Emerging Infectious Diseases and Vector-borne Diseases, Climate Change and Sustainable Options

 I feel that, sadly, we have forgotten the potential ‘new normal’ that many of us hope for when we imagined a world emerging from COVID-19 lock downs. In response, I figured this to be a good chance to revisit a call for sustainable practice by exploring the impact of anthropogenic climate change and other anthropogenic factors on the prevalence of emerging infectious diseases (EIDs) and known infectious diseases across the globe.

The question the world needs to answer is: Can sustainable practices mitigate against the risk of EIDs?

To address this question, let’s explore the risk of EIDs on global health before addressing the positive correlation between EIDs and anthropogenic factors such as climate change, globalisation and urbanisation. What we will find is that sustainable practices might assist in mitigating the risks generated by these anthropogenic factors, helping to reduce the rate of new EIDs and reducing the spread of known infectious diseases around the globe.

Vector-borne and zoonotic diseases

Since early 2020, the world has been dealing with a full-blown pandemic of the SARS-CoV-2 virus, causing a novel pneumonia (COVID-19) (Anderson, Rambaut, Lipkin, Holmes & Garry, 2020) which, as of 5 June 2022, was reported to have infected at least 535,233,208 people, and caused at least 6,320,069 deaths globally (Worldometer, 2022). Anderson et al. (2020) suggest two likely origins for SARS-CoV-2, natural selection in an animal host prior to zoonotic transfer, or natural selection in humans after zoonotic transfer. Zoonotic transfer, the direct transfer of a disease from animal to a human (Marshall, 2011) is the basis for both scenarios, and is viewed as a growing threat to global health (Wallace-Wells, 2019). Included in this threat is the transfer of vector-born zoonotic diseases (VBZDs), which are transmitted predominantly by blood feeding arthropods (Swei, Couper, Coffey, Kapan, & Bennett, 2020) such as mosquitoes, as well as rodent-borne and other mammalian based zoonotic diseases such as those carried by bats (Semenza, Rocklov, Penttinen, & Lindgren, 2016). Examples of infectious diseases carried by vectors include well known diseases such as malaria and zika, while an example of a zoonotic EID is SARS-VoC-2, as it was not known prior to its recent identification in humans.

The potential impact of vector-born and zoonotic diseases on global health

As the SARS-CoV-2 pandemic continues to highlight, EIDs have the potential to significantly impact all aspects of life across the globe, with the most severe impact being death due to a disease. Languon and Quaye (2019) state that 25 percent of the 60 million global deaths recorded each year are estimated to be due to infectious diseases, and that was before COID-19. Yet even without having a sizable mortality rate, the ability for EIDs to spread internationally in a short period means that the financial cost of a pandemic may amount to tens of billions of dollars (Semenza et al., 2016). The potential impacts on health, economics and the well-being of societies posed by EIDs is already a reality for much of the globe when considering the devastating impact of the vector-borne disease malaria. The World Health Organisation (WHO) (2019) reports there to be 219 million cases of malaria across the globe each year, with more than 400,000 deaths, 61% being children under the age of five. WHO further states that while there was a 22% reduction in cases and a 50% reduction in deaths between 2000 and 2015 due to eradication attempts, numbers have remained relatively unchanged since then. Malaria is one of several vector-borne infectious diseases impacting millions of people each year, a list that also includes yellow fever, dengue fever, zika virus and Marburg virus disease. As an example of the economic costs of such diseases, a 2011 study found the total global cost related just to dengue fever to be almost 40 billion USD (Selck, Adalja & Boddie, 2014).

The relationship between vector-born Zoonotic disease distribution and anthropogenic factors

Just as there is clear evidence of the potentially catastrophic impact of EIDs, and the already significant impact of known infectious diseases such as malaria, there is also evidence of a steady rise in the emergence of new EIDs (Swei et al., 2020) and in cases of known infectious diseases in certain geographical areas (Reiter, 2001). Neiderud (2015) indicates that of the 335 EIDs recognised between 1940 and 2004, more than 60% were zoonotic diseases, supported by Heffernan’s suggestion that “since the 1940s, the majority of emerging infectious diseases have originated from animal species” (2017, pg. 43). The increase of recognised EIDs has paralleled a range of factors closely linked to the rapid rise of global GDP and global population since 1960. The World Bank (2020) indicates that global GDP has grown from 1.37 trillion USD in 1960 to 85.911 trillion USD in 2018, and that the global population grew from 3.032 billion in 1960 to 7.594 billion in the same period (World Bank, 2020). Such rapid economic and population growth has resulted in activities found to be directly linked to increased disease emergence and prevalence, such as agricultural expansion to secure food supplies (Ahmed, Jeffree, Hughes & Daszak, 2019), increased global trade (Semenza et al., 2016), increased mining exploration (Kilpatrick & Randolph, 2012) and high rates of urbanisation (Neiderud, 2015).

In a summary of factors related to an increased risk of EID spread, Semenza et al. (2016) present a list of drivers of infectious disease threat events under three key headings:

1. Globalisation and environment: Climate, natural environment, human-made environment, travel and tourism, migration and global trade.

2. Social and demographic: Demographic, social inequality, vulnerable groups, prevention, lifestyle, occupation and terrorism.

3. Public health systems: Healthcare systems, animal health, food and water quality, and surveillance and reporting.

Of these, travel and tourism, food and water quality, natural environment, global trade and climate were found to be the most noteworthy driver categories regarding the threat of infectious disease events in Europe (Semenza, Lindgren, Balkanyo, Espinosa, Almqvist, Penttinen & Rochlov, 2016). Let’s mpw focus on one of these key risk drivers, climate, before discussing sustainable solutions to mitigate against it being a persistent driver of risk.

The impact of climate on vector-borne and zoonotic diseases

To accurately assess the impact of climate on vector-borne and zoonotic diseases, it is useful to shift from ‘outcome’ to ‘cascade’ measures, the latter being defined as “incremental impacts and influences of change across the biological, social and wider environmental factors important to identifying the interplay between climate change and disease.” (Heffernan, 2017, pg. 44). This allows for the identification of climate impacts as ‘synergistic’, the combination of abiotic (nonliving) and biotic (living) factors acting together to impact disease processes, as well as a range of amplifiers and mitigators that either enhance or decrease disease processes (Heffernan, 2017). In other words, lets assess things relationally, not in a linear fashion.

A cascade approach identifies that an anthropogenically induced increase in greenhouse gasses in the natural environment (an abiotic factor) are likely to expedite the rate of global warming (Mahmoud & Gan, 2018; Wallace-Wells, 2019), resulting in changes in global rainfall patterns (Khasnis & Nettleman, 2005) which directly increase biotic factors such as the breeding ability of specific mosquitoes (Ades aegypti for example). These mosquitoes act as vectors for malaria or dengue, and these climate factors also shorten the incubation period of the viruses within the mosquitoes (Shope, 1991; Reiter, 2001). These mosquitoes with these enhanced ability to act as vectors might then be amplified by another anthropogenic action linked with the earlier mentioned global GDP growth, the being the increasing urbanisation occurring in countries with low per capita income (Neiderud, 2015). This urbanisation acts as an amplifier in the spread of these vector-borne diseases (Reiter, 2001).

Other climate related events which amplify the emergence of EIDs includes extreme weather events which spawn clusters of disease outbreaks (Epstein, 2001), the melting of Arctic sea ice exposing diseases such as smallpox and the bubonic plague (Wallace-Wells, 2019) and the encroachment on forests by humans for means of agriculture and settlement, a possible cause of climate change, and an action that results in increased contact with zoonotic diseases (Languon & Quaye, 2019).

Deforestation, while admittedly a likely causal factor of anthropogenic climate change rather than a direct symptom of it, is of significance in relation to the emergence of zoonotic EIDs, perhaps even the earlier mentioned SARS-CoV-2 virus currently causing the ongoing global medical emergency. While the intermediate host of SARS-CoV-2 is yet to be determined, it appears likely to be a mammal such as a bat (Zhang, Shen, Chen & Lin, 2020). Deforestation has been linked with the outbreak of bat-born zoonotic diseases, forcing bats closer to humans due to habitat destruction and increasing human-bat encounters through actions such as mining operations (Simons, Gale, Horigan, Snary & Breed, 2014; Neiderud, 2015). The impact of deforestation is summarised by Languon and Quaye when they state that “Using remote sensing techniques, it has been found that a positive correlation exists between deforestations (in both time and space) and EVD outbreaks in Central and West Africa, suggesting that a reduction of deforestation could decrease the chance of future EVD outbreaks.” (2019, pg. 9).

Sustainable solutions as mitigating responses

If there is indeed a link between our rapid global economic and population growth and the emergency and prevalence of zoonotic EIDs and other known diseases, it stands to reason that sustainability practices can provide answers to mitigate the significant risk posed by these diseases. Sustainable practices can be simply defined as actions that seek to meet the needs of current and future generations by integrating environmental protection, social advancement, and economic prosperity (Newman & Jennings, 2008). The sustainability movement, while closely connected to the idea of anthropogenic climate change, provides answers to a wide range of human activities connected to rapid growth which have ongoing negative impacts across the globe.

One answer found in sustainability practice that mitigates several issues associated with the risk driver of climate change is the idea of bioregional cities and economies, or the ‘conservation economy’. The role of cities in anthropogenic climate change is significant as their continual growth makes them heterotrophic in nature, meaning they are unable to meet their own internal needs without looking outward and consuming from beyond the ecosystems in which they are located (Newman & Jennings, 2008). This is perhaps linked to the idea of ‘growth fetishism’, described by Hamilton when they state that “Despite high and sustained levels of economic growth in the West over a period of 50 years – growth that has seen average real incomes increase several times over - the mass of people are no more satisfied with their lives now than they were then.” (2003, pg. 3). The rapid rise of global GDP, when viewed in balance of the impact of related economic activities on climate change and in turn the increase of EIDs, demonstrates the need for a cleaner, greener economy in order to overcome fundamental challenges associated with rapid urbanisation (Newman & Jennings, 2008).

This rapid urbanisation is indeed significant. While one century ago, just 20% of the world’s population lived in cities, urban centres are now home to over half of our growing global population (Neiderud, 2015). These growing cities are seen to be responsible for a significant amount of global energy related carbon emissions, up to 71% according to the International Energy Agency (Rosenzweig, Solecki, Hammer & Mehrotra, 2010), a figure that is only likely to grow as the global population continues to urbanise. The need for sustainable solutions for cities is clear. Bai states that “Research and innovation for mitigating urban climate change and adapting to it must be supported at a scale that is commensurate with the magnitude of the problem.” (2018, pg. 25). The issue of zoonotic and vector-borne diseases increasing in prevalence because of climate changes is just one challenge facing cities across the globe, one that carries with is significant risk to global wellbeing.

A concept that might assist cities in reducing their impact on climate change is the idea of ‘cities as sustainable ecosystems’, where cities are able to take individual responsibility for their impact on greenhouse gases, oil depletion and biodiversity by seeing themselves as “part of the biosphere and as a part of the bioregions in which they aim to achieve ecological balance.” (Newman & Jennings, 2008, pg. 44). The need for such an approach is supported by Mundoli, Unnikrishnan and Nagendra, who state that “There is an urgent need to develop a framework in planning for urban sustainability recognising the uniqueness of the ecological context of each city, and bridging the social and ecological systems in cities.” (2017, pg. 116). Perhaps then, the collective actions of cities across the globe in seeking to reduce their negative environmental impact and supporting the development of their local bioregions might result in a world where reduced greenhouse gas emissions and flourishing local biodiversity work to reduce the risk of EID pandemics that cities, and the entire globe, wer likely to increasingly face. 

Wrapping Up

So we have identified the increasing risk to global health posed by the increasing prevalence of EIDs and known infectious diseases across the globe through zoonotic and vector-born infection. It seems that there is a correlation between this increase and the actions of humans that accompany the global growth of GDP and population rate since the 1940s- we’ve look at literature that shows anthropogenic behaviours such as deforestation, and the impacts of climate change, have resulted in an increased threat of EID outbreaks across the globe. To mitigate this, we should explore sustainable solutions such as the concept of bioregional cities and ‘cities as sustainable ecosystems’, as they might assist in reducing anthropogenic climate change, reducing the pursuit of unending economic growth and increasing bioregional diversity in a step towards reducing the threat posed by EIDs and vector-borne diseases.

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