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.

I am not joking.

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.

Comments

  1. #1 Selket
    September 1, 2011

    Yep Seems so. I just started to study Phages but i found they are quite remarkable “Lifeforms”. The phage 933 codes for the shiga toxin gene in ecoli 0157:h7 which effects (of the toxin) could be seen in this years EHEC epidemic.

    Its interisting that phages can have such a instinctive farsight. But well i guess thats how temperate phages work. They are lazy buggers. Sit all day in the host let the host replicate (to create new copies of phage along the way) and to ensure that this bacteria has no probs with that its giving the host some great advantage over others. Until the cell get a SOS respond and the phages flee the sinking ship.

    Wonder if there are some viruses for humans out there that could give us some advantage towards the uninfected. Would be sweet. But from my limited understanding this idea that some moron caused the Pest could be totally right.

    Bear in mind that i just(1 month) started to get interested in Biology in general (my Highschool didnt took biology serious so i had to start from scratch :( ) so if my answer made no sense feel free to have a nice laugh^^

  2. #2 Prometheus
    September 1, 2011

    The presence of morons tends to explain most problems.

    Does your moron proposal gibe with the 15th century descriptions?

    One of the hitches with modern Y pestis outbreaks is that necrosis in the three infection types doesn’t manifest with the drama and speed of the medieval plague.

  3. #3 Mox
    September 1, 2011

    We know that having a lysogenic phage in some bacteria can actually contribute to pathogenesis – this has been shown in some strains of E.coli in which induction of the phage leads to production of the Shiga toxin, as a previous commenter already noted!

    Your hypothesis about a phage in Y.pestis is neat – I’d like to see some bioinformatics people work on this if they have the sequence now for this “Black Death” strain, and see if they can find any phage associated genes that the other strains dont have.

  4. #4 CG
    September 1, 2011

    As a minor correction, the phage encoding shiga toxin 2 in E. coli O157:H7 is actually named BP-933W, which means bacteriophage W in strain EDL933, the first sequenced strain of this serotype.

    A lot of virulence genes are in phages. A lot of those phages end up cryptic though, they “die” and can no longer enter the lytic cycle. The phage genes themselves degrade over time. The moron genes on the other hand are often preserved since there is selection for keeping them. So from a gene’s perspective, being a moron can be a very good thing.

  5. #5 Poodle Stomper
    September 1, 2011

    “Wonder if there are some viruses for humans out there that could give us some advantage towards the uninfected.”

    Isn’t that the premise of most zombie movies? =P

    It sounds very plausible, that a phage could have made Y. pestis more dangerous. Even from a non-viral point of view. I mean, we have a ton of different morons in congress and the senate and those have been more dangerous lately than ever!

  6. #6 Birger Johansson
    September 1, 2011

    I wonder if the team of Svante Pääbo at Max Planck Institute could tease out even more genetic information. After all, 700 years is a lot less than 70 000 years, so degradation would be far less advanced.

  7. #7 pornalysis
    September 1, 2011

    “They are genes that make having the virus around attractive to the bacteria.”
    Now I know what morons are–and it’s time to kick them off my couch! They never buy beer ;-\

  8. #8 starskeptic
    September 2, 2011

    …I went through my moron phage in high school…

  9. #9 Steve West
    September 2, 2011

    This was a great post for a layperson. Nicely written and great explanation. I’d never heard of phages. Fascinating information.

  10. #10 Gurdur
    September 2, 2011

    Great post, and very interesting, will cite it in my blogs round-up very soon.

  11. #11 pornalysis
    September 2, 2011

    @9 I second that motion–all of the gobbeldy, and the goook, without the word-mess–and we all can relate to morons;-)

  12. #12 Bob Steele
    September 4, 2011

    As I use the moniker bobthemoron, I find it very insulting that any of this plague stuff is blamed on us morons. It’s the idiots that are the real problem. The majority of them are in the federal government.

  13. #13 Skepgineer
    September 6, 2011

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