There is no denying the impacts humans have on the environment, from the influence of extractive industries to the long-term effects of climate change. How we interact with the landscape and natural processes has consequences that we are only beginning to observe and fully appreciate on a global scale.
While COVID-19 was the first severe pandemic of the 21st century, it will not be the last. With continued climate change, infectious diseases like COVID-19 will continue to be of increasing concern. The sustainability of people and the planet are interconnected, just like a virus and its host. Like the game Jenga, where players remove one block at a time from an increasingly unstable structure, we are now toying with habit humanity.
Some of these interactions, like zoonosis, or the process by which a disease or virus can become transmissible between animals and humans, were covered widely with the onset of the COVID-19 pandemic in 2020. Diseases derived from zoonosis are not new, with some notable zoonotic diseases including Ebola Virus, West Nile Virus, Severe Acute Respiratory Syndrome (SARS), and Middle East Respiratory Syndrome (MERS). Now, it’s time we acknowledge the stark consequences of our actions. Like
While many factors exacerbate the prevalence and spread of zoonotic diseases, drivers such as climate change, deforestation, and urbanization play a significant role. As humans and wild animals are pushed into closer proximity, novel variations of diseases can emerge, causing them to “jump” from animal to animal and from animal to human.
Changing the Landscape
As humans move into forested lands and begin anthropization – the transformation or adaptation of the environment – a shared understanding holds that this decreases the area’s biodiversity. While this statement can be true, it is not always the case. In a 2018 paper, Bats, Coronaviruses, and Deforestation: Towards the Emergence of Novel Infectious Disease? The author Afelt et al. note that:
“…anthropization generates a highly diverse environment […] unlike natural environmental landscapes, which are highly selective, these altered landscapes are acceptable by a wide range of bat species, usually not encountered together.”
This allows for the spread of novel infectious diseases between bat species that might not otherwise be encountered together. The anthropized landscape may also offer environmental niches specific to each bat species that can bring them into more intimate contact with humans. Afelt et al. note that barns and houses can provide shelter and protection for cave-dwelling bats.
Simultaneously, orchards and farmland offer food sources for frugivorous bats, while houses and streetlights provide ideal hunting grounds for insectivorous bats. Pets and farm animals in these anthropized landscapes can become intermediate hosts of these emerging infectious diseases (EIDs). Dromedary camels, which played a role in the spread of MERS in 2012, are just one example of a notable intermediate host.
Climate Change and EID Acceleration
EIDs have been on the scientific radar for decades, but the rate at which EIDs arise has been increasing. In the 2008 paper entitled Global Trends in Emerging Infectious Disease, Kate Jones et al. note that between 1940 and 2004, 335 EIDs arose, and 60.3% were caused by zoonosis. Of these, 71.8% of zoonotic EIDs originate in wildlife.
The number of EIDs caused by zoonosis originating from wildlife has increased with time, supporting assertions that zoonotic EIDs will continue to threaten global health. The increased frequency of zoonotic EID-emergence, in tandem with environmental factors such as climate change, deforestation, and urbanization, suggests that the outbreak incidence of EIDs with epidemic potential is increasing.
The United Nations Environment Programme 2016 report on Emerging Issues of Environmental Concern notes that climate change is a significant factor in the emergence of zoonotic diseases. The UNEP notes that climate change “influences the environmental conditions that can enable or disable the survival, reproduction, abundance, and distribution of pathogens, vectors, and hosts, as well as the means of disease transmission and outbreak frequency.”
Just as the anthropization of the landscape can facilitate the emergence and transmission of novel infectious diseases, the effects of climate change can also play a role in the scope and severity of the disease by affecting changes in rainfall patterns, temperatures, and humidity.
Hantavirus pulmonary syndrome (HPS) is a viral respiratory disease transmitted to humans via aerosols that can be inhaled from rodent urine, feces, or nesting materials. In a 2016 paper titled Climate Change and Respiratory Infections, Mirsaeidi et al. looked at the first outbreak of Hantavirus in Central America in the Los Santos Province, Panama (1999-2000). Just before the HPS outbreak, Los Santos received a two- to three-fold increase in average rainfall between September and October. This helped increase the local rodent population, resulting in more rodent contact with Los Santos residents.
A 2004 paper published by United States Centers for Disease Control (CDC) looked into the Los Santos outbreak in greater detail and found a link between atypical rainfall patterns and increased rodent populations. HPS patients from the town of Las Tablas in the province of Los Santos reported seeing a substantially higher number of rodents in their neighborhood two months after the heavy rainfall.
The CDC paper also looked at other environmental factors contributing to the rodent outbreak, which, unsurprisingly, points to deforestation. The paper identified the short-tailed cane mouse and the Northern pygmy rice rat as possible Hantavirus hosts. The widespread conversion of forests to commercial logging and agricultural lands in the Los Santos province provides the ideal habitat for rodent populations. The increased rodent habitat and heavy rainfall led to an increased rodent population and the likelihood of rodent-human contact.
The example of the Hantavirus outbreak in Los Santos, Panama, finds itself at the intersection of human and climate factors that can render the environment hospitable for new infectious diseases. Deforestation and land conversion for agricultural practices and urbanization change the land and bring humans closer to wild animals, increasing the likelihood of an EID’s “jump” from animals to humans. Compounded the effect of climate change on temperature, humidity, precipitation patterns, heat waves, and droughts can facilitate the spread and severity of an EID outbreak.
What will happen next? When will the next epidemic strike? We should be asking and answering those questions now.