Back in 1346, Caffa was not a nice place to be. A Genoese trading colony on the Crimea, it must have seemed especially far from Italy right about then. Having gotten into a disagreement with their Mongol overlords, Caffa found itself besieged, hungry, and outnumbered by hordes of Mongols.
Then a miracle happened. Their infidel besiegers were suddenly struck with sickness and began to die off. God had clearly decided to intervene and save the Christians.
Unfortunately, their Satan-begot tormenters refused to simply accept God’s decision and go away. They went away, all right, but before they left they loaded their catapults with their own infected dead and flung them over the walls and into the town. It might have simply been a Mongol editorial comment or it might have been a primitive form of biological warfare.
In any case, the Plague came to Caffa.
Some weeks later, so the story goes, a Genoese ship from Caffa arrived in Sicily, bearing stories of the horrors of the siege and of the miraculous defeat of the Mongols. It was also carrying the Plague.
With horrifying speed, the Plague spread throughout Christendom. Estimates vary, but the consensus is that between a third and a half of Europe died. But that’s just an average. Many cities were entirely depopulated. We know now, although Europe at the time did not, that the Arabs and the Chinese were suffering, too. Demographers estimate that the world’s entire population was reduced by a full third.
The disease, we are told, was caused by a bacterium called yersinia pestis. It infected the rats common to all cities and all ships. The rats, in turn, infected their fleas. The fleas generously passed the bacterium on to humans. Soon the humans began to exhibit the swollen lymph nodes (buboes) and other symptoms that gave the disease its other name, the Bubonic Plague.
By the 19th century, what contemporaries called simply “The Great Mortality” or “The Great Dying” had acquired another name, “The Black Death.” Having come to understand bacteria as the cause of disease, every school child could be taught the rat-flea-human chain that devastated Europe. And so they have, from that day to this.
Except that the whole story is certifiably wrong.
Why? Because what we know about the Black Death doesn’t match yersinia pestis.
Let’s start with speed.
In the 19th century and again in the 20th, bubonic plague visited and revisited both India and China. As a result, we have a great deal of information about the life cycle and spread of the disease. We know that the natural reservoirs for the bacterium are Asian rodents, especially the marmot. We know that it can occasionally spread to other rodents that cohabit with human beings.
In medieval Europe, that would have been the black rat (rattus rattus). Now the black rat carries a flea commonly called the oriental flea (xenopsylla cheopis). This flea is a homebody, settling onto one rat for the duration. It does not normally bite humans, simply staying on its chosen rat, feeding and breeding. This is fine for the flea, but not so good for a bacterium that wants to spread.
The solution, for yersinia pestis, then and now, is simple: it kills the rodent. This forces the flea to jump to another rodent, infecting it and killing it until finally the fleas run out of rodents and are forced to move on to other warm-blooded creatures, e.g., us.
The result of this complicated process is that the spread of bubonic plague is slow. For each new area it has to first infect and kill all the rodents before it can get down to spreading some serious disease in people. 19th and 20th century outbreaks traveled at roughly 10 miles per year. We know the Black Death traveled at rates of about 3 miles per day!
And about those rats.
True bubonic plague is signaled, logically enough, by tremendous die-offs of rodents. Although the 19th and 20th century epidemics are replete with reports of rodent die-offs and dead animals littering the streets, the medieval narratives have no such reports.
Then there is the problem that Iceland suffered severely in the Black Death. This was true despite their complete lack of rats, which hadn’t migrated there yet.
Next, let’s talk about infectiousness.
Bubonic plague is not spread by human-to-human contact. That is, it’s not infectious. But despite a very shaky concept of infectiousness (before the Black Death, disease was assumed to be an individual affliction, probably caused by sin), all the medieval chroniclers agree that the Black Death was highly infectious. In fact, one of the favorite scenes of virtually all of them goes like this: Somebody, feeling himself unwell and knowing that meant he would soon die, calls in his lawyer, his heirs, and the requisite witnesses to make out his will. Within a short time, all, lawyer, heirs, and witnesses, follow him into death.
But suppose that the medieval bubonic plague was different? Suppose it somehow became infectious (like the pneumonic version). What then?
There’s still a problem: If you want to create a really good infectious agent, as I’m sure practically all of you do, then a long infectious/incubation period is essential. That is, you want lots of symptom-free Typhoid Marys walking around for as long as possible, infecting all and sundry.
Epidemiological modeling of the Black Death, based on the records, suggests that the time from original infection to recuperation/death was around a month, with the onset of symptoms being only at the last stage.
The parallel period for bubonic plague is 3-5 days. Pneumonic plague is even shorter.
Finally, let’s take a look at our genome.
Recent studies have shown that possession of a specific mutation, called CCR5-Δ32, gave some of our ancestors a measure of resistance to the Black Death. CCR5-Δ32 blocks an entry port into white blood cells that some pathogens (like HIV) use to take over the cells. What makes this interesting is that yersinia pestis doesn’t use that entry port! In fact, it’s fairly specific to viruses.
I could go on and on (one could say I already have), but what does it all mean? If the Black Death wasn’t caused by the bubonic plague, then what was it? If you match all of the collated data of the Black Death, here is what you get:
The Black Death was probably caused by a virus, one that attacked the white blood cells, passed up to the lymph glands, and caused swellings. It was highly infectious, quite probably via aerosols, with a very long symptom-free incubation period. Its mortality rate in susceptible persons was between 50% and 80% (some would say higher).
All of which would be of purely academic interest except for one thing: The Black Death disappeared around the end of the 17th century for reasons we don’t understand. It was succeeded in Europe by episodes of the true bubonic plague (which confused the historians).
The Black Death was the worst killer in recorded history. We have no idea where it came from, so we have no reason to think it doesn’t still exist somewhere. We can treat bubonic plague with antibiotics, since it is caused by a bacterium, but this is a virus. We have no treatments, save symptomatic ones, for viral diseases.
So just in case you’ve been getting too much sleep, consider this: while you are worrying about H1N1 (or H5N1, which has a far higher mortality), there may yet be a reservoir of the Black Death out there, just waiting for its call-back.