What caused The Black Death?
Its not only an interesting question from a paleomicrobiology standpoint, but of practical importance– While we have all kinds of technology here in 2011 that would have, no doubt, increased the survival rates of Plague victims in the 1400s, it would be more comforting to know exactly what caused that epidemic and why so we can be 100% prepared for it (or something similar to it) in the future.
One theory is that the Black Death was caused by a bacteria, Yersinia pestis. Weve got Yersinia pestis around today, but what made the Black Death Yersinia pestis really bad was that those bacteria picked up a particularly pathogenic plasmid.
Plasmids are circular bits of DNA that bacteria treat like Pokemon– trading with their friends collecting all the cool ones, etc. Thats one of the ways we get antibiotic resistant bacteria. The resistance genes arent part of the actual bacterial genome, its on an extra bit of DNA that bacteria trade with one another, which is a much faster way of spreading the ‘good’ gene than simple replication, selection, replication, selection.
Yeah… apparently that is *not* why the Black Death Yersinia pestis could have been worse:
Targeted enrichment of ancient pathogens yielding the pPCP1 plasmid of Yersinia pestis from victims of the Black Death
Our data reveal that the Black Death in medieval Europe was caused by a variant of Y. pestis that may no longer exist, and genetic data carried on its pPCP1 plasmid were not responsible for the purported epidemiological differences between ancient and modern forms of Y. pestis infections.
Not a plasmid. So what the heck was it??
For the most part, the sequence is similar to that found in modern strains of the bacteria. In contrast, some of the DNA they obtained from the bacteria’s chromosome showed some distinct differences, none of which are present in modern strains. Nevertheless, the sequence was clearly still from Y. pestis.
The authors conclude that this provides a clear indication that a single type of bacteria has been responsible for the Black Death and several other plague outbreaks, and is still causing modern diseases. For some of the parties involved, this is a bit of an about-face, one that was handled with a degree of candor that’s rare in scientific publications.
“Two of the authors (SW and JM) have previously argued that the epidemiology, virulence, and population dynamics of the Black Death were too different from those factors of modern yersinial plague to have been caused by Y. pestis,” said the paper. “Given the growing body of evidence implicating this bacterium as responsible for the pandemic, we believe scientific debates should now shift to addressing the genetic basis of the epidemic’s unique characteristics.”
My money is on phages, and specifically, those phages morons. Phages are kinda like bacterial ERVs– They are DNA viruses that insert themselves into the bacterial genome, and hijack that bacteria to generate more babby viruses. But phages dont always immediately start making babbies– sometimes they go latent. Its a dog-eat-dog world out there, and sometimes its safer to hide in a warm snuggly bacteria than to be out fending for yourself. But the bacteria have no interest in having this parasitic DNA contaminating their Specially Created genome. So phages bribe them.
Phages can encode for gene groups called morons.
These are viral genes that dont code for anything the virus wants, like structural proteins, or enzymes the virus needs– They are genes that make having the virus around attractive to the bacteria. And few things are more attractive to a pathogen than making you sick, thus spread the bacteria faster than if you werent pooping/oozing/puking/etc.
I bet its a moron.