The growing threat of new, mysterious viruses: Are bats to blame?

As another animal virus mysteriously finds its way into the human cells for the first time ever, infecting over 37,500 across the world, it has left researchers mulling over the same old question, yet again – “Why do these deadly viruses suddenly jump from their natural reservoirs to humans?”

The new strain of coronavirus has already travelled to 27 countries outside China, infecting over 37,500 and killing at least, surpassing those lost in SARS outbreak decade ago. All deaths have been reported across mainland China, except for two, one each in Hong Kong and Phillipines.

While there are still no clear answers as to how this deadly virus got transmitted into humans, studies suggests it may have come from ‘bats’- the only mammal naturally capable of flying, which harbours highly pathogenic viruses including those that caused Ebola, Nipah, Marburg and the Severe Acute Respiratory Syndrome (SARS). It may have happened directly, or through an ‘unknown host’. But what is making these viruses to increasingly invade humans?

“There is no single reason, but primarily it’s because of the increasing human-animal interface,” says noted virologist, Professor G ArunKumar who heads the Manipal Institute of Virology, “viruses are not self-living autonomous organisms like bacteria. They can only grow inside a living cell and have no ‘life’ outside of it. In most cases, they are host-specific, but sometimes, they can find ways to bind to cells of a new host.”

Viruses do so, by undergoing mutation -some genetic changes which enable them to efficiently spread among humans and become even more virulent. For instance, the avian influenza virus (H5NI) exists naturally among wild aquatic birds, but becomes highly pathogenic when it infects the poultry.

“Most often such outbreaks are related to these live animal markets. But, there are other reasons too - the large-scale deforestation, fragmentation of forests and animal trafficking. Wildlife habitats are shrinking at an unprecedented pace across the world," adds Dr ArunKumar

Bats are known to be sensitive to environmental changes. Studies have shown how bats roosting at human-made bridges experience physiological stress, which may reduce their immune system functioning, and render them more susceptible, leading to shedding of pathogens and decreased survival rates.

One of the studies led by German researchers in 2017 identified foliage-roosting species of bats, to be particularly sensitive to habitat deterioration and contended that it “may predispose them as potential sources for viral spillovers events when humans encroach into natural habitats”

“It’s quite similar to what happens in parasites. When a current host is under stress, they jump to another host to survive. Probably, that’s what happened here,” says Sumit Dookia, a wildlife biologist. Though, parasites are different from viruses, the stress on certain wildlife species remains a key concern, with more forests being cleared for new roads and new cities.

“Humans and wildlife cannot co-exist in all spaces. Each has separate habitats and we should not encroach into their natural habitats. But, unfortunately, we continue to interfere and there is rise of this animal-human conflict. Humans are majorly exploiting animals as source of food, most of the times, it is unsafe and risky,” says Dr Vibhu Prakash, Principal Scientist, Bombay Natural History Society (BNHS) who has been working on conservation of vultures for over two decades.

Even as world struggles to contain the current flu epidemic, more such viral strains continue to thrive in wildlife with potential to emerge among human populations. Considering the pace at which humans are altering the wildlife habitats, more such viruses could spill into the human populations in the near future.

But as virologists say, “until, we know the exact nature of transmission of each of these viruses to humans, it is difficult to stop future outbreaks.”

"There is need for deeper studies to find those answers. Till we find those, probably people can be more responsible in their behaviour towards animals and wildlife in general," says Dr ArunKumar.