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Smallpox
Overview

Causative Agent

  • Variola virus, a species of Orthopoxvirus

 

Incubation Period

  • 12-14 days (range 7-17 days)

Infectious Period

  • From fever onset (usually 2–4 days before rash) until last scab has separated; about three weeks.

Transmission

  • Aerosols/droplets from nasopharyngeal lesions and contact with contaminated articles.

Epidemiology

  • Last naturally acquired human case in the world occurred in Somalia in 1977; global eradication was certified two years later.

There are at least 2 strains, variola major and the variola minor.

  • Variola major: the more severe form with case fatality rate up to 30-50% in susceptible populations.
  • Variola minor: milder form of the disease with more diminutive pox lesions; case fatality rate of 1-2% in susceptible populations.
Detection & Treatment
  • Electron microscopy, PCR, viral isolation (culture of pharyngeal swab or lesions).
  • Guarnieri bodies on Giemsa or modified silver stain.
Care Management
  • Supportive care.
  • Antibiotics may be used for secondary bacterial infection.
  • Vaccination within 3 days of exposure may significantly ameliorate or prevent smallpox. Vaccination 4 to 7 days after exposure likely still offers some protection or modification of disease severity.
  • Notify MOH immediately on suspicion. Call MOH Communicable Diseases Surveillance team at: 98171463
  • Airborne and contact precautions. Isolate patients in negative pressure isolation room.
  • Patients should be considered infectious until all scabs separate and should be isolated during this period.
  • Droplet and airborne precaution for a minimum of 17 days following exposure for all persons in direct contact with the index case.

 

References

  • Henderson DA, Inglesby TV et al. Smallpox as a biological weapon: medical and public health management. Working group on Civilian Biodefense. JAMA 1999; 281: 2127-37
  • Committee on Epidemic Diseases. Clinical guidelines on anthrax, botulism, plague and smallpox. Epidemiological News Bulletin. 2001; 27:61-68
  • CDC (Atlanta), Smallpox overview. 2004. Available from http://emergency.cdc.gov/agent/smallpox/overview/disease-facts.asp. Accessed Dec 2010.
  • WHO. Smallpox. 2010. Available from http://www.who.int/mediacentre/factsheets/smallpox/en. Accessed Dec 2010.