Last night I watched a documentary on the Plague years of 1347-1351, the infamous Black Death that consumed Europe and the Mediterranean region back then. Now that I'm a budding genealogist, the program got me to thinking just how lucky we descendents of the survivors are to be here. After all, whatever individual ancestors were present in the mid fourteenth century, by the time the effects of the Black Death had waned, anywhere from a third to a half of everyone was dead. In some cities the death toll was even higher. Venice, Italy suffered a 60% death rate, while in the Italian city of Florence as many as 75% of the population died.
So how come we're here? What stroke of incredible luck decreed that our ancestors from 650 some odd years ago survived while so many did not? Naturally I turned to the internet to answer the question. I found the following possible explanation which was taken from a 2008 International Tribune article by Nicholas Bakalar:
"Many historians have assumed that Europe's deadliest plague, the Black Death of 1347to 1351, killed indiscriminately, young and old, hardy and frail, healthy and sick alike. But two anthropologists were not so sure. They decided to take a closer look at the skeletons of people buried more than 650 years ago. Their findings, published on Monday in The Proceedings of the National Academy of Sciences, suggest that the plague selectively took the already ill, while many of the otherwise healthy survived the infection. Although it may not be surprising that healthy people would be more likely to survive an illness, it is not always the case. The Spanish flu of 1918 killed thousands of healthy people in their prime while sparing many children and the elderly, whose weaker immune systems did not overreact to the infection. Sexually transmitted infections like HIV disproportionately affect the strongest and healthiest, for the obvious reason that they are the most sexually active.Plague is caused by a bacterium called Yersinia pestis, and it is usually transmitted to humans by fleas; flea-infested rats caused the 14th-century epidemic. The bacteria invade the bloodstream, causing internal bleeding that leads to shock and death. In the new study, the researchers examined 490 skeletons exhumed from the East Smithfield cemetery in London. The site, like many other cemeteries, was set up to bury victims of the Black Death and was almost certainly used for no other purpose. The scientists determined the victims' state of health when they died by counting bone lesions, defects that suggest previous infections and other existing health problems. The researchers also estimated age at death by noting dental development and using other established methods. As a comparison, they analyzed the bones of 291 genetically and culturally similar people buried in a Danish cemetery shortly before the plague began.
The aim was to find out whether the Londoners, who all died of the plague, were frail when the epidemic struck. In the nonplague Danish cemeteries, bone lesions were strongly associated with earlier death. If the Black Death killed without discrimination, such skeletal defects would not be associated with an increased risk of death in East Smithfield. Many of the victims would have had healthy-looking bones when the plague killed them. But this was not the case. Among the East Smithfield plague victims, bone lesions were also associated with excess mortality. In other words, many of those people were already in poor health when the Black Death struck. Most of the bone defects that the researchers found can be caused by malnutrition, and the scientists suggest that the findings may show effects of starvation on immune function. It is known from contemporary chronicles that many survived the plague, and they, the authors write, were probably well fed and healthy enough to mount an effective immune response.
'Even something as clearly deadly as the Black Death is still selective,' said Sharon DeWitte, a co-author of the study and an assistant professor of anthropology at the State University at Albany. The Black Death, she continued, is comparable in some ways to various emerging diseases of today like Ebola or SARS, and studying it "gives us some insight into who might be at highest risk for these new diseases."
The authors acknowledge that their findings are not conclusive. The samples used were from two geographic areas, and similar lesions could have been caused by diseases of varying severity in the two areas. Still, the authors write, the fact that a pattern of excess mortality was associated with different kinds of lesions suggests that the plague more often killed the weak than the strong."
The above piece was very interesting. But since I suspected that there must be other reasons, I kept looking. Here's another piece I gleaned from the internet which is equally intriguing in its implications:
"While we commonly think of the rat acting as a host for fleas and the plague bacillus, it was certainly not the only animal that carried the disease. Besides humans and rats, most animals were susceptible to the bacillus and were infested with fleas. There was, however, one exception -- the horse. According to Robert S. Gottfried in his book, 'The Black Death: Natural and Human Disaster in Medieval Europe,' however important black rats were in the dissemination of plague, it is essential to emphasize that they were not the only secondary carriers. Along with the rodents already mentioned, additional secondary vector hosts included virtually all household and barnyard animals save the horse, whose odor apparently repels even starving blocked fleas."
Wow! So now it seems our surviving ancestors may have been healthy horse owners. Seriously though, I suspect, as you probably do, there's a lot more to it than that. For instance, might there be a genetic reason? Following that tack, I found a piece by Dr. Barry Starr of Standford University in California, USA, who wrote:
"There may be. There are many stories where someone who was in constant contact with plague victims didn’t die. Maybe genetics is the explanation. For example, in 1665, the plague hit a small village in England called Eyam. The town quarantined itself to keep the Black Death from spreading into the rest of the country. A year later, the plague had burnt itself out but half of the townspeople were dead. Was there something special about the half that lived?
In 1996, researchers tracked down descendants of the people of Eyam and looked for any mutations they might have in common to explain this high survival rate. What they found was a mutation called CCR5-delta 32. The CCR5-delta 32 mutation was already known for a different reason—people with one copy of the CCR5-delta 32 mutation are resistant to HIV, the virus that causes AIDS. People with 2 copies are virtually immune to HIV.
The CCR5-delta 32 mutation probably arose a few thousand years ago in Northeastern Europe. It stayed rare until around 700 years ago when it suddenly became more common. The plague started in Europe around 700 years ago.
So, does CCR5-delta 32 protect people from the plague bacteria? Probably not. Mice infected with the plague bacteria died at around the same rates whether or not they had the CCR5-delta 32 mutation.
Why then is this mutation so common in Europeans and even more common in people whose ancestors came from Eyam? Maybe smallpox is the reason. Smallpox killed 3 in 10infected people for thousands of years in Europe. Recent studies suggest that smallpox, like HIV, can’t infect someone with the CCR5-delta 32 mutation.
Of course this doesn’t explain Eyam (unless there was a lot of smallpox in the area). A more controversial theory is that an unknown virus, not the plague bacteria, caused the Black Death. Besides the evidence of the CCR5-delta 32 mutation itself, some people contend that the disease shouldn’t have been stopped by quarantine and that it spread too quickly for a flea borne illness.
Anyway, as you can see, while genetics were probably involved, there isn’t yet a solid answer as to what genes were involved."
Now, that makes sense. We all know how immunity works. As kids, we get shots all the time to build up our immunity to nasty diseases. If our ancient ancestors, those that came before the plague survivors, had contracted some disease that provided them some protection against the Black Death, it would make sense that they might survive, especially if their non-surviving neighbors did not possess that genetic protection.
Of course, there's no way to know at present. But with the speed at which scientific advances are being made in genetics, I'm sure we're going to know more on this subject in the very near future. Until then, click here to see more information on the study being done on CCR5 delta-32.
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