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Anthrax

Epidemiology of Infectious Diseases: Anthrax

Causal agent
Bacillus anthracis

Common clinical features
There are three clinical forms of anthrax;

  1. Cutaneous anthrax accounts for >95% of cases and occur when the bacterium enters a cut or skin abrasion. Symptoms begin with a skin lesion that becomes papular, then vesicular and 2-6 days develops into a depressed black eschar. The head, forearms and hands are common sites of infection1.
    Untreated infections may spread to regional lymph nodes and the bloodstream with overwhelming septicaemia. Untreated cutaneous has a case fatality between 5-20%.
  2. Inhalation anthrax occurs following the inhalation of B. anthracis spores. Symptoms include productive cough, myalgia, fatigue and fever, sweating. This if followed by rapid deterioration with high fever, dyspnea, cyanosis and shock. Meningitis (often haemorrhagic) occurs in up to 50% of individuals with inhalation anthrax3.
  3. Intestinal anthrax is very rare and occurs after eating contaminated meat. Involvement of the pharynx is characterized by lesions at the base of the tongue and tonsils, with sore throat, dysphagia, fever and regional lymphadenopathy. Involvement of the lower intestine is characterized by acute inflammation of the bowel, nausea, anorexia, vomiting, fever, abdominal pain, vomiting of blood and bloody diarrhoea. The case fatality rate is estimated to be between 25-60%3.

Epidemiology

  • Endemic in parts of South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean and the Middle East.
  • Human anthrax is rare in the UK and is generally associated with occupations exposure such as those handling imported infected animal products or infected animals3.

Reservoir
Infected animals
Soil

Mode of transmission
Humans can become infected through direct contact with skin, ingestion or inhalation of B. anthracis spores originating from products of infected animals (e.g. animal carcasses, hair, wool, hides or bone meal) and inhalation of airborne oraerosolised B. anthracis spores2,4.

There is no known person to person spread via the inhalational route.

Animals become infected when they ingest or inhale the spores while grazing2.

Incubation period
Cutaneous anthrax - 1-12 days (rarely up to 7 weeks)
Inhalation/pulmonary anthrax - 1-7 days (commonly within 48 hours)
Intestinal anthrax - 1-7 days

Period of Communicability
B. anthracis spores can remain viable and infective in soil for years and maybe decades.

Treatment
Anthrax can be treated effectively with antibiotics if identified early.

Prevention and control
In the UK immunisation is recommended for;

•Workers dealing with infected animals
•Occupations involving processing of infected animal material

References

1.Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
2.National Immunizatin Program, Centers for Disease Control and Prevention, Epidemiology and Prevention of Vaccine-Preventable Disease 'The Pink Book', 9th edition, U.S. Department of Health and Human Services, 2006.
3.Salisbury DM, Begg NT. Immunisation against infectious disease (The green Book). London: HMSO, 1996. Available at http://www.dh.gov.uk/assetRoot/04/07/29/84/04072984.pdf
1.Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006