1 University of Reading, School of Agriculture, Policy and Development, Livestock Development Group
1&2 University of Reading, Walker Institute for Climate Research
In the coming decades, climate change is predicted to produce a range of direct and indirect impacts on both human and animal health. At the most basic level, rising temperatures and changes to rainfall patterns have a direct impact on vector populations and thereby, vector-borne diseases (VBDs).
For example, human diseases such as malaria and dengue are now occurring at higher altitudes and latitudes, which historically have been free of the disease (Dhiman et al., 2010). This change has been directly attributed to climate warming. Outbreaks of livestock disease in new geographies such as blue tongue disease in Europe have also been linked to climate change (more specifically seven of the warmest winters in Europe on record during the late 1990s to early 2000s)(Tabachnick, 2010).
The extreme weather events (EWE) associated with climate change such as droughts and floods in addition to direct effects, may also have indirect impacts on the incidence and prevalence of infectious disease. Extreme flooding often causes a break-down in sanitation, supporting an increase in water-borne diseases such as typhoid and cholera. EWEs also often forge food and livelihood insecurity, which in turn supports shifts in both human and animal populations. Thus, while changes to vector populations may alter the geographic spread of a climate sensitive disease, the displacement of the host population (both human and animal) is equally influential to disease distribution. Resident populations may be exposed to pathogens transferred by migrants or conversely migrants may be exposed to new pathogens in their new environment. Among pastoralist populations in Africa, droughts frequently displace populations into refuges camps. Recent epidemics of meningitis, hepatitis E and cholera have occurred in refugee camps in Kenya, Somalia and the Sudan (Ahmed et al., 2013).
Determining the role and influence of climate warming on disease highlights another issue: our approach to understanding this new disease landscape itself. Despite the drivers being the same for human and animal disease, historically, there has often been little synergy between veterinary and human disease investigations. However, in recent years the emergence of a range of threats originally attributed to animal pathogens such as Sudden Acute Respiratory Syndrome (SARS), Highly Pathogenic Avian Influenza (HPAI), Swine Flu and Ebola has underscored the need for a combined approach. With this recognition has come the rise of the One Health agenda which aims ‘to promote and improve the health of humans, animals and our environment, (AVMA, 2008). Crucially, One Health fosters collaboration between veterinary, medical, public health and environmental disciplines across the global health arena (FAO, 2011).
Despite this focus on the environment and in particular, the interface between disease and local ecologies, One Health, has not been widely utilized as a framework to perform detailed explorations of the impacts of climate change on infectious disease. Part of the problem is the very nature of the One Health discourse. While One Health has been a rhetorical force across the field of Global health it has been less sure-footed as an analytical device. Critical issues in operationalising One Health include problems with knowledge silos and the need for better metrics across projects and programmes (Kihu and Heffernan, 2015). Explorations of the role of climate change on disease require both a robust and yet inclusive analytical approach. Indeed, it has been argued that climate change is not a single driver of disease but rather an embedded context and as such, is likely to influence a range of diseases in the same landscape among resident human, livestock and wildlife hosts, at the same time (Heffernan, 2015). At its best, the One Health approach has the ability to identify the synergies and interactions important to disease transmission at the systems-level. The longevity and usefulness of the One Health paradigm is likely to depend on widening the frame to focus on climate change at the systems, as opposed to individual disease, level.
By Claire Heffernan1 and Kathy Maskell2
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