Research leads the way to preventing disease outbreaks in urban areas

A new paper describes important research conducted by scientists at the University of Liverpool with partners to show that disease transmission from animals to humans is more likely in parts of a city with high densities of people, livestock and urban-adapted animals in the wild, such as rats. The paper, “Epidemiological connectivity between humans and animals in an urban landscape,” is published in Procedures of the National Academy of Sciences.

The study, conducted in Kenya’s fast-growing capital Nairobi, shows that high-risk areas are often lower-income with a lack of adequate sanitation and waste management, as well as lower biodiversity. The long-term study is one of the first to unequivocally answer the questions about where and how disease transmission and emergence occurs in urban settings.

Significantly, the paper suggests public health recommendations, including places to prioritize disease surveillance, improve access to basic health care, and explore targeted disease control measures.

It was led from 2013–2017 and was led by Professor Eric Fèvre, Chair of Veterinary Infectious Diseases at the University of Liverpool and the then Ph.D. student at the University of Liverpool, Dr. James Hassell in collaboration with Kenyan partners. Dr. Hassell is now a veterinarian and epidemiologist for the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI)’s Global Health Program.

The study’s findings were based on genetic relationships between E. coli bacteria collected from a group of more than 2,000 humans, livestock and urban wildlife at 33 sites in Nairobi.

E. coli bacteria have a number of genes, called mobile genetic elements, that have properties such as drug resistance and can be passed on to other E. coli nearby. This allowed researchers to infer the same strain of close physical proximity between any E. coli that shared many of the same mobile genetic elements.

Dr. James Hassell said: “This genetic similarity is a good indication of the potential for disease transmission between two hosts. We can’t know whether the bacteria are human-to-animal or animal-to-human, but it tells us something important about the epidemiological connection between them.

“In these areas of high population density, humans and animals are very closely linked from a potential disease transmission point of view. These are the places where the ingredients for emerging pathogens to jump from animals to humans are, and places where it is easy to would be for those areas.” pathogens to multiply before they are discovered. This means that in these places it also makes sense to prioritize access to healthcare and disease surveillance.”

By comparing the E. coli bacteria collected from humans, wildlife and livestock across Nairobi, the scientists were able to map areas of the city that showed the most overlap in these bacterial genes and ultimately identify these areas as major battlegrounds for emerging diseases.

While the results apply directly to Nairobi, the city of Kenya is emblematic of many cities in the tropics experiencing what researchers call rapid, unplanned urbanization. When cities grow extremely fast without meaningful urban planning, they often lack basic infrastructure such as adequate sanitation or waste management systems, especially in low-income neighborhoods.

Combine these conditions with a high population density and large numbers of residents who still rely on livestock to support their families, and opportunities for disease to jump from animals to humans abound.

Follow-up research is currently trying to gather even more information about the mechanisms of disease transmission in Nairobi by placing tracking devices on livestock, bats and birds from many of the same households examined in the current study. The study will use GPS tracking as well as devices called proximity loggers that record when two animals wearing the devices move more than half a foot apart to build contact networks.

Kenyan partner organizations that contributed to this study and ongoing collaborative research include the International Livestock Research Institute, the University of Nairobi, the Kenya Medical Research Institute, the National Museums of Kenya and the Kenya Wildlife Service.

Other partners in this study and paper included the University of Edinburgh, the University of Minnesota, the University of Oxford, the University of Southampton, the University of Hokkaido, the University of Columbia, the University of Milan, and the Food and Agriculture Organization of the United Nations.