And There is Even More to it Than That!

If the change in global temperature brings more rain to an area than it is used to, as happened in Western Europe during the Middle Ages, then it also means plant disease can increase and that in turn can increase the devastation caused by human disease. For example, during the Late Middle Ages, a postharvest disease caused by a fungus called Fusarium is believed to have increased the deaths caused by the bubonic plague in areas with increased rain.

Generally this fungus contaminates the seeds either before they are harvested or at the time of harvest. This fungus then grows within the seed during storage. For this fungus to continue to grow it requires a high moisture content in the seeds. Today most grain is stored at a moisture content of 12-14% which is too low for the fungi to grow and the fungi die after a few months in storage and do not infect other seeds. However during the Late Middle Ages, the people had neither the technology nor the knowledge to store grain at this moisture content. During the 13 and 1400’s the moisture content of harvested grain was at the mercy of the weather. Because the weather was moist during this time the moisture content in the seeds must have been high. The fungi in contaminated seed would have continued to grow under these conditions and would have infected other seeds.

As the fungus grows within a seed it not only causes decay of the seed but it also produces substances called mycotoxins. The ingestion of moldy grain containing these toxins can lead to a disease whose symptoms include necrosis of the skin, hemorrhage, liver and kidney damage, and death. Fusarium molds produce a number of mycotoxins. These toxins in both lethal and sublethal doses not only cause the above symptoms but they can also cause an immune deficiency. The toxins attack the lymphoid cells critical for the body’s defense against infection.

According to Mary Kilbourne Matossian in her book Poisons of the Past, the highest moralities of the plague during the late Middle Ages occurred in areas where surplus grain was stored (thus there would also be a surplus of rats) and with the incidence of high humidity, rain, and flooding.

“For two years prior to the pandemic of 1348 in Europe the weather was extraordinary rainy and humid and crops were poor. The summer of 1348 was exceptionally wet in England, where the plague began its ravage; on the other hand it was not so wet in Scotland that year and the plague did not spread widely there until the wet summer of 1350.

The coldest and driest regions were untouched by plaque during the pandemic. Iceland, northern Norway and Sweden, Finland and large areas of Russia and the Balkans escaped the blight. So did the mountainous and desert areas of the Near East.”

Mary K. Matossian

Knowing that toxin producing fungi like Fusarium flourish in moist conditions, Matossian speculates that the ingestion of moldy grain by the rats markedly increased the mortality of rats thus increasing the likelihood that the rat flea would move to other animals including humans. (The mortality of horses, cattle, sheep and goats was exceptionally high during the wet period between 1345 and 1350). In addition, the humans were eating bread made with the moldy toxin-infested grain. The ingestion of mycotoxins would have compromised their immune system making them more likely to die when exposed to the plague pathogen. Thus, the increased mortality rates in some places most likely can be explained by a combination of the virulence of Yersinia pesti, the bacteria that causes disease known as the Black Death, and immune deficiencies caused by mycotoxin food-poisoning in both rats and humans

“Man does not live by bread alone - but he must have bread. And he must have bread that is truly the staff of life, not a scepter of death.”

Mary K. Matossian

Next Post: The Rats, the Flea and the Weather