Forewarned is forearmed

1st June 2020

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Sally Best investigates the environmental issues that led to Covid-19, and what health and safety issues need to be addressed to prevent further pandemics

In 2015, Bill Gates identified what he understood to be the next greatest risk to our World's population: “Not missiles, but microbes“. His insightful 'Ted Talk', 'The next outbreak? We're not ready' pointed towards viruses as the next cause of a global catastrophe. After such a clear warning, should we not have been more prepared for a pandemic five years later?

Zoonotic transmission

COVID-19 is 'zoonotic'; a disease known to exist in animals that can be transmitted to humans. Of emerging infectious diseases that affect humans, around 60% are zoonotic. Of this 60%, approximately two-thirds originate in wildlife. The International Livestock Research Institute showed more than 2 million people per annum die from zoonotic diseases spread from wild and domestic animals. AIDS is a primary example. It crossed into humans in the 1920s in Africa, following the butchering of chimpanzees by hunters for bush-meat. Other zoonotic diseases include Malaria, Lyme Disease and Ebola. Emerging diseases such as these have quadrupled in the last 50 years. Experts suggest this is due to expansion of human communities into wild habitats, many of which are disease 'hot spots'. Additionally, keeping many species in close proximity increases the risks of mutations and 'inter-species transmission' of viruses such as this latest one, SARS-CoV-2.

Other coronaviruses have caused large-scale pandemics over recent years. These viruses are: SARS-CoV (Severe Acute Respiratory Syndrome) in 2002 and MERS-CoV (Middle East Respiratory Syndrome) in 2012. Research epidemiologists have subsequently found large reservoirs of SARS-related coronaviruses in their natural host, bats. This research provided evidence to suggest that the zoonotic virus that caused SARS (SARS-CoV) originated in bats. Likewise, MERS-CoV, which caused MERS disease, was found to infect humans through direct or indirect contact with infected Dromedary Camels. Scientists believe this virus may have originated in bats and passed through an intermediary host (the Dromedary Camel).

It therefore comes as no surprise that analysis of the SARS-CoV-2 genome, shows 96% whole-genome similarity to a bat coronavirus; strongly suggesting the origin of this new coronavirus is also from a bat host. Additionally, further genome studies strongly suggest that SARS-CoV-2 passed from bats into an intermediate mammalian host, possibly the Malayan Pangolin (Manis javanica). These rare animals are illegally imported into Guangdong province in China, and distributed from there.

Wet markets

The most prominent theory is that SARS-CoV-2 was transferred into humans at a Chinese “wet market“ selling fresh meat and fish. Many early cases of people with COVID-19 can be traced back to the Huanan Market, located in Wuhan, one of many in China that sell live and freshly slaughtered animals. Live bats and pangolins are among the numerous species kept in close proximity. Markets such as these therefore continue to pose a major threat to public health. These markets act as a progenitor for viruses, and do not have well maintained hygiene standards as animals are kept and butchered on site.

This Chinese culture of 'exotic' dietary habits (in comparison to Western cultural practice) is not a new phenomenon, and for the past 20 years this 'Wild Food' has been increasingly branded as 'luxury'.

We understand that “wet markets“ such as the Huanan Market facilitate transmission of viruses. However, what is yet to be broadly understood in Western cultures is why markets such as these were formed in the first place, and additionally, why they are still allowed to exist. The 1990s saw the industrialisation of Chinese food production systems, which led to an increase in large-scale farming practice. As a consequence, the majority of smallholding farmers were pushed out of the livestock industry and some turned to the farming of “wild“ species, selling these species in niche markets for higher returns.

Wuhan closed and disinfected the Huanan Market on 1 January 2020. The Chinese government then issued a temporary ban on all trade of “wild“ animals and produce from 22 January. After a period of closure, the market reportedly reopened for business on the 30th March. The reopening of this market caused high levels of hostility and confusion as to why such a breeding ground for the transmission of deadly viruses was still in operation.

The great strength of evidence that SARS-CoV-2 was initially transmitted into humans at Huanan Market suggests these markets need reforming in order to prevent any future animal-borne disease. As “wet markets“ have been integral to Chinese culture and social life for a considerable time and account for up to 59% of Chinese food supplies, it would be difficult to place an immediate permanent ban on their existence, and could result in unintended consequences. In 2003 and 2013-14 after the SARS and avian influenza outbreaks resulted in closure of wet markets, it lead to an unprecedented increase in black market trade. This was arguably more of a threat to public and animal health than “wet markets,“ that are regulated. Scientists should therefore analyse the origins and epidemiology of this disease to facilitate the introduction of preventative measures. It is paramount that this is done without stigmatisation of entire ethnicities.

Early detection

In addition to identifying the origins of coronaviruses, it is important to identify the factors that facilitate its transmission. Early detection and action are crucial to prevent an outbreak becoming a pandemic. This involves containment (testing and isolation) of suspected cases and tracing and quarantining of all contacts. This method worked well for the SARS and MERS outbreaks. Although both these viruses had high mortality rates, infections were easy to detect and contain and fatalities were relatively few, due to symptomatic cases being either too ill to move and spread the disease, or easy to detect and isolate. SARS-CoV-2 differs in both these aspects. In 80% of cases the virus causes only mild infection, with a mortality rate of approximately 3%. So not only are most infected people well enough to go out and spread the infection, most are also not displaying detectable symptoms.

The SARS-CoV-2 virus is more infectious than either SARS or MERS. Transmission is measured using the 'reproduction number' (R), the average number of people one person infected with the virus will infect in turn. To control the rate or spread in an epidemic, R needs to be below 1. Seasonal flu has an R value of 1.4. COVID-19 has an R value of around 3, so one person is likely to spread it to 3 others. Once this interaction occurs 10 times, there will be 59,049 infected people. In contrast for seasonal flu, only 28.9 would be infected.

The value of R can be controlled by many factors, such as reducing the number of people we come into contact with by social distancing and quarantine, through the use of vaccines; in order to reduce R to less than one and create 'herd immunity', two thirds of the population requires vaccination. Finally, reducing infection time would also reduce the value of R, and clinical trials are testing a range of treatments.

International dimensions

The probability of passing on the infection is increased vastly by international travel. In spite of the lockdown of the city of Wuhan on the 23 January, since the beginning of 2020, 17 passenger flights had already flown directly from Wuhan to Britain. In addition, according to FlightRadar24, 614 flights from China had arrived in Britain without passengers being tested or quarantined. This increased the risk of the UK population contracting the virus as it was estimated that only one-third of infected people arriving in Britain had been detected. Altering behaviours such as socialising and travelling is a clear, if difficult strategy to reduce transmission as well as the obvious need for rigorous testing, tracing and quarantining.

South Korea responded effectively to the COVID-19 outbreak using strategies based on 'lessons learned' from the SARS outbreak. Their 'pandemic plans' led to immediate comprehensive testing including screening arrivals at airports (Koreans included) and asymptomatic people. They also used tracing and quarantining of citizens and implemented early lockdown. Another effective measure employed by South Korea was a 'central tracking app', 'Corona 100m' which informs the public of known cases of COVID-19 within 100m ensuring they exercise high levels of caution. Other European countries, for example, Germany also implemented rapid and extensive testing, tracing and quarantining of cases. Preventative measures such as these have meant South Korea and Germany have been relatively successful at controlling infection and mortality rates in comparison to the UK, some other European countries and the USA.

Taking a strategic approach

So if in 2015, Bill Gates said “we're not ready“, why were we still unprepared in 2020? In order to be 'ready' we require a co-ordinated global strategy that limits disease outbreak from animal hosts and reduces transmission of viruses between humans. The Predict project is currently identifying diseases with pandemic potential. Researchers are creating a library of viruses from high-risk species in anticipation of a future event where a new virus spreads into humans. Effective regulation of wet markets will also be required to control these sources of disease generation and conduits for transmission.

The end of the COVID-19 pandemic is not yet in sight. It raises the frightening prospect of further viral pandemics, with the resultant threats to human health and the world economy. We therefore need a coordinated global strategy and response to ensure spread is limited and managed effectively. This will require significant investment, increased transparency of planning and effective use of combined resources such as satellite maps and other technologies to monitor movement of people.

We have been warned once. We should not need to be warned again. Let the germ wars begin.

Sally Best is an environmental biologist and scientific journalist

Image credit: Getty


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