The Mystery of English Sweating Sickness

It’s easy to imagine how hard it must be to diagnose an ancient disease from bones alone. Many illness leave no trace on the skeleton, and soft tissues are rarely preserved, so in most cases it is impossible to even say that an animal or prehistoric human was sick at the time of their death, much less what they died of. Therefore occasions when we have an actual written account of a disease must be far easier to study, right? Many palaeopathologists don’t just focus on dinosaurs, they also look at diseases from what might be described as the archaeological record rather than the palaeontological one, such as the Black Death, but these can be just as challenging as decoding bones alone. One good example is a mysterious epidemic that haunted the summers of Tudor England sporadically for around 40 years before vanishing entirely. Sometimes called the English Sweats the disease is unknown today and doesn’t seem to resemble any common illness. It could kill in less than a day and was renowned for apparently affecting only the English, hence the name. Sometimes it was known as the ‘Summer Sweats’ or simply the ‘Sweats’ because of its appearances only between the months of June and November and the savage fevers it triggered in its victims. It was widely feared at the time and today remains poorly understood, but there are some intriguing theories about what it may have been.

Did Sweating Sickness come from Europe with Henry’s Tudor’s army? Source: Wikimedia Commons

In all studies of disease it is vitally important to establish the time and location of the first outbreak. This can obviously tell you where the pathogen comes from and can help you work out how it spreads. In the case of the Sweats this seems to be August 1485 in England. History buffs might notice that this coincides with a rather important period of English history and they would be right. August 22nd 1845 saw the defeat of Richard III by the armies of Henry Tudor at the Battle of Bosworth Field and it is within the triumphant army that we see the first recorded outbreak of the Sweats. This has led many researchers to speculate that the disease may have been brought over to England from Europe along with the mercenaries which formed the bulk of Henry’s army. However, although August 1485 is the best documented early case of the Sweats there are some hints that all is not as it seems. Three months before this in the northern city of York there is a written record of an outbreak of disease that sounds eerily similar to the later Sweats. If so this sickness can’t have been brought over by Henry’s forces. However, once arrived it certainly seems to have followed the army closely until eventually they, and the Sweats, arrived in London. The Sweats spread rapidly throughout the population, only finally fading away around the 31st October. In that time it killed an estimated 15,000 people. This pattern repeated in the next two outbreaks in 1508 and 1517 where the disease appeared suddenly in June and continued killing people across England until October (although the data about when the 1517 epidemic ended is confounded somewhat by an outbreak of plague in November).

After that the Sweats apparently laid low until 1528-29 and this outbreak is arguably the most important because for the very first time the disease travelled beyond Britain. Until now it was apparently entirely endemic to England, even going so far as to halt at the borders of Scotland and Wales. This fourth epidemic started the same way as the others, in Summer and in London but by 1429 swathes of Europe were also infected, albeit patchily. For instance the Netherlands and Flanders were affected while France escaped unscathed (except for the port of Calais which was in English hands at the time). Germany was especially badly hit and here the Sweats seemed to have had an unusually high mortality rate, certainly higher than that reported in other affected countries. The Sweats even travelled as far east as Russia although, to the south, Italy and Spain recorded no cases. After this outbreak there was another lull until 1551 when the last outbreak was recorded. Again it was limited to England, even forgoing the other parts of modern Britain, and after that there are no other major epidemics of the Sweats recorded. There are a couple of anomalies, like with all things, such as a 1578 outbreak in Colchester and another in Rottigen, Germany in 1802 but other than these exceptions the disease entirely vanished.

One question that might occur is why the strange time gaps between outbreaks? They aren’t occurring regularly each summer and there is no obvious pattern. The best current guess is that these outbreaks had something to do with fluctuations in climate. Random changes in rainfall or temperature over the decades could account for the rather haphazard timing of the outbreaks, especially since many have observed that the Sweats seemed to appear following periods of intense rainfall or flooding. Such events don’t happen every year (despite what you might think about the English summer!) and if these changes were impacting something else, such as the numbers of an animal carrier of the disease, then that could explain the pattern.

So now we know roughly when it appeared and where it spread but what did it actually do to people. How can we be sure all these outbreaks are cases of the same illness? The symptoms of the Sweats come from many of the writings of the time, from doctors, clergymen and other observers of the disease and all agree that this sickness was unlike anything else they had ever seen. In general the symptoms first appeared very rapidly, usually overnight or in early morning, and they started with chills and tremors which quickly progressed to a high fever and extreme weakness. Muscles aches and pains were also reported. Unlike many other disease of the time there was no apparent rash, although the body would be bathed in perspiration, and these symptoms usually lasted about 24 hours after which you either died or recovered. Mortality rates are difficult to calculate and seemed to vary widely from place to place but modern estimates based on the all available evidence put it at between 30-50%. For comparison the CDC puts historic small pox mortality at around 30%. It was greatly feared though, despite not being nearly as dangerous as other epidemics such as the plague, and some contemporary commentators actually put the mortality rate at nearly 90%. This seems excessive however and there is no other evidence of such a massive depopulation of England because of the Sweats such as is seen with the Black Death.

All this adds up to something of a mystery. We have repeated, but erratic, epidemics of an unknown pathogen, apparently limited to England, and which caused severe fevers that could kill around 30% of its victims and within 24 hours of symptoms first appearing. Some researchers have suggested that the Sweats were simply an unusual outbreak of common-place infections, such as typhus or influenza, but the speed of onset and the nature of the symptoms don’t seem to match any known diseases. Even anthrax has been put forward as a candidate and it is a good match for the speed and severity of the Sweats. The problem is that the anthrax spores would need to have been inhaled for them to cause the kind of symptoms reported  and it’s difficult to envisage a scenario when this could have occurred over such wide areas so abruptly and then also disappear equally rapidly. Even ergot poisoning has been put forward as a possible culprit but as rye (ergot’s favoured host) was mostly grown in Europe rather than England it is hard to explain the disease’s apparent fondness for English victims. One of the most recent and plausible hypotheses, published last year (2014) in the Journal Viruses, is that the Sweats were caused by some kind of hantavirus.

Hantaviruses are carried by rodents, not fleas like bubonic plague, but by the rodents themselves. Humans can catch them by either being in very close contact with an infected rodent or by breathing in their droppings or urine. They never spread person to person as far as we know. Some hantaviruses cause a disease called Hantavirus Pulmonary Syndrome (HPS) which starts with fatigue, muscles weakness and chills before leading to a high grade fever and profuse sweating. It can be fatal and patients are usually treated with artificial ventilation, something obviously not available in the 1500s. This might sound like a perfect match except for two things. One is that there is nothing to suggest why it would have been so especially fast-acting 600 years ago, and secondly all HPS-causing hantaviruses are limited to the USA. There are Old World hantaviruses too but they tend to cause hemorrhagic fevers which are a less convincing match symptom-wise and again they simply aren’t as fast acting as the Sweats. Also none of them are endemic to Britain and they never have been.

The black rat (Rattus rattus) may be a carrier of the hantavirus in England. Source: Wikimedia Commons

Before we discard the hantavirus theory completely though there is an interesting footnote to the tale. It was always thought that hantaviruses were not found in Britain but since 2012 this has changed. Since that date there have been six confirmed cases of acute kidney disease caused by hantaviruses in England and although four of them were attributed to captive rats two were not. These cases were in Yorkshire and when rats at the property of the patients were captured and tested they were found to be carrying a new hantavirus strain. It was found to be related to a known variant of the virus called the Seoul strain but it was novel enough to be given its own designation: the Humber strain. Public Health England were worried enough to start a survey testing volunteers who may have had contact with rats, either as pet owners or professionally as vets, pest-control workers or farmers, for evidence of hantavirus exposure. The results are preliminary at best so no conclusions can really be drawn yet but it showed that pet rat owners were far and away more likely to have been exposed to hantaviruses then were normal members of the public or those who were mainly in contact with wild animals. However, all groups had some individuals who seemed to have been exposed to a hantavirus or something very like one. This is odd indeed if there really are no wild hantaviruses in Britain.

These results, intriguing as they are, prove nothing. We still don’t know what caused the English Sweats, why they were so confined to England and why they vanished. Nevertheless hantaviruses certainly seem like a plausible candidate even if there are still some problems remaining such as ‘if it was caused by a disease that was endemic to the country, like an unknown hantavirus, then why did it stop causing periodic epidemics?’ And why were there no isolated, individual cases over the years as you might expect? Then again if it did come from outside the country why did only English victims display symptoms? And why did it then seem to spread outwards from England during the 1528-29 epidemic? These are all good questions and show just how difficult the work of palaeopathologists can be, even when there were recorded human witnesses to events. It might seem that this problem is somewhat abstract – “who cares what disease killed these people since it happened so long ago and hasn’t affected us since” – but by studying the past emergence of diseases like this we can begin to understand how modern epidemics might start. It might even help us to search for new diseases in our own backyard. Also this question is far from insoluble. By performing DNA tests on Medieval plague victims we were able to identify Y. pestis as the cause of Black Death. By performing similar tests on known Sweats victims it might be possible to find the molecular fingerprints of their killers.

Reference: Heyman, P. et al. 2014. Were the English Sweating Sickness and Picardy Sweats caused by Hantaviruses? Viruses. doi:10.3390/v6010151

One thought on “The Mystery of English Sweating Sickness

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  1. Some symptoms and the fast death are similar to the 1918 flu epidemic. Like the Sweating Sickness, the 1918 illness had never been seen before and disappeared afterward. Could they be the same???


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