One Health – not just a romantic concept

We Pagans have always said that what we do to the earth, we do to ourselves, that humans are an intrinsic part of nature and not separate from it. It’s easy to dismiss this idea as just a romantic arcadian notion, as humans become ever more estranged from the natural world living in cities, surrounded by technology. But the events of recent months, as the newest of what are classed as ’emerging infectious diseases’ has changed our world, should bring home the cold truth. We cannot separate planetary health from human health, it has been shown that the biggest drivers of emerging infectious disease are deforestation and forest fragmentation.

Deforestation causes many other problems; loss of carbon sequestration, climate change, soil loss and erosion, habitat loss and changes in local weather patterns to name a few, but according to researchers the emergence and spread of novel diseases, and the re-emergence of old threats is the most direct, measurable impact on human health from forest loss.

The list of emerging infectious diseases associated with forests is long…

So why does chopping down forests cause human disease?

Sometimes this is due to increased contact between humans and wildlife as we destroy their habitat and encroach on their territory. The very first epidemic-causing pathogens such as smallpox are believed to have emerged in tropical Asia due to large scale forest clearing and the mixing of humans, domestic animals and wildlife.

Sometimes this is because of an increase in the insect vectors that spread disease from human to human, or from animal to human. For example the malaria mosquito vector increases in number around forest edges, and clearing and fragmenting forests increases the amount of edge. In Peru, it has been shown that there are 278 times more malaria mosquito bites in deforested areas around human settlements than in forested areas. The worldwide scope and spread of malaria infections is widely predicted to increase alongside increasing deforestation. In Sumatra the risk of Dengue fever, another mosquito borne pathogen, decreases by 9% for every 1% increase in forest cover. Deforestation for agriculture is the most important factor in the spread of the mosquito borne Yellow Fever virus in Africa, and its recent resurgence in Brazil.

Another cause is the loss of biodiversity in fragmented forests, a good example of this is Lyme disease, a nasty human infection spread by ticks that have a complicated life cycle involving different animal hosts. When forest ecosystems are disturbed, there is a loss of diversity of animal species, especially large predators. This means a population explosion of small rodents such as the white tailed mice who act as super spreaders for the Lyme disease organism, and also herbivores such as white tailed deer – who are the main host for the adult ticks. Effectively the more the forest is fragmented, the higher the mouse density and the higher the disease risk to people. And cases are on the rise.

Sometimes removing forests and destroying habitat brings wildlife into human dominated areas. In South East Asia there has been loss of 30% of the forest cover over the last 40 years. This changing landscape has brought more and more bats to human settlements – forest is less available, house lights attract the insects they feed on and various handy niches mean different species of bat living together for the first time. All this leads to a high concentration and diversity of bat viruses with an increased risk of the viruses evolving, adapting to different species and being spread by direct contact, domestic animal infection or contamination by urine or faeces. This was the mechanism of the emergence of SARS virus via civets, Hendra virus via domestic horses and Nipah virus via domestic pigs. And bats are not the only culprits; wild rodents are the carriers of Hanta virus, which causes hemorrhagic fever or pulmonary syndrome in people, and the rodent populations increase following deforestation.

The deforestation of uplands also leads to soil erosion and flooding, this has led to outbreaks of leptospirosis in people living downstream, in addition to water borne pathogens such as norovirus, campylobacter, cholera and giardia.

Protect the forests, protect ourselves

So this is one of the many reasons that humans need to take stock of what forests really mean to us. ‘Regulation of pathogen emergence’ is just one more service to add to the list of amazing things that intact, undisturbed forest ecosystems do for humankind. If we want to avoid more and more future pandemics, we need to stop destroying what is left of the world’s forests.

If this has inspired you to want to take action, consider becoming an earth protector and support the introduction of a law against ecocide here: https://www.stopecocide.earth/become

Or consider becoming a treesister, giving money each month towards the reforestation of the tropics. More info here: https://treesisters.org/about-us

References:

Afelt et al (2018) Bats, Coronaviruses, and Deforestation: Toward the Emergence of Novel Infectious Diseases? Frontiers in Microbiology

Gottwalt, A (2013) Impacts of Deforestation on Vector-borne Disease Incidence; Journal of Global Health

Patz et al (2000) Effects of environmental change on emerging parasitic diseases; International Journal for Parasitology

Wilcox, B & Ellis, B (2006) Forests and emerging infectious diseases of humans; UNASYLVA-FAO-