Hassell and colleagues collected data from human, livestock and wildlife species faecal samples, and their shared environment in household settings, and then performed whole-genome sequencing on 1,428 Escherichia coli isolates. Transmission potential networks constructed from pairwise sharing of mobile genetic elements and incorporated in a multilayer network framework demonstrated that transfer of bacterial genes across wildlife–livestock interfaces was greatest when livestock were kept at higher densities in low-income settings characterized by low wildlife diversity (rodent interface), when manure was poorly disposed of in less biologically diverse and therefore natural-resource-poor habitats (rodent and avian interface), and when household environments are characterized by low diversity avian populations (avian interface). Rodents, humans and livestock were more likely to share mobile genetic elements with one another than with birds. Low-income areas of the city were associated with higher transmission potential between livestock and rodents, and this effect was partially magnified in the presence of low diversity wildlife assemblages.
Urban, small-scale livestock keeping is an important component of regional food security. Limited biosecurity practices and increasing gradients of urbanization, particularly in the tropics, leads to lower regional biodiversity, creating environments where rodent and bird populations can thrive. The work by Hassell and colleagues demonstrates that this combination of environmental factors creates urban settings that provide increased opportunities for zoonotic pathogens to spread. With increasing urbanization and growing human populations, food security in regions such as Nairobi will need to be supported with surveillance efforts — prioritizing identification of emerging infectious diseases and limiting their spread to protect human health.
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