The link between deforestation and pandemics

Human beings have spent thousands of years building a dysfunctional relationship with nature, working against an unstoppable force which is now slowly destroying both.

Although deforestation does not directly cause all disease outbreaks, it definitely has an impact on the emergence and re-emergence of sicknesses capable of reaching pandemic proportions.

United Nations Environment Programme (UNEP) executive director Inger Andersen warns that Covid-19 is not a silver lining for the environment. Despite reports that the air is cleaner and wildlife is returning to quiet urban streets, Andersen has lamented that for there to be any significant difference in carbon dioxide levels, a 10% global decline in fossil fuel use for more than a year would have to be practised.

“Human activity has altered almost 75% of the earth’s surface, squeezing wildlife and nature into an ever-smaller corner of the planet. And yet, nature is critical to our own survival,” she said.

Nature’s anger and our arrogance could mean an increase in virus and disease outbreaks.

Disease outbreaks linked to deforestation

The link does not at first seem obvious, but a 2016 study exploring landscape factors and malaria infections in Malaysia revealed that deforestation was one of the main catalysts in the region’s increase in malaria deaths.

Deforestation and related activities were associated with changes in malaria vectors (any agent that carries and transmits a disease), populations and related disease incidence globally, mostly affecting residents living in areas bordering forests.

Vector-borne and zoonotic viruses, also called arboviruses, refer to viruses transmitted through bloodsucking anthropods, such as mosquitos and ticks, and through animals, explained head of the zoonotic arbo- and respiratory virus research programme at the University of Pretoria’s medical virology department Professor Marietjie Venter.

“Arboviruses and zoonotic viruses usually circulate between an animal host and arthropod vectors or between animals, and are transmitted to humans incidentally. These viruses make up up to 70% of emerging and reemerging viruses,” Venter said.

The deforestation link comes in when the habitat of an animal host is disturbed, which forces them to move to areas where they come into contact with humans, Venter explained. Also, if an animal’s habitat is altered, this could cause mosquitoes that feed on humans to flourish, she added.

Professor and director of the Centre for Viral Zoonoses at the University of Pretoria’s Faculty of Health Sciences Wanda Markotter reiterated the links between deforestation being a factor leading to disease emergence.

“It brings people into contact with an ecological system where they did not normally live, including animals that can carry novel viruses that our immune system cannot protect us from,” Markotter said.

Clearing forested areas also draws animals out of the forest to where their new human neighbours live, which increases contact with them, such as rodents eating leftover food, or fruit bats feeding on nearby trees. Humans come into contact with wild animals by hunting and killing them, entering their habitats, or have animals invade areas occupied by humans, and coming into contact with urine and faecal matter, Markotter explained.

This facilitates viruses spreading from animals to humans.

The more people and wild animals interact, either due to illegal activities, urbanisation or live animal markets and the illegal wildlife trade, the more likely it is that diseases will move from hosts to vectors to human beings.

Current examples of habitat destruction and viruses

The world’s second-largest tropical forest, the Congo, is mostly located in the Democratic Republic of Congo (DRC).

Forest Legality states that the DRC’s portion of the Congo forest is between 112 and 154 million hectares, home to over 10,000 plant species, 409 mammal species, 1,117 bird species, and 400 species of fish.

But industrial logging, which has led to the construction of logging roads and subsequent poaching increases, has become a serious threat to the Congo forest.

This coupled with slash-and-burn techniques used to clear forests for agricultural activities, mining, the bushmeat trade, political uncertainty and civil unrest sealed the deal on damaging whole areas of previously untapped forest.

Observing the number of zoonotic diseases currently plaguing DRC residents – malaria, Ebola, measles, yellow fever, dengue fever, the zika virus and SARS-CoV-2, to name a few, reveals a pattern.

If this carries on, it is likely that pandemics and outbreaks will continue to infect and affect millions.

Although the DRC is an extreme example, the number of zoonotic diseases thought to have been caused, at least in part, by deforestation in this region alone, cannot be ignored.

This was confirmed by Markotter, who said studies conducted on the zika virus and malaria showed these viruses increased as more deforestation occurred. Lassa fever, a rodent-borne disease, is also spread when humans and rats come into contact due to landscape changes.

Habitat destruction has also been associated with humans getting sick with HIV, Sudden Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), Rift Valley fever, avian flu, swine flu, the West Nile virus, the Marburg virus, Chikungunya, and the Hendra virus, said Venter and Markotter.

Warning signs for future pandemic prevention

UNEP flagged the potential increase in zoonotic diseases four years ago, saying that 75% of all infectious diseases affecting humans were zoonotic, and linked to the health of ecosystems.

In UNEP’s ‘Frontiers 2016: Emerging issues of environmental concern’, it reported that, on average, one new infectious disease emerges in humans every four months.

But epidemics emerge during times of crises, such as disasters caused by climate change, and severely affect the most vulnerable communities and poorer regions.

The report also revealed that zoonoses are “opportunistic”, and target hosts already distressed by environmental, social or economic circumstances.

According to the United Nations Food and Agricultural Organisation (UNFAO), deforestation in natural forests in South Africa is at present “insignificant”, but cannot be ignored, due to the size and fragmented nature of this resource.

In South Africa, there are three forest types: natural forests, savannah woodlands and industrial plantations.

In 2015, the UNFAO reported the savannah woodland biome covered about 40 million hectares, but lost between 50,000 and 100,000 hectares to deforestation every year.

Global Forest Watch data showed that between 2011 and 2018, in dense canopy areas with 75% or more tree cover, 22,432 hectares on average were lost each year. Since 2000, tree cover in these areas diminished by just over 50%.

These areas are vital carbon sinks that help keep our air clean, but are being lost to deforestation at rapid rates. Between 2011 and 2018, KwaZulu-Natal lost 27,931 hectares of tree cover – more than any other province.

Striking a balance

For humans and animals to co-exist is mutually beneficial. But this can only be achieved when we acknowledge the link between destroying habitats and the prevalence of diseases, Markotter said.

“Living in close proximity to wild animals means basic risk-reduction activities can be included to minimise contact with humans as well as livestock and domestic animals. For example, proper waste management, restricting access to human dwellings and food, and alternative sources of food to avoid bushmeat consumption,” she explained.

Markotter warned that if a “spillover” occurs – when a virus or bacteria moves from a host animal to a human – there must be surveillance systems in place, both in humans and in animals, for early detection and intervention, to limit widespread disease dissemination.

South Africa can easily minimise its existing deforestation rates, and is not one of the African countries in focus when it comes to humans infringing on wildlife – yet.

Venter emphasised that urban planning and natural resources must be treated in an environmentally friendly way, “not only to ensure the sustained and safe future of wildlife in the wild and natural habitats, but also to minimise risk of exposure between potential reservoir host animals, intermediate hosts and humans, as well as establishment of microclimates where mosquito vector species such as Aedes aegypti and Aedes albopictus or Culex mosquitoes could flourish and establish new outbreaks.”

Venter lamented the illegal wildlife trade and the importation of animal or arthropod vectors into new regions, which increases the risk of unknown disease transmission. The abolishment of this industry must be an international effort, to prevent pandemics, for the sake of animal and human health.

There are many hectares of untapped South African forest that can easily be occupied by humans. Taking note of what has happened to our African neighbours living in areas surrounded by dense forest should be a wake-up call for us not to let our greed put our health at risk.

For more news your way, download The Citizen’s app for iOS and Android.