Answer :
Thucydides
During the Peloponnesian War, the first record of a pandemic by Thucydides was written. This epidemic expanded into the regions of Athens and beyond in 430 BC. The disease is thought to have emerged in the sea. (At port Pireo), the source of food and supplies.
In the midst of a war between Athens and Sparta, Thucydides relates the spread of an unknown disease that is believed to have originated in Ethiopia, crossing Libina and entering the "civilized world". Sparta, as well as other cities in the Mediterranean later, were affected and this resulted in huge human losses.
Thucydides states the enourmous social changes that were caused in an era where there was little knowledge on biology and medicine. Many of his stories describe the social change, the relgious changes and also the impact on demographics in the ancient world.