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The Impact of Climate Change on Human Health

The Impact of Climate Change on Human Health

This spring, PaCCS Communications Officer Kate McNeil spoke with Dr K. Marie McIntyre, a Epidemiologist at the University of Liverpool’s Institute of Infection and Global Health about her work on risk assessment of the impact of climate change on human health and well-being. This NERC-funded project on health and the environment was led by Professor Matthew Baylis and was designated as a Global Uncertainties project by the Research Councils.

Kate McNeil: Thank you for taking the time to speak with me today! Would you mind telling me a bit about what brought you to this research project?

Prior to this project, Professor Matthew Baylis’ group had developed work to identify and characterise the climate drivers of certain diseases, with a focus on the future impact of climate change on infectious diseases of animals. This work had involved predicting what the group thought was going to happen to diseases such as bluetongue disease – which is insect-borne and affects ruminant animals such as sheep – in the future as a result of climate change. We knew that bluetongue had moved through from North Africa to the Mediterranean basin and then onwards into Northern Europe and the UK, and a climate-driven model was developed which explained, in both space and time, many aspects of the recent emergence and disease spread.

Such work is invaluable to understand more about specific disease vectors and vector-borne diseases, but it doesn’t objectively examine the climate impacts upon disease ranges overall. This is what this project on risk assessment, which we call ENHANCE, or ERA-NET Health and Climate in Europe, aimed to do.

Can you tell me a little bit more about the aims of ENHANCE?

Through the project, we sought to create a large-scale horizon scanning mechanism to look at the sensitivity of ALL infectious pathogens to individual climate drivers. This is important because, when we started this work, we didn’t know how realistic the threat to human and animal health from climate change was. We also didn’t know if most diseases are likely to change with changes to climate, or whether only a few infections would become an issue; what would happen to the overall human and animal disease burden?

ENHANCE has helped us to identify emerging trends in which pathogens are most likely to be impacted by changes to the climate, which we hope will in turn help us refocus our work. I’m proud to say that our work has contributed to the dialogue surrounding diseases and climate change, and was recently quoted in a very highly cited article in Nature Reviews Microbiology.

What sort of things guided your approach to putting together this horizon-scanning tool?

We wanted our approach to be objective and repeatable, so we focused on bringing evidence together. As part of this, we needed to create some research methods and resources which we continue to use in our ongoing work.  

Prioritisation of infectious diseases for surveillance within the human and animal health policy and research communities is usually undertaken using qualitative or semi-quantitative framework methods and utilising the opinions of experts such as medical and veterinary clinicians and epidemiologists – limited resources mean that only a small number of infectious diseases or the pathogens which cause them can be prioritised. To overcome this barrier, we developed a method to rank many infectious pathogens using Hirsch’s H-Index, which is usually used to quantify academic productivity. Here, we used it to prioritize pathogens, so that government agencies can come in, look at priority pathogen lists, and use that as part of their process to determine which pathogens they need to think about more. 

We also realised when we started this project that while we needed to understand the full range of diseases humans and domestic animals have in Europe, that information wasn’t readily available. So, we created a database which describes pathogens and vectors for human, animal and plant hosts at different spatial and taxonomic-levels. We also produced lists of the top 100 most important human and domestic animal pathogens in Europe and collaborated with Canada’s University of Prince Edward Island on a similar list for North America.

What were some of the key takeaways from this project?

Evidence from our work suggested that zoonotic pathogens (those that go from animals to humans) are much more likely to have at least one climate driver for example be sensitive to changes in air temperature or rainfall, than either human-only or animal-only pathogens, respectively. In addition, zoonotic pathogens are associated with certain transmission routes. Foodborne and waterborne pathogens are much more likely to be zoonotic than non-zoonotic, and directly (non-sexually) transmitted pathogens are much less likely to be non-zoonotic than zoonotic.

So for example, most of the pathogens which had the greatest numbers of climate drivers were zoonotic, including:

  • The helminth Fasciola hepatica which is of significant concern to agricultural livestock causing liver fluke, but which can also affect humans.
  • The bacteria Bacillus anthracis which causes anthrax which is zoonotic and has also been used in germ warfare.
  • Borrelia burgdorferi which is also zoonotic and causes another emerging disease which has been in the news – tickborne Lyme disease.

 

Our work showed that a really significant proportion of infectious pathogens are sensitive to climate drivers and are therefore likely to be impacted in some way by climate change. Thinking how much potential change in disease impact we will see, the best estimates we have for the impacts of diseases come from the global burden of disease study, which estimates early deaths from disease but also includes how much long term illness and disability diseases cause.

This is important because some diseases don’t kill as much as they cause people to be disabled for a long time, which has implications for healthcare; tuberculosis is a good example of this. When we looked at the disease impacts from the global burden of disease study, for the cohort of pathogens we had examined in our work, 37% of disability-adjusted life years were likely to change with changes in climate. Diarrhoeal disease is ranked the fifth highest cause of early deaths and disability in mankind, particularly in poorer populations, and foodborne and waterborne pathogens are highly sensitive to climate change – we need to refocus our efforts.

Vector-borne diseases were also highlighted by our work, and we need to focus on these as well, though in our particular review they were less obvious for humans because we only examined pathogens we already had within Europe, so that that point we didn’t have Chikungunya for example.

Finally, developing the work and the resources showed how bad we are at collectively bringing together and reusing research results from other projects; this is partly because of the way research funding works in the UK currently. We’ve future-proofed some of the resources we developed as well as we can, for example by securing short-term funding to sustain the database, but as soon as the current funding ends, we’ll be in the situation of needing further funding.

What do you think policymakers need to know about the things you learned during your work on ENHANCE?

We identified certain groups of infections which weren’t getting the attention or resources they deserved. Diarrheal and gastrointestinal diseases contribute enormously to the global burden of disease, and food-borne and waterborne pathogens were shown to be highly sensitive to climate change. We also were able to highlight cases of emerging infections such as tick-borne diseases where distributions are changing and public health officials, governments and researchers need to be aware of those shifts.

There are also security ramifications to our research. We need to think about climate change and globalisation from a health security and a food security perspective. For global uncertainties, we need to be more aware of how political and economic changes can drive climate change, and how tightly linked infectious diseases are with our environment.

Do you think the project has had any impact in policymaking spheres?

The conversations we’ve had about ENHANCE definitely contributed to the policy conversation. We received a lot of media attention, including about our use of big data methods, and there was a lot of interest in the Nature Reviews Microbiology article. I also took part in a debate at the Barbican on whether big data can save the world.

Encouragingly, our improved understanding of the impact of recent and future climate change on vector-borne diseases and of where we’re heading next was included in the 2020 World Economic Forum Global Risks Report.

How has ENHANCE fed into the work your team has been doing since?

Since the ENHANCE project finished, we’ve had several grants to extend our database, and a research fellow is extending the technology using novel approaches to understand patterns of disease. We’ve also looked at domestication as a driver for animal diseases becoming zoonotic. Other more climate-focused work has continued to use presence data for pathogens and vectors in work predicting the impacts of climate change and in the study of pathogens such as Zika virus.

How has your work on ENHANCE influenced your trajectory in the years since?

The ENHANCE project was the beginning of a shift in focus for me. It demonstrated the importance of physical environmental impacts upon the health of mankind and animals – we need to take a One Health approach to our health, but we also need to be aware of the three pillars driving health – social and economic as well as environmental sustainability. We need to think about political change as a mechanism driving health.

At the moment we have researchers examining the impacts of climate change upon disease – one researcher will predict how climate variables will change and elevate health risks, whilst another identifies which climate variables and weather conditions favour aspects of the life history of pathogens and vectors. My work on ENHANCE really brought home the gap between understanding how the climate will change, how that will affect disease, and then what this translates to in a political and globalised world. What will actual impacts be within the landscape of different communities with different resources and healthcare systems? How can we consider socio-economic factors in a One Health approach? How can we engage with the groups of people involved in decision-making to improve not just our understanding but also our ability to change what is happening? These are the sorts of questions I’m interested in now.

Photo by Elena Mozhvilo on Unsplash