Disease Emergence in Urban Environments

In this week’s blog post, PaCCS Communications Officer Kate McNeil chatted with Professor Eric Fèvre, Chair of Veterinary Infectious Diseases at the University of Liverpool’s Institute of Infection and Global Health. Based in Nairobi, jointly with the International Livestock Research Institute,  Professor Fèvre’s MRC-funded work on the epidemiology, ecology and the socioeconomics of disease emergence in Nairobi and his efforts to measure, map, monitor and mitigate drivers of the emergence of zoonotic and food-borne diseases were designated Global Uncertainties projects because of their potential to give insight into pandemics and civil emergencies related to food and health security.

This conversation has been edited and condensed for clarity and conciseness.

Kate McNeil: Thank you for taking the time to chat with me from the field! It’s much appreciated.  Your work first came to my attention because of the grants you received to research the socioeconomics of disease emergence which fell under the Global Uncertainties umbrella. Would you mind getting started by telling me a little bit about that project?

Prof Fèvre: With the support of a really forward-looking stream of funding from the UK government, we established a project that was part of an ESEI grant on the environment and social ecology of infectious diseases. We already knew that urbanisation is a risk factor for the emergence of new diseases, and this project was an opportunity for us to try to scratch the surface of that. Using Nairobi as our case study, we wanted to try to understand that what mechanistic processes might underly a system which results in a pathogen emerging in an urban setting.

Were there particular aspects of urban life that your work has focused on?

We wanted to examine several aspects of a complex city in a developing country context, with a specific interest in zoonosis and human contact with animals. We didn’t limit our definition of ‘animal’ to live animals, and instead chose to include in our study how a city feeds itself and the animals that we eat. This means that the entire food system became a part of our process, and we’ve spent a lot of time mapping the food system and determining where there might be risk points within that system. We were interested in a variety of different animal-sourced food commodities, including milk, poultry meats, eggs, pork, ruminant meats, and camel products including meat and milk. 

We also spent a lot of time looking at the structure of the city with development experts and sociologists, looking at why the city is as it is, and how it is evolving. Then, we looked at peri-domestic wildlife, including rats, bats and birds; people and their livestock; and the broader environmental envelope in which all of these things co-exist. We wanted to know how they have contact with each other, and what opportunities they have to transmit pathogens to one another.

Was your project focused on any single disease?

We chose to focus on bacterial pathogens because there are well developed tracking tools to understand the movement of this type of pathogens between hosts, but we didn’t focus on a single specific pathogen. Rather, we looked at populations of multi-host organisms – with bacteria being of primary interest – and designed the project to focus on human public health and disease-causing elements of pathogens.

Were there particular things you found over the course of this project that surprised you?

What surprised me was the level of interaction and cross-over between what appeared on the surface to be parallel food systems. In a developing country setting, you tend to have formal and informal food chains which are organized very differently. The end product of the formal food chain would be a retail supermarket from an international chain, while the informal food chain might end with someone selling milk on the side of the road in a plastic bag with a straw.

Throughout this study, we learned that these food systems – which seem so separate at first glance – have a much higher level of interaction and cross-over than we had expected. In fact, there is a number of times when foods move from the formal to informal system or are handled by the same intermediaries during the cross-over points from production through to consumption. So, there’s a lot of potential for risky practices from one of these contexts to have impacts upon another.

We also learned that the wildlife species in urban areas are really important for ensuring the spread of strains of pathogens. Human populations that might be geographically far from each other are close from the perspective of bacterial connectivity, because species such as birds can move bacteria across cities. Those bacteria are then picked up by rodent populations who locally distribute the bacteria even further. While there are systems and structures at play, at the end of the day, everything is related, and everyone is swimming around in the same big bacterial soup.

From a public health perspective, did you learn anything over the course of this project which you believe might be useful for those in policymaking spaces?  

One of our key findings was that there is an ongoing shift in the primary risk factors for infection with bacterial pathogens in young children who live in low-income slum settings. Water, sanitation and hygiene (WASH) systems have historically been a major source of risk, but the WASH community has done a lot to ensure safe access to clean water, which means that drinking water is no longer the main thing that exposes people to risk in many of these environments. We’re working towards publishing findings demonstrating that access to animals, and particularly certain types of animal-sourced food, has taken over as the big thing that causes diarrhoea and disease in children. This is a major success for WASH, but my biggest public health message is that diseases in these slum populations are now coming from a different source that we need to tackle.

Your focus on zoonoses and the spread of pathogens through the food systems is reminiscent of the processes believed to be involved in the spread of the novel coronavirus (2019-nCoV) which is currently making news, which experts suggesting it may have started in a wet market – the Huanan Seafood Market in Wuhan.

Obviously we were working in Africa, so I can’t directly comment on the outbreak and potential future spread of a pathogen in China. However, our project was designed quite explicitly to inform exactly the processes that lead to that kind of outbreak. We’ve seen there are cases already popping up in the US, and the source of the outbreak appears to be contact with an animal. The way in which people who have been exposed to a pathogen have interacted with the animals they are eating, the way they have slaughtered them, the commercial process of supplying food, the links between rural areas and high density urban consumers, and the way foods have been cooked or not cooked, is exactly what we are studying.

In our study, we chose to focus on bacterial pathogens – although my research group also does some work with coronaviruses – bacterial pathogens were a convenient type of organism for us to examine in order to inform a broader process which is now coming to light on a day-to-day basis in China. We’ve seen this before, with things like SARS and Ebola, but 10 or 15 years ago people would never have really thought about the food system as a significant way in which large populations expose themselves simultaneously to zoonotic disease risk. The food system is a key part of this, because, unless you’re vegan, you’re in contact with animals 3-4 times a day, every day. Where those animals come from is of prime importance to your risk of exposure.

When we think of the risks posed by zoonoses and these pathogens, do you think we should factor this into our understanding of human security?

From the point of view of living safely in the world… these issues are definitely part of the security agenda to ensure that populations are safe from a multitude of threats that are out there. So yes, it ought to be on a human security agenda. More importantly, these risks should be on the agenda on a more routine, day-to-day basis. We need to ensure that we are funding research which more broadly works to understand these threats, and which ensures that understanding human interactions with their environment and with animals is consistently on the agenda. This is partially a surveillance issue, but it is also about changing the boundaries of research.

The work that we are doing now also highlights the links between food security, health security, and financial security. Which kind of underlies everything for everybody all of the time.

Would you like to tell me a bit more about that work?

My team’s current research continues to examine key nodes in the food system, including slaughterhouses, markets, and understanding how you mitigate risks with interventions designed to sanitize environments and ensure safer, cleaner, food.

What we’ve discussed in terms of food systems risks in urban environments also extends more broadly to the agricultural environment in which food is produced, and we have also been working on exploring how farming systems are changing in East African settings where populations are urbanizing and where patterns of demand for food are changing. As urban populations grow, food producers need to become more efficient and intensify operations in order to ensure food supply for those who are no longer growing food themselves. We’re examining how farmers are adapting to the demand that is being created in those settings. This is lateral thinking – not just about the pathogens, but about the systems as a whole.

We’ve been working with anthropologists and sociologists to understand the financial processes that results in farms intensifying. We know that these financially risky decisions matter in terms of the way you farm and feed into the system. If your risks pay off and your farm intensifies, your new farming practices may put your neighbours more at risk – for example, your farm could have increased run-off as you increase the size of your herd. Alternatively, if your investment in farming intensification fails, structural factors related to poverty in small farming systems can drive other forms of disease-related risk – particularly as poverty is a risk factor for neglected disease outcomes. So, it’s important that we learn how to adapt our systems of disease surveillance as these farming practices change, so that we can understand how the risks are changing in the food systems and in farming environments.

Photo Credit: 葉 正道 Ben（busy）– https://flic.kr/p/2ijCPya