What is it?

Anthrax is an infection caused by a bacterium, Bacillus anthracis. The infection can take three forms depending on the affected part of the body: cutaneous (on the skin), inhalational, and gastrointestinal. B. anthracis is a spore-forming microorganism that lives in the soil. The spore is extremely hardy and can lie dormant yet alive for many years. The bacterium primarily infects wild and domesticated grazing animals, such as cattle, sheep, and goats. Humans can then become infected by handling the animals or their hair, hide, or meat. Natural anthrax infection is not contracted through drinking milk from an infected animal. Human-to-human transmission is exceedingly rare.

Only cutaneous anthrax has ever been recorded from 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 from the complications of cutaneous anthrax, contracted after conducting post mortems on sheep, after he refused early medical treatment. Only ten human cases were reported in Australia from 1977 to 2010, one each in 2006 and 2007. Anthrax has been nationally notifiable since 1 January 2001.

Anthrax received substantial attention in 2001 when multiple people were exposed to anthrax spores sent through the US mail. Eleven cases were diagnosed as cutaneous and a further eleven as inhalational, with five fatal cases in the latter group.

The US cases in 2001 are believed to have been intentionally caused and raised concerns about the use of anthrax as a weapon. Many countries have investigated and experimented with anthrax as a biological weapon. Anthrax is not transmitted from one human to another, but it makes a potentially effective weapon because it causes deadly infections and the B. anthracis spores are hardy enough to survive dissemination through various routes. These characteristics also make it a potential weapon for terrorists.

Signs and symptoms

Bacillus anthracis infects and produces toxins that can damage cells directly and cause localised oedema. The three kinds of infection vary in their symptoms and prognoses:

• Cutaneous anthrax is the most common form and is usually caused by the bacterium getting into a cut or abrasion on the skin, as can happen from contact with contaminated meat, wool, hides, or leather. The incubation period is 1 to 12 days. The infection begins as a bump that looks like an insect bite and within days opens into a painless ulcer with a black area in the centre. Nearby lymph glands may swell. About 20 per cent of untreated cases result in death, but death is rare in those who receive antimicrobial therapy.

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• Inhalational anthrax is the most lethal form and is caused by breathing in spores. The incubation period is believed to be 1 to 7 days generally but may range up to 60 days. There are two stages to the infection. Initial symptoms resemble those of a viral respiratory illness, including sore throat, mild fever, muscle aches, a non-productive cough, and malaise. This first stage can last from hours to a few days, and the infected person may temporarily begin to feel somewhat better. The second stage may develop suddenly, with symptoms including shortness of breath, high fever, shock, meningitis, chest pain, and respiratory failure. The fatality rate is high, only about 15 per cent of patients survive overall after symptoms begin. With aggressive treatment, about 55 per cent of patients survive.
• Gastrointestinal anthrax, caused by the consumption of raw or undercooked contaminated meat, has an incubation period of 1 to 7 days. The symptoms include severe abdominal distress and fever. The symptoms can be concentrated around either the pharynx, with lesions at the base of the tongue, sore throat, fever, and enlarged lymph nodes, or the lower bowels, with nausea, loss of appetite, vomiting, and fever, followed by abdominal pain, vomiting blood, and bloody diarrhoea. The fatality rate is 25% to 60%.

Tests and treatment

Anthrax infection is diagnosed by culturing the bacteria, using a specimen appropriate to the form of the disease suspected, such as from blood, skin lesions, or respiratory secretions, or by measuring antibodies in the blood. For inhalational anthrax, a chest X-ray can also be helpful as can a test of cerebrospinal fluid if signs of meningitis are present.

Culturing of a sample from either an environmental source or a bodily fluid such as blood can take several hours to several days. The specimen is incubated in artificial media, where the bacteria can grow. (Read more about blood culture.) Conventional biochemical tests are then performed to identify the bacteria and susceptibility testing is done to select the best antibiotic for therapy.

Testing may also be performed to rapidly detect anthrax DNA in the blood and to confirm culture findings. Because of the US incident in 2001, there is great interest in being able to rapidly detect anthrax exposure and infection. Other tests are being developed with this in mind.

Treatment

There is a protective vaccine for anthrax, but it is recommended for use only in high-risk populations, such as military personnel, some veterinarians, and people who work with Bacillus anthracis in laboratories. It is not available to the general public.

If medical intervention begins early, before symptoms become severe, anthrax is treatable with antibiotics. The antibiotics ciprofloxin (Cipro), doxycycline, and amoxicillin are approved by the US Food and Drug Administration for treatment, and doxycycline and ciprofloxin are approved for preventive treatment in the case of exposure (or suspected exposure). Because the spores are so long-lived, the US Centers for Disease Control and Prevention recommend a preventive course of 60 days duration after exposure. Typical treatment courses are also for 60 days.