Viruses, bacteria and parasites have killed more human beings than anything else in the history. Throughout history more people were killed by diseases caused by infectious diseases than earthquakes or volcanoes. Not even wars have killed more people.
Malaria, a mosquito-borne disease has stalked humanity for thousands of years. Over the past 2o years, death tolls have dropped, but nearly half a million people are still killed every year by this mosquito-borne disease.
- The plague of Justinian struck in the 6th Century and killed as many as 50 million people.
- Some 50 to 100 million people died in the 1918 influenza pandemic – numbers that surpass the death toll of World War One, which was being fought at the same time.
- The 1918 flu virus infected one in every three people on the planet.
- HIV has killed an estimated 32 million people and infected 75 million, with more added every day.
In the not so distant past, epidemics were a terrible fact of life. but they are rarely discssed in history class.
Pathogens make such effective mass killers because they are self-replicating. This sets them apart from other major threats to humanity. Each bullet that kills in a war must be fired and must find its target. Most natural disasters are constrained by area: an earthquake that strikes in China can’t directly hurt you in the UK.
But when a virus – like the novel coronavirus – infects a host, that host becomes a cellular factory to manufacture more viruses. Bacteria, meanwhile, are capable of replicating on their own in the right environment.
The symptoms created by an infectious pathogen – such as sneezing, coughing or bleeding – put it in a position to spread to the next host, and the next, a contagiousness captured in the replication number, or “R0” of a pathogen, or how many susceptible people one sick person can infect. And because human beings move around – interacting with other human beings as they do so in every manner from a handshake to sexual intercourse – they move the microbes with them.
Global life expectancy was just 29 at the beginning of the 19th Century. this is because so many people used to be killed in infancy from disease, or from infection.
Sanitation, vaccines and antibodies changed all that. Thy helped us defeat pathogens, and we have been able to create modern world and big cities.
In the developed world, people are more likely to die from cancer, heart disease or any other non-communicable disease than from infection. This trend is catching up even in the developing countries.
The decline of infectious disease is the best evidence that life on this planet truly is getting better.
It has been reported defeat of infectious diseases have brought us from around 800 deaths from infectious disease per 100,000 people in 1900 to about 60 deaths per 100,000 by the last years of the century.
That’s the good news. The bad news, as Covid-19 reminds us, is that infectious diseases haven’t vanished. In fact, there are more new ones now than ever: the number of new infectious diseases like Sars, HIV and Covid-19 has increased by nearly fourfold over the past century. Since 1980 alone, the number of outbreaks per year has more than tripled.
Why Human Beings are still getting Infected
There are several reasons for this uptick. For one, over the past 50 years, we’ve more than doubled the number of people on the planet. This means more human beings to get infected and in turn to infect others, especially in densely populated cities. We also have more livestock now than we did over the last 10,000 years of domestication up to 1960 combined, and viruses can leap from those animals to us.
As Covid-19 is painfully demonstrating, our interconnected global economy both helps spread new infectious diseases – and, with its long supply chains, is uniquely vulnerable to the disruption that they can cause. The ability to get to nearly any spot in the world in 20 hours or fewer, and pack a virus along with our carry-on luggage, allows new diseases to emerge and to grow when they might have died out in the past.
This is an abridged version of a long Article, Covid-19: The history of pandemics, published on the BBC World’s website.