Smallpox is older than thought, according to results of a new technique reported in the Sept. 24 issue of the Proceedings of the National Academy of Sciences by researchers from Lawrence Livermore National Laboratory and the Centers for Disease Control (CDC).
The researchers created a molecular clock by looking at the rate of random mutations in the smallpox-causing virus collected in 47 locations around the world, from 1946 1977. The variation between the strains was compared to sequences from the most similar animal poxes.
The results indicated that a mild and more severe strain diverged either 16,000 or 68,000 years before present, depending on whether accounts from East Asia or Africa are used to calibrate the molecular clock. In either case, this divergence stretches further back in time than previously believed.
The authors compare hypotheses about where and when strains of the virus evolved. No one hypotheses is ruled out, but an ancient origin seems most plausible since the slowly evolving virus now exclusively infects humans, implying that any intermediate link to an animal host has long since died out.
Collaboration between LLNLs Pathogen Bioinformatics group and the CDCs Sequencing and Poxvirus groups took place under a Memorandum of Understanding between the Laboratory and the CDC initiated in early 2003.
The initial research focused on determining viral signatures by looking at unique genetic characteristics. The CDC had recently sequenced the genomes of the various smallpox strains, based on the repository it holds for the World Health Organization (the worlds only other declared smallpox storehouse is in Russia).
The disease was considered eradicated in 1980, three years after the last naturally occurring case in 1977. Vaccinations had been stopped in 1972, following an intensive worldwide effort to wipe out the virus. Smallpox, in its most severe form, was deadly in up to 30 percent o
|Contact: Nancy Garcia|
DOE/Lawrence Livermore National Laboratory