OK, so this is a bit of a trick question but, how old do you think is the earliest piece of evidence is that shows the presence of mosquitoes that could lead to malaria? The answer is in the tomb of Tutankhamun as research and scientific analysis has shown the presence of parasites preserved in the tomb that had the DNA that would ultimately lead to the development of malaria.
Of course, the disease itself will go back even further in time than 3,500 years ago, but this is undoubtedly the first piece of evidence that archaeologists have come across that can be verified. However, malaria was not the cause of death in the case of the Pharaoh.