Rats!

The Year of the Plague #2

Read here The Year of the Plague 1: The Worst Year Ever

In 2013, builders working on the new Crossrail line in central London found a heap of bodies buried between St John Street and Goswell Road in an area mostly known as Smithfield. Today this is a fashionable part of town, even if its chic is still a bit shabby, but it has an insalubrious history. The name derives from its medieval function as a ‘smooth field’ on the edge of the City, where all sorts of bawdy activity took place away from the eyes of the City authorities: summer fairs, wrestling matches, meat markets and prostitution.

Forensics indicated that many of the dead suffered malnutrition and one in six had rickets due to vitamin deficiency; a number also had back damage, suggesting a lifetime of gruelling manual labour, while later medieval skeletons ‘had a high rate of upper body injury consistent with being involved in violent altercations’.

On top of this, many of the corpses contained the DNA of Yersinia pestis, the bacterium which causes the Death Black - for what tunnelers had uncovered was a plague pit from the terrible year of 1348, one of several found over the centuries. In fact, thanks to the meticulous record keeping of London’s government over the centuries, we know much about the details; that the land here was bought by Bishop Ralph Stratford in late 1348 to deal with the thousands of deaths the City was witnessing, and that he had been helped by prominent philanthropist and soldier of fortune Sir Walter Manny, who had negotiated the deal with nearby St Bartholomew’s Hospital.

The bacterium in question is named after Alexandre Yersin, a Swiss-French bacteriologist who had investigated the 1894 Hong Kong plague, part of the last great outbreak of the disease. Yersin was not the only one to identify the villain of the Black Death; around the same time the Japanese bacteriologists Kitasato Shibasaburō had made the same discovery, but as with many medical breakthroughs, one person ended up getting most of the credit (although having the plague named after you is a slightly bitter-sweet legacy).

The late 19th century plague pandemic was significantly the first to alarm authorities enough that it was investigated by a team of health experts. With the world ever more globally connected, some feared that the dreaded Black Death might make a comeback - a disease which had caused such a lasting terror in the historical memory.

As it was, the Third Plague Pandemic which swept China and India was nothing like as contagious as the great outbreaks that begun in the 14^th century and lasted until the 17^th. This only added to the many mysteries around the plague, which has confused historians for centuries.

The nature of the Black Death has been debated since Yersin made his discovery, and many have argued that it may have been a different illness, like anthrax, flu or even Ebola (plague, anthrax and flu have identical early symptoms). It was Yersin who identified the role of rats, and yet no one at the time noted anything up with these animals dying. It was only relatively recently that scientists were able to take DNA from 1348 plague victims and confirm it was same disease caused by Yersinia pestis.

The Y pestis bacteria that causes the bubonic plague lives on rodents in central Asia, and most likely it was human population growth which allowed it to jump species and become far more deadly, a risk made much worse by climate change, which can push an infected species to migrate closer to human settlements. There are dozens of related types of bacterium but, as Rosemary Horrox has pointed out, even small mutations ‘in the plague bacillus can produce a massive increase in its virulence’.

Dozens of rodents carry plague, but it would only become deadly to humans when Yersinia pestis infected the flea of the black rat (rattus rattus, to give it its Latin name). Black rats are sedentary homebodies and don’t like to move more than 200 metres from their nests; they especially like living near to humans, which is what makes them so much more dangerous than more adventurous rodents. Black rats have been our not-entirely-welcome companion for thousands of years, and were living near human settlements in the Near East from as far back as 3000 BC; the Romans and their roads helped them spread across the empire and brought them to Britain, the oldest rat remains here being found from the fourth century, underneath Fenchurch Street in London.

Black rats were especially comfortable in the typical medieval house, and while stone buildings became a feature of life in the 12^th century, most were still made of wood and straw. In the words of historian Philip Ziegler, ‘The medieval house might have been built to specifications approved by a rodent council as eminently suitable for the rat’s enjoyment of a healthy and care-free life.’ This type of rat is also a very good climber, so could easily live in the thatched roofs which were common then.

Because of its preferred home, the black rat is also called the house rat or ship rat, while the brown rat prefers sewers. On top of this, the animals are fecund to a horrifying degree; one black rat couple can theoretically produce 329 million descendants in three years. So the typical medieval city had lots of rats, and with them came lots of fleas.

Fleas are nature’s great survivors. They can endure in all sorts of conditions, and some have developed the ability to live off bits of bread and only require blood for laying eggs. The black rat flea, called Xenopsylla cheopis, is also exceptionally hardy, able to survive between 6-12 months without a host, living in an abandoned nest or dung, although it is only active when the temperature is between 15-20 centigrade. As John Kelly wrote in The Great Mortality, the Oriental rat flea is ‘an extremely aggressive insect. It has been known to stick its mouth parts into the skin of a living caterpillar and suck out the caterpillar’s bodily fluids and innards’. What a world.

There are two types of flea: fur fleas and nest fleas, and only the former travels with its host rather than remaining in the nest. The rat flea is a fur flea, and while it prefers to stay on its animal of choice, they will jump on to other creatures if they’re nearby - unfortunately, in the 14^th century that happened to be us. (In fact, they will attach themselves to most farmyard animals, and only the horse was left alone, because its odour repulses them, for some reason.)

As part of the great and disgusting chain of being, the rats inadvertently brought the plague to humans, but it wasn’t fun for the rats either, or the fleas for that matter. When the hungry flea bites the rat, the pestis triggers a mutation in the flea guts causing it to regurgitate the bacteria into the wound, so infecting the rat. (Yes, it is all a bit disgusting). Y. pestis can be transmitted by 31 different flea species, but only in a rodent does the quantity of bacillus become large enough to block the fleas’s stomach.

The flea therefore feeds more aggressively as it dies of starvation, and its frantic feeding makes the host mammal more overrun with the bacterium. The fleas also multiply as the plague-carrying rat gets sick, so that while a black rat will carry about seven fleas on average, a dying rat will have between 100 and 150. Rats were infected with the disease far more intensely than humans, so that ‘the blood of plague-infected rats contains 500-1,000 times more bacteria per unit of measurement than the blood of plague-infected humans.’

When the disease is endemic to rodents it’s called ‘sylvatic plague’, and when it jumps to humans it’s called ‘bubonic’ plague. For Y pestis to spread, there will ideally be two populations of rodents living side by side: one must be resistant to the disease so that it can play host, and the other non-resistant so the bacteria can feed on it. There needs to be a rat epidemic to cause a human epidemic because it provides a ‘reservoir’ for the disease to survive. Robert Gottfried wrote: ‘Y pestis is able to live in the dark, moist environment of rodent burrows even after the rodents have been killed by the epizootic, or epidemic. Thus as a new rodent community replaces the old one, the plague chain can be revived’. The rat colony will all be dead within two weeks of infection and then the fleas start attacking humans.

The first human cases would typically appear 16-23 days after the plague had arrived in a rat colony, with the first deaths taking place after about 20-28 days. It takes 3-5 days after infection for signs of the disease to appear in humans, and a similar time frame before the victim died. Somewhere between 20-40 per cent of infected people survived, and would thereafter mostly be immune.

What happened next would have been terrifying. ‘From the bite site, the contagion drains to a lymph node that consequently swells to form a painful bubo,’ or swelling lump, ‘most often in the groin, on the thigh, in an armpit or on the neck. Hence the name bubonic plague.’

Bad breath was one of the first signs. There was also a prickling sensation, similar to pins of needless, or a sudden coldness and drop in body temperature, a lightheaded feeling and a sense of nausea. This was followed by extreme fatigue and a feeling of despair. Then would come a very high fever, vomiting and headaches; a pain in the groin and the first terrifying sign of bulbos, coughing up bloody mucus, then delirium. Victims would cough out bloody sputum, which was plague-infected and could spread. Understandably, then, people tended to avoid people with the plague.

Although people generally died between two and seven days after first showing symptoms, sometimes people might expire on the same day. The bubo, known as the gavocciolo in Italy, created distinctive deformations: a limp if it was on the leg, or a neck afflicted with a crick, or an outstretched arm if it was under the armpit. A witness recorded: ‘The stench... sweat, excrement, spittle [and] breath [was] overpowering’.

Plague confused historians, because not every victim had the telltale buboes or suffered fever, and it also comes in three distinct forms. Bubonic was the most common, which was seen with the characteristic bubos; people caught this from either a flea bite, or if exposed material passes through a break in the skin, like a scratch or cut. This was mostly spread by people arriving with rat fleas in clothing or belongings.

There was also pneumonic plague, in which the lungs are infected; this spread through the air, could be passed from person to person, and might kill within 48 hours. Although it is unique in being transmitted directly from human to human, pneumonic plague was not common, except in cold weather when it was easier to pass on cough droplets and frozen sputum.

Pneumonic plague caused the victim to cough blood, which eventually led to blood pouring from the victim’s mouth in scenes of sheer horror. The death rate from the pneumonic form was even higher; only about 10% survived. During the early 20th century outbreak in Manchuria, life expectancy for pneumonic plague from onset of symptoms was just 14 hours 30 minutes, with a 90-95 per cent fatality rate.

There was also a third form, septicaemic plague, which could also be transmitted by the human flea, appropriately named P. irritans, the Latin word, of course, for ‘irritating’. With septicaemic plague, the blood was infected and began to congeal, causing dark blotches which became known as ‘God’s tokens’. Septicaemic plague starved the body of oxygenated blood, and also led to grisly vomiting blood. This had close to a 100 per cent death rate. Haemorrhaging also brought psychological disorders, ‘which may explain the danse macabre rituals that accompanied the Black Death’, as Gottfried put it, as a collective sense of madness overwhelmed a world gripped by terror.

It must have been horrific, and yet the 1348 outbreak wasn’t the first, nor even the most destructive, outbreak of the illness. Thanks to recent studies of DNA from bodies from a far more distant period, we also know that the same illness had struck before a number of times, with cataclysmic results - in fact it had previously caused the collapse of an entire civilisation.