Here's a useful description of zoonoses like COVID-19 that helps explains how these diseases are transmitted and what risk they pose to humans. Ref: Walzer C, “The COVID-19 Pandemic Has Introduced Us to a New Word: Zoonosis (Op-Ed)” (Live Science, April 2020)
Zoonoses are infectious diseases — caused by bacteria, viruses, fungi or parasites — that spread from animals to humans. They can be transmitted through direct physical contact, via air or water, or through an intermediate host like an insect. Often these zoonotic pathogens do not affect the animals in which they reside, but they can represent an enormous risk to humans who have no natural immunity to them.
Around 60% of the emerging diseases reported globally are considered to be zoonoses, and 75% of new human pathogens detected in the last 30 years originated in animals.
Current investigations of potential zoonotic viruses, funded by the U.S. Agency for International Development's (USAID) PREDICT program, suggest that there are over 1.6 million unknown viruses in birds and mammals. Based on decades of expertise, an estimated 700,000 of these agents could pose a zoonotic risk, according to the Wildlife Conservation Society.
The more we come into contact with wildlife, the more we risk being affected by pathogens we have no immunity against. Animals coming into contact with other animals also creates an opportunity for pathogens to get into new hosts, creating new strains.
Contact between different living things can increase due to the following environmental issues:
- Destruction of forest habitats for logging, mining, housing, road building, to create land for crops (including bio fuel plants), etc. Main causes for this destruction include consumer demand from richer countries and population growth both in both rich & poor countries.
- Densely packed populations where humans, animals, birds and other living things live together.
- Live animal markets, where animals are slaughtered and sold, provide much of the food for Africa and Asia. In poorer countries these can be close to open refuse dumps.
- There are massive concentrations of domesticated animals in large livestock farms around the world, some of which can be home to pathogens, like the flu.
- As the planet heats up due to global warming, animals are headed to new habitats nearer to the poles to get out of the heat. Read “What Are the Main Causes of Climate Change?” (OneSharedEarth, July 2018) for causes of global warming.
“Coronavirus, Climate Change, and the Environment” (Harvard T.H. Chan School of Public Health, March 2020)
“First Person: COVID-19 Is Not a Silver Lining for the Climate, Says UN Environment Chief” (UN News, April 2020)
THE EDITORS, “Stopping Deforestation Can Prevent Pandemics” (Scientific American, 2020)
Vidal J, “‘Tip of the Iceberg’: Is Our Destruction of Nature Responsible for Covid-19?” (The Guardian, March 2020)
Walzer C, “The COVID-19 Pandemic Has Introduced Us to a New Word: Zoonosis (Op-Ed)” (Live Science, April 2020)