Also: Sweating sickness, sudor anglicus, febris ephemera britannica.

A mysterious epidemic disease that erupted suddenly in England in 1485 and disappeared entirely after 1551.

The Sweate appeared first in the army of Henry Tudor (later Henry VII). After the battle of Bosworth Field, Henry's soldiers, returning home, spread it to London and the countryside. The epidemic subsided the following year, but the disease returned in 1508, 1517, 1528 (when it spread to continental Europe), and 1551.

Except for the 1528 pandemic, the sweating sickness was restricted to the borders of England itself -- Wales and Scotland were spared. It reportedly even passed over foreigners in England and attacked Englishmen across the channel in Calais.

Victims suffered pain in the head and chest, sometimes with rashes. A fever brought the furious sweating. Death came very quickly, sometimes within hours. Modern attempts to identify the disease have come up variously with typhus, influenza, scarlet fever, and, most sensationally (and improbably), a hanta virus1. Parallels have also been noted with the Picardy Sweat, a French epidemic of the 18th century. As with many epidemics of the more distant past, the vague descriptions that survive2 support any number of speculative diagnoses but no single definitive one.

Whatever its identity, the microbe's strange anglophilia suggests that it was endemic in parts of Europe but not in England: This would explain its devastating effect in that country and the resistance of foreigners. In this scenario, Henry's French mercenaries are identified as the carriers.

The sweating sickness may have been responsible for the death of Henry VIII's elder brother Arthur in 1502 (and therefore the accession of Henry himself). Henry is said to have made a point of leaving the vicinity immediately whenever a case was reported nearby.

1 See, e.g.,
2 The most-cited account of the disease is the contemporary one of John Caius, who in 1552 published A Boke or Counseill Against the Disease Commonly Called the Sweate, or Sweatyng Sicknesse. I haven't been able to find a publicly-accessible copy on-line; if you find one, please let me know.

Zinsser, Hans, Rats, Lice and History, 1934.
McNeill, William H., Plagues and Peoples, 1977.
Conrad et al., The Western Medical Tradition, 800BC to AD 1800, 1995.