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Smallpox was declared eradicated by the World Health Organisation in 1980. It was a hugely devastating disease that claimed hundreds of millions of people's lives in the 20th century alone, and was caused by the variola virus, a type of orthopoxvirus.

It's thought that the virus reached humans tens of thousands of years ago, through an African rodent. Its mode of transmission is mainly airborne via infected patient droplets, and potentially via other intimate contact items such as bedding. The virus spreads through the respiratory system as it incubates, at which point it travels from cell to cell, relatively slowly. Initial symptoms include fever, fatigue, nausea, and other general flu-like symptoms.

When the virus has replicated and erupted from cells into the bloodstream, it is able to spread and replicate in lymph nodes and cause systemic disease. This is when the characteristic skin pustules develop over a few weeks, following similar ones on the mucosa first e.g. in the mouth. These release many more viruses in the body and can potentially infect a bystander.

They are fluid-filled pustules that erupt on the face and spread elsewhere on skin. The fluid becomes opaque and it contains tissue debris, not pus. Over time, scabs form and leave behind depigmented skin. There are multiple forms of the disease in terms of progression. The malignant and haemorrhagic types are more fatal. In the haemorrhagic type, no blisters form on the skin, as it remains flat, but vessels burst underneath and lead to a dark appearance of the skin. Overall across all types, smallpox accrued a mortality rate of 30%.

Quarantine of infected individuals could help limit the spread if this contagious disease. Treatment consists of managing the symptoms e.g. hydration, taking care of the blisters, assistance with breathing.

A worldwide vaccination effort led to its eradication. Early forms of vaccination were carried out in ancient times in China, India and elsewhere, by exposing children to infected tissue such as a pustule from a child who'd contracted the disease. The concept of building immunity following exposure had been known in various forms for a long time.

The fancy forms of vaccination developed and deployed to tackle the disease throughout the 19th and 20th centuries involved a solution containing the active virus and a bifurcated needle. Once dipped in the solution, the needle was used to pierce the skin multiple times in quick succession. The area would become red and itchy and eventually leave a scar. Vaccination is most protective closer to the time of administration, with the effect decreasing over time.

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