What are the causes of the epidemics and how did people fight them?

An epidemic is an excess of an indicator (epidemic threshold) of a disease in a certain area. The onset of the disease (cause) may be a virus, bacteria, lack or excess of a substance in the body. For example, the most common epidemics: flu, tuberculosis, scurvy. To fight the epidemic, people acted on the source (cause), stopped the pathways of infection and destroyed the transmission mechanisms. The source is affected by antibiotics, antiviral drugs. On the ways and mechanisms of transmission: hand washing, personal hygiene, isolation of the patient and quarantines, masks and filters, sterile medical instruments, replenishment of the missing substance with food (fortification of dishes, iodization of salt).