bats are among mammals, which carry the highest number of zoonotic viruses that spread from animals to humans. The Wuhan coronavirus of 2019 is yet another bat-borne virus that has caused an outbreak bearing striking similarities to the Sars outbreak of 2002. The coronavirus pandemic took over eight lakhs lives and infected more than 23 million people, the world over.
The 2002 severe acute respiratory syndrome (Sars) epidemic, caused by another type of coronavirus, also originated in bats. Sars infected more than 8,000 people across the globe, and killed 774 people. The virus jumped from bats to civet cats and then on to humans. For Middle East respiratory syndrome (MERS), also from the coronavirus family of viruses, camels served as the intermediate host.
Wuhan Coronavirus
Abbreviated as nCoV-2019, the Wuhan novel coronavirus is named for the spikes that protrude from the membrane and resemble a crown or the sun’s corona. It is classified as a ‘zoonosis,’ which is a type of disease that spreads from animals to humans. Researchers are of the opinion that this particular strain of virus likely originated in a common species of bats in China, the horseshoe bats. Humans were infected by consuming animals, already infected by these bats. As per Chinese researchers, the endangered pangolin, also known as the scaly anteater, may be the ‘missing link’ between bats and humans.
Another contributing factor for the outbreak is China’s poorly regulated, open-air markets where animals are kept in cages stacked on top of each other, with bodily fluids and secretions mixing, at the time of slaughter and selling. Initially, more than 49 of the 99 patients were related to one such market in Wuhan.
It soon spread to other parts of the world due to the availability and frequency of cheap air and rail travel, and dense urban settlements.
Bats: Carrier of Viruses
According to researchers, bats around the world carry at least 200 types of coronaviruses. They are also natural carriers of Marburg, Hendra, Nipah, Ebola, and rabies viruses. There was a Nipah outbreak in Kerala, which originated in fruit bats in 2018.
Bats host several viruses without getting sick due to their unique immune system. Over time, bats adapted the ability to fly because of changes to their immune system. The energy demands of flight cause cells in bats’ bodies to break down and release pieces of DNA. Bats have ‘weakened’ immune systems, which would normally cause inflammation in such instances so as not to mistake these pieces of DNA as disease-causing organisms. Due to a weakened immune response, bats can tolerate viruses more than other mammals and do not overreact to their presence in its body.
Another factor is their large population across the world. One-fourth of all mammals are bats, found on every continent except Antarctica. Coupled with the ability to fly and live for 20-40 years they are capable of spreading viruses much farther than other land mammals. Bats are also eaten in some parts of the world like China, and are often sold in open livestock markets.
Major Outbreaks
In China, three major virus outbreaks have occurred. A variety of climates and biodiversity in China help many species of bats thrive. Researchers view that the majority of coronaviruses exist in China, the world’s most populous country. It is increasingly becoming urbanised. Due to encroaching upon the wilderness, including the natural habitats of bats, more and more bats and other disease-carrying organisms are getting closer to human settlements and spreading infection either directly to people or through livestock. A combination of these factors make China a hotspot for disease outbreaks.