The Foreign Curse, Written and Researched by Tabitha Alba is a book found in Dishonored 2.
The Great Rat Plague. The Spreading Death. The Foreign Curse. These are names we give to the disease that bloomed briefly, taking tens of thousands of lives as it spread across Gristol from home to home, town to town, preferring neither rich nor poor. The capital city of Dunwall suffered the most, settled so thickly by both people and rats.
Many feared the plague would spread to Serkonos, but even beyond the naval blockade effected at the time, several factors kept the sickness from reaching our shores.
First, in Serkonos, the population of disease-carrying rats was kept in check by bloodflies. Natural enemies, rats are known to feed on bloodfly larvae, and fully mature bloodflies lay their eggs in rats. Second, it is simply true that Serkonans are healthier than most. With the best foods, morning constitutionals, and a strong work ethic, we have some immunity to diseases that afflict less vibrant folk. Lastly, mining dust was found in trace amounts in Serkonans even during the time of Dunwall's great crisis, and that dust played a critical role. It's true that the plague was spread by rats, but some natural philosophers now believe that it was also carried on wind currents. As such, we can be thankful that in addition to bringing us wealth from the silver, the mines also protected us from the greatest plague in living memory.