First, some definitions. The incidence of a disease is the number of new cases of a disease that occur over a defined time period. An epidemic, then, is defined as occurring when the incidence of a disease escalates beyond what would normally be expected in a given population. The term pandemic means that a given disease has extended to more than one continent.
There are Common Source Epidemics, usually coming from a contaminated water or food source. This was the case of the cholera outbreak seen in Haiti after the catastrophic magnitude 7.0 earthquake in January of 2010. Or many of you may recall the Pittsfield, Massachusetts “Beaver Fever” Giardiasis outbreak over the three months beginning November, 1985 through January of 1986, when there were 703 confirmed cases of the disease originating from the contaminated City reservoir. (As an aside, Harold Hutchins did a paper of the same title that year—but, true to Monday Evening Club tradition, the subject turned out to be a discussion of the pre-American Revolution trapping industry in the upper Midwest!)
But, the topic tonight is Host-to-Host Epidemic. These are infections that are transmitted from person to person—either directly (such as the common Flu) or through a vector. A vector is an organism that serves as the intermediary, transmitting agent of the pathogen (such as mosquitoes, fleas or ticks).
The reservoir is the organism that sustains a pathogen for the long term. In this case, consensus is that the Plague originated amongst marmots living along the steppe in Central Asia in what is now Kazakhstan, the Gobi desert of China and the northern Himalayas. Marmots are related to prairie dogs and are part of the squirrel family. They burrow and live in underground nests. They weigh 6 to 15 pounds and their fur is widely prized for its use in making warm, attractive clothing.
Enter the vector. In this case it’s the Indian rat flea, Xenopsylla cheopsis. As with mosquitoes, only the female bites the host and can spread the infection. This flea seems to prefer rodents, which is why it so easily spread from the marmot population to the ubiquitous Black rat, Rattus rattus. But as the local domestic rat community dies off, the fleas’ alternative become whatever warm blooded mammal is in the vicinity.
The black rat likely first evolved in India, sometime before the last Ice Age, 2.6 million years ago. It can weigh four to twelve ounces and has incredible powers of reproduction. It is also know for its agility. It can jump three feet from a standing position, fall from a height of fifty feet without injury, scale a vertical wall, and squeeze through a hole as small as a quarter of an inch. The word rodent derives from the Latin verb, rodere, meaning “to gnaw.” Rattus can eat its way through lead pipe and adobe brick.
And what makes the flea such a vicious and effective vector? In an uninfected flea, the blood it withdraws from its host goes directly to its stomach, satisfying its hunger. But in an infected flea, plague bacteria build up in the foregut, producing a blockage. This means that no blood is reaching the stomach so the flea, chronically hungry, bites constantly. Because undigested, infected blood can’t get through the blockage in the foregut, the flea proceeds to vomit plague contaminated blood as it bites one host after another, thereby spreading the disease. Considering that fleas can jump several feet, the rapidity of the spread of infection is easily explained.
Also, this flea can survive for six weeks off a host—on clothing or food shipments for example—long enough to travel hundreds of miles by sea or overland.
It is also interesting to note that there are over thirty-one different flea species capable of transmitting plague. (By comparison, of all the mosquito genera, only the Anopheles is capable of transmitting Malaria).
Of course, not all diseases become epidemics. As old hosts die off or become immune, the microbe requires new hosts to continue reproducing. It’s possible, then, that in a small town everyone could acquire the disease in such a short time that the process could die out. Historical records seem to indicate that in human populations, the critical mass is about 250,000 people. Thus major epidemics do not seem to occur until cities expand to this density.
Plague is caused by a rod shaped Gram negative bacterium—Yersinia pestis. It is so toxic that as little as one organism can result in infection. It has been said to be able to kill most mammals, including camels and lions. But there are also a number of animals resistant to the infection including black bear, skunk and coyote. Most of the time Yersinia pestis and the rodent kingdom live in a state of uneasy coexistence. Animals continue to get sick and die, but there are enough partially resistant rodents to sustain the bacterial population in the community. This phenomenon is termed enzootic.
There are three human manifestations of plague:
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| A bubo |
The buboes may spontaneously rupture and then drain an especially foul smelling fluid. Medieval chroniclers referred to this as the stench of the Black Death.
Contemporary accounts also describe agitation, confusion, staggering gait, high fever and delirium.
This form of plague, if untreated, carries a mortality of 60 percent. The few survivors were quite fortunate in having an immune system capable of handling the bacteria.
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| Blackened feet of a victim |
3. Pneumonic Plague is the most virulent form of the disease. As the victim begins coughing a bloody froth, the aerosol droplets are highly infectious directly from person to person, avoiding the need for any vector at all. This form carries a 100 percent mortality rate as well—often within hours of developing the cough.
Common nursery rhymes, which have been handed down through the centuries reflected the times:
Ring around the rosies,Rosies refer to rosary beads—an effort to ask for divine intervention against the disease. Posies suggest the need for flowers to mask the terrible smell. Ashes were all that was left of a burnt corpse. And to fall down, of course, meant to die.
A pocket full of posies
Ashes, ashes!
We all fall down.
The mystery of what causes plague was finally discovered in 1894 during a reemergence of the disease in China (sometimes referred to as the Third Pandemic). Alexandre Yersin, for whom the bacterium is named, was a protégé of Louis Pasteur. He was sent to Hong Kong at the request of the French government to investigate the disease outbreak. He was the first to identify that: “the pulp of the buboes always contains short, stubby bacilli." And perhaps as importantly, he discovered that the same bacteria were present in rodents, thereby outlining, for the first time, a possible method of transmission.
So, let’s set the stage for early 14th century. Sometime around 800, Europe entered what’s known as the “Little Optimum”—a period of global warming. Average temperatures increased by over one degree Celsius. Warm weather turned even marginal farmland to productive use. England and Poland became wine-growing countries. As agricultural productivity increased, living standards rose, and populations increased dramatically. Between 1000 and 1250 the population of Europe tripled. The Continent contained at least 75 million people. It would take four to five hundred years for parts of Europe to regain those population levels following the catastrophe of the Black Death.
Furthermore, as populations grew, trade flourished. In the year 1000, an Italian merchant had virtually no chance of doing business in England. By 1280 a trader could travel a reconnected European land route through Flanders or through Germany to the Baltics. Or, by water via Gibraltar, to the busy port of London. From the bustling ports of the two rival sea powers of the time, Venice and Genoa, merchant vessels travelled to Alexandria, Aleppo, and Tyre (southern Lebanon), searching for sugar, camphor, ivory, ebony, wax, ambergris, or muslin.
Genghis Kahn, whose name translates as “Emperor of Mankind,” had conquered China and Central Asia in the previous century. His children and grandchildren inherited the Mongol Empire for the Tartars, including all of China, most of Russia, Central Asia, Iran and Iraq. They set up a communications network consisting of messengers capable of traveling 100 miles a day for weeks on end and slower commercial caravans and armies marching to and fro across vast distances. These maneuvers helped to hold this vast empire together.
The recently publicized exploits of Marco Polo informed Europeans of opportunities for buying treasured goods imported via the Silk Road trade route to the Far East. Thus, merchants were inspired to sail through the Bosporus, and on to the Crimean peninsula in southern Russia so as to have access to caravans bringing goods from the cities of Samarkand, Merv, and the emerald city of Hangchow.
But early in the 14th century, the weather changed dramatically throughout the Continent and Asia. Known as the “Little Ice Age”, this change created hardship conditions including scarcity of food resources throughout Europe and central Asia. It is generally thought that what is now referred to as the Black Death, originated near Lake Issyk Kul, Kyrgyzstan, which was a bustling trading center along the route to China. This hypothesis suggests that the Tartar herdsmen were forced out of their traditional pastureland by the climate change in a desperate search for new grazing land. They found themselves on the northern steppe, exposed to the endemic marmot population with its plague carrying bacteria. From the herdsmen, the plague would have spread to Arab, Italian, or Central Asian merchants, Tartar soldiers, or Chinese laborers.
And so the rise of the Mongol Empire and the burgeoning development of the global trading economy, allowed Y pestis to overcome the vast distances and small populations that had previously provided a firewall to its global spread. Each oasis resting spot for caravans likely had a supporting cast of fleas and rats attracted by the abundance of foodstuffs needed to satisfy hundreds of travelers and their horses
From here eastbound travelers could pick up the fast road to China (an eight to twelve month trek); westbound travelers found their way back home via Caffa (now Feodosiya) on the Crimean peninsula.
In 1266, when the Genoese first arrived in southern Russia, Caffa was a small fishing village. Eighty years later, seventy to eighty thousand people called Caffa home. Items for trade included silks from Central Asia, Sturgeon from the Don River, slaves from the Ukraine, timber and furs from the Russian forests to the north. The deep water port was perfectly situated to take advantage of the burst of globalization. And the legendary Genoese mariners were happy to provide the skills required to bring these goods to the West. The port of Caffa was held under a grant from the Mongols.
This arrangement was highly advantageous to the Mongols as it provided a direct link to Italy’s largest commercial center and encouraged trade across all corners of their vast empire. However, tensions and disagreements were a common feature of the commercial relationship, arising predominantly from their religious differences. The Italians were devoutly Christian and the Mongols had been practicing Islam since the 1200s. Furthermore, the Mongols considered the Genoese haughty, proud, and duplicitous.
In 1343 at the Crimean town of Tana, on the mouth of the Don River, tensions turned to violence. A fight broke out between locals and the Italians that left one Muslim dead. Faced with the threat of execution by the Mongols, the Italians fled to Caffa. Here they were given sanctuary. The people of Caffa refused to let the Tartars in and, in the face of such defiance, the Mongols decided to lay siege to the city.
By 1346, the first reliable accounts of plague appear in Russian reports on the western shore of the Caspian Sea. Within a year the disease arrived at the Crimean Peninsula. When the Tartar army suddenly found itself succumbing to this strange, new disease in huge numbers, it resorted to catapulting the infected corpses into the besieged city, in what is thought to be the first incidence of germ warfare! It was written that: “rotting corpses tainted the air, poisoned the water supply and the stench was so overwhelming that hardly one man in several thousand was in a position to flee the remains of the Tartar army.”
By the spring of 1347 the dying and decimated Tartar army faded back into the hillsides, leaving the remaining, living Genoese finally free to sail from the harbor of Caffa, bringing the pestilence of the Black Death with them. Europeans had no way to know that they stood on the edge of the most lethal catastrophe in recorded history.
Any ship leaving the Crimea had to pass through the Dardanelles and stop at Constantinople—the wealthiest city in Christendom. Thus, sometime in the early summer of 1347, the plague bearing Genoese arrived in the harbor. By the fall of that year there were reports that the city was becoming emptier and emptier as the number of graves increased. Some contemporary estimates suggest that 90 per cent of the city population perished. Royalty was not immune — Ioannes IV, the Byzantine emperor, lost his 14-year-old son to the disease.
From here the plague followed the trade routes. One strain swung northward through Greece, Bulgaria and Romania. A second went southward toward Egypt and the Middle East. A third found its way to Cyprus. And a fourth to Sicily, which is where Plague enters the historical record in Europe.
A local Franciscan Friar, Michele da Piazza, wrote: “In October 1347 twelve Genoese galleys put into the port of Messina.” Apparently, nothing about the vessels seemed suspicious. But almost immediately people began to fall ill. And in ways that no one in Messina had ever seen before. Friar Michele described: “a sort of boil…the size of a lentil, erupted on the thigh or arm, then the victims violently coughed up blood, and after three days of incessant vomiting for which there was no remedy, they died. And with them died not only everyone who had talked to them, but also anyone who acquired, touched, or laid hands on their belongings”.
Messina quickly expelled the Genoese, but it was too late. The contagion had been set loose. These merchant ships were captained by men of innate greed who had personal financial stake in the cargoes they were carrying. And so, despite holds full of dead and dying sailors, their ships continued to sail from port to port selling their wares—spreading disease along the way.
It was the Venetians who developed the process of quarantine—derived from the Italian word for forty. They made ships stay in a restricted area of nearby islands for forty days as a means of clearing their crew for arrival. Of course, forty was a completely made up number and probably derived from multiple biblical references.
It took all of two months for the disease to travel the eighty-one kilometers from Pisa to Florence where the Black Death is well described. One author wrote: “such was the multitude of corpses that huge trenches were excavated in the churchyards in which the new arrivals were place by the hundreds, stored tier upon tier like ships’ cargo till the trench was filled to the top.” Another described the pattern as layering bodies like layering cheese on lasagna. In an age when nothing moved faster than the fastest horse, the Black Death spread throughout the entire European Continent in just a few years.
Sometime in the summer of 1348, the plague jumped the English Channel from Calais to Weymouth, either by soldiers returning from the Hundred Years War or with the aid of commercial shipping vessels. By the following year, half of the English population had perished.
As the plague spread eastward across France, Germany and Switzerland in the summer of 1348, people began to believe that the mortality was a Jewish plot. Christians claimed they were dying because their wells were being contaminated with Jewish plague poison. Plague was not a vengeful act of God or of infected air, but of an international Jewish conspiracy aimed at achieving world domination.
Between the summers of 1348 and 1349, huge numbers of Jews were exterminated. Some were marched into public bonfires, others burned at the stake. Still others were beaten to death or stuffed into empty wine casks and rolled into the Rhine. In some localities, killings were preceded by show trials, but often Jews were killed simply as a preventative measure.
As we have seen so many times over the centuries, blameless, innocent Jews became scapegoats because of superstition, ignorance and fear.
Multiple factors contributed to the rapid spread of the Black Death.
The Great Famine, the collective name for the crop failures associated with the dramatic weather changes of the early 1300s, was devastating throughout the region. A half million people died of starvation in England, and 10 to 15 percent of the population of Flanders and Germany succumbed for lack of food. Thus young children from this era, who did survive, would have been in their forties and fifties at the time of the Black Death. Their immune systems, likely permanently impaired by the poverty of their nutrition, made them much more susceptible to the disease.
Population centers were producing much more garbage than they could dispose of. The situation was exacerbated by the influx of peasants forced off surrounding countryside by crop failures and loss of pastureland. They brought their livestock with them adding to the unsanitary conditions. Pigs, cattle, chickens, goats, and horses roamed city streets as freely as they did the countryside. Workers in outdoor slaughterhouses would simply pour the blood and offal of their carcasses into the gutters of the city streets where they plied their craft. Of course, this led to an explosion in the population of black rats.
Another urban polluter was the full chamber pot. No one wanted to walk down two flights of stairs, especially on a cold or rainy night. Medieval citizens were supposed to shout: “Look out below!” three times before draining the pots contents out the window. The stench of the city streets was notorious.
Personal hygiene was likewise a contributing factor to the spread of plague. The Greeks considered cleanliness a virtue, and the Romans thought hygiene so important that their public baths looked like temples. Yet, somehow, early Christians considered bathing a vice. St. Benedict said: “To those who are well, and especially the young, bathing shall seldom be permitted”. Saint Francis of Assisi considered God’s water too precious to squander on bathing. Undressing and changing clothing were also infrequent. One can imagine how easy it was for fleas to thrive under these circumstances.
Yet another factor underlying the spread of plague was war. Few centuries have been as violent as the fourteenth. In the decades before the plague, the Scots were killing the English; the English, the French; the French, the Flemings; and the Italians and the Spanish — each other! In those savage decades, the nature of battle grew bloodier, civilians were attacked more frequently and property destroyed more routinely — all helping to make the medieval battlefield and soldier more efficient agents of disease. Larger armies produced larger concentrations of dirty men and debris, which, in turn, attracted larger populations of rats and fleas.
Not only did the plague seem to strike out of nowhere, but it caused death on a scale that no one had ever seen, no one had ever even imagined was possible. Death not in the hundreds or thousands — but in the hundreds of thousands — in fact millions. Today the Earth’s population is 7.1 billion. The equivalent loss of life calculates to 2.8 billion people! Or, more parochially, the current population of Berkshire county is 130,000 people — so the equivalent loss of life would be 52,000 people dead in this county alone!
According to the Foster Scale, a measure of human disaster similar to the Richter Scale, the medieval plague is the second greatest catastrophe in recorded history. Only World War II produced more death, physical destruction, and emotional suffering says the Canadian Harold D. Foster, the inventor of the scale. Harvard historian David Hebert Donald also ranked the Black Death high on the list of history’s worst catastrophes. However, the greatest tribute to the destructiveness of plague comes from the Atomic Energy Commission which used the medieval pestilence to model the consequences of all-out global nuclear war. According to the commission’s Cold War-era study of thermonuclear conflict, of all recorded human events, only the devastation of the Black Death comes the closest to mimicking “nuclear war in its geographical extent, abruptness of onset, and scale of casualties.”
But this is ancient history, I hear you saying. The Black Death couldn’t repeat itself. We have vaccinations for such deadly diseases as Yellow Fever, Measles, Anthrax, and Influenza. Small Pox has been eradicated from the planet (except for the reserve samples held by the CDC in Atlanta and the Research Institute for Viral Preparations in Moscow—oh, and the six vials of virus accidentally discovered unprotected at the NIH this past summer). Yet, we continue to squander antibiotics thereby promoting resistant bacteria. Might we someday not have any effective drugs to treat such infections? And just suppose, that as the unheard-of-before AIDS virus emerged in 1980, that it could be transmitted by a mosquito. Or imagine that the Ebola virus mutates so that it can be transmitted by airborne particles like the common cold. This is really nothing more than Darwin’s evolution in action. It’s certain to happen sometime—will Medical Science be up to the challenge before it’s too late?
Material for this essay was derived from the following sources:
The Great Mortality by John Kelly
A Distant Mirror by Barbara Tuchman
Plague and Peoples by William McNeill
Viruses, Plagues, and History by Michael Oldstone
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