Prioritisation of areas for early detection of southward movement of arctic fox rabies based on historical surveillance data in Quebec, Canada.

Arctic rabies virus variant (ARVV) is enzootic in Quebec (Canada) north of the 55th parallel. With climate change, increased risk of re-incursion of ARVV in more densely populated southern regions raises public and animal health concerns. The objective of this study was to prioritise geographical areas to target for an early detection of ARVV incursion south of the 55th parallel based on the historical spatio-temporal trends of reported rabies in foxes in Quebec. Descriptive analyses of fox rabies cases from 1953 to 2017 were conducted. Three periods show increases in the number of fox rabies cases in southern regions and indicate incursion from northern areas or neighbouring provinces. The available data, particularly in central and northern regions of the province, were scarce and of low spatial resolution, making it impossible to identify the path of spread with precision. Hence, we investigated the use of multiple criteria, such as historical rabies cases, human population density and red fox (Vulpes vulpes) relative abundance, to prioritise areas for enhanced surveillance. This study underscores the need to define and maintain new criteria for selecting samples to be analysed in order to detect rapidly ARVV cases outside the current enzootic area and any potential re-incursion of the virus into central and southern regions of the province.

A simple geometric validation approach to assess the basic behaviour of space- and time- distributed models of epidemic spread - an example using the Ontario rabies model.

Dynamic mathematical modelling and stochastic simulation of disease-host systems for the purpose of epidemiological analysis offer great opportunities for testing hypotheses, especially when field experiments are impractical or when there is a need to evaluate multiple experimental scenarios. This, combined with the ever increasing computer power available to researchers, has contributed to the development of many mathematical models for epidemic simulations, such as the individual-based model (IBM). Nevertheless, few of these models undergo extensive validation and proper assessment of intrinsic variability. The Ontario rabies model (ORM) will be used here to exemplify some advantages of appropriate model behaviour validation and to illustrate the use of a simple geometric procedure for testing directional bias in distributed stochastic dynamic model of spread of diseases. Results were obtained through the comparison of 10 000 epizootics resulting from 100 epidemic simulations started using 100 distinct base populations. The analysis results demonstrated a significant directional bias in epidemic dispersion, which prompted further verification of the model code and the identification of a coding error, which was then corrected. Subsequent testing of the corrected code showed that the directional bias could no longer be detected. These results illustrate the importance of proper validation and the importance of sufficient knowledge of the model behaviour to ensure the results will not confound the objectives of the end-users.

Elimination of rabies from red foxes in eastern Ontario.

The province of Ontario (Canada) reported more laboratory confirmed rabid animals than any other state or province in Canada or the USA from 1958-91, with the exception of 1960-62. More than 95% of those cases occurred in the southern 10% of Ontario (approximately 100,000 km2), the region with the highest human population density and greatest agricultural activity. Rabies posed an expensive threat to human health and significant costs to the agricultural economy. The rabies variant originated in arctic foxes: the main vector in southern Ontario was the red fox (Vulpes vulpes), with lesser involvement of the striped skunk (Mephitis mephitis). The Ontario Ministry of Natural Resources began a 5 yr experiment in 1989 to eliminate terrestrial rabies from a approximately 30,000 km2 study area in the eastern end of southern Ontario. Baits containing oral rabies vaccine were dropped annually in the study area at a density of 20 baits/km2 from 1989-95. That continued 2 yr beyond the original 5 yr plan. The experiment was successful in eliminating the arctic fox variant of rabies from the whole area. In the 1980's, an average of 235 rabid foxes per year were reported in the study area. None have been reported since 1993. Cases of fox rabies in other species also disappeared. In 1995, the last bovine and companion animal cases were reported and in 1996 the last rabid skunk occurred. Only bat variants of rabies were present until 1999, when the raccoon variant entered from New York (USA). The success of this experiment led to an expansion of the program to all of southern Ontario in 1994. Persistence of terrestrial rabies, and ease of elimination, appeared to vary geographically, and probably over time. Ecological factors which enhance or reduce the long term survival of rabies in wild foxes are poorly understood.

Phylogeographic patterns exhibited by Ontario rabies virus variants.

A previous study on N gene variation of rabies viruses circulating in Ontario red foxes identified four viral variants. This study confirms the geographical localization of these variants and extends the analysis to the less conserved G gene of these viruses. A greater number of regionally localized variants was revealed and their phylogenetic relationships have been examined. Ongoing surveillance on recent disease outbreaks revealed that variants do not always persist in specific areas. The distribution of these variants did however appear to be influenced by topographical features of the study area likely to affect host animal movements and contacts. The majority of G gene base changes were synonymous and limited glycoprotein sequence variation predominantly to the C-terminal transmembrane and endo-domains. These data are most readily explained by random appearance of genetic viral variants followed by their spread throughout sub-populations of the fox host according to the easiest routes of transmission.

Planning for rabies control in Ontario.

Ten geographic cells of rabies cases were identified within southern Ontario. Some had regular 3-year peaks, whereas others had weak cycles with mean periods of up to 9 years. Incidence of rabies was related to soil types (highest on sandy and clay loams), land use (abundant where hay and pasture were dominant), and drainage (poor drainage supported only low levels of rabies). A spatial stochastic simulation model is being used to evaluate risks and tactics associated with reduction of rabies by use of vaccine baits. The model indicated that persistence of rabies is unlikely in areas with less than 4,000 km2 of contiguous fox habitat. In sensitivity tests the model was most affected by the values of four input parameters: rate of contact among foxes, incubation period of rabies, fox density, and a density-dependent feedback that reduces fox recruitment when density approaches or exceeds a predetermined "carrying capacity." In a majority of model experiments, a single vaccination of 60% of a fox population eradicated rabies, but only if vaccination took place just after a rabies outbreak, when the number of both foxes and rabid animals was reduced. Rabies control will probably be applied to individual cells or clusters of cells rather than to the entire 98,000 km2 enzootic zone, at least at first. If rabies is eradicated the fox populations may increase, but modestly. Skunks were more important than foxes as vectors of rabies in urban Ontario. Since there is no effective oral rabies vaccine for skunks, skunks were trapped alive and vaccinated by injection.(ABSTRACT TRUNCATED AT 250 WORDS)

The Universal Transverse Mercator Code: A location code for disease reporting.

Since November 1987, all rabies specimen reports submitted by Agriculture Canada's District Veterinary Officers have required a new location code, the Universal Transverse Mercator Code (UTMC). In addition to the previously required entries for county, district, legal address and mailing addresses, the new code is set up for computer analysis and mapping. It is capable of pinpointing the origin of the specimen to within 100 meters anywhere in Canada that is covered by the National Topographic System 1:50,000 maps. Because of its 100 meter spatial resolution, the code is of great interest to those studying the occurrence and spread of rabies. The code will also be important in the detailed planning and evaluation of the Ontario rabies control scheme, scheduled for 1988. Agriculture Canada anticipates that the UTMC will also be used for reporting other animal diseases as well as for emergency disease reporting.

Studies on the 1967--68 foot and mouth disease epidemic: incubation period and herd serial interval.

The incubation period during this epidemic was studied using both a spectral analysis-cum-filtering method and analysis of case histories. Using spectral analysis, the modal herd serial interval was estimated to be 8--10 days based on the record of the daily number of outbreaks and an adjusted cattler series. The case histories tended to confirm these estimates but indicated that the serial interval varied considerably between species. The filtering method revealed that the herd serial interval apparently changed during the epidemic. For the first 4 weeks the interval was 8 days, while in the latter stages it was about 2 weeks.