Integrating the human and natural world may be having larger implications than we initially thought. Is the spread of viruses from natural sources the reason for the rise of pandemics in the 20th century?
The Word Forest Organisation works with local Kenyan people to plant trees and help support their communities. We know that reforestation can help to combat one of the biggest threats to our civilisation – climate change. But that’s not all. Recent research has highlighted that reforestation could also help prevent future pandemic outbreaks, by helping rebalance ecosystem equilibriums and separating humans from the wild animal populations that hold viruses with pandemic potential.
COVID-19
There is no question that the recent coronavirus pandemic has been the biggest disruption to our lives this century. Through lockdown, it completely stripped our social calendars and more drastically has led to over 600,000 deaths worldwide. [1] However, even though there are aspects of COVID-19 that are unique, the start of its journey is not. COVID-19, like many other recently emerging pathogens, first entered humans from a wild animal. [2] This transition of viruses from animals to humans is expected to increase in the future due to globalisation. As well as connecting people, globalisation has brought us closer to wild animal populations. Increased human-animal interactions up the chances of humans becoming infected with a disease that we have never seen before, increasing the likelihood of a pandemic.[3]
COVID-19 started with a bat. Bats are a known reservoir for many viruses, 31% of which are part of the coronavirus family. [4] Viruses found in bats can adapt to humans with relative ease compared to viruses from other sources. This is because these viruses are adapted to the high temperature produced by bats when they fly, which is similar to our body temperature.[5] However, it is thought that COVID-19 likely entered humans with an almost double jump-like stunt, passing from bats to pangolins and subsequently to people at a wet market in Wuhan, China. [6]
It is not uncommon for viruses to come from animals
Viruses that jump from animals to humans are known as zoonoses, or zoonotic diseases, and interestingly are not a common feature of past pandemics. However, some established human diseases, such as HIV/AIDS, are thought to have started their journey on a similar path, and zoonotic diseases cause over 700,000 deaths per year. [7] It is estimated that over three-quarters of newly emerging infectious diseases come straight from nature and this number is expected to rise. [8]
But why? The first thing we need to consider is that natural and human worlds have become increasingly interconnected throughout the 20th century. Dr Peter Daszak, president of the EcoHealth Alliance, recently announced his concerns that:
“Rampant deforestation, uncontrolled expansion of agriculture, intensive farming, mining and infrastructure development, as well as the exploitation of wild species have created a ‘perfect storm’ for the spillover of diseases.” [7]
Dr Peter Daszak, president of the EcoHealth Alliance
Cutting down trees increases the likelihood of pandemics
The first human practice that Dr Peter Daszak lists in the above statement is ‘rampant deforestation.’ When you look at the scientific research, this actually makes a lot of sense, as major viral outbreaks have been linked to forest clearance in the past. One virus that has been connected to deforestation in sub-Saharan Africa is Ebola. This disease is extremely deadly, with around 90% of those infected losing their lives. [9]
Multiple studies have shown a convincing connection between patterns of deforestation in Africa and outbreaks of Ebola, which is thought to be derived from forest fruit bats. These studies have found that towns situated close to major areas of deforestation are more likely to experience more Ebola cases. [10, 11, 12] The results of this research suggests that conserving our forests could reduce the likelihood of new pandemics. Reforestation schemes could help tackle 6 of the Sustainable Development Goals set out by the United Nations, by both mitigating climate change and protecting human health. [8]
Malaria rates have also been linked to increased levels of deforestation, with a recent study finding that a 4.3% increase in deforestation in the Brazilian Amazon led to approximately 50% more malaria cases over 3 years. [13] Malaria is caused by tiny parasites carried by mosquitoes and is one of the world’s biggest killers. Cutting down trees can affect mosquito behaviour and boost their breeding success, which can lead to an increase in infections. [14]
Climate change can also affect viral transmission
When The Word Forest Organisation plants new trees in the tropics, they grow rapidly, absorbing and storing greenhouse gases, especially carbon dioxide. This helps combat climate change and, therefore, helps reduce warming of the planet. Offsetting global warming can also have an effect on viral outbreaks, as climate change will likely increase the range of virus-carrying critters like mosquitoes. [14, 15] This means that mitigating global warming could reduce the ease with which tropical diseases spread across the globe.
This puts a new spin on the climate change debate and shows the importance of understanding ecological systems when predicting disease emergence. It is obvious that in the future we need to deepen our understanding of how interactions between the environment and human populations play a part in the emergence of disease. This is known as the ‘One Health’ approach and involves surveillance of both human and natural systems when understanding disease transmission and when trying to find potential pandemic candidates. [16]
Intensive agricultural practices have also been linked to pandemics
By situating agriculture closer to wild habitats, we increase the chance of humans coming into contact with wild animals that harbour their own viruses. A recent study found that humans and livestock living close to forest fragments in Uganda had bacteria in their stomachs that were genetically similar to the bacteria found in the primates within these forests. This study found a direct correlation between the level of human disturbance of forest communities and pathogen crossover between human and animal communities. [17]
The fact that livestock have a higher chance of contracting these new pathogens is also a problem. A Malaysian outbreak of Nipah virus in 1998-1999 was directly linked to the intensification of the pork industry, as pig farms expanded and ventured closer to forests. [18] It is thought that fruit bats living in the forests were attracted to the pig farms, as the farmers were growing fruit trees. This led to the virus infecting pigs that ate contaminated fruit, which subsequently led to over 105 people dying of Nipah virus by 1999. [14]
The nature of intensive farming also increases the likelihood of zoonotic disease establishment. Farmers usually keep animals of the same breed, which are genetically very similar. They are often packed closer together than natural populations, increasing the ease of viral spread. [19] A recent study from the University of Bath found that the first incidence of humans becoming infected with the food-poisoning bacterium Campylobacter jejuni most likely occurred following an expansion of the UK cattle industry between 1875 to 1974, where the number of cattle in the UK rose by approximately 9 million. [20]
This shows that as a community we should be more aware of how our farming practises affect the likelihood of disease emergence. One of the main ways we can make a difference is by understanding how our eating habits put pressure on agricultural systems. Eating less meat, for example, could reduce the amount of land needed to produce our food and, therefore, reduce the need for intensive systems and farms positioned near wild habitats. [21]
We need to remember that we are all interconnected
All of this shows the importance of understanding our natural environment and how it can affect the state of our health. In the future, the importance of integrating our knowledge of natural, agricultural and human systems in disease prevention schemes will become paramount to pandemic mitigation. [16] Likewise, tackling the root of the problem will involve reducing unnecessary deforestation and natural population disturbance. This highlights how the conservation work of The Word Forest Organisation and other charities is crucial for not only conserving biodiversity, but also protecting human health.
Elle Campbell and The Team
References:
[1] European Centre for Disease Prevention and Control, n.d. COVID-19 situation update worldwide, as of 22 July 2020 [Online]. Available from: https://www.ecdc.europa.eu/en/geographical-distribution-2019-ncov-cases [Accessed 23 July 2020].
[2] Made for minds., 2020. How deforestation can lead to more infectious diseases | World| Breaking news and perspectives from around the globe | DW | 29.04.2020 [Online]. Available from: https://www.dw.com/en/how-deforestation-can-lead-to-more-infectious-diseases/a-53282244 [Accessed 23 July 2020].
[3] The University of Bath, 2020. Intensive farming increases risk of epidemics, warn scientists [Online]. from: https://www.bath.ac.uk/announcements/intensive-farming-increases-risk-of-epidemics-warn-scientists/ [Accessed 23 July 2020].
[4] Afelt, A., Frutos, R. and Devaux, C., 2018. Bats, coronaviruses, and deforestation: Toward the emergence of novel infectious diseases? Frontiers in Microbiology, 9(APR), p.702. Frontiers Media S.A.
[5] O’Shea, T.J., Cryan, P.M., Cunningham, A.A., Fooks, A.R., Hayman, D.T.S., Luis, A.D., Peel, A.J., Plowright, R.K. and Wood, J.L.N., 2014. Bat flight and zoonotic viruses. Emerging Infectious Diseases, 20(5), pp.741–745
[6] Cyranoski, D., 2020. Mystery deepens over animal source of coronavirus. Nature, 579(7797), pp.18–19.
[7] Settele, J., Diaz, S., Brondizio, E. and Daszak, P., 2020. COVID-19 Stimulus Measures Must Save Lives, Protect Livelihoods, and Safeguard Nature to Reduce the Risk of Future Pandemics | IPBES [Online]. Available from: https://ipbes.net/covid19stimulus [Accessed 23 July 2020].
[8] Scientific American, 2020. Stopping Deforestation Can Prevent Pandemics [Online]. Available from: https://www.scientificamerican.com/article/stopping-deforestation-can-prevent-pandemics1/ [Accessed 23 July 2020].
[9] Greshko, M. 2019. What is the Ebola virus, and can it be stopped? National Geographic. 9th April.
[10] Olivero, J., Fa, J.E., Real, R., Márquez, A.L., Farfán, M.A., Vargas, J.M., Gaveau, D., Salim, M.A., Park, D., Suter, J., King, S., Leendertz, S.A., Sheil, D. and Nasi, R., 2017. Recent loss of closed forests is associated with Ebola virus disease outbreaks. Scientific Reports, 7(1), pp.1–9.
[11] Rulli, M.C., Santini, M., Hayman, D.T.S. and D’Odorico, P., 2017. The nexus between forest fragmentation in Africa and Ebola virus disease outbreaks. Scientific Reports, 7(1), pp.1–8.
[12] Wilkinson, D.A., Marshall, J.C., French, N.P. and Hayman, D.T.S., 2018. Habitat fragmentation, biodiversity loss and the risk of novel infectious disease emergence. Journal of The Royal Society Interface, 15(149), p.20180403.
[13] Olson, S.H., Gangnon, R., Silveira, G.A. and Patz, J.A., 2010. Deforestation and malaria in Mâncio Lima county, Brazil. Emerging Infectious Diseases, 16(7), pp.1108–1115.
[14] Zimmer, K., 2019. Deforestation is leading to more infectious diseases in humans [Online]. BioMed Central Ltd. Available from: https://www.nationalgeographic.com/science/2019/11/deforestation-leading-to-more-infectious-diseases-in-humans/ [Accessed on the 11th August 2020.]
[15] Daszak, P., Zambrana-Torrelio, C., Bogich, T.L., Fernandez, M., Epstein, J.H., Murray, K.A. and Hamilton, H., 2013. Interdisciplinary approaches to understanding disease emergence: The past, present, and future drivers of Nipah virus emergence. Proceedings of the National Academy of Sciences of the United States of America, 110(SUPPL. 1), pp.3681–3688.
[16] Carrington, D., 2020. Halt destruction of nature or suffer even worse pandemics, say world’s top scientists. The Guardian. [Online], 27 April. Available from: https://www.theguardian.com/world/2020/apr/27/halt-destruction-nature-worse-pandemics-top-scientists [Accessed 23 July 2020].
[17] Goldberg, T.L., Gillespie, T.R., Rwego, I.B., Estoff, E.L. and Chapman, C.A., 2008. Forest fragmentation as cause of bacterial transmission among nonhuman primates, humans, and livestock, Uganda. Emerging Infectious Diseases, 14(9), pp.1375–1382.
[18] Epstein, J.H., Field, H.E., Luby, S., Pulliam, J.R.C. and Daszak, P., 2006. Nipah virus: Impact, origins, and causes of emergence. Current Infectious Disease Reports, 8(1), pp.59–65. Curr Infect Dis Rep.
[19] Graham, J.P., Leibler, J.H., Price, L.B., Otte, J.M., Pfeiffer, D.U., Tiensin, T. and Silbergeld, E.K., 2008. The animal-human interface and infectious disease in industrial food animal production: Rethinking biosecurity and biocontainment. Public Health Reports, 123(3), pp.282–299.
[20] Mourkas, E., Taylor, A., Méric, G., Bayliss, S., Pascoe, B., Mageiros, L., Calland, J., Hitchings, M., Ridley, A., Vidal, A., Forbes, K., Strachan, N., Parker, C., Parkhill, J., Jolley, K., Cody, A., Maiden, M., Kelly, D. and Sheppard, S., 2020. Agricultural intensification and the evolution of host specialism in the enteric pathogen Campylobacter jejuni. Proceedings of the National Academy of Sciences, 117(20), pp.11018–11028.
[21] A.U.M Films and First Sparks Media, 2014. COWSPIRACY: The Sustainability Secret [Online]. Available from: https://www.cowspiracy.com/ [Accessed 23 July 2020].
