In 542 AD an epidemic of plague struck Constantinople (now Istanbul...

In 542 AD an epidemic of plague struck Constantinople (now Istanbul, Turkey) and killed half of the population. In 1347, one of the most disastrous plague burst out in Europe which killed 40,000,000 people - about a fourth of the European population at that time. This pandemic plague is called Black Death in history. In 1800's a third epidemic appeared suddenly in China and spread like a fire. It killed more than 20 million people.

Scientists have tried to guess some of the probable causes of these epidemics but are puzzled by their mystified origin. For instance, they can not answer such…