Friday, March 5, 2010

Smallpox questions

Parchment signed at Geneva on 9 December 1979, by the members of the Global Commission for Certification of Smallpox Eradication.

A couple of interesting questions during and after class that I had to look up the answers to but thought would be of enough general interest to post here.

1) Where did smallpox come from?

Human disease likely attributable to variola virus (VARV), the etiologic agent of smallpox, has been reported in human populations for >2,000 years. VARV is unique among orthopoxviruses in that it is an exclusively human pathogen....Our results show two primary VARV clades, which likely diverged from an ancestral African rodent-borne variola-like virus either ≈16,000 or ≈68,000 years before present (YBP), depending on which historical records (East Asian or African) are used to calibrate the molecular clock.
From: On the origin of smallpox: Correlating variola phylogenics with historical smallpox records
But see also: How long ago did smallpox virus emerge?

2) When was smallpox officially declared eradicated?

Both the WHO and CDC have information on their respective websites. Here is an account from the CDC website of the final years of the eradication project and the final certification of eradication which occurred two years later.

By the end of 1975, smallpox persisted only in the Horn of Africa.

Conditions were very difficult in Ethiopia and Somalia, where there were few roads. Civil war, famine, and refugees made the task even more difficult. With the interruption of smallpox transmission in Asia, more resources were made available in Africa, including more staff and transport.

An even more intensive surveillance and containment and vaccination program was initiated in the spring and summer of 1977. As a result, the world’s last indigenous patient with smallpox on earth was a hospital cook in Merka, Somalia, on October 26, 1977 with variola minor.

Searches for additional cases continued in Africa for more than 2 years, during which time thousands of rash illnesses were investigated. None proved to be smallpox.

Although 2 cases of smallpox occurred in England in 1978 as a result of a laboratory accident, smallpox was gone as a naturally transmitted disease.

The World Health Organization officially certified that smallpox had been eradicated on December 9, 1979, 2 years after the last case in Somalia. In 1980 the World Health Assembly recommended that all countries cease routine vaccination.

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