Keys has a great chapter about Justinian's plague in his book Catastrophe.

He subscribes to the theory that that plague in particular came from Africa, but the concept is the same. Basically, plague (Y. pestis) exists in several natural "reservoirs" around the world. These reservoirs consist of rodents such as wild gerbils that are: a) highly resistant to the effects of Y. pestis but nonetheless propagate the disease and b) are solitary and do not often come into contact with other susceptible rodents and/or primates.

The spreading of the disease of course comes from the fleas, who become infected when they feed on the infected members of the reservoir. Worse, the effect of the plague on fleas is that they can't process food properly, so they panic and feed on everything in sight, hastening the spread of the disease.

So how do outbreaks happen? Well, during periods of extreme weather, the territory of these reservoir gerbils (or whatever) can be pushed into new areas. This may cause the spread of the disease to a more invasive species, like the black rat. Rats have no problem infringing on human living spaces, so when rats hitch a ride along trade routes, such as with goods coming from Africa to the Byzantine Empire during the time of Justinian, you see the spread of the disease to areas other than the source of the plague reservoirs themselves. To make matters worse, Justinian was working to reconquer the lost Western Roman Empire, and also dealing with the Persians under Khusrau at the same time, so that particular plague spread to those areas, too.

Note that it seems Justinian's plague did in fact affect African port cities along the trade route, as well. I am less certain about the effects on China that the Black Death plague had, but this is nonetheless a relevant counterpart.

Edit: clarity

Hello everyone,

In this thread, there have been a large number of incorrect, speculative, or otherwise disallowed comments, and as such, they were removed by the mod-team. Please, before you attempt answer the question, keep in mind our rules concerning in-depth and comprehensive responses. Answers that do not meet the standards we ask for will be removed.

Additionally, it is unfair to the OP to further derail this thread with off topic conversation, so if anyone has further questions or concerns, I would ask that they be directed to modmail, or a META thread. Thank you!

Follow up question: what do we know about the black plague in China? Are there any written records? Did it originate in China or did it spread from somewhere else and get a foothold in China? Is there any evidence to support the theory of multiple plague outbreaks over the years, as mentioned by a poster in this thread?

During the Late Yuan and Early Ming there were a series of catastrophic epidemics that struck China, their severity being what you might imagine given that the Yellow and Yangtze River valleys were perhaps the mostly densely inhabited areas in the world. These plagues started at roughly the same time as the Black Death in Europe, 1344 for China and 1346 for Europe, but it is uncertain whether they were struck by the same disease. One problem with asserting these are the same is that they occur too closely together, and it is doubtful whether a disease could travel between China and Europe in two years given the speed at which it later spread through Europe.

One problem you will have here is that plague studies in general tend to have a particularly unfortunate noise to signal ratio. I don't mean to cast academic stones, but it isn't unusual for doctors or medical scientists to do hobby diagnoses of historical diseases without really having the background in source analysis needed. For example, in my particular area, hobby diagnoses of the Plague of Athens are thick as fleas on a plague bearing rat.

My source is Timothy Brooks' The Troubled Empire, which is about the Yuan and Ming Dynasties.

It is not China, but I can speak to Egypt and the Caliphate during this time: There was a pretty profound impact, especially in Egypt, where the trade routes were amongst the most well-connected. Physicians writing at the time described the plague and its impact fairly graphically. However, the death toll was not as extreme as it was in Europe. This is probably due to several factors, such as better medical care (the Islamic physicians borrowed methods of inoculation from India and China which included inhaling dried scabs of plague victims, for example), and because such plagues hit trade hubs fairly regularly. This latter means that many who did not die of it were either survivors of smaller resurgences, or the descendants of those who did.

Source: Islam: From the Prophet Muhammad To The Capture of Constantinople Vol 1 and Vol 2 by Bernard Lewis

A History of Immunology by Arthur Silverstein

I have an unpublished source on this, that references several published Chinese sources. Here is a Summary:

There was a significant population drop (>30%) between 1200-1368 in China. The first area hit was the north, with the Song-Yuan transition, and the second the south during the Yuan-Ming transition. War and migration do not in themselves explain the significance of the fall.
The Song-Yuan drop in population was likely not as large as previously thought, as losses in the north were offset by gains in the south, and the rest of the civic structures and cultural output do not reflect such a major loss in population. But the Yuan-Ming drop seems to be far more powerful and lasting in effect. Some evidence surrounding this claim:

1. The bureaucratic reach and control of the early Ming was significantly greater than either of its predecessors - the Yuan and Song. The author suggests that one rational explanation is that the Ming were dealing with a much smaller base population (67million vs 100-120million), and so control was simply easier.
2. Cultural output, measured in the article by book printing (measured through surviving books), and development of new academies and monasteries were all significantly lower than the Yuan. This lower output lasted for about 150 years, after which the population recovered enough to fuel what William Rowe calls China's second commercial revolution of the late Ming.
3. This all jives with the significant records of population loss and epidemic of the late Yuan/early Ming to suggest that the theory of a bubonic plague epidemic in China between 1331-1353 is reasonable and rational.

What we lack is further evidence.

If this is out of place, I apologize and won't do this again. Are there any good book recommendations about the Plague, that really delve into the event from different angles (social, medical, political, or however)?

EDIT: Suggestions don't have to focus on China, although that would be cool too. I was thinking from a contemporary perspective. And I'll check out The Decameron. Thank you.

Thanks again, to everyone!

fyi, you'll find a few more comments here

• Why did the Bubonic Plague not strike places like China and India where populations were obviously dense and in contact with the rest of Europe?

• Were there plagues in China or India as there were in Western Europe in medieval times?

Most history classes, especially in the west, tend to focus on what white people were doing because that's the most interesting to the old white guys that write textbooks. That's the most honest answer, even if not the most politically correct around reddit.