 The social history of viruses describes the influence of viruses and viral infections on human history . Epidemics caused by viruses began when human behaviour changed during the Neolithic period , around 12 @,@ 000 years ago , when humans developed more densely populated agricultural communities . This allowed viruses to spread rapidly and subsequently to become endemic . Viruses of plants and livestock also spread from human populations to their animals and plants. sierpni 2019.
The first documented epidemic of smallpox occurred in the 1st century BC. It was caused by the variola virus , which is still one of the most contagious viruses known. Smallpo