A disease called sweating sickness killed thousands of people — then disappeared

Death and illness have never been strangers to humanity. But for a brief time around the 1500s, there was one particular ailment that was both brutal in its devastation and completely undecipherable to medical practitioners of the time. This malady was known as sweating sickness, and even today, scientists don’t know where it came from, why it seemed to suddenly leave, and whether it could ever return again.

Much of what we know about sweating sickness comes from the writings of British physician John Caius, who was at ground zero of the last big outbreak that occurred in Shrewsbury, England in 1551. It’s now thought that there were at least five major sweating sickness epidemics throughout England and some parts of Europe, with the first recorded in 1485. Some researchers have also argued that two smaller outbreaks may have occurred in 1578 and 1802.

Killer sweats

The intense episodes of perspiration that victims experienced obviously gave rise to the disease’s name, which was also known as the sweats. But the sweating was commonly preceded by chills, headaches, severe exhaustion, and pain around the limbs and shoulders. One striking feature was how rapidly people fell ill, with the sweats seeming to arrive within hours of the first symptoms.

All but one of the documented epidemics had high mortality rates, with as many as 50% of victims dying. If people made it through the first day of sweating, they would typically survive, but even this wasn’t a complete reprieve, since some people were unfortunate enough to catch it multiple times. The disease did seem to have its limitations, as outbreaks often swept across a region and ended within a few weeks.

Adding to the mystery is that outbreaks of sweating also showed up throughout France in the 18th and 19th century, which came to be blamed on a disease called Picardy sweat. The original outbreaks of sweating sickness never reached this region of Europe, and the described symptoms of Picardy sweat don’t completely align with sweating sickness, tending to be milder and commonly featuring a rash that could last up to a week. So it’s not clear if the two illnesses are even related.

Origins debated

It would take centuries more for scientists to widely accept the existence of microorganisms and that they could cause contagious illnesses like sweating sickness (Caius, for his part, assumed that filth was responsible for it). But though we’ve been able to concretely tie many epidemics of the past to now-known germs like plague, typhus, and influenza, the identities of sweating sickness and Picardy sweat have eluded us to this day.

Scientists have posited a wide array of potential culprits for the sweats. These include species of Borrelia bacteria spread by ticks and lice that can cause relapsing fever, hantaviruses (typically spread by rodents), and even an inhaled form of the bacterial disease anthrax. But the established description of the sweats, particularly its rapidly worsening progression and quick disappearing act from an afflicted area, doesn’t quite match any one germ—at least not enough to declare an open-and-shut case based on circumstantial evidence alone.

In a 2022 paper, virologist Antoinette C. van der Kuyl speculated about another possible suspect: an unknown species of rhabdovirus, part of the same broad family that the rabies virus belongs to. Van der Kuyl also offered a potential way to definitively solve the mystery of sweating sickness.

Digging up the dead?

She noted that Caius’s description of the 1551 outbreak blamed sweating sickness for the deaths of the 15-year-old Duke of Suffolk, Henry Brandon, and his younger brother Charles. Since their graves are still around today, their “remains could possibly be subjected to ancient DNA analysis,” she wrote. But even if such an excavation could be carried out right now, it might not be smart to do it just yet. According to van der Kuyl, current techniques aren’t optimized enough to effectively analyze ancient samples of RNA viruses from bone and teeth—including most but not necessarily all potential rhabdoviruses that might be lingering within the bodies of the Brandon brothers.

For now, the origins of sweating sickness remain a mystery, leaving scientists and medical historians with much to ponder. Hopefully, sweating sickness will remain a historical curiosity and never become a contemporary health threat. The recent covid-19 pandemic has certainly shown us that infectious diseases continue to be a danger even in the era of modern medicine. The last thing we need is the reemergence of a fast-killing mystery sickness from the past.

More: Mysterious Disease Outbreaks That Were Never Solved

A version of this article originally appeared on Gizmodo.