We tend to imagine that plague was constantly ravaging medieval Europe, perhaps due to clever parodies like “Bring out your dead!” in Monty Python and the Holy Grail. But most of the time, sickness followed predictable patterns and wasn’t out of control.
Infectious diseases could be chronic, more or less constant, like leprosy and tuberculosis. Modern medical knowledge tells us that leprosy and tuberculosis are both bacterial infections spread by nasal droplets from coughing and sneezing. Leprosy is also spread by armadillos, but armadillos weren’t a big factor in medieval Europe, in fact it’s safe to say that no armadillos had ever been near medieval Europe. People sneezed on each other, wiped their noses on their sleeves, and otherwise had no consciousness of the role of the nose in spreading disease.
Tuberculosis and leprosy tended to infect some of the population most of the time, rather than coming in short-term epidemics. Most people are immune to leprosy and many people fight off tuberculosis infections. These diseases were always in the background of medieval life, attacking people with vulnerable immune systems. They were a normal part of life, the way many cancers are today. We’re afraid of cancer, but when half of us have survived some kind of cancer treatment, it’s become a household problem.
Other infectious diseases came in waves of epidemic. Smallpox came to Europe from Asia, with returning Crusaders. It spread during the 12th century. Measles and St. Anthony’s Fire, which may sometimes have been shingles but sometimes described a more dangerous and painful skin affliction, came in epidemics.
They also had epidemics of intestinal-borne bacteria: diphtheria, cholera and dysentery. All sewage was more or less open to flies, since pit toilets at the back of a yard were the best sanitation they could manage. When the infectious bacteria of these three deadly diseases began to breed, many people got sick within a short time. Weather conditions almost certainly influenced the sewage-based epidemics. Heavy or frequent rain kept pit toilets from drying out or allowed sewage to flood into drinking water.
Malaria was another epidemic related to weather. Chronic rain and wet kept mosquito populations high. Of course, transmission had not been traced to insects yet, so they weren’t aware that standing water was the main issue. During the 13th century, many people dug chains of fish ponds all over France, Germany and even Poland. They were growing carp, a warm-water fish that moved up the Danube during the Warm Period, for fast-day castle and monastery tables. Malaria became a common illness near fish ponds and during wet years.
Leading up to the 1348 plague, the early 1300s were very cool and wet. Between 1304 and 1317, crops failed more often than not. 1315 began the harshest period of famine. Fields were flooded, dikes in the Netherlands failed. Seed rotted. Children were abandoned. By the time the food supply had recovered, about ten years later, between 10% and 25% of the population had died either directly from famine or indirectly from disease in a malnourished state.
The survivors of the famine period were not in good condition. They had been exposed to disease and depleted of fat and vitamin stores. They were also the adult population alive to face the plague when it struck in 1347-1350. Adults aged 30-40 had been born during famine years; they had been underfed during their childhoods. Their immune systems were poor, although they had survived contact with many diseases. Lean, short and often frail, they were not prepared for the greatest challenge faced in several centuries.