Causes of smallpox

Smallpox was caused by the variola virus, a large DNA virus in the orthopoxvirus family. It infected only humans, which is one reason it could be eradicated. There was no animal reservoir that could keep the virus alive.

How it spread

• Mostly through droplets from the nose and mouth of an infected person, usually after face-to-face contact over a period of time.
• Through contact with the rash, blister fluid and scabs.
• Through contaminated bedding and clothing, which could carry the virus for some time.
• Rarely through the air in enclosed spaces.

A person was contagious from the time the first rash appeared until the last scab fell off, with the highest risk in the first week of the rash.

Who was at risk Anyone who had not been vaccinated or previously infected. Crowded homes, travel, trade routes, wars and poor access to health care helped the virus spread across continents and centuries.

Why it disappeared The virus had no animal host, produced clear and visible illness, and a very effective vaccine existed. This allowed health teams to find cases, vaccinate their contacts (ring vaccination) and stop transmission.

Where the virus exists today Stocks are kept in two authorised high-security laboratories, under international oversight. Smallpox cannot arise again from nature, though related viruses in animals can cause occasional human illness.

Ayurvedic view (interpretive) Texts explain Masurika through imbalance of Pitta and Rakta and through contagion linked to poor conditions. These ideas are historical and are not a substitute for modern virology.

When to seek help A new fever with widespread blisters needs a doctor. Call 112 for severe breathlessness or collapse.

Remember Smallpox was caused by a human-only virus, and vaccination ended it.