Smallpox natural history
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Natural History
Complications
Common complications of smallpox include:
- Respiratory complications (viral or bacterial):
- Bronchitis
- Fatal pneumonia
- Secondary bacterial skin infection
- Encephalitis - 1 in 500 patients, commonly in adults
- Permanent pitted scars
- Eye problems - 2% of all cases; pustules can form on the eyelid, conjunctiva, and cornea, leading to:
- Conjunctivitis
- Keratitis
- Corneal ulcer
- Iritis
- Iridocylcitis
- Optic atrophy
- Blindness - occurs in 35% to 40% of eyes affected with keratitis and corneal ulcer
- Subconjunctival and retinal hemorrhages.
- Osteomyelitis - lesions are symmetrical, most common in the elbows, tibia, and fibula
- Arthritis may lead to limb deformities
- Ankylosis
Prognosis
The prognosis of smallpox depends on the form of the disease:
Variola major
Ordinary smallpox
- Fatality rate about 30%
Flat-type smallpox
- Fatality rate about 90%
Hemorrhagic-type smallpox
- Fatality rate near 100%
Variola minor
- fatality rate about ≤1%
In fatal cases of ordinary smallpox, death usually occurs between the tenth and sixteenth days of the illness. The cause of death from smallpox is not clear, but the infection is now known to involve multiple organs. Circulating immune complexes, overwhelming viremia, or an uncontrolled immune response may be contributing factors. In early hemorrhagic smallpox, death occurs suddenly about six days after the fever develops. Cause of death in hemorrhagic cases involved heart failure, sometimes accompanied by pulmonary edema. In late hemorrhagic cases, high and sustained viremia, severe platelet loss and poor immune response were often cited as causes of death. In flat smallpox modes of death are similar to those in burns, with loss of fluid, protein and electrolytes beyond the capacity of the body to replace or acquire, and fulminating sepsis.