Whatever Happened to the Bubonic Plague?

Eric York on right. The Mountation Lion did not get him, but the Black Rat Flea did.


A wildlife biologist at Grand Canyon National Park has died after coming down with the Bubonic Plague. Eric York, age 37, seems to have contracted the disease while performing a necropsy on a Mountain Lion which tested positive for the disease.

The good news about the Bubonic Plague is that it is now a treatable disease, thanks to antibiotics.

The bad new is that it it still with us.



Whatever Happened to the Bubonic Plague?

In school, no one ever mentions what happened to the Black Death. Nor do they mention that we now have it in this country. Like so much that is fundamental to history (Whatever happened to the Dust Bowl? Why did the Japanese bomb Pearl Harbor?), the question is sidestepped by grade-school teachers.

First, a little history. Plague has probably swept through the Old World time and time again. Plague-like pestilences are mentioned in the Bible (the so-called “scourge of the Philistines”), and at least five great outbreaks are noted by historians.

For modern purposes, however, the "big plague" was the so-called "Black Death" that swept through Europe beginning in the 14th Century and carried forward, with fits and starts, until the middle of the 17th Century.

The first wave of this plague killed off one-third of the population of Europe within two years of its arrival in the port of Messina, Sicily in 1346.

The vector, or transmission agent, for this wave of Bubonic Plague was the Black Rat, Ratus ratus, which was host to the Oriental Rat Flea, Xenopsylla cheopis, which in turn was host to the bacterium Yersinia pestis that actually causes the Plague.

Large-scale incidents of Plague in Europe ended with the arrival of a very aggressive new immigrant to Europe -- Ratus norvegicus, aka the Brown or "Norwegian" Rat.

In fact this rat is in no way Norwegian. It probably originated in Asia, and got to Europe through the Middle East, having first arrived in England on a load of timber from Norway (hence the name given to it by the British).

The Brown Rat and the Black Rat look somewhat similar, but they have very different temperaments. A Brown Rat is not only larger that its Black Rat cousin, it is also far more aggressive.

When the Brown Rat arrived in Europe and began to multiply, it quickly pushed the smaller and more mouse-like Black Rat out of buildings, alleys, storage sheds and sewers. In fact, over time, it pushed the Black Rat almost totally out of existence in the temperate world.



A Flea With an Affinity

Though fleas and lice are opportunists, they tend to gravitate towards, and specialize in, certain hosts. Different species of bird lice, for example, specialize in different species of birds. In fact, many species of bird lice can only be found on specific species of bird.

Many types of flea also gravitate towards, and specialize in, certain kinds of hosts. Though a species of flea may theoretically be able to draw a blood meal from a wide variety of mammalian hosts, most thrive on a specific list of hosts and generally fail to thrive if these particular hosts are not around.

So it is with Xenopsylla cheopis, the Oriental Rat Flea, which is the flea most likely to be implicated in transmission of the Bubonic Plague.

The Oriental Rat Flea thrives on a few species of rodents, including the Black Rat and the Tarvag, or Monglian Marmot , which is found in the dry steppe country of central Asia. It may have been on on Tarvag skins carried along the Silk Road that the Plague first reached the Middle East around 541 AD.

While the Mongolian Marmot was probably the first host of the flea that carries the Bubonic Plague, the Xenopsylla cheopis flea has managed to due well on the Black Rat as well.

With the rapid spread of the Brown Rat, however, the Black Rat was bullied and beaten into extirpation across most of the civilized world.

Today the Black Rat is commonly found only in the tropics. Even there it is most likely to be found high up (running along roofs and feeding at the tops of date palms) in order to avoid running into the neighborhood bully, the Brown Rat.

Bottom line: the Bubonic Plague was brought to Europe by fleas riding on Black Rats, while Brown Rats largely drove that species of rat out of Europe (and much of the rest of the world), thus eliminating the Oriental Rat Flea and the Yersinia pestis bacteria that brought with it the Bubonic Plague. In short, rats not only brought the plague, they also worked to get rid of it.

A young Mongolian sharpshooter with Tarvags bound for the pot.

The Plague Comes to the New World

Plague-carrying Black Rats arrived on the West Coast of the U.S. in 1900 in a load of Chinese illegal aliens smuggled into San Francisco.

The exact date and circumstances are known, because two dead Chinese immigrants tested positive for the disease, and a massive roundup of rats was immediately begun.

Plague cases continued to bubble up in San Francisco for the next few years, but a local war on rats continued unabated, and it is possible the plague might been locally extirpated had the San Francisco earthquake of 1906 not hit.

The earthquake, of course, created a nearly-perfect environment of chaos, spilled food, and social disorder. After the earthquak, the Black Rat population began to climb, and with it the incidence of Plague.

Where was the Brown Rat? Believe it or not, Brown Rats (aka Norwegian rats) did not arrive on the West Coast of the U.S. until around 1940.

Eventually, a combination of poisoning and trapping, along with a massive city-wide cleanup, managed to knock down the Black Rat population of San Francisco and rid the city of the Plague.

Unfortunately, somewhere along the line, a Black Rat caught a train west, and with it Xenopsylla flea rode into the deserts of the American Southwest where it found the smaller, American version of the Tarvag -- the Prairie Dog.

A Prairie Dog, of course, is not a dog, but a type of small, communal-living, marmot.

Communal-living marmots and a dry climate presented the Xenopsylla cheopis flea with ideal living conditions, and it quickly multiplied. As a consequence, and to this day, Bubonic Plague can be found as a permanent feature of Prairie Dog towns (and, to a lesser extent, Richardson's Ground Squirrel colonies) in the American West.

It was, no doubt, from from a Prairie Dog that the Mounain Lion got the Bubonic Plague that was eventually passed on to National Park Sevice biologist Eric York.

Could the Plague Come East?

Could the Plague come East to take up residence in the common Groundhogs? For some reason this has not yet happened. It's hard to know what the barrier is, but the Xenopsylla flea may not find the Groundhog a suitable host -- perhaps they have a bad taste to the flea. As noted earlier, most flea species are very host-specific.

Another problem may be that it is simply too wet for the Xenopsylla flea to thrive in the kind of hedgerows we have here in the Eastern U.S. The Plague bacillus and its host flea generally thrive in desert or near-desert conditions. Though Europe is as cold and wet as the Eastern U.S, the Black Rats of the European Middle Ages tended to live under warm and dry roofs. The Xenopsylla flea apparently found this habitat quite suitable, while the wet and frozen hedgerows of the Eastern United States are the exact opposite of what the Oriental Rat Flea might consider home.

Rat collection station, Philadelphia, date unknown but shortly after 1900.