Were Rats to Blame?

Rat “From April 18 onwards, quantities of dead or dying rats were found in storehouses and public buildings (…) The situation worsened in the following days. There were more and more dead vermin in the streets and the scavengers had bigger cartloads every morning. On the fourth day the rats began to come out and die in batches. From basements, cellars and sewers they emerged in long wavering files into the light of day, swayed helplessly, then did a sort of little dance and fell dead at the feet of the horrified onlookers. People out at night would often feel underfoot the squelchy roundness of a still warm body. It was as if the earth on which our houses stood was being purged of their secreted humours….”

An extract from Boccacio’s account of the Black Death in Florence in 1348 which serves as a preface to his Decameron ?  No. The passage is taken from the opening of Camus’s famous novel La Peste in Stuart Gilbert’s translation (with two or three words altered so as not to give the game away). In Camus’ novel the plague which attacks Oran in Algeria (where Camus was born) commences as an epizootic (animal epidemic) amongst the rat population of the town. This is how one would expect an outbreak of bubonic plague to begin since the usual carrier of the bacillus, the flea Xenopsylla cheopis, is a parasite on rodents  and normally only transfers to humans when there are no available (living) rodents.

So why didn’t Boccacio and other fourteenth century chroniclers of the ‘Great Mortality’ of 1348-50 mention a preliminary wave of very heavy rat mortality preceding human cases? There are no convincing answers to this question. Most writers state, or rather assume without stating, that the inhabitants of fourteenth century Europe were so thoroughly unscientific, filthy and unobservant that they either failed to notice, or deemed unworthy of mention, the enormous quantities of dead rats that must have accompanied bubonic plague as it swept through Europe at breakneck speed, taking less than three years to get from Sicily to upper Norway and visiting most rural areas, even very remote ones,  on its way. As for being ‘unscientific’, well, I personally do not expect fourteenth century man to have a knowledge of microbiology centuries before the construction of a decent microscope ¾ it was only in 1894 that the French doctor, Yersin, identified the plague bacillus during the so-called Plague of Canton. Whatever the ‘Great Pestilence’ was — the term ‘Black Death’ is of much later date — it was almost certainly a bacterial or viral disease and, equally certainly, there was very little that medieval doctors and Public Health authorities could have done other than what they did do, which was to  recommend flight to those who had somewhere else to go such as Boccacio’s wealthy Florentines, to clean up the streets and to enforce strict quarantine on incoming vessels in ports. Although there was a certain amount of talk about ‘God’s judgment on man’, and naturally some attempts to blame minority groups such as Jews, medieval Health authorities and doctors did make an attempt to understand the phenomenon in a ‘scientific’ manner and the theories proposed were by no means idiotic. It was, for example, suggested that the origin of the pestilence was probably ‘vapours’ emitted by rotting corpses and this same theory was proposed by Creighton in the latter nineteenth century.

It is essential to continually bear in mind that medieval man was not an animal lover : the cultural and religious climate of medieval Europe was utterly different from that of, say, India where devout Hindus stubbornly resisted the attempts of authorities to exterminate the rats that shared their habitations as late as the  early twentieth century. As to medieval men and women being indifferent to dirt and filth, this assumption needs some qualification, at any rate as regards the towns which one would expect to be the most promising foyers of infection. To judge by the frequency and venom of ecclesiastical tirades, bath-houses during the later Middle Ages were only too well-attended, though it was perhaps more the nudity of these unisex establishments that attracted men rather than the opportunity to get a good wash. Public latrines existed in large towns — there were at least thirteen on London Bridge — and municipal authorities were extremely concerned about the dangers that, notably, butchers’ offal represented. Boccacio himself, who lived through the Black Death, speaks of “the cleansing of the city [of Florence] by officials appointed for this purpose, the refusal of entry to sick folk, and the adoption of many precautions for the preservation of health  (Decameron, p. 5 Everyman Edition). But, though Boccacio does mention a pig dying in the street, nowhere is there any mention of rats.

There is, moreover, one very good reason why medieval man would have been more, not less, attentive to rat mortality than people living today, for he would have envisaged a wave of dying rats as a portent. Folklore and folk wisdom in China, India and many parts of Africa have traditionally associated mortality of rodents with human epidemics. There is a Chinese poem quoted by the plague specialist Wu Lien-Teh  containing the lines

“A few days after the death of rats
Men pass away like falling walls.”

likewise an Indian saying, “When the rats begin to fall it is time for people to leave their houses”.

In the country, although peasants may well have become resigned to the permanent presence of unwanted guests under their roofs, they can scarcely have felt much affection for them. I myself  have inhabited a traditional  one room ‘long house’ in a remote area of France, and was extremely annoyed by the racket that rodents living in the eaves made each night. But no medieval poet or chronicler writer mentions rats. During a visitation as severe as that of 1348, dying rats would have been falling down into the living quarters and dwelling-places everywhere must have stank of putrefying rat corpses.

For we are speaking of a very substantial rat presence across the whole of Europe. Shrewsbury, an out-and-out bubonic plague believer, estimated that around 69 rats per square mile were needed to sustain an epizootic of the scale of the Black Death — the term incidentally was not used until two centuries later — and this works out, given the population density of the time, at the incredible figure, as Shrewsbury himself admits, of over a 100 rats per two-room peasant cottage in many rural areas of Great Britain !  It is only too typical of otherwise reputable historians that, instead of questioning the hypothesis (that the Black Death was bubonic plague), Shrewsbury dismisses the medieval evidence as unfounded rumour and categorically affirms that the pestilence could not have visited large areas of Great Britain.

But are rats indispensable for an epidemic, or pandemic (world-wide epidemic), of the disease we now, rather irritatingly, call plague?  The answer is that rodents, not necessarily rats, are absolutely indispensable for an initial outbreak of bubonic plague and it seems most unlikely that there were any other rodent candidates available in fourteenth century Europe. There exist permanent reservoirs of plague amongst squirrels in North America, but they cause little harm since individual squirrels very rarely interact intimately enough with humans to infect them. And in Asia there are enormous foci of plague amongst burrowing rodents such as marmots, which, again, considering the numbers involved, cause very little damage.

Bubonic plague is not properly speaking a disease of humans, nor even of rodents, but of fleas. It is caused by the bacillus Yersinia pestis, named after the scientist who identified it at the end of the nineteenth century, which, in certain conditions, gets established in the stomach of certain fleas, especially Xenopsylla cheopis. The bacteria multiply, filling the stomach entirely and, because of this, the flea cannot take in nourishment and, in desperation, feeds all the more frantically, or tries to. In the process it regurgitates some of the blood it cannot ingest, and also defecates, depositing bacteria in the faeces (see Illustration I). The bacteria infect the host, the host infects other fleas and so on.

It is not in the interests of a parasite to kill off too many of its potential hosts, fortunately for us or pandemics would be more frequent than they actually are, and in general a status quo results as in the bacillus-flea-rodent tripartite biological system. Only about 12% of the fleas get blocked, and we can assume that only a small percentage of rodents such as marmots die, since marmots were, and still are, extremely numerous. Epizootics flare up, of course, from time to time, on occasion spreading to other rodents and thus to man who gets involved quite co-incidentally. Since the black rat, Rattus rattus, the only rat present in Medieval Europe, is an almost exclusively domestic animal who, typically, lives in houses, warehouses or ships, i.e. in close proximity to man, Rattus rattus is a good deal more dangerous than the rest of the rodents put together from our point of view. Xenopsylla cheopis will normally only transfer to a human being when there are no available living rats — it leaves the corpse as soon as the body temperature cools. And the bacteria can only enter the human body by flea-bite or, just conceivably, very close physical contact such as wound-to-wound, so, contrary to what most people believe, bubonic plague is not a contagious disease. The human flea, Pulex irritans, is a much less efficient transmitter of plague since it rarely becomes blocked even when feeding on infected humans : there is widespread (though not quite total) agreement that it can be ruled out as an insect vector for plague except in the case of septicaemic plague, a complication of bubonic plague that remains very rare.

We know a considerable amount about bubonic plague today because the last big outbreak, the so-called Plague of Canton, occurred when there were plenty of trained doctors and Health Officials available and the secret of bacterial infection was at long last known. Officials from the Plague Research Commission chronicled the relentless spread of bubonic plague through India in great detail, though they were incapable of doing much more than taking preventative measures prior to the discovery of antibiotics.

The most striking feature of the Plague of Canton was its extremely slow rate of dissemination despite the availability of modern methods of transport. It is thought that the pandemic originated in the Yunnan during the eighteen-fifties, but it was only in 1894 that it reached Canton and Hong Kong. It reached Calcutta in 1895, presumably by sea, and a year later found ideal conditions in the teeming, insanitary city of Bombay (Mumbai). Something of the Camus scenario of rats coming out to die on the streets was in fact observed, though not usually quite so dramatically. Plague maintained itself at these locations spreading outwards throughout much of India for some thirty years and, in Bombay itself, its progress was often no more than two or three miles a year!  Compare this with the lightning sweep of the 1348-50 Black Death which covered the ground from Messina in Sicily to Northern Norway in less than three years!

George Christakos and fellow authors (Interdisciplinary Public Health Reasoning and Epidemic Modelling: The Case of the Black Death, 2005, Springer), using advanced modelling techniques estimates that “plague advanced at an accelerated pace that peaked in October of 1348, when it infected a quarter of a million km2 in one month” (p. 230). To get an idea of what this area represents, I have roughly marked it out on a map of France (see Illustration II), though I hasten to add that the actual territory allegedly covered was not restricted to France and was a much more elongated shape.

The assumption that the Black Death so-called was caused by rats is of relatively recent date, since it only goes back to the late nineteenth century,  when Yersinia pestis was discovered and Koch, amongst others, immediately identified the bacillus as the cause of the 1348 pestilence. Practically all history books today, when discussing the issue, speak of three main onslaughts of bubonic plague in Europe, the Plague of Justinian, the medieval Black Death and the Plague of Canton. It is somewhat alarming to see how quickly an assumption becomes unassailable dogma, for that is what the rat theory has become. The principal; stumbling blocks to the identification of the Black Death with plague are, then :

1. Bubonic plague requires a rodent epizootic to get going, while contemporary witnesses nowhere mention rats in connection with the pestilence;

2. A very large native rodent population is required, and references to rats throughout the entire medieval period are few and far between, to say the least;

3.  The rate of spread was phenomenal and the mortality enormous — between a quarter and a third of the entire population of Europe.

On (2) further evidence that there can hardly have been a substantial rat population in the mid fourteenth century in Britain comes from the design of dovecotes. Everyone is agreed that the more familiar Brown Rat, Rattus norvegicus, only arrived in Britain in the early eighteenth century rapidly spreading inland from ports. According to Dr Twigg, who cites McCann, The Dovecotes of Suffolk (Suffolk Institute of Archaeology & History 1998 p. 21 -2), dovecotes were re-designed at around this period because of rats which climbed inside and ate both doves and eggs. Staddle stones, large toadstool-like constructions of stone on which barns, and even small houses, were laid, and which are very common in the area where I live (Dorset) appear to date from this period also. Now, in Tudor and late medieval times, one would expect there to have been more, not less, dovecotes as, apart from their value for food in monasteries and such establishments, the droppings were collected, mixed with earth and boiled to produce saltpetre, the main ingredient in gunpowder. Rattus rattus is actually a better climber than the Brown Rat so, had there been a substantial rural rat population in the preceding centuries, one would have expected to find mentions of it as a pest. Also, since  grain losses from manorial granaries were a recurring bone of contention, one would have expected bailiffs to have attributed them to rats, which, as far as we know, they never did.

Incidentally, for what it is worth, the story of the Pied Piper of Hamelin does not go back to the mid fourteenth-century (though conceivably based on earlier sources) and the first versions do not specifically mention rats as carriers of disease. Defoe, in Journal of the Plague Year, a partly fictionalized account of the seventeenth century Plague of London, does mention rats though he nowhere suggests that they were responsible for the epidemic. Black rats may well have become something of a nuisance in cities by Stuart or Commonwealth times, but the problem remains that the Black Rat is a strictly sedentary animal that has rarely been found even more than a mile or two from its, usually urban, birth-place.

Some readers are perhaps already getting impatient because I have not, as yet, mentioned pneumonic plague. Pneumonic plague is simply bubonic plague which affects the lungs : it is, however, a very different kettle of fish in many ways. Prior to the discovery of antibiotics, it was almost invariably lethal and can be spread person to person rather like influenza through droplets released into the air, by sneezing for example. This ties in quite nicely with the common medieval belief, not so long ago dismissed by historians as rank superstition, that you could ‘catch the pestilence’ simply by being in the same room as an afflicted person. Medieval doctors were themselves so worried about the possibility of contagion that they often refused to visit their patients !

However, the pneumonic plague hypothesis does not quite do what many people think it does. We know a lot about pneumonic plague, because of the 1910/11 and 1920 Plagues of Manchuria, voluminously recorded by a practising physician on the spot, Lien-Teh. In the first place, if the Black Death actually was plague, it cannot have been entirely, or even mainly, the pneumonic variety. For all medieval observers mention buboes (swellings) especially at the groin or armpit as being the principal symptom. In the case of pneumonic plague, there is not enough time for the buboes to form — in fact, paradoxical though it may sound, pneumonic plague is too deadly to make it a good candidate for a pandemic. For an epidemic to develop, we need an abundance of healthy carriers, or at any rate persons who appear healthy — precisely why AIDS is such a danger, likewise influenza, the cause of the last major pandemic in the West, that of 1918 which killed far more people than World War I. In the case of septicaemic plague the afflicted person dies within six hours, which makes it a very unlikely candidate for even a local epidemic. But pneumonic plague does not rate much better : it has been officially estimated that an afflicted person dies within an average of 1.8 days.

Why, then, the substantial mortality in Manchuria? The Manchurian outbreak had the benefit of extremely favourable conditions (from the bacillus’s point of view) which are most unlikely to repeat themselves  : migrant workers in the trapping industry travelled about in winter on heated trains and by night slept on platforms in crowded steam-heated hostels. Moreover, the authorities were taken by surprise in 1910 with the result that the 1920 outbreak was a good deal less serious though practically the only methods available were the ‘medieval’ ones of isolation and quarantine. And the Manchurian outbreaks, though severe, do not even remotely compare with the Black Death. Not everyone in 1349 could have avoided all contact with other human beings, since they had to procure food, but, as we know from Boccacio, people certainly kept as far away from each other as they possibly could with the honourable exception of the clergy called in to hear bedside confessions — they paid for their zeal by heavier mortality than amongst other professions especially in Germany. So the same difficulties for the rapid transmission of pneumonic plague by person to person contact would have applied in the fourteenth century, only more so given the absence of railways and steamships.

The second point to be stressed is that pneumonic plague does not get rid of the need for rats. Infected rodents in serious numbers are still required to start the epidemic, and we simply have no evidence to suppose that there were enough rats around in 1348 — except the circular ‘reasoning’,  “No rats, no plague”.  In the Manchurian case, it was marmots who started the epidemic : the first human victims handled them directly on a day to day basis and, it has been observed, were largely inexperienced migrant workers unaware of the dangers involved. Whether an outbreak of pneumonic plague can persist without an accompanying epizootic amongst rodents, is still a matter of learned debate, or rather controversy, but it seems more probable to me that an outbreak restricted to humans would burn itself out fairly quickly. Note that, if we accept de Mussis’ account (which almost everyone does with some reservations), the Black Death entered Europe via a Genoese galley hailing from the Crimea. The trip, even under very favourable conditions, would have taken a good six weeks, and this is ample time for an outbreak of any known form of plague to have either burned itself out, or, at the very least, to have killed off enough of the crew to make the harbour authorities at Messina most suspicious, which apparently they were not.

Frankly, the case for the identification of the Black Death with plague as we know it, just doesn’t stack up. As an amateur with no vested interests either way, when I first did some research into the Black Death for an article back in the eighties, it was not a matter of whether I did, but whether I could, in all honesty believe the two were one and the same. I decided I couldn’t, especially after reading Dr Twigg’s epoch making book, The Black Death (Batsford, 1984), also the very interesting Ph. D thesis of Palmer into the history of plague in Venice (though this does not cover the 1348 period). Since then, the small band of bubonic plague sceptics has been swelled by various other figures, notably Scott and Duncan (Return of the Black Death, Wiley 2004), Professor Cohn (Epidemiology of the Black Death and Successive Waves of Plague), Lerner (Fleas : Some Scratchy Issues Concerning the Black Death, Journal of the Historical Society June 2008) and, most recently of all, Gummer (The Scourging Angels, 2009) to mention only the main authors known to me.

The best that can be said for the bubonic plague hypothesis — and that is all it is — is that the description of the surgeon Guy de Chauliac and one or two other contemporaries of the symptoms of the disease does sound rather like bubonic plague. The buboes are not specific to plague but there is no doubt that they are distinctive. Bubonic plague can also give rise to small, black pustules, which fits the description of ‘God’s tokens’ as they were often called. However, these are much less distinctive than the buboes and it is worth noting that these marks, the “ring, a ring of roses’ of the (18th century) nursery rhyme, seem, over the years, to have become a more typical symptom than the buboes, assuming that subsequent outbreaks of ‘pestilence’ had the same cause, which they may well not have done. There is, annoyingly, just enough plausibility to the bubonic plague theory to keep it alive. Though far from being as lethal as the Black Death, or even, globally, smallpox and malaria, no one is going  to deny that plague is a serious disease since it caused over 12.5 million deaths in India during the twentieth century (over a period of forty-three years though, not two and a half).

What of DNA testing ? The jury is still out on this issue. A French team led by Michel Drancourt and Didier Raoult tested three skeletons from a grave pit in Montpellier for bubonic plague and reported positive results. However, various geneticists and archaeologists such as Mike Prentice, Alan Cooper, Carsen Pusch and others have disputed these claims, some attributing them to laboratory contamination. No one has, since then, managed to repeat these positive results and we await a more extensive and thorough investigation which, according to some unconfirmed reports, is currently underway.

The trouble with disbelieving that the Black Death was plague is that it is a negative option : its advocates find themselves pushed into making risky guesses about what the Black Death really was, and this has proved to be a dangerous game. Dr.  Twigg came up with anthrax as a possible alternative. This suggestion does have the advantage that it solves the problem of rapid dissemination since anthrax spores can be spread about by the wind, and are extremely resistant to extremes of temperature (which fits what we know of the Black Death). One might seriously doubt that, given medieval population density levels, any disease could have covered such a vast area so swiftly other than by dispersion in air currents. For what it is worth — and in my eyes is worth something — contemporary (medieval) observers thought that the pestilence was spread both by direct contact and by ‘vapours’, perhaps emanating from decaying corpses. This suggestion was by no means idiotic : the ‘miasmic’ theory of disease was still going strong in the late nineteenth century amongst the scientific establishment.

In other respects, however, Dr Twigg’s mention of anthrax proved to be an unfortunate suggestion since anthrax, in its present form at any rate, is not very contagious as we know from the post 9/11 scare. To invoke a ‘stronger strain of anthrax’ is a dangerous ploy, since it invites the plague lobby to counter by claiming that the bubonic plague bacillus of 1348 was a ‘stronger strain’ than what we are used to today. Dr Twigg’s suggestion, though it is contained only in the ten last pages of his book, simply gave his opponents a good excuse to dismiss, or simply not to read, the remaining densely argued two hundred odd pages.

Scott and Duncan have since then come up with haemorrhagic fever or ebola, a deadly viral disease. Much of their work is outside the remit of this article, since it deals with successive waves of ‘pestilence’ in Europe, not just, or principally, the 1348-50 outbreak, but deserves mention nonetheless. Using modern statistical methods, they have worked out an “average time from infection to death” for plague cases over a period of centuries and have come up with the figure of 37 days. This fits quite well with the ebola hypothesis but, more strikingly, with the Venetian institution of 40 days quarantine for incoming vessels, a period which soon came to be accepted throughout the whole of Italy. There were, subsequent to 1348, only 11 outbreaks of ‘pestilence’ in 300 years in Italy, which compares very favourably indeed with France and other countries. This quarantine was a considerable annoyance to merchants and may even have contributed to the commercial decline of Venice, so the Venetian Health authorities must, at least in their own eyes, have had serious reasons for instituting it. Of course, on the bubonic plague hypothesis, any quarantine is entirely pointless.

One  reason why the rat theory of the Black Death is still up and going, is that we do not, as humans, much like rats, viewing them as ugly and dirty creatures. If a similar pandemic had been initiated by squirrels, as just conceivably it might have been, one wonders whether the bubonic plague hypothesis would have remained established dogma for over a hundred years with very few daring to question it. Even if it were eventually proved to be utterly misguided, people for a long time to come will unthinkingly associate rats with the Black Death much as we automatically associate Nero with the burning of Rome or Louis XIV with the Man in the Iron Mask  — indeed I sometimes find it hard to get rid of the association myself despite having been in the non-bubonic camp for at least twenty-five years already. As a matter of fact, rats have probably been a good deal more serviceable to mankind than squirrels, who we find cute, since, apart from the rather unpleasant IQ maze experiments, rats have long been used to detect unexploded mines because of their excellent sense of smell.

There must, anyway, have been plenty of diseases which have disappeared without a trace, since diseases, being merely forms of life that we, as humans, do not view favourably, are subject to evolutionary pressures like everything else. One such is “the sweats”, a very serious disease prevalent at the time of the Reformation and which no one has subsequently successfully identified.  So it may well be that we shall never know with certainty the micro-organism responsible for what someone called, with not too much exaggeration, “the most nearly successful attempt to wipe out the human species” — a worthy adversary indeed !

Sebastian Hayes


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