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Microbial keratitis is an old disease and is not limited to humans, but we have a unique ability to change its prevalence and epidemiology, unlike other animals.
Ten to eight thousand years ago, we were a hunter-gatherer species with an average life span of 20–30 years.1 Trauma was likely to be the principal cause of keratitis, with soil-based bacterial and fungal agents the main pathogens. Societies were mostly tribal and contact with other tribal groups was infrequent and often violent.
Eight to four thousand years ago as we began congregating in villages and becoming more agrarian, lifespan increased slightly, and community organisation improved. The domestication of animals contributed to these improvements. Animals would be valuable, and value would mean close contact. Domesticated animals would be so important and valuable, in fact, some would be kept in the home or at least in holding pens very close to the home to prevent theft and predation. With those changes, though, came zoonotic and communicable diseases. The rise of diseases such as smallpox,2 leprosy and probably trachoma would have become a major societal problem and keratitis a consequence. Personal hygiene would have been difficult and probably deemed unnecessary, or at best limited. Infectious microbial keratitis would have increased in prevalence with new pathogens to complement the older pathogens. Village settlements in certain areas, perhaps where rich soils would increase yields, might provide opportunities for odd and often very local organisms, such as onchocerciasis. Viral agents such as the herpes viruses, measles and smallpox would be provided the opportunity to colonise, infect and spread further.
Four to two thousand years ago as trade and travel increased, epidemics of contagious diseases may have wiped out some of these isolated communities as plagues such …