Did Yersinia pestis really cause Black Plague? Part 5: Nail in the coffin

Despite its reputation as a scourge of antiquity, Yersinia pestis–the bacterium that causes bubonic plague–still causes thousands of human illnesses every year. In modern times, most of these occur in Africa, and to a lesser extent in Asia, though we have a handful of cases each year in the U.S as well.

When Y. pestis was first confirmed as the cause of bubonic plague during an 1894 outbreak in Hong Kong, most people assumed that we also now knew the cause of the 14th-century Black Death, and the later plague outbreaks that resurfaced periodically. However, there has been lingering resistance to the idea that Y. pestis actually caused the Black Death. I covered the reasoning behind this resistance in a series of posts back in 2008, so I’ll just give the Cliff notes version here. Basically, many of those advocating “not Y. pestis” pointed to differences in the epidemiology of the Black Death compared to modern outbreaks of Y. pestis. Today, people are much less likely to die of plague; the outbreaks aren’t nearly as big; and the pneumonic form (which infects the lungs and is therefore able to spread directly person-to-person) seems too rare to account for the number of cases that occurred during the Black Death. Also, they argue that transmission across Europe was much too fast, given that rodents (typically rats) are the disease vector. Instead of Yersinia, some authors have suggested that the Black Death was instead caused by a hemorrhagic fever virus, or perhaps by an unknown microbe that went extinct sometime in the last 600 years.

More recently, we’ve been able to test these claims, using paleomicrobiology to look for molecular evidence of Y. pestis in skeletons that presumably died of plague. Many of these come from mass graves that have been dated to the time of the Black Death–some also have parish or other town records to attest to the timing of the grave. In most cases, investigators found Y. pestis DNA. In a few cases, they didn’t, which led to controversy and charges of contamination in the positive samples.

However, the tide has turned. In 2010 and 2011, three papers came out which, um, put the nail in the coffin for the Y. pestis naysayers. At the time, the papers got press not necessarily because of what they explained, but because the ancient Y. pestis strains looked fairly ordinary–there was nothing obvious to suggest why, from the bacterial point of view, the Black Death was so deadly. However, I hadn’t had a chance to read these closely until now, and one of the punches never made it into the mainstream media. From the discussion section of this paper, the authors note:

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 (13). 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.

The reference cited within is this paper, where the authors cast doubt on another group’s finding of Y. pestis DNA in ancient corpses. So it took them 10 years and probably a dozen or more papers, but two “Black Death doubters” have now come around. Score one for the weight of scientific evidence changing minds.

Works cited

Schuenemann VJ, Bos K, DeWitte S, Schmedes S, Jamieson J, Mittnik A, Forrest S, Coombes BK, Wood JW, Earn DJ, White W, Krause J, & Poinar HN (2011). Targeted enrichment of ancient pathogens yielding the pPCP1 plasmid of Yersinia pestis from victims of the Black Death. Proceedings of the National Academy of Sciences of the United States of America, 108 (38) PMID: 21876176

Bos KI et al. A draft genome of Yersinia pestis from victims of the Black Death. Nature, 2011.

Haensch, S et al. Distinct Clones of Yersinia pestis Caused the Black Death. PLoS Pathogens, 2010.

Previous posts in the series

Part 1

Part 2

Part 3

Part 4

Wait, the infamous “Black Death” still plagues the United States?

This is the eighth of 16 student posts, guest-authored by Michelle Formanek. 

For many of us in the scientific world, particularly budding infectious disease epidemiologists like myself, the Plague (or, more dramatically, the “Black Death”) is a prime example of the rapid and devastating spread of an infectious disease. So devastating, in fact, that it wiped out nearly one-third of the population in Europe in the mid-1300’s. That’s roughly equal to 25 million people. It then persisted and has caused various outbreaks throughout history, most notably the Great Plague of London in which 1 in 5 residents died.

So why should be care about the Plague today? Isn’t that old news?

While I will go into more detail about the history of the plague a little later, I first want to mention what prompted me to write about what many people consider to be a no-longer-relevant disease. In order to gauge modern perceptions of the plague, I took a very unofficial survey of friends and family from various backgrounds about what they knew about the Plague. While the knowledge base ranged quite a bit, most were very surprised to hear that we still have cases of the Plague here in the United States.

Yes, you heard me right. The Plague still exists in the United States.

Of course, due to increased knowledge and antibiotic therapy, we no longer see the sweeping epidemic that caused so much turmoil throughout history. Nevertheless, an Oregon man is currently suffering from a rare case of the “Black Death.”

According to reports, a stray cat bit the unidentified man while he was trying to pull a mouse away from the cat. (I won’t even begin to speculate as to why this man was attempting to steal a mouse away from what was likely a very hungry stray cat, but that’s another story.) Several days later the man began to feel ill and presented to the hospital with symptoms typical of the Plague. These included fever, swollen lymph nodes and stomach pain. It has since progressed to bleeding mouth, nose and anus, and dying tissue.  Although the CDC has yet to confirm the diagnosis, all signs point to the Plague.

Only 10-15 people report becoming ill with the disease each year in the United States; this man is the fifth person in Oregon since 1995.

The Plague is caused by the bacterium Yersinia pestis., a rod-shaped bacillus that can live in various species of animals including rats, mice, squirrels, cats, prairie dogs, camels, and rabbits, among others. Yersinia pestis can then be transferred to humans through direct contact with infected animals, bites from fleas that have previously fed on infected animals (this is most common), or human-to-human through the air. Historically, the high population of small rodents and their flea friends in urban areas were attributed to the rapid spread of the disease.

While the Bubonic plague may be the most well known form of the disease, there are actually three different types of the Plague.  The Bubonic plague is the most common form and is characterized by buboes – painful, swollen lymph nodes – in the groin, armpit or neck. Septicemic plague occurs when the bacteria begins to spread in the bloodstream. Lastly, the most infectious form of the disease is Pneumonic plague. This advanced stage strikes when the bacteria can be passed from person to person through airborne droplets coughed up from the lungs. Bubonic plague is fatal roughly half the time, while Septicemic and Pneumonic are almost uniformly fatal without antibiotic treatment.

The man in Oregon was first believed to be suffering from Bubonic plague, but is now beginning to show signs of Septicemic plague, meaning it has entered his bloodstream and is able to reach all different parts of the body.  Luckily, antibiotics are effective in the treatment of the Plague if given early enough. Without antibiotics, 1 in 7 people infected end up dying.

So you may be asking yourself, as I did, where a deadly disease like this came from in the first place. The puzzling start of the epidemic went something like this:

“The Black Death arrived in Europe by sea in October 1347 when 12 Genoese trading ships docked at the Sicilian port of Messina after a long journey through the Black Sea. The people who gathered on the docks to greet the ships were met with a horrifying surprise: Most of the sailors aboard the ships were dead, and those who were still alive were gravely ill. They were overcome with fever, unable to keep food down and delirious from pain. Strangest of all, they were covered in mysterious black boils that oozed blood and pus and gave their illness its name: the “Black Death.” The Sicilian authorities hastily ordered the fleet of “death ships” out of the harbor, but it was too late: Over the next five years, the mysterious Black Death would kill more than 25 million people in Europe–almost one-third of the continent’s population.”

Unfortunately, the cause of the disease was not discovered until 1894, long after it swept through Europe with alarmingly high death rates. People had their ideas about what was causing the Black Death, but no one could actually figure it out. Some believed it was the spirit escaping the eyes of a sick man and infecting the nearest healthy person, others believed it was God’s way of punishing those who had sinned.  Citizens were so panicked that they went to extreme lengths to avoid contracting the disease, even so far as to completely abandon loved ones who got sick. More details here.

As mentioned before, antibiotics can be extremely effective in fighting this bacteria. As of right now, the Oregon man is still fighting for this life, but thanks to modern medicine, his chances of living are fairly high. The man likely contracted the disease from the cat; however, the cat died shortly after and its remains have since been sent to the CDC for testing.  Who knew that a stray cat in the Northwest U.S. could have possibly been harboring bacteria that once had the potential to wipe out entire cities. Fortunately, modern medicine is on our side.

So is the re-emergence of the Plague something that we should really be concerned about? Probably not. But it never hurts to be informed.

References:

http://www.cdc.gov/ncidod/dvbid/plague/index.htm

http://ocp.hul.harvard.edu/contagion/plague.html

http://science.nationalgeographic.com/science/health-and-human-body/human-diseases/plague-article/

http://www.cbsnews.com/8301-504763_162-57452519-10391704/oregon-man-diagnosed-with-black-death-plague/

http://www.mayoclinic.com/health/plague/ds00493/dsection=symptoms

http://www.cdc.gov/ncidod/dvbid/plague/bacterium.htm

http://www.cdc.gov/ncidod/dvbid/plague/qa.htm

http://www.who.int/mediacentre/factsheets/fs267/en/

http://www.history.com/topics/black-death