible for most of the clinical features of anthrax. The toxin is so deadly that it can kill even after the infection is brought under control.

Symptoms

Symptoms of disease vary depending on how the disease was contracted, but symptoms usually occur within 7 days.

Cutaneous

Most (about 95%) anthrax infections occur when the bacterium enters a cut or abrasion on the skin, such as when handling contaminated wool, hides, leather or hair products (especially goat hair) of infected animals. Skin infection begins as a raised itchy bump that resembles a mosquito bite but within one to two days develops into a liquid-filled sac and then a painless ulcer, usually 1-3 cm in diameter, with a characteristic black dead tissue area in the centre. Lymph glands in the adjacent area may swell. Deaths are rare with appropriate antibiotic treatment.

Inhalation

Initial symptoms may resemble a common cold. After several days, the symptoms may progress to severe breathing problems and shock.

Intestinal

The intestinal disease form of anthrax may follow the consumption of contaminated meat and is characterised by an acute inflammation of the intestinal tract. Initial signs of nausea, loss of appetite, vomiting, fever are followed by abdominal pain, vomiting of blood, and severe diarrhoea.

Course

Deaths from cutaneous anthrax are very unusual with the appropriate treatment, and the mortality rate is between 10 and 20% if it is not treated. However, pulmonary anthrax carries a mortality of nearly 100% even when treated. Gastrointestinal anthrax has a mortality of 50% and anthrax meningitis is usually fatal.

Diagnosis

Anthrax is diagnosed by isolating the bacterium from the blood, skin lesions, or respiratory secretions or by measuring specific antibodies in the blood of persons with suspected cases. These antibody tests are not, however, widely available, mainly due to the rarity of this condition.

After the anthrax scares in the USA in 2001/2002, a new diagnostic test was developed which detects the DNA of the bacterium in clinical specimens. This test could be used to determine whether a patient did in fact have anthrax, or even whether the person had been exposed and had spores in the nasal passages. However, since the attacks have subsequently ceased, it is hard to say how often this sort of test will need to be used, and how widely available it would be.

Treatment

Early treatment is essential. Natural strains of anthrax may be resistant to many antibiotics, but most are sensitive to penicillin. However, the antibiotic of choice is either doxycycline or ciprofloxacin. Antibiotic treatment should continue for at least 60 days.

Prevention

Anthrax is now almost unknown in the Western world, other than in stockpiles of spores which could potentially be used for biological warfare - such as the case in the USA.

Pulmonary anthrax was virtually eliminated in Britain before 1940 by developing methods to decontaminate wool and goat hair and by improving working conditions for those handling animal products.

Good livestock and abattoir control usually means that the disease is seldom seen.

There is a vaccine for humans available in the USA, but apparently no stocks are kept in South Africa. The vaccine is reported to be 93% effective in protecting against the disease.

Following the anthrax attacks in the USA, a lot of effort was put into new vaccine development, and although a number of interesting and promising studies are ongoing, there is no new vaccine presently availble.

Reviewed by Dr Andrew Whitelaw, MBBCh (Witwatersrand), MSc (UCT), FCPath (Micro) (SA) Senior registrar, Department of Microbiology, University of Cape Town and Groote Schuur Hospital

 
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