Zoonosis and emerging diseases

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TWH – The last forty years have seen many new Emerging Infectious Diseases (EIDs) arise, some of which have become pandemics, including COVID-19.

These diseases have had varying severity with about 60% of them originating in wild animals,  The diseases then spill over into the human population. Scientists label these spillover diseases as zoonotic diseases.

Increased human penetration into a shrinking wilderness is driving an increase in some zoonotic diseases. In the developing world, poverty and agricultural expansion into forests causes this penetration. In the developed world, people recreating and developing forested areas drive it.

Image credit: Pixabay

 

Zoonosis

Zoonotic diseases do not always emerge from exotic origins nor are they fatal or uncommon.  The fungal infection commonly called ringworm is considered a zoonotic disease in that it can be transmitted from a domestic animal like a dog or cat to a human.

But there are rarer and often more serious and even untreatable doses that can merge from human contact with wild animals. That type of zoonosis typically occurs when humans interact with animals species that make their way into urban environments.

Some of these diseases can be dangerous. A famous example is Yersinia pestis, the bacteria that causes plague transmitted to humans via fleas from rats. And of course, rabies.  These represent interactions humans have with non-domesticated animals in urban environments and many of these diseases are well known to science.

However, new diseases can enter human populations as humans attempt to exploit and sometimes even urbanize the wilderness. The effort results in increased contact between different species, including humans, that rarely interact naturally.

Habitat fragmentation is one such example of how those interactions are propelled.  The term refers to breaking a large forest habitat into an archipelago of forest patches. The result is increased human interaction with the wilderness in a manner that rarely favors wildlife. But the interaction has a dangerous effect on the human population as well.

Satellite image of deforestation in Brazil – Image credit: Planet Labs, Inc. –  CC BY-SA 4.0,

Fragmentation restricts foraging, mating, and predation to small areas. Animals are in closer contact with one another and ultimately humans, facilitating disease transmission. In an intact forest, animals can go deeper into the forest to avoid human contact. In a fragmented forest, this becomes impossible. This increases the chances for diseases to move from an animal species to the human species.

Recent zoonotic EIDs include the H5/N1 avian influenza outbreak, the “swine flu” H1/N1 influenza pandemic, and the West African Ebola outbreak. Not all of these were the result of habitat fragmentation and increased human penetration into forests.

However, of all recent zoonotic diseases, HIV has produced the greatest number of fatalities. According to the World Health Organization (WHO), HIV has killed 32 million people around the world as of November 2019.

There is also little evidence that human encroachment on the wilderness will abate. Increases in the human population, changes in the climate, and poverty will all impact the interaction humans have on wilderness areas and wild animals.

Agricultural expansion into tropical forests

Humans have cleared extensive amounts of previously forested lands for agriculture. Recent years have seen this expansion speed up at the expense of tropical forests. About 75% of all forest loss in Africa results from this agricultural expansion. Indigenous wildlife raid crops for food. Humans go into the forest to hunt and to forage. According to Dr. Eric Lambin of Stanford, “We are forcing the interaction through transformation of the land.”

“Logging and subsistence agriculture in Africa are reducing habitat for wild primates.” Gillespie said, “They have less forest to forage in. That can make them unhealthy and more susceptible to disease. And it may drive them to risk encounters with humans, raising risks of the exchange of pathogens.”

Diseases can move more easily between similar species, such as humans and other primates; but occasionally they move across intermediate animal populations as well before entering human hosts.

Poverty also drives the interactions with wildlife as individuals seek new land for planting food as well as enter wild areas in search of food.

Zoonotic diseases do not just occur in the Tropics

Spillover events occur outside of the Tropics. Lyme disease, for example, emerged in the U.S.

Cities, particularly through the development of suburbs and exurbs, are expanding deeper into forested areas. Hiking, canoeing, and recreational activities, as well as hunting, bring people into the wilderness. These factors increase the chance of contact between humans and wild animals in various parts of the U.S.

The good news is that zoonotic diseases can easily be prevented and avoided. The CDC recommends that everyone wash their hands anytime they interact with animals even if you don’t touch them.  They also suggest wearing appropriate clothing while outdoors to prevent bites from fleas, mosquitoes, and ticks; all of which can harbor diseases.

And of course, enjoy wildlife from distance.

Many Pagans relish their time outdoors and do so safely whether that means a visit to the wilderness or simply exploring the backyard with an animal friend. Visiting nature can be a positive and healing experience as long as we respect our place within it and honor our relationship to the planet.