Smallpox

Epidemiology

  • Last naturally occurring smallpox case was in Somalia in 1977
  • Remaining stocks are in US and Russia

Physiology

  • Single-stranded DNA virus (in the same family as monkeypox and vaccinia virus)
  • Reservoir: no natural non-human reservoir
  • Transmission: respiratory droplets from infected person (patients are infectious after development of rash until final sloughing of crusts)
  • Incubation: 7-17 days

Diagnosis

  • Culture/PCR/EM: available at CDC

Clinical

Symptoms/signs:
1) Febrile prodrome (2-3 days): severe headache and backache
2) Oral exanthem (1 day):
3) Macular rash over face and extremities -> papules -> pustules (5-8 days)
-Usually 4-6 mm subepiderml pustules (with normal skin between lesions)
-Lesions appear in synchronous crops in one body area
-May involve palms and soles, but trunk is spared
-Distribution is centrifugal with spread from face to extremities
-Pustules crust and slough


Treatment

No proven antiviral agents
-Cidofovir: may be modestly efficacious in animal trials (however, has nephrotoxicity)

Vaccinia immune globuin (currently in short supply): not effective in acute smallpox (but useful for vaccination-related complications)

Smallpox vaccination: prevents disease in 95% of cases, but was discontinued in 1972 (all persons <30 y/o are unprotected, others have only partial protection due to waning immmunity after 5-10 years)

-Prophylactic vaccination (given within 3 days of exposure): highly effective in preventing or modifying disease, but is relatively contraindicated in AIDS, transplants, pregnant women, chronic eczema, and others with immunocompromised state

-Post-exposure vaccination: not contrindicated in immunocompromised patients, as risk of vaccine is much less than risk of disease in this case

-Complications of vaccination: virus shedding from vaccinated persons to others, disseminated vaccinia, vaccinia necrosum, eczema vaccinatum, encephalitis, death

-Treatment of severe vaccination-related severe complications: vaccinia immune globulin

Infection control: respiratory and contact precautions


References

  • xxx