Urban Landscapes & COVID-19
Author: Brenna Crossley
MPH Student: Environmental Systems and Human Health
Exponential growth of the human population significantly impacts urban expansion and land utilization. As cities grow and landscapes are shaped for agriculture, irreparable damage to environmental health promotes the spread of infectious diseases.
Animal Ecology Meets Urban Landscapes
Key Points
- Expansion of urban areas impedes on the natural habitats of wildlife, forcing humans and wildlife in close proximity, creating opportunity for transmission of zoonotic pathogens
- Forest degredation and fragmentation from expanding urban areas changes the intra- and interspecies interacations and behaviors of wildlife.
- Hot spots of zoonotic diseases are clearly where urbanization trends are rising (Neiderud 2014).
Bat Ecology, Urbanization, and COVID-19
Anthropogenic (human) changes shape animal ecology; the subsequent interactions between humans and animals are responsible for newly emerging infectious diseases (EIDs), including the novel coronavirus, SARS-CoV-2.
Bats are important reservoirs to public health
They inhabit every continent and harbor multiple pathogens of clinical significance to humans, including coronaviruses, henipaviruses, and filoviruses (Letko et. al 2020).
Human influences create environmental stressors that cause fundamental changes in the ways bats behave - SARS-CoV-2 is an example of one outcome (White 2020).
Zoonosis: any disease of infection that is transmissible from vertebrate animals to human hosts (WHO).
Vector Biology: Bats
Distruptions to the natural balance of biological systems creates disturbances in the "chain of infection," leading to conditions that favor the transmission of infectious agents.
This photo illustrates the intricate biological systems that are key for bats to tolerate high levels of virus. Note that reservior host ecolgy, changes in human-animal contact rates, and viral mutation rate are deeply interconnected to land-use.
Spillover of viruses from animal reserviors
During times of stress, bats start to shed infectious viral particles, whic can lead to "spillover"events (Letko et. al, 2020)
Spillover events: viral transmission between two different species
For viruses to spillover from bats to susceptible hosts hosts, certain factors need to be met such as ecological opportunity for contact, molecular compatibility, and lack of detection by the innate immune system of the host (Letko et. al 2020).
Wet markets are human-created "microenvironments" that house different types of animals in small cages. This situation is stressful for bats and can initiate viral spillover. This environment also fosters suscepetible hosts with clear entry points for disease (cuts on hands, body fluids) that allows for transmission of viruses (Jandu, 2020.)
Adaptive capacity: the ability of an animal to respond to ecosytem and climate changes.
This capability is highly dependent upon specific species; however, some bats are able to build large roosts and thrive in urban environments (Field 2009).
Bats can be chronic carriers of disease, but are not always pathological because the immune system can keep viruses "in-check."
When bats (the reservoir) begin to shed the virus (SARS-CoV-2), people at risk can become infected.
COVID-19: Not First and Not Last
75% of emerging infectious disease over the past decade were from zoonotic origins (Ahmed et. al 2020)
Human urbanization trends are only increasing and therefore bat ecology will continue to shift and threaten future spillover of clinically significant novel viruses (Nabi et al. 2020.)
Bats have been the culprit behind previous significant and deadly outbreaks: Ebola, Nipah virus, and other SARS-like coronaviruses (Field 2009), such as Middle Eastern Respiratory Syndrome
Evidence suggests several of these viruses are ancient in the bat population, but have only recently become "emerging pathogens" due to ecological stressors on bat populations from urbanization and agriculture (White 2020).
"Given the enormous diversity of viruses in wildlife and their ongoing evolution, arguably the simplest and most cost-effective way to reduce the risk of future outbreaks is to limit our exposure to animal pathogens as much as possible" (Zhang, 2020).
Inequities of Urbanization and COVID-19
Critical relationships exist between urbanization, the increasing poverty gap, and zoonotic diseases. The factors that influence emerging infectious diseases (including land use changes and increased animal trade) disproportionately impact those living below the poverty line (Ahmed et. al 2020).
Urban centers act as force multipliers that can make residents more susceptible to zoonotic diseases, specifically those living below the poverty line and without health insurance (Wu et al. 2016).
And while COVID-19 has (rightfully) caught international attention, emerging zoonotic diseases in developing countries may go unnoticed and unresearched (Wu et al. 2016).
Current Research & Future Opportunities
Bat ecology is poorly understood and efforts to understand mechanisms of virus-host interactions are important to predict patterns of emerging infectious diseases
Research to better understand mechanisms of viral spillover and environmental stressors that favor spillover from animal reservoirs to susceptible hosts (Letko et. al 2020)
Implementation of stronger surveillance systems in at risk populations
Bans on wildlife trade and legislation to protect natural environments
Focus on environmental health in new urban development planning
Video (1:10m)
Video Text
The environment is intimately connected to our public health. As cities expand and human activity irreparably damages environmental health, infectious dieases spread. Exponential growth of the human population and rising urbanization trends create hotspots for zoonotic pathogen transmission. That is because anthropogenic influences shape animal ecology by fragmenting habitats and by forcing humans and animals into closer contact. These factors create environmental stressors that lead to newly emerging infectious diseases. The global burden of disease is not shared equally, and COVID-19 has brought into clearer focus the extent of the disproportionality of zoonotic diseases. As we look to the future, action prioritizing environmental health and equity must be at the forefront. Without a healthy environment, public health suffers.
References
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