Infectious Diseases, Animals, and Our Natural Environment
According to a 2018 Rockefeller Foundation report changes to our natural environment are responsible for a “continued regularity of infectious disease outbreaks in humans”? The World Bank estimates that infectious disease outbreaks cost the international community $30 billion US a year. The Severe Acute Respiratory Syndrome (SARS) outbreak in 2003, which was felt in Canada, was estimated to cost $54 billion US. The current COVID-19 disease – which is thought to have jumped from animals to human’s in a dense animal market in Wuhan, China – has already, by several times over, exceeded the 774 deaths due to the SARS. One of the core but not well-known contributors to infectious disease are human-caused changes to the environment – known as environmental drivers.
Background
Infectious diseases are caused by microorganisms such as bacteria, viruses, fungi or parasites. Infectious diseases can be transferred to a human in different ways. Direct transmission occurs when an infected human or animal comes into contact with another human through, for example, inhaling germs from the infected person or animal, touching a surface with germs left by the infected person, or being bitten by an infected pet. Indirect transmission occurs from an infected human or animal to another human via a carrier such as a mosquito, tick or flea (known as a vector organism) or coming into contact with contaminated food or water. According to the US Center for Disease Control 3 out of 4 emerging infectious diseases are from animals – COVID-19 is an example. Thus we need to reconsider how we interact with vector organisms and other animals such that future outbreaks are reduced. Environmental drivers such as climate change, intensive animal farming, and deforestation significantly contribute to these interactions.
Climate Change and Infectious Disease
Climate change contributes to infectious disease transmissions due to increased temperatures and changing patterns of precipitation. These changes affect organisms (known as vectors) such as mosquitoes that carry diseases to humans. Temperature increases lengthen the disease transmission period as well as the geographical range of vectors. Put in another way an early spring means more mosquitoes in high-latitudes with more time to take the disease to a human host. What is worse is that, in Canada, climate warming is predicted to be increasing at twice the rate of the rest of the world. According to recent research, within the next century more than a billion people could be threatened with infectious diseases such as dengue, chikungunya, and zika due to the greater presence of mosquitos and the research predicts a net increase in transmission risk for Canada. The federal government’s own website indicates that Canada will need to face infectious disease risks currently faced by the US and will also need to face the re-emergence of infectious diseases endemic to Canada.
Intensive Livestock Farming and Infectious Disease
Intensive animal farming is the keeping of animals at high densities to gain economic efficiencies in order to produce great quantities of meat and other animal by-products. To ensure that animals do not get sick in these highly dense environments significant quantities of antibiotics are used. According to the WHO in some countries over 80% of medically important antibiotics are used for livestock and recent research also says that a majority of antibiotic usage occurs in agricultural settings. As a result, targeted bacteria develop what is known as Antimicrobial Resistance (AMR) and can get into meat consumed by humans. Fruits and vegetables can also become contaminated through contact with animal waste. A working group created by the British government to review AMR said that if AMR were to continue unchecked, by 2050, ten million people worldwide would die annually from infections that could no longer be treated. According to the World Health Organization (WHO) “Antibiotic resistance is one of the biggest threats to global health, food security, and development today.” Bacteria resistant to antibiotics can spread all around the world. Examples of diseases that are already more difficult to treat include urinary tract infections which affect one in two women and one in ten men, pneumonia tuberculosis, gonorrhoea, and salmonellosis.
Infectious diseases have also come about just from the domestication of animals itself (even without the use antibiotics). This been researched by Dr. Michael Greger in his book Bird Flu: A Virus of Our Own Hatching published in 2006. He quotes a US Center for Disease Control (CDC) 2004 statement indicating that “11 of the last 12 emerging infectious diseases that we’re aware of in the world, that have had human health consequences, have probably arisen from animal sources.” and cites the domestication of animals as the root cause of these new as well as old infectious diseases throughout history. The author indicates that for early human settlements “it was the domestication of animals for agriculture that brought people in contact with a whole new array of pathogenic germs”. These pathogens spread rapidly from different members of the same species to humans due to the close proximity of humans to the confined spaces occupied by domesticated animals. The author lists various diseases thought to be transferred from animals to humans due to the above normal density of these domesticated animal settings. “We domesticated pigs and got whooping cough, domesticated chickens and got typhoid fever, and domesticated ducks and got influenza.” He continues by providing other examples. Evangelyn Alocilja, a professor of biosystems at Michigan State University, said to Global News that the probable source of COVID-19 disease – the wet markets with live animals in Wuhan, China are – “the narrow, crowded markets — brimming with everything from freshly caught fish to live poultry and reptiles — are a breeding ground for new and dangerous infections”. Moving away from these high density animal settings is thus an objective that must be pursued.
Deforestation and Infectious Disease
New research is showing that deforestation is leading to infectious disease transmissions. Newly cleared forests – cleared for human uses – bring animals and vector organisms closer to humans. This close interaction between vectors, animal hosts and humans has led to infectious diseases spreading to humans. The risk of a disease outbreak is much greater after forests have been cleared for agriculture and roads. Research has also shown that preserving forests to a certain degree (instead of converting to agriculture land) is cheaper than treating patients with infectious diseases arising from the corresponding deforestation. The results recommended the reforestation of 769 million hectares of land globally to minimize the economic impacts of emerging infectious diseases (the calculation for this amount included profits from agricultural land use). Also, consider the case of one region of Peru where in the 1990s malaria went from 600 to 120,000 cases after deforestation for roads and farms.
Conclusion
Other environmental drivers not discussed above but relevant to infectious diseases include irrigation, urbanization and marine pollution. Dealing with these causes of infectious disease requires dealing with the aforementioned environmental challenges. For instance, taking action on your own to fight climate change, reducing intensive animal farming practices by eating less meat, and reducing deforestation by always recycling when appropriate are steps you can take to face these environmental challenges and thus help reduce infectious disease outbreaks. It is important to recognize that a healthy environment has protective effects when it comes to preventing infectious disease.
