The DNA of Yersinia pestis shows, in evolutionary terms, a highly successful germ to which the population of 14th-century Europe had no immune defences, according to a study published Wednesday in the British journal Nature.
Comment: Even if it's true that these cadavers from a London cemetery tested positive for Yersina pestis, keep in mind that the field of DNA analysis has been plagued by problems of contamination from the DNA that is ever present on human hands, bacteria and other sources. Alan Cooper, head of the Ancient Biomolecules Centre at Oxford University has said that Yersinia DNA found in bodies buried in France have been a case of mistaken identification because of accidental contamination of samples. In addition to that, it is not the first time that bodies buried in "medieval" graves actually belonged to an earlier or later period other than that of the Black Death. In Italy, health authorities in the northern states called outbreaks of bubonic plague "minor pests", to distinguish them from the "major pests", which they took much more seriously.
There is compelling evidence that the Black Death was not an outbreak of bubonic plague, but was in fact caused by a hemorrhagic virus. This case is synthesized in the book Return of the Black Death, in which Susan Scott and Christopher Duncan from Liverpool University carefully put all the available clues together, tracking the plague from its first appearance out of nowhere and chronicling its unprecedented catastrophic effects on European civilization.
Studying the parish records and the historical data registered in English provinces, using information about the critical events in the lives of real people and computer modeling, Duncan and Scott were able to not only surmise the amount of time from the appearance of symptoms to death, but also to establish the following about the pandemic:
"It seems that the plague's latent period was 10-12 days", says Chris Duncan, "while the infectious period prior to the appearance of symptoms lasted 20-22 days, giving a total incubation period of about 32 days. This is exceptionally long and it explains why the plague could jump very long distances even in the days of primitive transport: for three weeks, people didn't realise they had been infected. People generally died five days after the first symptoms appeared, so the average time from infection to death was about 37 days. This is an interesting finding, because European health authorities had quickly determined on 40 days as a safe quarantine period for the plague." [From legend to legacy]
It also lays bare a pathogen that has undergone no major genetic change over six centuries.
© AP Photo/Museum of London ArchaeologyThis undated handout photo provided by Museum of London Archaeology shows skeletons in the East Smithfield Cemetery in London, where Black Death victims were buried in the 13th Century. Scientists used skeletons from this graveyard to decode the genome of the plague.
"Humans were (immunologically) naive and not adapted to this disease," he said in an email exchange.
No bug or virus has wiped out a greater proportion of humankind in a single epidemic than the Black Death.
Brought to Europe from China, it scythed through the continent from 1347 to 1351, killing about 30 million people - about one in three of Europe's and nearly one in 12 of the world's population at the time.
Comment: The reader is encouraged to review this in-depth article which sheds more light on this subject: New Light on the Black Death: The Cosmic Connection by Laura Knight-Jadczyk.