Study Reveals Rapid Transmission of Animal Diseases to Humans in Nairobi

By Phyllis MUCHOKI

A recent study conducted in Nairobi, Kenya has shed light on the increased likelihood of pathogens jumping from animals to humans in areas of the city with high population densities, urban wildlife, and livestock.

These areas, characterized by lower income levels and inadequate sanitation and waste management, also tend to have lower levels of biodiversity.

The study, published in the Proceedings of the National Academy of Sciences, emphasizes the importance of disease surveillance, improved healthcare access, and targeted disease control measures.

Led by Dr. James Hassell, a wildlife veterinarian and epidemiologist from the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI) Global Health Program, the research utilized genetic analysis of E. coli bacteria collected from over 2,000 individuals, livestock, and urban wildlife in 33 locations across Nairobi.

Mobile genetic elements within the E. coli genes allowed the researchers to identify close physical proximity between bacteria sharing these elements, indicating potential paths for pathogen transmission.

By comparing the genetic data from humans, wildlife, and livestock, the study mapped areas of the city with significant genetic overlap in the E. coli bacteria.

These areas were identified as crucial battlegrounds for emerging diseases, highlighting the potential for pathogens to be transmitted between hosts.

While the study specifically focuses on Nairobi, Hassell notes that the findings are applicable to many rapidly growing cities in the tropics facing unplanned urbanization. As cities expand without adequate planning, the lack of infrastructure, particularly in low-income neighborhoods, creates favorable conditions for disease transmission.

Additionally, these neighborhoods, despite reduced overall biodiversity, provide suitable environments for disease-carrying wildlife species such as rodents, birds, and bats. As urbanization continues globally, the issue of emerging diseases in rapidly growing urban areas is expected to intensify.

To gather accurate data and provide effective public health recommendations, the research team embarked on a comprehensive data collection project in Nairobi in 2016 as part of the UrbanZoo project led by Eric Fevre at the University of Liverpool.

Samples of E. coli were collected from humans, livestock, and wildlife in and around 99 households selected to represent diverse wealth levels in 33 areas of Nairobi. Through genetic sequencing and analysis, the team constructed a network of genetic overlap between bacteria from different hosts, identifying the parts of the city with the highest genetic similarity.

The study highlights the importance of addressing poor livestock manure management, particularly within households in these high-density areas, as a significant source of genetic overlap between wildlife and livestock. Hassell emphasizes that these areas require prioritized access to healthcare and disease surveillance.

Interventions based on the study’s findings include improving sanitation and waste management, especially regarding livestock manure. Hassell emphasizes the necessity of improving living conditions for both humans and their animals and increasing access to quality healthcare for early detection and identification of new pathogens.

Continuing research aims to gather further insights into the mechanisms of disease transmission in Nairobi by tracking livestock, bats, and birds from the same households as the current study. Tracking devices, including GPS and proximity loggers, will help build contact networks by recording close interactions between animals.

The study and ongoing research involve collaboration with Kenyan partner organizations, such as the International Livestock Research Institute, the University of Nairobi, Kenya Medical Research Institute, National Museums of Kenya, and the Kenya Wildlife