Microbiology · Other DNA viruses
Variola virus !
- Virus
- Enveloped
- Contact
- Airborne
- For completeness
The poxvirus of smallpox, a disease eradicated in 1980 thanks to vaccination; it now exists only in authorized laboratories.
Updated 2026-11-01
Also called: smallpox, variola
At a glance
- Shape
- Large, brick-shaped, enveloped
- Genome
- Linear double-stranded DNA
- Envelope
- Enveloped
- Family
- Poxviridae (genus Orthopoxvirus)
- Size
- About 300 nm
Morphology
- Large brick-shaped virus
- Cytoplasmic replication with inclusion bodies (Guarnieri bodies)
Transmission
- Prolonged face-to-face contact (respiratory droplets and aerosols)
- Contact with lesions, clothing or contaminated bedding
Reservoir: Humans only: that is why it could be eradicated
Isolation precautions
What the care team adds to standard precautions.
- Contact
- Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.
- Airborne
- N95 respirator and a negative-pressure room.
Virulence factors
- Proteins that inhibit complement and interferon
- Considered a high-priority bioterrorism agent
Diseases it causes
- Smallpox
Clinical picture
- Incubation of 7 to 19 days, with no contagiousness during that time
- High fever and prostration, then a rash in the mouth and face that spreads to the limbs, palms and soles (centrifugal)
- All lesions in one area are at the same stage: macule, papule, vesicle, pustule and crust
- Severe forms: flat (malignant) and hemorrhagic
Diagnosis
- A single case would be a public health emergency: immediate notification
- PCR in high-containment reference laboratories
Treatment
There have been no natural cases since 1977. Antivirals such as tecovirimat are stockpiled for emergencies, along with supportive care.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Live vaccinia virus vaccine, which protects if given before or soon after exposure
- Airborne and contact precautions until all scabs have fallen off
Vaccine: The vaccinia vaccine (given with a bifurcated needle) made eradication possible; it is no longer given to the general public.
Test yourself
Think of the answer, then tap the question to see it.
In which year was smallpox declared eradicated?
In 1980, by the World Health Assembly; the last natural case was in 1977.
Which virus does the smallpox vaccine contain?
Vaccinia virus, a related orthopoxvirus that does not cause smallpox.
Which isolation precautions would a smallpox case require?
Standard, airborne and contact precautions for the whole illness, until the scabs have fallen off.
Related
← Back to the group: Other DNA viruses
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Clinical Signs and Symptoms of Smallpox (CDC, 2024); About Smallpox (CDC, 2024); Smallpox Vaccine (CDC, 2024); Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions (CDC, 2024).
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Representative model, for educational purposes only.