Deadliest viruses by total deaths
The history of humans can be seen as a continuous battle for survival against microbes that have the ability to evolve much more quickly than us. In ancient times, the human population was not large enough for pandemics to occur. Changes in farming methods and agriculture, as well as increasing population densities and the formation of cities, contributed to the spread of viruses. Since then, infectious attacks have regularly changed the course of history. Below are four deadly viruses that have had a large impact on history.
Smallpox
Smallpox emerged around 10,000 BC and has been one of the most devastating human diseases throughout history. The highly contagious disease, caused by infection with variola virus, has led to various disastrous epidemics, starting in ancient Egypt and moving on to India, China, and Europe. Voyages from Europe to the New World introduced the virus there too, devastating native American populations. Estimates indicate fatality rates of 80-90% during epidemics. The disease also killed around 50% of the native population of Australia during the early years of British colonisation, making it the principal cause of death in Aboriginal populations between 1780 and 1870.
It is estimated that smallpox was responsible for 300-500 million deaths during the 20th century. In 1796 Edward Jenner developed the first vaccine for smallpox and after successful vaccination campaigns the WHO certified the eradication of smallpox in 1979.
Measles
The Persian physician Rhazes (860-932 AD) was the first to give a scientific description of measles. Historically, this highly contagious disease was prevalent throughout the world, causing many millions of deaths. The Antonine plague from 165-180 AD was probably caused by measles (or smallpox) brought back to the Roman Empire by troops returning from the Near East. The total death rate has been estimated at five million. Even today, with safe and cost effective vaccines available, measles is one of the leading causes of death among young children. The WHO reports that there were 158,000 deaths from measles in 2011.
Spanish flu
The 1918 pandemic infected a third of the world’s population and caused 100 million deaths worldwide, many more than the 20 million who died in the first world war. Unusually, this flu mostly killed young adults. This is thought to be because the virus killed by a “cytokine storm”—an immune overreaction—meaning that it was deadliest in those with the strongest immune systems. The virus crossed the globe before vanishing completely within 18 months. Around the time of the flu pandemic children would skip rope to the rhyme:
I had a little bird,
And its name was Enza.
I opened the window,
And in-flu-enza.
Yellow fever
This acute haemorrhagic disease has caused several devastating epidemics in the past, including those in the United States and Spain during the 18th and 19th century (president George Washington fled from Philadelphia, together with about half of the residents, during one of the largest epidemics of yellow fever, which killed around 10% of the population). The virus is not eradicated yet; there are an estimated 200,000 cases of yellow fever worldwide, killing 30,000 people each year.