This is an interesting subject. This is an always problem both Russian and Soviet army's have faced. Those areas have those water borne diseases in the swamps and soils, those diseases affect the populations of those areas all the time.
It plagued Baba Vanga's husband during his WWII service, and was in part a cause of his death at a young age despite him surviving the war, his health was ruined. The reason I brought it up Baba Vanga was a legendary soothsayer. There's a long film about here and this issue is a large part of her story. This film will show you a lot about the peasant life in the rural areas in Bugara where she was.
A lot about the culture of the bottom end of wealth, a lot about the Russian Orthodox Church.
For the year that the large Russian nuclear sub was lost at sea, she had predicted a horrible drowning of many people in Kursk, it turns out that the city Kursk wasn't were the drowning of so many occured, her prediction was misunderstood, that nuclear sub was also named Kursk.
There are also scores of video's like these about her predictions for the future. She's been dead for quite a while but one of her predictions which is coming up, is that she predicts the assassination of Putin. I don't know if the example video I'm posting has that in it. I didn't watch the video, I was posting it as an example of a type of video, and the cover shows what she looked like toward the end of her life.