Epilogue• 287ent DNA found on ribosomes within the cells of all organisms. From seventy
specimens of plague in sixteen different places in the world, they distin-
guished three plague types, or biovars, whose territorial coverage appears to fit
the spread of plague in its three historical pandemics. These types have been
appropriately named Antiqua, Medievalis,andOrientalis(see appendix D).^49
TheAntiquaribotype, O, is believed to have moved from an ancestral
home in central Asia into the heart of Africa, then up to lower Egypt, and to
Alexandria. From there it spread by ship to Emperor Justinian’s capital at
Constantinople and throughout the Late Roman imperial lands, where only
O types are found today. The Medievalisgroup also has type O but is distin-
guished from Antiquaby its inability to reduce nitrates as part of its metab-
olism. Its geographic locations today fit the historical path of the second
pandemic, originating in central Asia as well. It traveled along the silk route
to the Crimea, migrated into the Mediterranean, and spread throughout Eu-
rope. The widespread locations of Orientalis,with its distinctive type B, span
four continents plus the Pacific islands, mirroring the known travels of the
third pandemic from its origins in China’s Yunnan province to Hong Kong
in 1894 and then by steamships, with infected rats and their fleas, around the
globe.
A fundamental link in the evolution of Yersinia pestisis suggested by mi-
crobiological understanding of both B and O types.Orientalistype B lost its
ability to ferment glycerol as part of its metabolism (both O types can) but is
believed to have evolved from the first Antiquastrain, since they share the
ability to reduce nitrates.
Definitive proof that Yersinia pestiscaused the first two pandemics awaits
evidence from the testing of dental pulp DNA in skeletal remains from the
first and second pandemics. Samples of dental pulp from cadavers of the
fourteenth, sixteenth, and eighteenth centuries, discovered in mass burial
sites and charnel houses in southern France, have been analyzed. These sam-
ples tested positive for Yersinia pestis,on the basis of DNA testing. Some
specialists conclude from this evidence that the Black Death and later visit-
ations during the second pandemic were definitively bubonic plague similar
to what we have today. Another group questioned the findings, suggesting
the possibility of contamination; testing of large numbers of cadavers is
needed for convincing proof.^50 Papers on this research were discussed at a
world conference on plague in Marseilles in July 2001.^51