Tag Archives: Yersinia pestis

Black Death Still Lives

Two new “black death” patients.

Black rat, Rattus rattusFor the second time this summer, health officials in California are investigating a case of plague that a camper most likely contracted while visiting Yosemite National Park.

The Centers for Disease Control and Prevention is testing a visitor from Georgia who camped at Yosemite, the Sierra National Forest and the surrounding areas in early August. Two campgrounds were closed after another case was announced two weeks ago. Since then the authorities have been warning visitors of possible plague risks.

New York Times
August 19,2015

Plague, also known as “bubonic plague,”  “black plague,” “black death,” and several other appellations, wiped out at least a third of the population of Europe in the 14th century — some historians estimate as high as two thirds — and also very large numbers of people several other times and places. Before entering Europe this time, it had ravaged China, India, and areas along the trade routes of the East.

The same germ had also been responsible for the Plague of Justinian that killed an estimated 25 million people in Europe in 541–542 A.D. and maybe that many more over the next two centuries. It came to Europe and spread there in the blood of the ironically named black rat (pictured above).

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 20 million people in Europe–almost one-third of the continent’s population.


It’s rare among humans now, but it survives in rodent populations in the southwestern United States and elsewhere. The rodents are generally immune to it, but their fleas are not. Fleas ingest the bacteria and become infected when they drink the blood of an infected animal. The bacteria actually multiply in the flea’s gut until they clog up its digestive system and make it vomit when it bites another animal and tries to feed again. It regurgitates infected saliva and blood into the new animal, passing the infection to it. Occasionally, humans gets infected this way.

Yersinia pestis bacterium causes black death.

The disease is caused by the Yersinia pestis bacterium, which can also cause “pneumonic plague” or “septicemic plague.” The difference between the three forms depends only where the infection exists in the body, but that difference is important.

Pneumonic plague, a severe type of lung infection, is one of three main forms of plague, all of which are caused by the bacterium Yersinia pestis. It is more virulent and rarer than bubonic plague. The difference between the versions of plague is simply the location of the infection in the body; the bubonic plague is an infection of the lymphatic system, the pneumonic plague is an infection of the respiratory system, and the septicemic plague is an infection in the blood stream.


Three forms of the disease

An untreated Yersinia pestis infection in the lymph nodes, the bubonic form, may be fatal in humans around 30% of the time.  An untreated infection in the lungs, the pneumonic form, is not only more likely to be fatal, but is also more contagious; it is spread through the air when the patient coughs, like the flu is. The untreated septicemic form, in the blood, is fatal in 99% to 100% of patients. However, this form is rare.

The bubonic form is usually caught from the bite of an infected flea. Only rarely does this become one of the other forms. However, in those rare cases when the infection does settle in the lungs (possibly because of a prior lung infection), then it becomes pneumonic and spreads through the air to the lungs of other people. In this form, it can wipe out a whole family in a week.

“In men and women alike,” the Italian poet Giovanni Boccaccio wrote, “at the beginning of the malady, certain swellings, either on the groin or under the armpits…waxed to the bigness of a common apple, others to the size of an egg, some more and some less, and these the vulgar named plague-boils.” Blood and pus seeped out of these strange swellings, which were followed by a host of other unpleasant symptoms–fever, chills, vomiting, diarrhea, terrible aches and pains–and then, in short order, death.


Patients with all forms of this disease usually recover if treated soon enough with antibiotics. Probably the worst danger from black death now is that it’s so rare it’s not always identified in time for treatment to work.

There are a series of short videos on the subject here, where you can learn more than you ever wanted to know about the black death in about 26 minutes total. But be warned, they are gruesome.



Yersinia pestis a.k.a. Black Plague a.k.a. Black Death

Yersinia pestis

Yersinia pestis, Black Plague, Black Death.

Yersinia pestis (formerly Pasteurella pestis) is a Gram-negative, rod-shaped coccobacillus, a facultative anaerobic bacterium that can infect humans and animals. It causes the deadly disease named plague. Human Y. pestis infection takes three main forms: pneumonic, septicemic, and bubonic plagues. All three forms were responsible for a number of high-mortality epidemics throughout human history, including: the sixth century’s Plague of Justinian; the Black Death, which accounted for the death of at least one-third of the European population between 1347 and 1353; and the 19th century’s Third Pandemic. These plagues probably originated in rodent populations in Europe or much less likely China.

Y. pestis was discovered in 1894 by Alexandre Yersin, a Swiss/French physician and bacteriologist from the Pasteur Institute, during an epidemic of plague in Hong Kong. Yersin was a member of the Pasteur school of thought. Kitasato Shibasaburō, a German-trained Japanese bacteriologist who practiced Koch’s methodology, was also engaged at the time in finding the causative agent of plague. However, Yersin actually linked plague with Y. pestis. Originally named Pasteurella pestis, the organism was renamed in 1967.


During the past few days, I’ve posted beautiful pictures of MERS and ebola viruses attacking monkey cells. This picture is of Yersinia pestis bacteria in the gut of an infected flea.

Y. pestis has been far deadlier than either of the two viruses, but probably only because it’s been around longer and attacked before the advent of modern science or medicine. During a six-year period between 1347 and 1353, it wiped out a third of the population of Europe. Such an outbreak now would be relatively minor, since it’s susceptible to treatment with antibiotics. Viruses, unfortunately, are not.

Live plague bacteria; dead MERS and ebola viruses

Keep in mind that bacteria are live single-celled organisms, whereas viruses are just dead chemicals. Nevertheless, they both reproduce inside appropriate hosts and sometimes cause disease and death. Viruses can do this because they contain genes corresponding vaguely to some of the genes in living organisms. When they enter a living cell, their host’s machinery copies them along with its own DNA. By blindly and unintentionally taking advantage of the cell’s reproductive processes, they reproduce themselves like exceedingly tiny little chemical zombies and even evolve into new forms, just as if they were living creatures. But they are not.

Certain bacteria, like Y. Pestis, also grow mainly inside a host, but for a different set of reasons. That’s where it gets the best combination of nutrients it requires, as well as precise environmental needs like moisture, temperature, protection from the elements, and maybe a thousand other little things. But bacteria are real living creatures many times larger than most viruses, and they have the ability to engulf nutrients, make use of oxygen as we do (in most cases), and make their own proteins and genetic materials without hijacking the host’s chemical factories to do it.

As seen from the Wikipedia quote above, Y. pestis has been a deadly enemy of mankind for at least 1,700 years and strikes in at least three forms. It’s not likely to go away soon, either; because it infects a variety of rodents and other small mammals without killing them. Fleas usually transfer it to humans, although the pneumonic form spreads through coughing and sneezing once somebody gets it.

Ring around the rosie.

The popular children’s game “Ring Around the Rosie” may have originated during one of the ancient epidemics, although some experts disagree about this. English versions include references to sneezing and falling down, as well as “pockets full of posies.” It is said that sneezing was a symptom of the disease, while falling down refers to dying. A “pocket full of posies” was to ward off the smell of death. The “rosie” in the title may have been a rose bush.

Ashes to ashes, we all fall down.

Similar games, using similar tunes and similar lyrics, appear in several other European languages; but experts don’t agree on their sources. The game seems pretty morbid, if that really is what the words refer to; but I suppose a little bit of morbidity is to be expected when it seems as if everybody you know is dying.