Anthrax

Causative agent

Anthrax is an acute infectious disease caused by the bacterium Bacillus anthracis. The disease most commonly occurs in animals and can also infect humans.

It is infrequent in most industrialized countries. It is most common in agricultural regions where anthrax in animals is common. In humans, the disease more often affects agriculture and wildlife workers who may handle infected animals. The disease has been made notifiable in Hong Kong since July 2008 and no case has been reported since listed as notifiable disease.

Mode of transmission

Anthrax spores can cause infection on entry via skin, gastrointestinal tract, respiratory tract or direct injection. For example, they may enter the body through abraded skin, get swallowed, or inhaled as a fine, aerosolised mist, or through injection of contaminated drug.

Transmission from person to person is very rare.

Incubation period

Symptoms vary depending on how the disease is contracted. Symptoms usually occur 1 to 7 days after exposure, but the incubation period can be up to 2 months.

Clinical features

Cutaneous anthrax: It is the most common form of Anthrax. It begins as an itchy papule which later develops into a painless ulcer with a black centre. There may be fever, headache, muscle ache, vomiting and regional lymphadenopathy. The disease can be readily cured with appropriate treatment.

Inhalation anthrax: It is the most severe form of anthrax. Initial symptoms resemble an influenza like illness but then rapidly progress to severe breathing problems and shock. Inhalation anthrax without early treatment is usually fatal.

Gastrointestinal anthrax: Initial symptoms include nausea, loss of appetite, vomiting/ blood vomiting, abdominal pain, fever, and severe diarrhoea. Intestinal anthrax can be fatal without early treatment.

Injection anthrax: Symptoms may be similar to those of cutaneous anthrax with skin lesions appearing where the drug was injected. Abscesses deep under the skin or in the muscle of the injection site may occur. Injection anthrax can spread throughout the body faster and be difficult to recognize and treat.

Management

Hospitalization is required. Anthrax can be treated with antibiotics. The disease may be prevented after exposure to anthrax spores by early treatment with appropriate antibiotics.

Prevention

There are vaccines to prevent anthrax, but completion of the whole course of vaccination requires multiple doses.  Human vaccines are used primarily for protection of selected individuals with possible occupational exposure to anthrax.

To prevent anthrax, members of the public are also advised to:

1. Maintain good personal, food and environmental hygiene.
2. Perform hand hygiene frequently, wash hands thoroughly with liquid soap and water before handling food or eating.
3. Clean the broken skin immediately and cover properly with waterproof adhesive dressings. Wash hands before and after touching wounds.
4. Avoid contact with infected animal and contaminated animal product.
5. Thorough washing and cooking of food before consumption.