High Rates of Escherichia coli Transmission between Livestock and Humans in Rural Uganda

Abstract

Escherichia coli is a zoonotic bacterium that is important to both public health and livestock economics. To date, most studies of zoonotic E. coli transmission have been conducted in developed nations with industrialized agricultural economies. In this study, E. coli bacteria were collected from people and livestock in two communities in rural western Uganda in order to investigate patterns of interspecific bacterial transmission in a developing rural economy characterized by very close human-livestock associations. Six hundred seventytwo E. coli isolates were genotyped using repetitive element-PCR (Rep-PCR) fingerprinting, and genetic distances between populations of bacteria from different hosts and locations were calculated. Genetic distances between human and livestock bacteria were generally very low, indicating high rates of bacterial gene flow among host species. Bacteria from humans and livestock in the same communities were virtually indistinguishable genetically. Data from surveys administered at the time of sample collection showed that people who did not regularly wash their hands before eating harbored bacteria approximately twice as similar genetically to bacteria of their livestock as did people who regularly washed their hands before eating. These results suggest that both rates of human-livestock interactions and patterns of human hygiene affect human-livestock bacterial transmission in this setting. This conclusion has implications not only for human and livestock health in subsistence-based agricultural economies but also for the emergence of zoonotic diseases out of such areas as a result of increasing globalization.Infectious agents transmitted between humans and their livestock are important to both public health and livestock economics. Taylor et al. (30) previously estimated that 75% of emerging human infectious diseases are zoonotic or have recent zoonotic origins, with livestock serving as important reservoirs of infection. Escherichia coli is of special concern as a livestock-associated bacterial zoonosis (2, 6). E. coli can range in virulence from a benign commensal to highly virulent enteropathogenic forms, such as the O157:H7 serovar (7, 31). Although all forms of the bacterium are zoonotic, few cause clinical disease in infected animals (10) despite the potential of some for high virulence in people (7, 35). Also, E. coli shed by animals can persist in soil, water, manure, and feed, where it can spread to other uninfected animals (15) and to humans (7).Despite significant advances in our understanding of E. coli transmission in industrialized nations, little is known about the transmission of the bacterium in the developing world. Zoonotic transmission of E. coli and similar pathogens may in fact be very common in rural, subsistence-based agricultural economies. In rural Africa, for example, people traditionally keep livestock in close proximity to the homestead or even inside the domicile. In such situations, humans and livestock come into exceptionally close contact both direct...

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