Plague, also known as the Black Death, was a highly contagious disease that had killed hundreds of millions of people over the past millennium, and in the worst of the Middle Ages, the Black Death had killed a third of Europe's population. But in fact, the plague has not been eradicated, and their crisis is still buried on the earth.
Like many other conditions, the causative agent of plague is Y. pestis, a very fragile bacterium that dies quickly if exposed to the environment without protection. Still, plague outbreaks are resurgent in more than 30 countries around the world. For example, in October 2017, plague broke out in Madagascar.
Plague has caused three deadly global pandemics. Between 541 and 750, in the Eastern Roman Byzantine Empire under Justinian the Great, millions of people died as a result of the raging plague. This was followed by the period from 1330 to 1480. The infamous Black Death ravaged much of Asia and Europe, with about 30 percent of Europe dying as a result of the Black Death, followed by the Black Death ravaging Europe for hundreds of years. Subsequently, the plague broke out in Hong Kong at the end of the 19th century and spread across the globe, killing about 12 million people in a century.
Hundreds of years later, in the 21st century, it can still erupt, suggesting that Y. pestis was able to find refuge on Earth and survive for years, then suddenly reappear at some point, beginning another cycle of infection, understanding what they were hiding and how they survived was important for humans to control their outbreaks. Colorado State University's Center for Infectious Disease Research suggests that amoeba, a microbe commonly found in soils and water sources, may have played a role in protecting the killer and giving them the chance to make a comeback.
Amoeba are a single-celled microbe that lives widely around the globe and feeds on bacteria, but scientists have found that some bacteria resist being digested by amoeba. Their study notes that several plague bacillus engulfed by the amoeba are still alive in the amoeba and can replicate themselves, which allows it to survive replication under adverse environmental conditions. Even if the amoeba dormant for many years, they can continue to live in the amoeba, which may explain why plague can circulate for thousands of years and continue to erupt.
Amoeba can not only act as a transport ship for pathogens, infecting bacteria with new hosts. Some scientists believe that amoeba can guide harmless bacteria to evolve into dangerous pathogens. The reason behind this is that amoeba are very similar to macrophages, which are responsible for finding and killing invading bacteria in mammals' immune systems. If harmless soil bacteria can survive and multiply in amoeba, they can also evade the immune system and thus become new human pathogens.
The study shows that even if public health services are well done today, amoeba can still be a serious public health threat, releasing not only dangerous Y. pestis, but also more dangerous pathogens. Since we currently have no way to effectively monitor and predict them, this makes some epidemic infectious disease outbreaks elusive. This may be a time bomb in the contemporary environment.