Over the years, scientists have been trying to find one particular reason for the abrupt disappearance of the Indus Valley civilization. But they have not been able to zero in on any such reason apart from the water-borne diseases.
In the book called Germs, Genes and Civilization: How Epidemics Shaped Who We Are Today, the author Dr. David Clark has described the story of the microbe-driven epidemics that have repeatedly molded human destiny for centuries. It was mentioned in the book that Cholera emanated from India and then spread across the world in the past two centuries. But did it affect the world's earliest civilization?
The disease which emerged from the Indian subcontinent
Some evidence suggests that cholera or a closely related water-borne disease infection might have been instrumental in the collapse of the world's oldest civilization which had flourished in sites in today's Pakistan and part of Northern India. But to understand it, understanding of cholera is required.
It should be noted that the victims of cholera suffered severe diarrhea and can die of dehydration if not cared for. This disease is thought to have origins in India and started to affect the world in the 19th century. Even though early physicians in India described cholera around 400 BC, the disease became an epidemic in the Indian subcontinent much earlier.
The disease stayed in India until the early 1800s and during the following century, half a dozen worldwide pandemic erupted. In 1817, cholera made its mark from the western to the Middle East and Southern Russia as well as in Malay, Thailand, and Japan. The disease reaches England in 1831 and then North America. During the Crimean War from 1854 to 1856, cholera killed 250,000 soldiers from the British regime and around 20,000 soldiers from the allies.
In 1832, investigators noticed a cholera outbreak at Killingworth Colliery near Newcastle in England and they concluded that the disease was carried by bad air or passed directly from person to person. Then the investigator, John Snow blamed constant diarrhea, unwashed hands, and shared food.
The collapse of Indus Valley civilization
It flourished from about 3,000 BC to 2,000 BC and was located around the Indus and Saraswati Rivers. The two ancient cities of this civilization Harappa and Mohenjo-Daro are now in Southern Pakistan. It was estimated that Mohenjo-Daro had around 30,000 to 100,000 population. More relevant to any kind of infectious disease, like today's Coronavirus, several towns of various sizes were located in the region, resulting in a large population, all in a reasonable contact.
It should be mentioned that Indus Valley towns were known for its well-designed streets, houses and drainage system. But its mysterious and sudden collapse left no obvious successor culture.
Around 1900 BC the Saraswati River dried up and its ancient course was rediscovered by scientists in the 1990s using satellite images. As per some of the archaeologists, the changes in the river is responsible for the fall of the Indus Valley civilization. Some of the researchers also relate the collapse with the arrival of the Indo-European invaders from the north. But as per some claims the invaders arrived long after Harappa and Mohenjo-Daro were already abandoned.
The latest archaeological levels of these two ancient cities revealed large numbers of unburied skeletons. Even though it suggested the invasion and conquest, the examination of the skeletons has shown that they don't have marks left by the sword, axes, and other weapons. Since there is no evidence of slaughter, the only alternative is some kind of epidemic.
In this case, it needs to be mentioned that the water distribution system of the cities might have helped to spread waterborne diseases. A similar case was noticed between 1946 and 1977 when the outbreak of waterborne disease documented in the U.S.
The drainage system in Harappa and Mohenjo-Daro was underground. So, whenever these drains backed up due to flood or blockage, there would have been massive contamination of the water supply. During the research, the archaeologists also came to know that latrines connected directly to the drainage system and the presence of wooden mesh baffle for screening out solid waste. But if that is the reason then how they got away with this for a thousand years? The answer is simple- the waterborne diseases had not yet evolved when the Indus Valley cities were built.
As more than a thousand years passed between the Indus Valley collapsed and the earliest description of cholera, other similar diseases caused by bacteria such as Shigella or Salmonella might have affected the ancient inhabitants. Late, when a virulent form of cholera evolved, it would have rapidly spread throughout the Indus Valley cities.