Rats as a Source for Emerging Zoonoses: Understanding the Interactions Between Rats, Pathogens, and the Urban Environment

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Rats have been, and continue to be, the source of numerous zoonotic pathogens (i.e., pathogens transmissible to people) responsible for significant human morbidity and mortality in cities around the world. A number of these pathogens (including the etiologic agent of the plague) are transmitted among rats and from rats to people by fleas. While disease in rats is influenced by a variety of factors including health status and chronic stress, the subsequent spread of disease to other rats and to people is directly related to how rats move within and interact with their environment. Despite anecdotal evidence that rats are thriving in Canadian cities, there is little data in our country on rats, their fleas, and their pathogens. Vancouver’s Downtown Eastside (DTES), known as one of Canada’s poorest postal codes, is of particular concern because factors associated with poverty are known to promote rat infestations, rat-human contact, and disease transmission. In addition, cities which feature large international ports (such as Vancouver, Montreal, and Halifax) may serve as entry points for rats carrying novel pathogens from abroad. To begin to address this lack of data on rats and their pathogens, the Vancouver Rat Project (VRP; vancouverratproject.com) was founded in 2010 with the overarching objective to characterize the ecology and epidemiology of rat-associated pathogens in Vancouver’s DTES. For Phase II of the VRP, we will study rats and their fleas collected during Phase I, as well as rats obtained through additional trapping at Vancouver’s international port and other Canadian port cities. These specimens will be analyzed to: 1) determine how rat health, movement, and environmental characteristics influence pathogen distribution among rats; 2) resolve whether rats and their pathogens are introduced to a city through international shipping, and compare the presence of certain pathogens between cities; and 3) describe the bacterial communities associated with fleas to look for known and novel pathogens. By integrating information on rats, fleas, their pathogens, and the urban environment, we will explore whether rats could serve as a source for emerging infectious zoonoses. This research will allow us to determine whether rats pose a potential health risk to people living in cities across Canada. Knowledge gained from this approach will be essential for developing informed approaches to assess, monitor, and mitigate rat-associated risks now and in the future.