Dog ownership, abundance and potential for bat-borne rabies spillover in Chile.

Rabies is a viral infectious disease that affects all mammals, including humans. Factors associated with the incidence of rabies include the presence and density of susceptible hosts and potential reservoirs. Currently, Chile is declared free of canine-related rabies, but there is an overpopulation of dogs within the country and an emergence of rabies in bats. Our objectives are to determine potential areas for bat-borne rabies spillover into dog populations expressed as a risk map, and to explore some key features of dog ownership, abundance, and management in Chile. For the risk map, our variables included a dog density surface (dog/km(2)) and a distribution model of bat-borne rabies presence. From literature review, we obtained dog data from 112 municipalities, which represent 33% of the total municipalities (339). At country level, based on previous studies the median human per dog ratio was 4.8, with 64% of houses containing at least one dog, and a median of 0.9 dog per house. We estimate a national median of 5.3 dog/km(2), and a median of 3680 dogs by municipality, from which we estimate a total population of 3.5×10(6) owned dogs. The antirabies vaccination presented a median of 21% of dogs by municipality, and 29% are unrestricted to some degree. Human per dog ratio have a significant (but weak) negative association with human density. Unrestricted dogs have a negative association with human density and income, and a positive association with the number of dogs per house. Considering dog density by municipality, and areas of potential bat-borne rabies occurrence, we found that 163 (∼48%) of Chilean municipalities are at risk of rabies spillover from bats to dogs. Risk areas are concentrated in urban settlements, including Santiago, Chile's capital. To validate the risk map, we included cases of rabies in dogs from the last 27 years; all fell within high-risk areas of our map, confirming the assertive risk prediction. Our results suggest that the use of dog population parameters may be informative to determine risk areas for bat-rabies spillover events. In addition, we confirm that dog abundance is a neglected and emerging public health concern in Chile, particularly within urban areas, which deserves prompt intervention.

Spatial and temporal trends of bat-borne rabies in Chile.

In Chile, while dog rabies has decreased markedly over the last 30 years, bat rabies is still reported frequently. In order to shed new light on the spatiotemporal trends of these reports, we analysed active and passive data from years 1985 and 2012, which included 61 076 samples from 289 counties of Chile. We found that from 1994 to 2012, more than 15 000 bat samples were submitted for diagnostics through passive surveillance, 9·5% of which tested positive for rabies. By contrast, the prevalence of infection was only ~0·4% among the nearly 12 000 bat samples submitted through active surveillance. We found that the prevalence of dog rabies dropped steadily over the same period, with just a single confirmed case since 1998. None of the 928 samples from wild animals, other than bats, were positive for rabies. Although there has been only one confirmed case of human rabies in Chile since 1985, and a single confirmed case in a dog since 1998, bats remain a reservoir for rabies viruses. While active surveillance indicates that rabies prevalence is low in bat colonies, the high proportion of positive bats submitted through passive surveillance is a concern. To prevent human rabies, local public health agencies should increase research on the basic ecology of bats and the role of stray dogs and cats as potential rabies amplifiers.