The researchers said the correlation of historical record and a molecular clock provides a framework that could be applied to studying the natural history of other diseases. Although no particular hypotheses of its evolution is supported or disproved, said corresponding author Inger Damon, M.D., Ph.D., acting chief of the CDCs Poxvirus and Rabies Branch. It shows the delineation of tantalizing potential connections between different isolates.
Analysis of isolates from geographically dispersed areas indicated that local pools of old, and perhaps ancient, strains existed. The human disease may have originated from a rodent-borne virus in Africa. The evolutionary analysis suggests that smallpox disease slowly spread westward from East Asia, which would agree with the oldest smallpox-like descriptions from ancient China as far back as 1122 BC. It is unclear when it first reached the New World some evidence suggests an ancestral virus arrived with early humans and diversified into a mild version there.
The slow spread out of Asia could explain why smallpox descriptions are missing from ancient Greece or Rome as well as the Old and New Testaments.
The Laboratorys Shea Gardner and CDCs Yu Li devised a way to concentrate point mutations in the viral DNA, single nucleotide polymorphisms, or SNPs. Four nucleotide bases, arranged in varying sequences, spell out the hereditary information encoded in DNA, the genetic material.
As cells multiply and divide, occasional errors creep in to new copies of the genetic instructions. Some errors are more critical than others. The variation allows some individuals among the offspring to be better-adapted to changing conditions, providing an evolutionary advantage that is passed down to their progeny. Over time, some lines flourish and others die out.
For a reliable molecular clock, it would be nice to see the steady rate of mutation in a general sense without a marked e
|Contact: Nancy Garcia|
DOE/Lawrence Livermore National Laboratory