Pandemics: In 20 years we have attempted to dodge six bullets in the shape of Ebola, SARS, MERS, Swine Flu (H1N1), Avian Flu (H5N1) and COVID-19.
Humour is always a good cure for anxiety in a time of pandemic. As one American said, ‘calm down, everyone, a six-time bankrupted reality TV star is handling the situation’. There is a vague symmetry in numbers only as our Prime Minster has at least six children from different marriages and affairs. On an entirely different topic people on Twitter have also been poking fun, although perhaps a little unfairly.
One person posted that ‘Nicola Sturgeon has announced that Scottish people are now allowed to exercise more than once a day, lifting a restriction that has been in place since 1853.’
Biodiversity Loss Creates Landscapes That Promote Disease Transmission and Pandemics
Unhappily, there are thousands of pathogenic bacteria, parasites and viruses that are known to science which is why we require a sense of humour! In the last twenty years we have attempted to dodge six bullets in the shape of Ebola, SARS, MERS, Swine Flu (H1N1), Avian Flu (H5N1) and COVID-19. We obviously succeeded except for the last one. Our encroachment on the natural world unfortunately increases the chances and frequency of similar occurrences.
Our interactions with nature historically became more intimate a long time ago. The moment when we as hunter-gatherers laid down our spears and began farming around 11,000 years ago, we began changing our surroundings to suit our purpose. This represented one of the most significant transitions in human history for several reasons. Agriculture amongst other things profoundly affected our diet, health, and the structure of our society.
As hunter-gatherers we may have eaten about 150 species of plants, but once corn and other cereals were domesticated from wild grasses, our diets in general changed significantly over a few hundred years. To do this we required land for the monoculture of cereals and to obtain land we began the process of gradual deforestation and encroaching on wildlife habitats. In the last hundred years this rate has accelerated as almost half the world’s rainforest has disappeared.
At present even in the last 10 years an area the size of 38,600 square kilometres (24,000 square miles) has been deforested in the Amazon. Biodiversity loss can create landscapes which can promote the chances of disease transferring to human population. Historically when we developed ecosystems with low biodiversity this was destructive for most species but some, such as rodents, are much more tolerant to human disturbance.
Rodents are huge reservoirs for disease and they readily transmitted them as they became pests in all phases of our food supply and found shelter in virtually anything we constructed.
According to the ‘Rentokil’ website (where our furry little friends are public enemy number one) rodents are responsible for more deaths than all wars put together over 1000 years. This might seem a little unfair but surprisingly it is not far from the truth! Historically there have been at least three global pandemics where rats have been key.
The Black Death of 1347 was one of the Worst Pandemics in History but was a Driver for Economic Change
The pathogen Yersinia pestis for instance that caused the Black Death was disseminated by flea-based transmission. Fleas of course live on rats and fleas abandon their host and seek another warm-blooded animal such as us. Today of course Yersinia pestis infection is easily cured by antibiotics but at the time it was lethal and caused three key pandemics.
Global movement and connectedness are not a new phenomenon, nor is the potential for, and the occurrence of, pandemics. This disease was carried along the trading corridors of the ancient silk routes from China. ‘The Plague’ was the most widespread deadliest pandemics in history and between 1347-51 it devastated medieval Eurasian populations. It had an estimated death global death toll of between 75-200 million people.
In England alone it was responsible for the deaths of a third of the entire population. It was a brutal disease matched only by the speed with which it spread. Estimated R numbers for the plague suggest values somewhere between 2.8-3.5, not too dissimilar to the virus that causes COVID-19.
Historically pandemics have always had profound economic and social impacts. We are only too aware of the economic impact of COVID-19. As multiple government travel reactions sweep across the globe, many airlines have probably already been driven into technical bankruptcy and this is just the tip of the iceberg. Economies have contracted sharply due to the interventions necessary to contain COVID-19.
According to OECD (Organisation for Economic Co-operation and Development) our GDP will contract significantly plunging us into a deep recession. Sometimes however pandemics can be drivers for positive economic change. In medieval Europe, social, political, and economic changes were profound but ultimately ended up shaping a better world. It effectively led to the end of the feudal system created in 1066 by William the Conqueror.
This was created to consolidate his power but resulted in the subordination of peasants. The plague ultimately resulted in a huge labour shortage, wages went up, taxes went down, the drastic decrease in the population meant that there was an oversupply of goods. Prices dropped and for those that survived standards of living went up.
The rapid depopulation of society and ending of the feudal system also loosened the grip of the Catholic church. Their congregations suddenly decreased in size and scepticism in the very existence of God was manifest because of the gruesome impact of the plague.
Interfaces Between Rainforest and Human Activity are Pandemic Hotspots
Today interfaces between rainforest and human activity are particular hot spots for potential pandemics. It is now widely accepted that humans contracted HIV from chimpanzees, most likely by butchering them for bush meat. Simian immunodeficiency virus (SIV) in chimpanzees, which is believed to have been transmitted to humans to become HIV-1—the virus that causes AIDS—did not start its life in chimps.
Researchers believe the chimpanzee virus is a hybrid of the SIVs naturally infecting two different monkeys, the Red-capped Mangabey (Cercocebus torquatus) and the Greater Spot-Nosed Monkey (Cercopithecus nictitans). Chimps eat monkeys, which is almost certainly how they acquired the virus. The hybrid virus then spread through chimpanzee species and was later transmitted to humans to become HIV-1.
This neatly demonstrates how complex ecosystems and how our behaviour can put us at risk. According to the WHO, 32 million people have died of HIV since the beginning of the pandemic in 1981 and roughly 37.9 million people live with HIV today.
Five years before the beginning of AIDS another virus also emerged in Africa in what is now the Democratic Republic of Congo, formerly known as Zaire. In 1976 a virus was discovered near the Ebola River in Zaire, where it gained its name. The first outbreak of Ebola infected over 284 people in Sudan (2-3 months before it occurred in Zaire), with a mortality rate of 53%.
A few months later, a second Ebola virus emerged in Zaire with the highest mortality rate of any of the Ebola viruses (88%), infecting 318 people. The most serious outbreak of Ebola Virus Disease (EBV) was of course in 2014 when it affected three West African countries (Guinea, Liberia, and Sierra Leone). This resulted in more than 28,000 cases of EVD and more than 11,000 fatalities.
Despite tremendous effort the natural reservoirs of the EBV virus have never identified although it is known to affect nonhuman primates (such as monkeys, gorillas, and chimpanzees) as well as bats. It is speculated that at the point of onset in 2014 that both chimpanzee and gorilla populations were declining dramatically pointing to the possible grim harvest of bush meat. Happily, a vaccine has been developed for EBV (‘Ervebo’) which was FDA approved last year thus diminishing its threat.
Bats Harbour more Zoonotic Diseases than any other Species
As the human population expands, human contact with wildlife will also continue to increase, not just in Africa, but on all continents. Our current struggles against the coronavirus are perhaps not entirely surprising given that we had two warning shots across our bows with SARS (Severe Acute Respiratory Distress Syndrome) and MERS (Middle East Respiratory Syndrome) which were contained. Like COVID-19, as most of us are aware, SARS and MERS were associated with coronaviruses spread by bats.
Bats are an ancient and diverse group of 1300 species. Next to rats, bats harbour more zoonotic viruses per species than any other animal making them significant reservoirs of disease. They are ecologically important mammals and inhabit every continent except Antarctica. Their characteristics such as diet, ability to fly, seasonal migration and daily movement patterns, hibernation, life span (some live up to 35 years), roosting behaviours in colonies, make them great hosts for viruses and other disease.
Many of the viruses in bats can cause disease in humans and farm animals. To date, over 200 novel coronaviruses (CoV) have been identified in bats making up 35% of the viruses they carry. Bats are viewed scientifically as major evolutionary and ecological drivers of CoVs. This has been well recognised for several years. So why didn’t we predict our current situation?
The answer is quite simple as other viruses theoretically pose a much greater global threat. Clearly the influenza virus has been seen to have the highest potential of a severe pandemic and this is endorsed by our own history with pandemics such as Spanish flu. In fact, one scientific paper published in 2017 which reviewed pandemic risk did not even mention CoVs but instead mentioned another bat borne virus called the Nipah virus.
The first outbreak of Nipah virus was in 1999 in Malaysia again at the interface between rainforest and human activity. This virus is carried specifically by fruit bats. Fruit bats were feeding on fruit trees surrounding a farm at the edge of a rainforest and inevitably pigs ate some of half-eaten the fruits that dropped to the ground that were coated in bat saliva.
More than 250 people who worked in close contact with the infected pigs caught the virus and of these 100 died. The case fatality rate of the Nipah virus was an alarming 40-75%. To stop the outbreak, more than a million pigs were euthanized, causing tremendous trade loss for Malaysia.
Harvesting of bush meat, farms on the edge of forests, markets where animals are bought and sold – all serve to blur boundaries between humans and wildlife, and are places where diseases are more likely to emerge. The emergence of disease on this basis is highly likely to be repeated. From the plagues of biblical times to the HIV and influenza pandemics of today, infectious diseases have played an indisputably major role in human history.
As human populations expand successive invasions of the human population by increasing numbers of different pathogens is inevitable. Our ability to recognise any potential sources will be significant as will rapid scientific intervention and vaccine development. According to new research an estimated 3.2 million people would have died by 4th May in the EU if lockdown measures had not been put in place.
That is why we are ‘guided by the science’. For more information on COVID-19, read this previous article.
