I've been looking into pandemics that predate the Black Death and in general have only found European ones. The Athenian plague, the Antonine plague, Cyrian plague, the Plague of Justinian etc.
Most of these are mysteriously described as having come from the East or from North Africa/Middle East via India/China but I've been unable to find anything on the origins of these epidemics. Are the sources there but just not well known or are there no sources?
I'm 2 months late to the show here, but Michael W Dols's "Plague in Early Islamic History" describes the effect of the Plague of Justinian on the early Islamic Empire, and talks about how it affected population growth and society during the Umayyad period. In it, he examines many plague treatises written at the time. Dols also did a lot of great work in regards to the Black Death in the Middle East. Primary sources, though, are pretty hard to come by for this period.