Smallpox (Variola Virus)

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • Smallpox is a life-threatening, acute, contagious, eruptive disease caused by variola virus.
  • The disease is characterized by a febrile prodrome followed by the development of rash.
  • Rash evolves in a stereotypical fashion: macules → papules → vesicles → pustules; scabs form and fall off, leaving scars called pockmarks.
  • There are two clinical forms of smallpox:
    • Variola minor is a less common and milder form of disease.
    • Variola major is the more common and serious form of disease, of which there are five types:
      • Ordinary smallpox
      • Modified smallpox
      • Flat (malignant) smallpox
      • Hemorrhagic smallpox
      • Variola sine eruption

EPIDEMIOLOGY

  • The last documented case of endemic smallpox was in Somalia in 1977.
  • The last case in the United States was in the late 1940s.
  • Smallpox was declared eradicated by the World Health Organization in 1979.
  • Historically, in unvaccinated individuals, ordinary smallpox accounted for 90% of cases, flat smallpox for 7% of cases, and hemorrhagic and modified smallpox making up the remainder. Modified smallpox was rare in unvaccinated individuals but accounted for 25% of cases of disease in vaccinated individuals.

ETIOLOGY

  • Variola virus is a member of the poxvirus family and Orthopoxvirus genus.
  • Variola is a double-stranded DNA virus usually transmitted during face-to-face contact via respiratory aerosols or direct contact with infected skin lesions.
  • Transmission of the virus via infected fomites is uncommon.
  • Humans are the only vectors.

GENERAL PREVENTION

  • Prior to 1971, smallpox vaccination was part of the routine childhood schedule in the United States.
  • Vaccines are produced from the vaccinia virus, a closely related orthopoxvirus to variola.
  • Due to concern for use of smallpox as an agent of bioterrorism, the U.S. Strategic National Stockpile still stores smallpox vaccine.
  • Two vaccines are approved for use in patients with occupational exposure to orthopoxviruses: ACAM2000 and JYNNEOS.
  • Currently, the Advisory Committee on Immunization Practices (ACIP) recommends smallpox vaccination for the following:
    • Public health response teams responsible for investigating suspected smallpox cases
    • Hospital-based health care teams responsible for assessing and caring for suspected smallpox cases
    • Laboratory personnel who work with the virus that causes smallpox or other orthopoxviruses
  • Prior to administration of vaccines, clinicians should review the current indications, contraindications, and known adverse events available at https://www.cdc.gov/smallpox/clinicians/vaccines.html

PATHOPHYSIOLOGY

  • The virus infects the upper respiratory tract and replicates; rarely, primary infections can occur via skin, conjunctival, or placental routes.
  • The virus enters the bloodstream (primary viremia) and is taken up by macrophages.
    • Patient is asymptomatic during this time.
  • Next, the virus enters the reticuloendothelial system where it continues to replicate.
  • Secondary viremia occurs as the virus reenters the bloodstream and infects organs.
    • Can cause epidermal necrosis and swelling
    • Infections of the bone marrow, kidneys, liver, lymph nodes, spleen, and other organs result in coagulopathy and multiorgan system failure.
  • Exact mechanisms of viral toxicity are not understood but may involve both viral cytopathic effects and inflammatory pathology.

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