The correct answer to this open question is the following.
Although the question does not provide any context, time, or date, we can say that the diseases that were spreading amongst the migrant farmers were infectious diseases and parasites in their digestive tracks. These impacted their already poor health due to starvation in that their immunology systems were weak. Lack of proper nutrition, lack of sleep, and the work they did all day long made them week individuals whose life span was limited to 49 years, instead of the 75 years average or other people who lived in different conditions.