What Caused the Deadly English Sweating Sickness?

Sudor Anglicus, the so-called “English sweating sickness,” remains one of medicine’s enduring mysteries. The disease appeared abruptly, could turn fatal within hours in some cases, and then vanished from England after the 1551 outbreak. Between 1485 and 1551, it struck repeatedly across England, usually in the summer or early fall. Despite decades of study, the causative agent has never been identified. A 1991 clinical-historical analysis suggested enteroviruses as the most plausible explanation, while a 2014 virologic reassessment pointed instead to hantaviruses and also examined the later Picardian Sweat.An Epidemic With a Tudor SignatureThe English Sweat belongs to a narrowly defined historical period. It first appeared in 1485 at the time of Henry Tudor’s victory at Bosworth Field and did not reoccur in England after the outbreak in 1551. In between, there were epidemics in 1508, 1517, and 1528. The disease usually began in the summer and subsided in the fall.According to contemporary accounts, Sudor Anglicus came on abruptly, and in some patients, death followed within just a few hours. That swift course was a key reason the illness was so feared. Reports also suggest a striking clustering of cases among wealthy adult men, and in the early outbreaks, clergy appear to have been disproportionately affected as well. With the exception of the 1528 epidemic, the disease was largely confined to England. Even in Calais, accounts indicate that those most affected were chiefly Englishmen.Clinical PresentationThe name is somewhat misleading. John Caius, whose 1552 treatise is among the most important contemporary sources, already emphasized that the disease was not merely about sweating but about fever. The disease usually began acutely, with few or no warning signs. The primary symptoms were high fever and profuse, foul-smelling sweating. These were accompanied by thirst; headaches; delirium; pain in the back, shoulders, arms, or legs; abdominal discomfort; and palpitations or tachycardia.Skin rashes do not appear to have played a central role; only one early report mentioned black spots. Those who survived the acute phase were left exhausted, with a strong need for sleep and severe weakness. The illness often lasted less than a day. Fluid and electrolyte loss due to profuse sweating is discussed as a possible cause of death, but this cannot be definitively proven.Five OutbreaksThe first outbreak in 1485 occurred during the weeks surrounding the Battle of Bosworth Field and the beginning of Tudor rule. London was hit hard. Two Lord Mayors died, one within a few days of his appointment. For the year 1508, more detailed records have been preserved, particularly for the cities of Chester and London. In Chester, 91 deaths were reported within 3 days, 71 of them on a single day. Only four or five of these 71 patients were women.In 1517, the disease likely spread from London to the rest of England. Several members of the royal court are said to have died within 1-2 hours after symptoms began. The 1528 outbreak was especially significant from an epidemiologic standpoint. It spread to Calais and then to parts of continental Europe. For 1529, the virologic review notes outbreaks in Netherlands, Flanders, Germany, Denmark, Sweden, Poland, Switzerland, and Russia, among other places. By contrast, France, Italy, and Spain appear rarely, if at all, in the sources reviewed.Chester in 1551The fifth outbreak came during a period of social change in England. The dissolution of the monasteries had reduced the number of institutionalized clergy, the same group that had been heavily affected in earlier epidemics. At the same time, population growth, rising prices, increasing costs for land and food, and growing migration to cities were all reshaping society. While the dissolution of the monasteries does not explain the outbreak itself, it may help account for why, in 1551, clergy were no longer as clearly overrepresented among those affected as they had been in previous epidemics.For Chester, the reports sound dramatic. Mayor Edmund Gee died within a few hours, and 40 citizens are said to have died within a single day and night. Nevertheless, the clinical-historical analysis from 1991 found no clear evidence of a sharp increase in annual mortality. However, the sources remain limited. Burial records could be incomplete during times of crisis, and wills primarily documented wealthy adults.Enterovirus or Hantavirus?Several explanations were examined in the clinical-historical analysis.A fungal toxin hypothesis involving contaminated grain seemed unconvincing because there were no common weather conditions, and contaminated crops would have had to trigger illness over a longer period. Neisseria meningitidis, influenza, arena, and arboviruses were also discussed. Enteroviruses appeared to be the most plausible. They circulate in the summer and fall, are highly infectious, are transmitted via the fecal-oral route, and can cause more severe illness in adults than in children.The virologic review takes a different approach.It focuses on hantaviruses. According to the review, factors supporting this include seasonality, possible ecological triggers following periods of rain, brief local outbreaks, and the similarity to the later Picardian Sweat. The comparison lists headaches, myalgia, sweating, abdominal symptoms, delirium, palpitations, and shortness of breath. However, without evidence of the pathogen, both interpretations remain hypothetical.Picardian SweatPicardian Sweat emerged much later. Heyman and colleagues dated its onset to the year 1718 in France and cited 196 localized outbreaks extending into the 19th century.The disease was generally milder than English Sweat but also featured fever and profuse sweating. Unlike English Sweat, it was more frequently associated with skin manifestations and tended to last 10-14 days.It is precisely these similarities and differences that make the comparison intriguing. According to the compiled reports, Picardian Sweat was more rural in nature, more localized, and less fatal. Observations of rodents following floods and of illnesses among people who slept close to the ground support Heyman and colleagues’ idea of a zoonotic, possibly hantaviral disease. For Sudor Anglicus, this hypothesis is less directly supported. Later, clearly documented hantavirus infections in the UK are rare.What Retrospective Studies ContributeMedically, Sudor Anglicus is fascinating because it defies familiar ways of thinking. It was not the plague, not classical influenza, not typhus, and not typical food poisoning — at least according to the criteria discussed. It exhibited extreme acuity, a striking seasonality, an unusual social and geographic distribution, and an abrupt disappearance.Retrospective diagnoses remain tricky. The sources consist of chronicles, medical treatises, burial records, and wills. They provide only an incomplete picture of symptoms, deaths, and social groups. For this reason, Sudor Anglicus remains more than just a mystery regarding its causative agent. It illustrates how uncertain medical interpretation becomes when clinical observations have been handed down but biological evidence is lacking.This story was translated from Univadis Germany, part of the Medscape Professional Network.