Most of the world’s recent pandemics have originated from animals – so called ‘reservoir hosts’ that harbour large quantities of a nascent virus, but are unaffected by the disease that the virus causes. New viruses can transmit from a reservoir or intermediate host during contact with humans, in an interspecies jump called a ‘zoonotic spillover’. Spillovers have underpinned the world’s recent pandemics; SARS-CoV is thought to have originated from bats in 2003; while the Ebola virus that resurfaced in West Africa in 2014 has been attributed to the consumption of bushmeat likely bitten by a bat reservoir host. With the 2019 novel coronavirus sweeping through Europe, teams are working to identify the original animal host – the closest viral match has been isolated from a bat in China’s Yunnan province, sharing 96% of its DNA with the 2019 novel coronavirus.
Tracing back to the source of infection can reveal how a virus spreads, but it can also indicate where the next one will come from. David Quammen, author of the prescient 2012 book Spillover, thinks that the history of infectious disease was etched with warnings of the 2019 coronavirus outbreak. ‘We knew that the next pandemic would be caused by a quickly mutating virus; that it would be transmitted from a wild animal, very possibly a bat; that it would spillover from [an animal] at a place where they come into contact with humans; and that people would shed the virus when they are asymptomatic – all of that has come true,’ he says.
Once the route of transmission of the virus from reservoir host to humans is known, countries can focus mitigation efforts on controlling animal reservoirs and monitoring people working at the animal interface who may be at risk. Poverty often drives the consumption of wild animals for food and traditional practices of consuming exotic wildlife products can also endanger humans to spillover events. ‘There’s always a chance that wildlife consumption can cause viral outbreaks. The wet market of Wuhan is just another example. Public health education needs to discourage wildlife consumption, and needs to alert populations to the risk of animal-human contact,’ says Quammen.
The more we know about the ways in which viruses break out from wildlife and the human behaviours that exacerbate the spread of the infection, the better we can inform intervention approaches. In Liberia, researchers have recently identified the strain of the Ebola virus responsible for the recent outbreak in bats, spurring public education campaigns on ways in which contact with the animals can be prevented.
With constraints on health infrastructure in more susceptible countries, international collaboration between health bodies is needed to control outbreaks. PREDICT is a project of USAID’s Emerging Pandemic Threats Programme (EPT), launched in 2009. The surveillance scheme helps to rapidly detect viruses with pandemic potential in susceptible regions, such as those with high human-animal exposure, and where behavioural practices such as bushmeat hunting and ‘traditional medicine’ increase the likelihood of spillovers.
In late 2016, USAID revamped the PREDICT programme, launching EPT2. The programme integrates state-of-the-art disease modelling approaches with the aim of generating ‘pandemic hotspots’ in which land-use, socioeconomic and agricultural data are linked with surveys of human behaviour to model where zoonotic infections could spillover. Global health initiatives are using these models to better focus healthcare resources in identified hotspots, and readily deliver public health interventions to control the spread of a virus. As of March 2020, PREDICT has surveyed over 145,000 animals and humans to help minimize spillovers, detected 931 novel viruses including Bombali ebolavirus, Marburg virus and MERS- and SARS-like coronaviruses, and trained over 2,500 health workers in biosafety and surveillance.
Experts hope that the 2019 coronavirus outbreak will enable lessons to be learnt about how to prevent future pandemics. Quammen’s philosophy is clear: ‘It’s important for us not to think of COVID-19 as an individual crisis event – it’s the latest in a series, and there will be more. We need to learn the lessons about consuming wildlife, adjust our practices of deforestation in diverse ecosystems that place humans in close contact with wildlife, and we need to more rapidly distribute better test kits to deal with new viruses before they break out’.