Rats 'not main cause of Black Death'

http://www.bbc.com/news/science-environment-31588671

Black rats may not have been to blame for numerous outbreaks of the bubonic plague across Europe, a study suggests.

Scientists believe repeat epidemics of the Black Death, which arrived in Europe in the mid-14th Century, instead trace back to gerbils from Asia.

Prof Nils Christian Stenseth, from the University of Oslo, said: "If we're right, we'll have to rewrite that part of history."

The study is in the Proceedings of the National Academy of Sciences.

The Black Death, which originated in Asia, arrived in Europe in 1347 and caused one of the deadliest outbreaks in human history.

Over the next 400 years, epidemics broke out again and again, killing millions of people.

It had been thought that black rats were responsible for allowing the plague to establish in Europe, with new outbreaks occurring when fleas jumped from infected rodents to humans.
Rat reservoir

However, Prof Stenseth and his colleagues do not think a rat reservoir was to blame.

They compared tree-ring records from Europe with 7,711 historical plague outbreaks to see if the weather conditions would have been optimum for a rat-driven outbreak.

He said: "For this, you would need warm summers, with not too much precipitation. Dry but not too dry.

"And we have looked at the broad spectrum of climatic indices, and there is no relationship between the appearance of plague and the weather."

Instead, the team believes that specific weather conditions in Asia may have caused another plague-carrying rodent - the giant gerbil - to thrive.

And this then later led to epidemics in Europe.

"We show that wherever there were good conditions for gerbils and fleas in central Asia, some years later the bacteria shows up in harbour cities in Europe and then spreads across the continent," Prof Stenseth said.

He said that a wet spring followed by a warm summer would cause gerbil numbers to boom.

"Such conditions are good for gerbils. It means a high gerbil population across huge areas and that is good for the plague," he added.

The fleas, which also do well in these conditions, would then jump to domestic animals or to humans.

And because this was a period when trade between the East and West was at a peak, the plague was most likely brought to Europe along the silk road, Prof Stenseth explained.

'Perfect storm'

"To me this was rather surprising," he said.

"Suddenly we could sort out a problem. Why did we have these waves of plagues in Europe?

"We originally thought it was due to rats and climatic changes in Europe, but now we know it goes back to Central Asia."

The team now plans to analyse plague bacteria DNA taken from ancient skeletons across Europe.

If the genetic material shows a large amount of variation, it would suggest the team's theory is correct.

Different waves of the plague coming from Asia would show more differences than a strain that emerged from a rat reservoir.

The plague died out in Europe after the 19th Century, however outbreaks continue to this day in other parts of the world.

The World Health Organization said there were nearly 800 cases reported worldwide in 2013, including 126 deaths.

In another paper, published in the American Journal of Tropical Medicine and Hygiene, researchers in the US said that the expansion of agriculture was placing East Africa at an increased risk of the plague.

As cropland increased, rodent populations were also rising, creating "the perfect storm for plague transmission", the researchers said.

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A bit of old news, I'm afraid. (Well, at least to those familiar with the plague.) But nice to see the BBC has gotten hold of it.

Some newspapers repeat the same news sometimes.

I've never heard of gerbils rampaging across Europe.

That makes two of us then.

As I understand it, the original outbreak was caused by gerbils, but in Europe, infected fleas would still be carried by rats...

Keep in mind the consensus is the disease was airborn by the time it spread through Europe (it had changed from Bubonic Plague to Pneumonic Plague). I think that's part of the article's premise. Gerbils in Asia led the plague to foster and then, when it Europe, people were sufficient to carry the plague.

I suspect rats were a factor in the plague's staying power. The plague came in cycles so it would have to stay somewhere when it wasn't infecting people (and the mortality rate was so high that people would die off before it could be transmitted). But it wasn't just flea bites that did in the people of Europe.

Keep in mind the consensus is the disease was airborn

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Not really. Viruses and bacillae only become airborne in special circumstances. They don't fly, you know.

Yeekim said:

As I understand it, the original outbreak was caused by gerbils, but in Europe, infected fleas would still be carried by rats...

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Fleas is correct, but again they were only carriers.

In this case, they had entered the lungs and had become contagious at short distances through coughing or sneezing. They don't need to fly, but people were the carriers. Certainly, it wasn't Asian Gerbils when we're talking about Europe. I guess consensus is too strong a word, but I thought it was the majority thought now.

Gerbils (great gerbils or giant gerbils) and marmots make a good natural reservoir. When the gerbil population gets large, they get more in contact with rats and humans and a wave of plague goes across Europe. It probably is a factor, as would be population cycles of other wild rodents.

There was an earlier series of bubonic plagues starting in the reign of Justinian. The odd thing is that they died out before the fourteenth century.

In America we have a nice plague reservoir among prairie dogs, and every now and then someone comes down with plague. It's not common because people don't come in contact with prairie dogs that often.

Do we know Justinian's Plague was Yersinia pestis?

It's really a moot point. The vector was fleas regardless of the species that carried them. As fleas are powerful jumpers (watch a video sometime...it's remarkable), then any number of species could have carried them, and probably did so, and that includes humans given sanitation at the time plus poverty.

Under collapse conditions, closed contaminated spaces would result in major cycles of flea infestation (talk to cat/dog owner who's had this happen in three cycles), and you have a persistent situation. Any movement to resupply or gain water, which meant transferral to gathering places like wells or markets meant further transmission.

Other diseases have far more complex vectors with various lifeforms carrying pathogens and then you have water and air bourne considerations as well. It's one of the more fascinating aspects of contagion and the extreme difficulty of controlling its spread due to the various species within a niche and modern transportation dependencies of civilizations.

If you want to see something freaky, research Toxoplasma gondii in common housecats to see a remarkable infection in lots of nations as a silent pandemic.

Louis XXIV said:

Keep in mind the consensus is the disease was airborn by the time it spread through Europe (it had changed from Bubonic Plague to Pneumonic Plague). I think that's part of the article's premise. Gerbils in Asia led the plague to foster and then, when it Europe, people were sufficient to carry the plague.

I suspect rats were a factor in the plague's staying power. The plague came in cycles so it would have to stay somewhere when it wasn't infecting people (and the mortality rate was so high that people would die off before it could be transmitted). But it wasn't just flea bites that did in the people of Europe.

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I thought pneumonic and bubonic plagues were two different things that existed at the same time - certainly, the Black Death in Europe involved patients with buboes that were often lanced with hot irons.

It's quite complex when contagion truly strikes and overwhelms medical systems regardless of the time period in history.

Medical workers are of varying degrees of competency plus the primary care givers are following what instructions they received and trying their own cures.

The contagion can be easily transmissible but to varying degrees of lethality. Regardless the contagion can adapt in its attributes and the means of spreading it.

Say the disease is easily transmissble, and the health care professionals get the disease. Depending upon the time period and the levels of sanitation and protocols, then one of them can transmit the pathogen to another patient. In the case of insect vectors and poor sanitation and poverty, then fleas could have jumped onto physicians and then they themselves transmitted those vermin.

Since fire was a primary means of preventing the spread of contagion, and fear could cause rioting, then the authorities and locals could bar the door and fire the home with the patient and family within. This could vasty increase mortality statistics, right? Fires can spread easily in those days of a lack of fire control.

If physicians (such as they were back then) acquired the disease themselves, all manner of spread could occur in any number of diseases. This happened recently with Ebola. Patients wouldn't conclusively have the disease. Protocols were not in place, and even if they were, then due to graft, money that had been allocated to pay the salaries of medical staff and for equipment went into the pockets of politicians. Ill patients who could just as easily have malaria as Ebola due to how it presented, transmitted the illness to medical staff, who in turn spread to patients with other ailments.

In a strong contagion, the other patients are not being treated due to prioritization, and so they could die of curable things. Later as hording and sheltering-in-place occurs, then supplies are limited and while this can slow the spread of disease, people can die from inadequate water or food.

Things can happen when in survival mode, the immune systems of survivors becomes compromised by poor sanitation due to an overwhelming number of the dead, and the human body is loaded with many kinds of pathogens all the time. Your skin is a protective barrier, but when compromised by pustules and buboes, then other bacteria (like Staph and Strep) can also attack. Poor sanitation can result in the ingestion of these as well to cause gastrointestinal symptoms. Since the body's wastes are full of things like E coli, you can rapidly have an extremely complex number of pathogens affecting the family and patient.Patients die not only of the plagues, but they die of a host of pathogens that attack the body. It's multifactorial in these attacks.

Both the burial of the dead, the lack of burial leading to run off by rainwater into local water sources, the depressed immune systems due to inadequate sleep/food/clean water all combine to ravage the survivors.

Some physicians reported both skin lesions as well as respiratory issues. Without evidence we don't know the cause as other pathogens could have caused mucus to build up in the bronchial tubes, causing coughing and airbourne transmission of those illness simultaneously while the Yersina was being transmitted.

Survivors die of just as complex issues as well as the mayhem of lack of government control. In history the leaders would flee and that could spread illness since they had servants who they themselves might have the illness. It also means no rule of law, at a time of a severely stressed desperate citizenry.

With some pathogens, they can target younger people, who ordinarily have stronger immune systems, but if something like a cytokine storm is involved (where the immune response is out of proportion to the disease), then the response is what greatly contributes to mortality.

Even should patients survive, without supplies/clean water/sanitation, plus caregivers since they're in a weakened state, then they still can die while in recovery. Because of fear, their families might abandon them. That last part happened with Ebola in some villages where patients where left in the street to fend for themselves.

Without a ton of archaeology and unless we find extremely good written records, we may never know the causes of the Black Death. A lot of our ideas may just be suppositions with scant evidence.