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The Plague: It's Still Kicking and Still Killing

Aug 05, 2014 10:59 PM EDT

Just last month the Chinese government sealed off a city of more than 100,000 people, fearing the spread of a plague outbreak. More than 151 people exposed to the deadly disease were quarantined in that time, and one middle-aged man died from the infamous bacterial infection that is commonly called the Black Death.

A nine day quarantine was placed upon the city of Yumen in the northwest Gansu Province after a 38-year-old man died from what was later identified as an infection of the Yersinia pestis bacterium, according to state news agency Xinhua.

The "pestilence" of old, Y. pestis was carried by rodents and fleas throughout Europe and Central Asia, peaking in the years 1346 to 1353, and killing an estimated 75 to 200 million people in a global tragedy later referred to as the "Black Death." The plague was around long before that time, but it is speculated to have reached devastating pandemic levels after global trade - and thus the spread of invasive rodents - was expanded by the Silk Roads.

Interestingly, despite being well past its hay-day of the Middle Ages, the plaque is far from finished.

Black Death was officially tied to Y. pestis  in 1967, 70 years after revered bacteriologist Alexander Yersin happened to discover the plague-causing bug in the first place. Since then, the World Health Organization (WHO) has identified 10 major Y. pestis plague outbreaks, starting in 2001 in Zambia.

Thankfully, this latest Chinese incident won't make that list. By July 24, Chinese authorities were able to lift the Yumen quarantine after it was determined that all potentially exposed residents of the city were not infected.

Plague is Still Very Much Around

What's surprising is that, according to the WHO, plague is pretty common. It's even likely that there are a good number of people who deserve a "plague survivor" T-shirt and don't even know it.

The plague variant that caused the Black Death more than 600 years ago, bubonic plague, is considered the most harmless form now, easily being treated with modern intervention and antibiotics. Health organizations even suspect that minor cases of plague often go unreported in developed countries, and are treated as a potential bacterial infection without ever being fully identified.

Bubonic plague is spread by flea bites, infecting the lymph system and swelling nodes - which is usually more than enough of a cue for doctors to administer strong antibiotics, even if they don't know which bacteria they are dealing with.

However, even before antibiotics were wide-spread, the plague was always contained and kept underreported for fear that the world "plague" would cause panic in the streets.

According to the Centers of Disease Control and Prevention (CDC), a flea-associated plague actually broke out in Los Angeles in 1924-1925, and has been circulating among urban rodent populations ever since. Even squirrels and prairies dogs have been identified as carriers of Y. pestis, and isolated incidents of plague pop up in the United States from time-to-time.

It is assumed that this is how the Black Death has survived, even after the first powerful antibiotics were put into use in the mid 1900s.

So Why is it Still Killing People?

Unfortunately, not everyone has access to antibiotics. Plague is still a nuisance that is being kept under control in a number of developing countries, and efforts by the WHO have been taken in the past to ensure that residents of plague affected areas understand that proper hygiene (to avoid fleas) can almost entirely prevent the spread of the disease.

Bubonic plague is also not the only form of Y. pestis infection. When the bacteria enters directly into the blood stream, often through a rodent bite, it is called septicemic plague. While also not fatal if promptly treated, the infection can force doctors to make amputations.

Back in 2012, a US man lost some fingers and toes after doctors identified a Y. pestis infection in the Oregon native's blood stream.

"We all thought it was crazy," Andrea Gibb, the victim's niece, told World News. "Even the doctors thought, 'No way, it can't be.' They did not think at all. It was like turning a page in a book."

For the extremely unfortunate, there is also pneumonic plague. An infection of the lungs, this illness makes victims weak and light headed; they find it increasingly hard to draw air, further weakening their bodies and immune system in the process.

This is not only the most deadly - killing victims within a matter of days at most - but also the most easily spread. While other forms of infection must spread through blood or bite, pneumonic plague can be spread by a carrier through saliva alone, becoming airborne in cough droplets.

According to the CDC, this kind of plague transmission has not been documented in the United States since the arrival of antibiotics, but has been seen in some developing countries and China. It has also been identified in cat populations, who are especially susceptible to becoming infected after making contact with rodent prey.

This, unfortunately, was the kind of plague that infected this year's 38-year-old victim, and was certainly why the Chinese government felt it prudent to quarantine a city of 100,000 people until experts gave the "all-clear."

The Black Death Again?!

Disturbingly, researchers have recently speculated that the Black Death could happen again given the right circumstances.

According to research first conducted in 2008, the lethality of the plague strain we see today was the result of really bad luck. Robert Brubaker of the University of Chicago reportedly analyzed modern strains of Y. pestis, mapping out its probable evolutionary history.

"Y. pestis evolved from its ancestor Y. pseudotuberculosis within the last 20,000 years, suggesting its high lethality reflects only a few genetic changes," he explained in a release. "We discovered that a single mutation in the genome of Y. pestis means the enzyme aspartase is not produced."

And without this enzyme, the bacteria loses it, releasing lethal levels of aspartic acid into the cells of the host.

Interestingly, a study recently published in the journal The Lancet Infectious Diseases takes analysis of the Black Death and even earlier plagues a step forward, finding that a different chance mutation sparked each major pandemic. While a modern threat is not as dire, author Dave Wagner does say that another chance mutation could cause plague to surge once more.

"If plague could erupt in the human population, cause a massive pandemic, and then die out, it suggests it could happen again," he told Io9. "Fortunately we now have antibiotics that could be used to effectively treat plague, which lessens the chances of another large scale human pandemic."

Lessen the chances, but don't snuff them entirely.

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