Smallpox Etiology: Variola Virus, Not Microbes

Smallpox is caused by the variola virus (genus Orthopoxvirus, family Poxviridae), a large, complex, double-stranded DNA virus. It is not caused by bacteria, fungi, or other microbes—a distinction critical for understanding transmission, prevention, and the success of eradication.

Key Virological Features

• Brick-shaped, ~300 × 250 nm; replicates in cytoplasm (unlike most DNA viruses).
• Two clinical forms: Variola major (CFR ~30%) and Variola minor (CFR ~1%).
• Human-only reservoir; no animal vector or environmental persistence.
• Transmission: respiratory droplets, direct contact with lesions/fomites.

Why "Not Microbes" Matters

• Antibiotics are ineffective; antivirals (tecovirimat, brincidofovir) were developed post-eradication.
• Vaccination (live vaccinia virus) conferred cross-protective immunity—possible only because of viral specificity.
• Eradication (certified 1980) was achievable precisely due to human-only host and stable viral genome.

Accurate etiological classification underpins effective public health strategy.