Climate change and coronavirus: Is the Covid-19 pandemic really a surprise?
A study in China estimates that there are now more than 30 strains of SARS-CoV-2 spread across the globe. This pandemic is no surprise. It was coming, and so will others.
Walking towards the school gate, as I adjusted the N-99 face mask on my four-year-old, I felt deeply disturbed. The AQI numbers in our city had soared to hazardous levels and the air pollution was causing worrisome adverse effects on the tiny lungs of our children.
Pollution was not the only cause for anxiety. The extreme weather conditions, the rise of vector-borne diseases like dengue and chikungunya, the continuing emergence of novel viruses, the increasing resistance of infectious agents to medication: everything was pointing towards an extremely grim future in the world of health. The thought of our children being the bearers of such a future perplexed me, both as a mother and as a pulmonologist.
Thus started my exploration of the obvious, yet oft-ignored, changes taking place in our ecosystems and led me to my research on climate change.
The direct effects of climate change on our health are easy to guess. The average global temperature of the earth, which has increased by 1°C since the pre-industrial era, is rising at a rate of 0.2°C per decade. It may soon reach a level that is irreversible (2.5°C above the pre-industrial average). 95 per cent of this global warming is being caused by greenhouse gases, the atmospheric levels of which are increasing alarmingly due to human activities. This global warming is causing melting of ice masses, the rise of sea levels and major alterations in regional precipitation patterns, resulting in unprecedented and extreme weather conditions — heatwaves, wildfires, earthquakes, floods, tsunamis and snow-storms. These natural calamities are leading to deaths, diseases, malnutrition and mental health issues. Extreme temperatures are causing heat strokes, respiratory and cardiovascular diseases. Greenhouse effects are leading to diseases because of air pollution.
But what is more important and less obvious is the gradual and persistent damage that is being caused by climate change to the natural habitats and ecosystems of the world, and its quiet yet devastating effects on our health. Think about it — why are we having newer and frequent viral infections to deal with? Why are our children falling sick so often? Why is every simple viral cough leading to bronchitis? Why is the prescription of anti-inflammatory inhalers, medicines that were reserved for asthmatics, increasing rampantly?
Climate change, human behaviour and emerging infections
75 per cent of emerging infectious diseases, like Influenza, HIV/AIDS, Ebola, SARS and MERS are zoonotic. It means that they exist in animals but can be transmitted to humans. Most of them are caused by viruses — predominantly RNA viruses.
Loss of Biodiversity: Climate change and land loss cause loss of habitat, leading to extinction or relocation of native species, with growing predominance of invasive, resilient species. These become likely to harbour and transmit pathogens (so-called reservoir hosts). In a healthy ecosystem, where biodiversity is high, multiple species dilute the effect of the reservoir species, the so-called “dilution effect”. Studies on hantavirus, West Nile virus etc. have shown strong links between low biodiversity and high rates of viral transmission.
Migration of species: Global warming causes many species to migrate away from the equator and toward higher altitudes, bringing them in contact with new pathogens, to which they have not evolved resistance. These animals are also stressed and immunosuppressed, hence more susceptible to infection.
Contact with humans: Disruption of pristine forests by anthropogenic activities like mining, road building, urbanisation and livestock ranching brings people into closer contact with forest species, increasing the interaction between them. Ebola fever has had several outbreaks in Africa since 1970 because of increased interaction of local population with fruit bats due to population growth and encroachment into forest areas. Kyasanur forest disease, once limited to Karnataka, has spread to adjacent states over the last five years, because of conversion of forests into plantations and paddy fields, that has brought the locals nearer to monkeys.
Intermediate hosts and inter-species transmission: Although most of the novel viruses, including SARS-CoV-2, are “generalist” viruses that infect many different hosts, jumping into human species from wildlife species is not easy because of significant biological barriers. Transmission from mammalian species which are genetically closer to humans (the intermediate hosts), like pigs, is easier. Pig farming around forests facilitated the transmission of Nipah virus from bats in Malaysia, and civet cats sold in wet markets transmitted SARS-CoV from bats in China.
The market connection: In informal “wet” markets, animals are slaughtered, cut up and sold on the spot. The Wuhan wet market sold numerous wild animals - live pangolins, wolf pups, crocodiles, foxes, civets. Wet markets in Africa sell monkeys, bats, birds, etc. They are a perfect platform for cross-species transmission of pathogens as novel interactions with a range of species occur in one place. 39 per cent of the early cases in the SARS outbreak were wildlife food handlers, likely connected to the wet market of Guangdong, China.
Human transmission: Once inside new hosts, most viruses, fortunately, adapt, replicate and transmit inefficiently. Out of the 1,399 recognised human pathogens, 500 are transmissible between humans, and only 100 to 150 are sufficiently transmissible to cause epidemics or pandemics. Restrictions occur at many cellular levels like entry into host cells by receptor binding, trafficking within cell, genome replication and gene expression. Each barrier requires a corresponding genetic change or mutation in the virus. RNA viruses, especially single-stranded RNA viruses like coronavirus, replicate rapidly and are prone to mutations due to lack of a proofreading mechanism. Only after extensive replications and re-assortments in the genome of H3N2 influenza A virus, was it capable of causing the 1968 pandemic.
Human behavioural changes: Factors like international travel, international trade of wildlife, urbanisation, and increase in population density further facilitate transmission.
Covid-19: What do we know?
In late December 2019, Wuhan Centre for Disease Control and Prevention detected a novel coronavirus in two hospital patients with atypical pneumonia. It sent the samples to the Wuhan Institute of Virology for further investigation. The genomic sequence of the virus, eventually named SARS-CoV-2, was 96 per cent identical to that of a coronavirus identified in horseshoe bats in a bat-cave in Yunnan during virus-hunting expeditions. It belonged to the SARS group of coronaviruses.
The expeditions were carried out by the Director of the Centre for Emerging Infectious Diseases at the Wuhan Laboratory, Shi Zhengli (nicknamed “China’s Bat-woman”) and her team, from 2004 for over 16 years, in an attempt to isolate the SARS coronavirus. They discovered hundreds of bat-borne coronaviruses with incredible genetic diversity in bat-caves deep inside forests. In bat dwellings, constant mixing of different viruses creates a great opportunity for dangerous new pathogens to emerge and the bats turn into flying factories of new viruses.
But bats were not present at the Wuhan wet market. The wild pangolin, sold for its exotic meat and medicinal scales, became suspect as an intermediate host when a SARS-CoV-2 like coronavirus was discovered in pangolins that were seized in illegal trade markets in southern China.
Whether or not the SARS-CoV-2 was accidentally or deliberately released from the Wuhan Laboratory is a debate not proven. None of the coronaviruses that were under study in this laboratory were identical to the SARS-CoV-2 virus. Also, researchers believe that the spike proteins present on the viral surface, that target the ACE2 receptors on human cells, are so effective in binding the virus to the cells, that they could have developed only by natural selection and not by genetic engineering. When computer simulations were carried out, the mutations in the SARS-CoV-2 genome did not work well in binding the virus to human cells, leading to the argument that if scientists were to deliberately engineer the virus, they would not choose mutations that computer models suggested did not work.
Whatever the origin of the virus, the response to develop what is needed to control the present outbreak remains the same, as do the policies needed to prevent such outbreaks in the future.
A recent analysis done in China estimates that there are now more than 30 strains of the virus spread across the globe. This means that it has already mutated 30 times, which filters down to roughly one mutation every two weeks. More studies are needed to determine the effects of these mutations on the virulence and transmissibility of the virus. But going by the rapidity with which Covid is taking over the world, it should be an easy guess.
So really, is the Covid-19 pandemic a surprise? Not at all. It was coming, and so will others.
Covid-19 has thrown us into a world of turmoil and uncertainty. The impacts on health and economy have been devastating. The only thing that is flourishing is nature! Maybe nature will make us see what innumerable climate-related world conferences could not. It is there for us to appreciate in its full glory — the blue skies, the clean air, the blooming flowers, the variety of birds and the wild creatures returning to claim the land that was once theirs. Nature is sending us a message. It would do us good to heed to it.