After Ebola and COVID-19: insights for future disease outbreaks
“There are currently zero cases of #Ebola in #DRC after over a year of fighting this outbreak,” Dr Matshidiso, the World Health Organization (WHO) Regional Director tweeted on 3 March 2020. The Democratic Republic of Congo (DRC) had been fighting a long and tiring battle against the Ebola virus, which had officially been declared a new outbreak in August 2018. Giving the country next to no time to take a breath, COVID-19 has also been starting its spread in the country, with nearly 100 cases and eight deaths reported up until 31 March 2020. As large-scale epidemics succeed each other rapidly, and many innocent lives are lost or permanently damaged, are there some lessons we can take with us for future outbreaks?
April 2018, DRC. Although previous Ebola outbreaks had been successfully overcome, people in North Kivu Province started reporting worrying symptoms. They had a bad fever, a sore throat, headaches and muscle pain, which turned into vomiting, diarrhoea, impaired kidney and liver function, and sometimes internal or external bleeding as time went on. The Congolese Ministry of Health sounded the alarm. What would follow was the largest Ebola virus outbreak in the history of the country, with, on average, one out of two people dying from the disease after having been infected.
Now, another disease outbreak is to hit the country: COVID-19, while simultaneously striking hard in many other parts of the world. In the heat of the battle, it might, however, pay to take a step back and look at some lessons learnt, among others from former Ebola outbreaks.
Reviewing our relationship with nature
When wood is burned in a fire until it is charred, the remains from the wood can be recuperated as charcoal. The latter is very important as cooking fuel, in medicine, for writing and many other purposes. To this end, people in African forests are chopping down trees. However, the consequences might have been graver than they could have imagined. Researchers think that in some areas this deforestation — along with hunting for bushmeat and (illegal) mining — might be linked to Ebola and monkeypox outbreaks.
As part of a project by, among others, the Royal Belgian Institute of Natural Sciences, the University of Antwerp and the University of Kisangani, researchers will have a look at how biodiversity conditions affect the spill-over of infectious agents such as viruses to humans in African forests in DR Congo and Côte d’Ivoire in particular. In these forests, there is often a steep decline in biodiversity as people clear forests for charcoal, hunt animals for bushmeat and mine (illegally).
At the same time, the researched areas have seen more and more outbreaks of emerging infectious diseases with small wild mammals as the hosts, monkeypox and Ebola, among others. “To develop strategies that reduce and prevent the risk of diseases spreading from animals to humans, we are trying to gain an insight into how pathogens are transmitted within their host populations,” says Erik Verheyen from the Royal Belgian Institute of Natural Sciences and the University of Antwerp, a researcher participating in the project.
Although the real origins of the Ebola virus are still unclear, researchers think that animals — fruit bats to be more specific — were the virus’ hosts before it infected its first human victim. In general, diseases originating in animals — zoonotic diseases — seem to be on the rise. According to the European Food Safety Authority, about 75% of infectious diseases affecting humans have their origins in animals. HIV, hantavirus, West Nile virus, bird flu, Rift Valley fever and Zika virus are all said to have been transmitted from animals to people, and some of them have become infections that can spread among humans without further need for animal hosts. Many link people’s behaviour towards animals and their environments and a loss in biodiversity with the increase in transmissions and disease outbreaks.
Deforestation seems to have an impact on the spill-over of disease from animals to people in two ways: firstly, it increases contact between humans and animals and therefore increases the chances of transmission. “People go further into the woods to hunt species that are not prevalent near them anymore. They might also intensify hunting for new species that they were not interested in originally, for example for the trade in bushmeat,” says Verheyen.
Secondly, in an environment where there is less biodiversity, the animals that people encounter might be more likely to be disease hosts, although these effects are contested among scientists and dependent on contextual factors. The basic idea is that if you have fewer species of a certain type of animal, and there is one species, in particular, that is a good host to the virus, then there may be more individuals of the ‘good host’ species within the entire group than in a higher biodiversity context. As a lot of other species have died out, there are fewer species to ‘dilute’ the effect of the ‘good host’ species.
“There is a hypothesis that animals that only have a short lifespan invest less in building their immunity, but do reproduce abundantly — which makes for great potential hosts for a virus.”
Additionally, when species become extinct, it is possible that the animals that are good hosts to the virus are the ones that survive. “There is a hypothesis that animals that only have a short lifespan invest less in building their immunity, but do reproduce abundantly — which makes for great potential hosts for a virus,” says Herwig Leirs from the University of Antwerp, also a participant in the research project.
Research published in a Nature article called More species means less disease gives proof of the existence of a certain ‘dilution effect’ as well. The research studied twelve diseases, such as West Nile fever and Lyme disease in ecosystems around the world. Time and again, the aforementioned diseases became more prevalent as more biodiversity was lost. However, more recent research proves that these effects should not be generalised, but rather each transmission and pathogen examined case by case. In quite some research, for example, researchers found higher biodiversity resulting in a higher potential transmission of disease.
When we ask Leirs whether we can directly link biodiversity loss to an increase in disease outbreaks, he tries giving us the complete picture. “A lot of studies have given proof of this dilution effect, but the effect of biodiversity loss is dependent on various factors, such as the characteristics of the pathogen. For example, monkeypox seems to infect many species, whereas Ebola probably circulates in one or very few species only. The impact of biodiversity conditions will affect the transmission of both pathogens differently,” he illustrates.
“The outcome of our study will be determined by context as well,” Verheyen adds. “This context entails the fact that the pathogens are transmitted directly and includes the type of interactions between wildlife and the local people (hunting, housing goats, chickens and pigs) and a lack of insight into the dangers that contact with living or freshly killed mammals can bring about.”
What does seem to be entirely sure is the fact that nowadays, people mingle more with wild animals, and that this mingling increases transmission risk. “Without hunting and wild animal trade for human consumption, this COVID-19 outbreak might not have happened,” says Verheyen.
“Without hunting and wild animal trade for human consumption, this COVID-19 outbreak might not have happened.”
Some programmes have already tried altering people’s behaviour. In Central Africa, education programmes focused on reducing people’s consumption of primates they had found dead in forests, which could prove to be an effective way of reducing the risk of an Ebola outbreak. Other experimental projects tried reducing people’s dependency on bushmeat by having them rely on other farming of wildlife species or by expanding their livestock production, again with measures in place to prevent other zoonoses. “All behavioural changes that could decrease the number of interactions between humans and wild animals are likely to reduce the chances of transmission,” Verheyen concludes.
Prediction or surveillance of disease outbreaks
Many scientists are having a look at various options on how to go about preventing outbreaks or at least curbing their negative impacts. On the one hand, there is the possibility of predicting outbreaks by looking at all potential viruses within animals populations and determining which ones could emerge next, an approach more focused on prevention. On the other hand, researchers could screen people for viruses proactively, so that the latter can be stopped in their tracks.
Referring to the 2014 and 2018 Ebola outbreaks, researchers from the University of Edinburgh, the University of Sidney and the Scripps Research Institute argue in favour of surveillance of human populations over setting up predictive models. ‘No amount of DNA sequencing can tell us when or where the next virus outbreak will appear,’ they argue in a commentary in Nature. For the epidemic that followed the 2014 Ebola outbreak in DR Congo, they argue for example, that a lot of data was collected to do set-up models by genome sequencing, but that this did not prevent the virus from resurfacing again in 2018.
According to Kate Jones, a researcher specialising in ecology and biodiversity from University College London, “An effective way to limit the public health, economic and conservation impacts of emerging disease outbreaks in people, wildlife and livestock, is to identify, treat and contain them as early as possible.” She continues on how this could be done in practice. “One important facet of this is improving surveillance and healthcare capacities in areas that are at high risk of disease emergence — for example, at deforested, agricultural or urbanising frontiers — and conducting systematic, routine human, livestock and wildlife surveillance for both known and newly emerging pathogens in these areas.”
Jones does believe in preventive measures in ecological disease control. “For example, the ecological restoration of dammed rivers has been effective in reducing the schistosomiasis burden in parts of Africa and also helps to protect local ecosystems. Understanding when these kinds of ecological disease control interventions may be effective or appropriate, and putting communities at the heart of designing them, will be an important challenge for the future.”
“For example, the ecological restoration of dammed rivers has been effective in reducing the schistosomiasis burden in parts of Africa and also helps to protect local ecosystems.”
Responsibility of governments and scientists
So, as well as changing our behaviour towards nature and looking at ways to predict or do surveillance of future outbreaks, what about the role of governments? “I think outbreaks such as SARS and Ebola have perhaps made politicians in richer, industrialised countries falsely believe that pathogen spill-overs are other people’s problems and that they will remain localised,” says Jones. “This has led to a lack of political will to properly prepare for this type of outbreak leading to a lack of power afforded to the bodies such as WHO, and a lack of funding for containment and management. China put a concerted and unprecedented effort into managing the latest outbreak, and if the rest of the world had taken this seriously as a global problem and taken steps at the same time, it could perhaps have been contained.”
According to Jones, this holds a lesson for scientists as well. “As scientists, we need to communicate our research better to convince those in power to act forcefully and quickly next time.”
