Before the 20th century, the plague caused by rats was the recurring pandemic (there had been other pandemics though like cholera and small pox). There had been three big plague pandemics, the last being in the late 19th century. And rats were seen as responsible for the plague and they had spread it by travelling on ships.
In the last 100 years, flu became the new plague. Although the first influenza epidemic is recorded in the 16th century, the flu became pandemic from the time of the 1889-90 flu, now called the Russian flu. The Spanish Flu of 1918-19 was the most damaging as it infected a third of the entire population of the world with more people dying from it than from World War 1. Then followed the Asian Flu of 1957-58, the Hong Kong Flu of 1968-69 and, more recently, the Swine Flu of 2009-10, which ended up infecting more than a billion people and killing a few lakhs.
In the last 50 years, there has been another interesting pattern: pandemics originating in bats. It started in 1976 with Ebola, which ravaged West Africa and killed 13,500 people; the Nipah virus of 1998 with a 78% fatality; and then the Coronaviruses of the last 20 years: SARS of 2002, which spread to 29 countries with 774 deaths; MERS in 2012 that spread to 28 countries resulting in 858 deaths; and of course COVID-19, the pandemic that has devastated the world more than anyone in this world today probably remembers. The coronaviruses are also contagious viruses causing respiratory diseases like the flu. In fact, the Centers for Disease Control and Prevention (CDC) of the US estimates, three quarters of new or emerging diseases that infect humans originate in animals.
Scientists discovered the bat origins of certain viruses after the outbreak of SARS or Severe Acute Respiratory Syndrome in 2003. It was discovered that bats contain hundreds of other coronaviruses, a group of related viruses causing respiratory ailments ranging from harmless ones like the common cold to MERS that had a fatality rate of 34%. As they grow, (COVID-19 is a novel coronavirus or a new strain of the virus), the different strains infect bats, which seem to be co-evolving with the viruses. Hence, bats have powerful immune systems and do not fall sick. But when these viruses jump from them to other species such as a civet or a pangolin or a human, the result can be deadly, as we see now.
Bats play a significant role in the transmission of coronaviruses like COVID-19 as bats are special in their ability to harbour viruses that are zoonotic, i.e., that can jump from animals to humans. Bats are even better than rats, who also host a huge number of such viruses. The reason for this is generally attributed to the ability of bats to fly, the only mammals to do so and to their long lifespan for their body size as that helps in their resistance to chronic infections. And the danger of future pandemics of bat origin continues to loom large. As Richard Ostfeld says, “Rats and bats thrive when we disrupt natural habitats. They are the most likely to promote transmissions (of pathogens). The more we disturb the forests and habitats, the more danger we are in.”
David Quammen, the author of Spillover: Animal Infections and the Next Pandemic, gives us the reason. “We cut the trees; we kill the animals or cage them and send them to markets. We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.”
Also Read: Pandemics In History 1: ‘Shipping’ The Virus
Also Read: Pandemics In History 2: Rats And The Plague
