No trees: What the landscapes where all recent pandemics originated have in common

Covid-19 was no surprise. After the 2003 outbreak of SARS and the 2012 outbreak of Middle East Respiratory Syndrome (MERS), it was only a matter of time before another lethal coronavirus stung us.

Why were we unprepared?

Let me rephrase that question: Why did we let it happen again?

We failed to prevent it because we failed to recognise a truth that stares us in the face.

It would be more correct to say we refused to recognise it.

Here is a litany of the landscape of this very inconvenient truth: yellow fever, zika fever, dengue, chikungunya, ebola, SARS, Nipah virus, Kyasanur Forest disease, MERS, rabies, Rocky Mountain spotted fever, sleeping sickness, hantavirus-caused diseases, Japanese encephalitis, malaria and counting ...

Though these diseases are very different, their landscape of origin is the same. And it is a shockingly familiar one, no matter where you live.

It is a landscape without trees.

All these diseases emerged – or re-emerged, more virulent and dangerous – as a result of human encroachment on forests. Historically, we might trace them to tropical rainforests, but right now we must look closer to home. Because the forest was, till very recently, right here somewhere, in and about your housing colony, around that gated high-rise and its adjacent slum.

Diseases emerge when we clear forests, cut down trees, flatten hills, dam rivers, and squat on all this usurped territory. Within a 5 km radius of my home are breeding grounds for at least seven of those listed diseases. It’s not something we think about.

If we go by environmental policy alone, disease is the default position.

We brag that our species achieved twelve extinctions last year, mostly insects one is duty-bound to squash. We have shoot-on-sight orders for other vermin. Our babies imbibe DDT in their very first mouthful of milk.

Can policy do more? In every way, it helps the virus push us to the brink of extinction.

Many emerging diseases, like those listed above, are zoönoses – diseases transferred from other vertebrates. Their origins can usually be traced to wildlife. They may have stayed on, unnoticed, in the wild and never made the species jump to infect us if a stable ecosystem had been left undisturbed. All our woe, with loss of Eden.

Covid-19 started this way too. Even if we haven’t yet traced its origins, we’ve known for years that coronaviruses circulate in bats.

Bats make up 20 per cent of mammalian species. They are ubiquitous; except at the poles, they are global citizens. There is something magical about a mammal capable of sustained flight, one that can echolocate prey in the pitch-dark. Every culture, not excepting DC Comics, has substantial bat lore, and human gullibility has allowed the bat to be avidly hunted. In Southeast Asia, sixty-four species of bats are regularly exploited for meat and medicine.

The urban push into the forest forces bat populations to colonise human spaces and increases their vulnerability – and ours.

This isn’t all that bad from the bat’s point of view. Urbanisation provides new roosts, new sources of food and new company. Bats are sociable creatures. They form lasting relationships with home, and their urban circle of friends may embrace species that won’t roost together in the wild. And this commingling means a richer, more diversified stew of bat-borne viruses.

From the virus’s point of view, the bat is a bijou residence. Long lease, a little compact, yes, but comfortably air-conditioned and well connected, with a reliably frequent taxi service – can one ask for more? Apparently, a virus does.

These long-lived, vagile and generously gastronomic hosts have just one snag: bats don’t get sick. Not as often as they should, considering the range of viruses they harbour. (In all, fifteen zoönotic virus families have been identified across 200 species of bats.)

Why is the bat bursting with rude health despite this terrifying arsenal of viruses?

When a bat flies, its metabolic rate rises to meet the exorbitant energy demand of flight, and its body temperature spikes to a high fever. In all mammals, fever upticks the immune process and slows viral replication. As the only mammal capable of sustained flight, the bat has evolved this pattern of spiking body temperature. The benefit is a more efficient immune system.

Bats also spend a great deal of time in torpor – a state of suspended animation, when the body’s temperature drops. Was it this that encouraged viruses to co-evolve the ability to flourish across a wide range of temperatures?

Coronaviruses are 30 per cent of the healthy bat’s virome. They cause diseases in other species – diarrhoeas and dysenteries; respiratory infections in cattle, dogs and swine; even peritonitis in cats. But before 2002, the worst illness they gave us humans was the common cold. Then, in 2002, SARS emerged. It had a death rate of 10 per cent. What had changed?

We know now that, before SARS erupted as epidemic, there had been small outbreaks of the disease from spillovers into civet cats and humans. A pattern was in the making.

Words like “coincidental” and “fortuitous” have no place in the narrative of an emerging disease. Instead, we must look for the motive force, the driver that brought about disease. Southeast Asia has lost 30 per cent of its forests in recent years. The deforested land is intensively cultivated. Urban growth is invasive. This abrupt proximity between humans and bats allows greater exposure to the viruses shed in bat saliva and guano, and provides an environment conducive to a rapidly diversifying spectrum of viruses. And since bat coronaviruses cause infections in domesticated species, intermediate hosts are aplenty.

The dynamics of the interspecies circulation of coronaviruses before they cause disease in humans are very complex, and their genomic associations are only partly known. What is known is that when there is a spillover, humans are immunologically naïve to the virus. This results in a virulent infection, and the virus quickly adapts to rapid spread between humans.

It isn’t just coronaviruses that spill over from bats as we encroach on their habitat. The story of the Nipah virus is a classic of zoönosis literature. The Nipah virus first emerged in Malaysia in 1998, when Kalong bats from a deforested area roosted in a barn. Their droppings infected pigs and, eventually, the farmer. Human-to-human infection was not observed.

The Bangladesh outbreak of 2001 was a case of direct bat-to-human transmission. Date-palm (Phoenix dactylifera) sap is a favourite with villagers – and also with fruit-eating Pteropus bats. Villagers and bats shared the pot, as sap collected from the date-palm tree. This time, the virus also spread rapidly between people. This has been the pattern in both India and Bangladesh. Nipah virus is chillingly lethal – it has a mortality rate of 75 per cent.

At present, there are thousands of coronaviruses circulating in bats. Just seven of them have declared themselves in humans. As crowding increases, more may emerge. Can we predict what the next one will be like?

Absolutely not.

The West has long jeered at Asia and Africa as “virus machines”. Such a label is deeply offensive to more than half the people on this planet, besides being scientifically untrue. Viruses are everywhere. Asia and Africa have been historically impoverished by European nations, either through genocide or colonisation. Disease was driven by conquest in the past, and racism in science is rooted in that memory. The language of science often echoes that inequality of power, and, thankfully, we’re growing more sensitive to it.

Disease is driven by capitalism today: the forests of Asia, Africa, Central and South Americas are enslaved to richer nations to produce goods that serve few and bankrupt millions.

The use of forests to fuel the greed of capitalism must cease. Else, a landscape without trees may soon become a landscape without people.

Excerpted with permission from A Crown of Thorns: The Coronavirus and US, Kalpish Ratna, Context.