Emergency response to raccoon rabies introduction into Ontario

Evaluation of contingency actions to control the spread of raccoon rabies in Ohio and Virginia

The raccoon (Procyon lotor) variant of the rabies virus (RRV) is enzootic in the eastern United States and oral rabies vaccination (ORV) is the primary strategy to prevent and control landscape spread. Breaches of ORV management zones occasionally occur, and emergency "contingency" actions may be implemented to enhance local control. Contingency actions are an integral part of landscape-scale wildlife rabies management but can be very costly and routinely involve enhanced rabies surveillance (ERS) around the index case. We investigated two contingency actions in Ohio (2017-2019 and 2018-2021) and one in Virginia (2017-2019) using a dynamic, multi-method occupancy approach to examine relationships between specific management actions and RRV occurrence, including whether ERS was sufficient around the index case. The RRV occupancy was assessed seasonally at 100-km2 grids and we examined relationships across three spatial scales (regional management zone, RRV free regions, and local contingency areas). The location of a grid relative to the ORV management zone was the strongest predictor of RRV occupancy at the regional scale. In RRV free regions, the neighbor effect and temporal variability were most important in influencing RRV occupancy. Parenteral (hand) vaccination of raccoons was important across all three contingency action areas, but more influential in the Ohio contingency action areas where more raccoons were hand vaccinated. In the Virginia contingency action area, ORV strategies were as important in reducing RRV occupancy as a hand vaccination strategy. The management action to trap, euthanize, and test (TET) raccoons was an important method to increase ERS, yet the impacts of TET on RRV occupancy are not clear. The probability of detecting additional cases of RRV was exceptionally high (>0.95) during the season the index case occurred. The probability of detecting RRV through ERS declined in the seasons following initial TET efforts but remained higher after the contingency action compared to the ERS detection probabilities prior to index case incidence. Local RRV cases were contained within one year and eliminated within 2-3 years of each contingency action.

Local Surveillance and Control of Raccoon Rabies Virus in Striped Skunks (Mephitis mephitis) in Southwestern New Brunswick, Canada

Targeted surveillance for raccoon rabies virus was conducted between February and May 2017, near Waweig, New Brunswick, Canada, in response to detection of a rabid striped skunk (Mephitis mephitis) on 8 February 2017. A total of six skunks, 11 raccoons (Procyon lotor), and two porcupines (Erethizon dorsatum) were live-trapped, euthanized, and tested for rabies virus antigens using the direct rapid immunohistochemical test. Of these, only two skunks tested positive for rabies. All three rabid skunks came from the same location, an abandoned barn used as a denning site. Four of five skunks removed from this barn were males. Feeding, aggression, extreme response to noise and light stimuli, and exposure to porcupine quills were observed in two rabid skunks. No additional cases of rabies in wildlife were detected in the area since 8 March 2017. A targeted surveillance approach that removed potentially infected wildlife followed by localized oral rabies vaccine distribution was implemented in this locality.

VIRUS NEUTRALIZING ANTIBODY FOLLOWING ORAL RABIES VACCINATION OF RACCOONS (PROCYON LOTOR) ON SUBURBAN LONG ISLAND, NEW YORK, USA

Vaccine-laden baits were distributed to interrupt and halt raccoon (Procyon lotor) rabies transmission in suburban Nassau and Suffolk counties on Long Island, New York, US. Fishmeal polymer baits containing the RABORAL V-RG® vaccine were deployed with helicopters, bait stations, and vehicles at a target density of 250 baits/km2 during annual September campaigns (2006-10). Semiannual campaigns (500 baits/km2) were also initiated in a portion of the treatment zone (2007-09) in response to a persistent focus of rabid raccoons. The last enzootic case was reported in January 2009. The final vaccination campaign was completed in 2010. The raccoon variant of rabies virus is no longer circulating in Nassau or Suffolk counties. Significantly greater probabilities of raccoon seroconversion were observed in helicopter-deployed bait zones. The lowest probabilities of seroconversion were identified in vehicle and bait station-deployment bait zones, with a marginal advantage associated with bait-station deployment. Seroconversion was negatively associated with developed, medium-intensity areas and increasing human population density. Significantly higher rabies virus neutralizing antibody endpoint titrations were detected in helicopter and bait station-deployment zones.

ORAL RABIES VACCINATION STRATEGIES TOWARD RACCOON (PROCYON LOTOR) RABIES ELIMINATION ON SUBURBAN LONG ISLAND, NEW YORK, USA

Approximately 1.86 million baits containing a vaccinia-rabies glycoprotein recombinant vaccine were distributed with helicopters, vehicles, and bait stations during 2006-10. A bait density of 250 baits/km2 effectively controlled rabies cases in enzootic and preepizootic areas. However, a cluster of 11 rabid raccoons at the eastern edge of infection resulted in the initiation of semiannual, high-density (500 baits/km2) vaccination campaigns in approximately 20% of the oral rabies vaccination zone during July and September (2007-09). Bait success (i.e., chewed sachets or removed baits) at bait stations was negatively associated with station distances from water. Conversely, bait success improved with increasing distances from roads. Bait stations deployed significantly more baits in developed open space when compared to low- and medium- to high-intensity developed areas. However, a difference was not detected between developed open space and forest habitats. Rabies was confined to 86 raccoons within 317 km2 (10%) of a 3,133 km2 suburban landscape, with a disproportionate number of rabid raccoons (n=74) in developed areas, when compared to 10 cases in forest-wetland habitats. Two rabid raccoons did not fall within either general land-use classification. Rabies advanced 15.1 km eastward at a rate of 6.4 km/yr during a 28-mo interval (2004-06).

Comparable Long-Term Rabies Immunity in Foxes after IntraMuscular and Oral Application Using a Third-Generation Oral Rabies Virus Vaccine

The live genetically-engineered oral rabies virus (RABV) variant SPBN GASGAS induces long-lasting immunity in foxes and protection against challenge with an otherwise lethal dose of RABV field strains both after experimental oral and parenteral routes of administration. Induction of RABV-specific binding antibodies and immunoglobulin isotypes (IgM, total IgG, IgG1, IgG2) were comparable in orally and parenterally vaccinated foxes. Differences were only observed in the induction of virus-neutralizing (VNA) titers, which were significantly higher in the parenterally vaccinated group. The dynamics of rabies-specific antibodies pre- and post-challenge (365 days post vaccination) suggest the predominance of type-1 immunity protection of SPBN GASGAS. Independent of the route of administration, in the absence of IgG1 the immune response to SPBN GAGAS was mainly IgG2 driven. Interestingly, vaccination with SPBN GASGAS does not cause significant differences in inducible IFN-γ production in vaccinated animals, indicating a relatively weak cellular immune response during challenge. Notably, the parenteral application of SPBN GASGAS did not induce any adverse side effects in foxes, thus supporting safety studies of this oral rabies vaccine in various species.

A little goes a long way: Weak vaccine transmission facilitates oral vaccination campaigns against zoonotic pathogens

Zoonotic pathogens such as Ebola and rabies pose a major health risk to humans. One proven approach to minimizing the impact of a pathogen relies on reducing its prevalence within animal reservoir populations using mass vaccination. However, two major challenges remain for vaccination programs that target free-ranging animal populations. First, limited or challenging access to wild hosts, and second, expenses associated with purchasing and distributing the vaccine. Together, these challenges constrain a campaign’s ability to maintain adequate levels of immunity in the host population for an extended period of time. Transmissible vaccines could lessen these constraints, improving our ability to both establish and maintain herd immunity in free-ranging animal populations. Because the extent to which vaccine transmission could augment current wildlife vaccination campaigns is unknown, we develop and parameterize a mathematical model that describes long-term mass vaccination campaigns in the US that target rabies in wildlife. The model is used to investigate the ability of a weakly transmissible vaccine to (1) increase vaccine coverage in campaigns that fail to immunize at levels required for herd immunity, and (2) decrease the expense of campaigns that achieve herd immunity. When parameterized to efforts that target rabies in raccoons using vaccine baits, our model indicates that, with current vaccination efforts, a vaccine that transmits to even one additional host per vaccinated individual could sufficiently augment US efforts to preempt the spread of the rabies virus. Higher levels of transmission are needed, however, when spatial heterogeneities associated with flight-line vaccination are incorporated into the model. In addition to augmenting deficient campaigns, our results show that weak vaccine transmission can reduce the costs of vaccination campaigns that are successful in attaining herd immunity.

Zoonotic pathogens pose a significant health risk to humans. Mass vaccination programs have shown promise for controlling zoonoses in reservoir populations and, in turn, lessening the health burden posed to neighboring human populations. Despite some significant successes, major logistical challenges remain for programs that seek to establish and maintain herd immunity in free-ranging animal populations. Specifically, limited host access and costs associated with vaccine distribution may hinder efforts to vaccinate a host population and preempt spillover of a zoonotic pathogen. We use mathematical models, parameterized with data from campaigns in the US that target rabies in wildlife, to illustrate how transmissible vaccines can overcome these challenges. Specifically, we find levels of vaccine transmission necessary to boost vaccination efforts that seek to preempt the spread of rabies, and also predict the cost savings that could be realized with a transmissible vaccine.

RACCOON (PROCYON LOTOR) RESPONSE TO ONTARIO RABIES VACCINE BAITS (ONRAB) IN ST. LAWRENCE COUNTY, NEW YORK, USA

Oral rabies vaccination (ORV) campaigns have been conducted annually in the US over the past two decades to prevent raccoon (Procyon lotor) rabies, which is enzootic along the eastern region of the country from southeastern Canada to Alabama. Because raccoon rabies has been eliminated from neighboring Canadian provinces, continued detection of the variant in the US is of concern due to the potential for infected raccoons to cross the border via the St. Lawrence River. Ontario Rabies Vaccine Baits (ONRAB) containing a live, recombinant human adenovirus expressing the rabies virus glycoprotein have been under experimental use in the US since 2011. We distributed ONRAB in St. Lawrence County, New York, from 2013 to 2015 as part of field trials to evaluate serologic responses in raccoons. Prior to ONRAB distribution, rabies virus neutralizing antibody (RVNA) seroprevalence in raccoons was 45.2% (183 of 405) and increased to 57.7% (165 of 286) after 3 yr of ONRAB baiting. Postbait RVNA seroprevalence increased each year, with a lower response observed in juvenile compared with adult raccoons. The pre-ONRAB seroprevalence detected in 2013 was relatively high and was likely impacted both by elevated rabies activity in the county and the use of ORV with a different vaccine bait for 14 consecutive years prior to our study. Tetracycline biomarker prevalence increased from 1.4% prior to ONRAB baiting to 51.3% from 2013 to 2015, demonstrating bait palatability to raccoons. These data complemented related field trials conducted in West Virginia and the northeastern US.

Processes Underlying Rabies Virus Incursions across US-Canada Border as Revealed by Whole-Genome Phylogeography

Disease control programs aim to constrain and reduce the spread of infection. Human disease interventions such as wildlife vaccination play a major role in determining the limits of a pathogen’s spatial distribution. Over the past few decades, a raccoon-specific variant of rabies virus (RRV) has invaded large areas of eastern North America. Although expansion into Canada has been largely prevented through vaccination along the US border, several outbreaks have occurred in Canada. Applying phylogeographic approaches to 289 RRV whole-genome sequences derived from isolates collected in Canada and adjacent US states, we examined the processes underlying these outbreaks. RRV incursions were attributable predominantly to systematic virus leakage of local strains across areas along the border where vaccination has been conducted but also to single stochastic events such as long-distance translocations. These results demonstrate the utility of phylogeographic analysis of pathogen genomes for understanding transboundary outbreaks.

Oral vaccination of wildlife using a vaccinia-rabies-glycoprotein recombinant virus vaccine (RABORAL V-RG®): a global review

RABORAL V-RG® is an oral rabies vaccine bait that contains an attenuated ("modified-live") recombinant vaccinia virus vector vaccine expressing the rabies virus glycoprotein gene (V-RG). Approximately 250 million doses have been distributed globally since 1987 without any reports of adverse reactions in wildlife or domestic animals since the first licensed recombinant oral rabies vaccine (ORV) was released into the environment to immunize wildlife populations against rabies. V-RG is genetically stable, is not detected in the oral cavity beyond 48 h after ingestion, is not shed by vaccinates into the environment, and has been tested for thermostability under a range of laboratory and field conditions. Safety of V-RG has been evaluated in over 50 vertebrate species, including non-human primates, with no adverse effects observed regardless of route or dose. Immunogenicity and efficacy have been demonstrated under laboratory and field conditions in multiple target species (including fox, raccoon, coyote, skunk, raccoon dog, and jackal). The liquid vaccine is packaged inside edible baits (i.e., RABORAL V-RG, the vaccine-bait product) which are distributed into wildlife habitats for consumption by target species. Field application of RABORAL V-RG has contributed to the elimination of wildlife rabies from three European countries (Belgium, France and Luxembourg) and of the dog/coyote rabies virus variant from the United States of America (USA). An oral rabies vaccination program in west-central Texas has essentially eliminated the gray fox rabies virus variant from Texas with the last case reported in a cow during 2009. A long-term ORV barrier program in the USA using RABORAL V-RG is preventing substantial geographic expansion of the raccoon rabies virus variant. RABORAL V-RG has also been used to control wildlife rabies in Israel for more than a decade. This paper: (1) reviews the development and historical use of RABORAL V-RG; (2) highlights wildlife rabies control programs using the vaccine in multiple species and countries; and (3) discusses current and future challenges faced by programs seeking to control or eliminate wildlife rabies.

Enhanced Rabies Surveillance to Support Effective Oral Rabies Vaccination of Raccoons in the Eastern United States

Enhanced rabies surveillance (ERS) is essential for sound oral rabies vaccination (ORV) decisions to prevent the spread of specific rabies virus variants in meso-carnivores and to achieve disease elimination. Use of a direct rapid immunohistochemistry test (dRIT) in North America for timely, accurate rabies diagnosis in the field has facilitated greater ERS emphasis since 2005. ERS used in tandem with exposure-based public health surveillance provides a comprehensive understanding of the geographic distribution of rabies as an aid to formulate effective management strategies for raccoons and other meso-carnivores. In 2015, best management practices were implemented for improving, reinvigorating, and standardizing ERS. A point system for weighing ERS sample categories was evaluated, to determine whether sampling emphasis should be focused upon ill or strange-acting animals, the highest quality category. During 2016, 70.7% of rabid animals detected through ERS in raccoon rabies management states were obtained from strange-acting animals, followed by animals found dead (14.1%), road kills (9.1%), and nuisance-collected specimens (6.1%). Sample category weights may be adjusted based on additional evaluation to ensure continued emphasis on the highest value samples. High quality ERS, in conjunction with serologic evidence of population-based immunity, form the backbone for ORV decisions in the elimination of raccoon rabies.

Management and modeling approaches for controlling raccoon rabies: The road to elimination

Rabies is an ancient viral disease that significantly impacts human and animal health throughout the world. In the developing parts of the world, dog bites represent the highest risk of rabies infection to people, livestock, and other animals. However, in North America, where several rabies virus variants currently circulate in wildlife, human contact with the raccoon rabies variant leads to the highest per capita population administration of post-exposure prophylaxis (PEP) annually. Previous rabies variant elimination in raccoons (Canada), foxes (Europe), and dogs and coyotes (United States) demonstrates that elimination of the raccoon variant from the eastern US is feasible, given an understanding of rabies control costs and benefits and the availability of proper tools. Also critical is a cooperatively produced strategic plan that emphasizes collaborative rabies management among agencies and organizations at the landscape scale. Common management strategies, alone or as part of an integrated approach, include the following: oral rabies vaccination (ORV), trap-vaccinate-release (TVR), and local population reduction. As a complement, mathematical and statistical modeling approaches can guide intervention planning, such as through contact networks, circuit theory, individual-based modeling, and others, which can be used to better understand and predict rabies dynamics through simulated interactions among the host, virus, environment, and control strategy. Strategies derived from this ecological lens can then be optimized to produce a management plan that balances the ecological needs and program financial resources. This paper discusses the management and modeling strategies that are currently used, or have been used in the past, and provides a platform of options for consideration while developing raccoon rabies virus elimination strategies in the US.

Preparing for and responding to recent incursions of raccoon rabies variant into Canada

By the late 2000s, Canada had successfully eliminated the incursion of racoon rabies from the south and remained free of this rabies variant from approximately 2009 to 2014. However, new incursions of raccoon rabies variant have recently been detected in three Canadian provinces: Ontario, Quebec and New Brunswick. Actions to address previous and current incursions of this rabies variant include enhanced surveillance programs, a point infection control strategy to respond to cases, a trap-vaccine-release program and oral rabies vaccination campaigns in targeted areas to prevent further cases and spread. It is hard to predict when and where new incursions will appear because of the ecological adaptability of raccoons and the significant risk associated with inadvertent translocation events by vehicles, trains and ships and raccoon movements across bridges. To date, no cases of raccoon rabies variant have been detected in domestic animals in Canada. However, until racoon rabies can be pushed back from the Canadian border, it is important to remain prepared for the reappearance of this disease.

Assessing Movements of Brushtail Possums (Trichosurus vulpecula) in Relation to Depopulated Buffer Zones for the Management of Wildlife Tuberculosis in New Zealand

In New Zealand, managing the threat of bovine tuberculosis (TB) to livestock includes population reduction of potentially infectious wildlife, primarily the brushtail possum (Trichosurus vulpecula). Population control is often targeted on forested buffer zones adjacent to farmland, in order to limit movements of possums across the buffer and reduce the risk of disease transmission to livestock. To assess the effectiveness of buffers in protecting livestock we analysed GPS telemetry data from possums located in untreated forest adjacent to buffers, and used these data to characterise patterns of movement that could lead to possums reaching farmland during the season when most dispersal occurs. Analyses of movement data showed that the direction of dispersal by sub-adult and adult possums and the extent of long exploratory movements were not biased toward forest buffers, even though these provided vacant habitat as suitable for possums as untreated forest. Instead, dispersal and exploratory movements were uncommon even for sub-adult possums and such events typically lasted <10 days. Dispersing possums settled predominantly in river valleys. A simulation model was developed for the 3-6-month dispersal season; it demonstrated a probability of <0.001 that an infected possum, originating from a low-density population with low disease prevalence in untreated forest, would move across 3 km of recently controlled forest buffer to reach farmland. Our results indicate short-term reduction in the risk of TB transmission from possums to livestock in New Zealand by the use of depopulated buffer zones, while acknowledging that the threat of disease spread from untreated forest is likely to increase over time as possum population density and, potentially, TB prevalence among those possums, increase in the buffer zone.

Human Rabies Post-Exposure Prophylaxis and Animal Rabies in Ontario, Canada, 2001-2012

In Ontario, Canada, the implementation of an annual rabies control programme in wildlife that began in 1989 resulted in a marked, steady decrease in the number of animal rabies cases. The number of animal rabies cases decreased from 1870 in 1989 to 183 in 2000 (Nunan et al., 2002 Emerg Infect Dis 8, 214). In our study period, the number of animal rabies cases continued to decrease from 210 in 2001 to 28 in 2012. The marked decrease in animal rabies cases since 1989 has resulted in a decrease in the risk of human infection. A concomitant decrease in the number of rabies post-exposure prophylaxis (RPEP) administered was anticipated but failed to occur. The mean rate of RPEP, 13.9 RPEP administered per 100,000 persons, from 2001-2012 was approximately the same as the rate in the 1990 s. Two possible reasons that the rate of RPEP administration has not decreased include strict adherence to RPEP recommendations and administration of RPEP when it is not recommended. A reduction in the number of RPEP administered, consistent with the decrease in the animal rabies cases, would provide some financial savings for the government. Ideally, an increased use of the risk assessment approach in keeping with recent guidelines, rather than adhering to previous prescriptive recommendations for RPEP administration, coupled with a continuing low incidence of animal rabies cases will result in decreased, and yet appropriate, use of RPEP. Consideration should be given to identify how guidelines could be revised to more effectively target high-risk exposures and reduce the administration of RPEP for instances in which the risk of rabies virus exposure is exceedingly low.

Spatial patterns of neutral and functional genetic variations reveal patterns of local adaptation in raccoon (Procyon lotor) populations exposed to raccoon rabies

Local adaptation is necessary for population survival and depends on the interplay between responses to selective forces and demographic processes that introduce or retain adaptive and maladaptive attributes. Host-parasite systems are dynamic, varying in space and time, where both host and parasites must adapt to their ever-changing environment in order to survive. We investigated patterns of local adaptation in raccoon populations with varying temporal exposure to the raccoon rabies virus (RRV). RRV infects approximately 85% of the population when epizootic and has been presumed to be completely lethal once contracted; however, disease challenge experiments and varying spatial patterns of RRV spread suggest some level of immunity may exist. We first assessed patterns of local adaptation in raccoon populations along the eastern seaboard of North America by contrasting spatial patterns of neutral (microsatellite loci) and functional, major histocompatibility complex (MHC) genetic diversity and structure. We explored variation of MHC allele frequencies in the light of temporal population exposure to RRV (0-60 years) and specific RRV strains in infected raccoons. Our results revealed high levels of MHC variation (66 DRB exon 2 alleles) and pronounced genetic structure relative to neutral microsatellite loci, indicative of local adaptation. We found a positive association linking MHC genetic diversity and temporal RRV exposure, but no association with susceptibility and resistance to RRV strains. These results have implications for landscape epidemiology studies seeking to predict the spread of RRV and present an example of how population demographics influence the degree to which populations adapt to local selective pressures.

Safety and immunogenicity of Ontario Rabies Vaccine Bait (ONRAB) in the first us field trial in raccoons (Procyon lotor)

In 2011, we conducted a field trial in rural West Virginia, USA to evaluate the safety and immunogenicity of a live, recombinant human adenovirus (AdRG1.3) rabies virus glycoprotein vaccine (Ontario Rabies Vaccine Bait; ONRAB) in wild raccoons (Procyon lotor) and striped skunks (Mephitis mephitis). We selected ONRAB for evaluation because of its effectiveness in raccoon rabies management in Ontario and Quebec, Canada, and significantly higher antibody prevalence rates in raccoons compared with a recombinant vaccinia-rabies glycoprotein (V-RG) vaccine, Raboral V-RG®, in US-Canada border studies. Raccoon rabies was enzootic and oral rabies vaccination (ORV) had never been used in the study area. We distributed 79,027 ONRAB baits at 75 baits/km(2) mostly by fixed-wing aircraft along parallel flight lines at 750-m intervals. Antibody prevalence was significantly higher at 49.2% (n=262) in raccoons after ONRAB was distributed than the 9.6% (n=395) before ORV. This was the highest antibody prevalence observed in raccoons by US Department of Agriculture Wildlife Services for areas with similar management histories evaluated before and after an initial ORV campaign at 75 baits/km(2) with Raboral V-RG. Tetracycline biomarker (TTCC) was significantly higher among antibody-positive raccoons after ONRAB baiting and was similar among raccoons before ORV had been conducted, an indication of vaccine-induced rabies virus-neutralizing antibody production following consumption of bait containing TTCC. Skunk sample size was inadequate to assess ONRAB effects. Safety and immunogenicity results supported replication of this field trial and led to a recommendation for expanded field trials in 2012 to evaluate safety and immunogenicity of ground-distributed ONRAB at 150 baits/km(2) in residential and commercial habitats in Ohio, USA and aerially distributed ONRAB at 75 baits/km(2) in rural habitats along US-Quebec border.

Modelling the dispersal of the two main hosts of the raccoon rabies variant in heterogeneous environments with landscape genetics

Predicting the geographic spread of wildlife epidemics requires knowledge about the movement patterns of disease hosts or vectors. The field of landscape genetics provides valuable approaches to study dispersal indirectly, which in turn may be used to understand patterns of disease spread. Here, we applied landscape genetic analyses and spatially explicit models to identify the potential path of raccoon rabies spread in a mesocarnivore community. We used relatedness estimates derived from microsatellite genotypes of raccoons and striped skunks to investigate their dispersal patterns in a heterogeneous landscape composed predominantly of agricultural, forested and residential areas. Samples were collected in an area covering 22 000 km² in southern Québec, where the raccoon rabies variant (RRV) was first detected in 2006. Multiple regressions on distance matrices revealed that genetic distance among male raccoons was strictly a function of geographic distance, while dispersal in female raccoons was significantly reduced by the presence of agricultural fields. In skunks, our results suggested that dispersal is increased in edge habitats between fields and forest fragments in both males and females. Resistance modelling allowed us to identify likely dispersal corridors used by these two rabies hosts, which may prove especially helpful for surveillance and control (e.g. oral vaccination) activities.

Current and future trends in the prevention, treatment and control of rabies

Rabies remains a global zoonosis of major public health, agricultural and economic significance. Dogs are the major animal reservoirs in developing regions, wildlife maintain cycles of infection even in developed countries and new viral etiological agents continue to emerge. Nearly all human rabies cases are related directly to animal bite and thus, primary disease prevention requires minimization of suspected exposures. Once exposure occurs, modern prophylaxis entails immediate wound care, local infiltration of rabies immune globulin and parenteral administration of modern cell culture vaccines in multiple doses. Pre-exposure vaccination should occur in selected population groups at risk of occupational exposure. Historically, survival from fatal rabies by at least five human patients, vaccinated prior to the onset of clinical signs, signaled initial optimism as to the theoretical utility of medical intervention. Recently, the heroic recovery of an unvaccinated teenager from clinical rabies offers hope of future specific therapy. Canine rabies elimination is the key towards ultimate reduction of the disease burden, as first illustrated in developed countries. Implementation of oral vaccination in free-ranging carnivore hosts demonstrates the feasibility of disease abatement in particular wildlife populations, such as demonstrated in Europe and North America, with an enhanced need for application to developing countries in the Americas, Africa and Eurasia.

Strategic model of national rabies control in Korea

Rabies is an important zoonosis in the public and veterinary healthy arenas. This article provides information on the situation of current rabies outbreak, analyzes the current national rabies control system, reviews the weaknesses of the national rabies control strategy, and identifies an appropriate solution to manage the current situation. Current rabies outbreak was shown to be present from rural areas to urban regions. Moreover, the situation worldwide demonstrates that each nation struggles to prevent or control rabies. Proper application and execution of the rabies control program require the overcoming of existing weaknesses. Bait vaccines and other complex programs are suggested to prevent rabies transmission or infection. Acceleration of the rabies control strategy also requires supplementation of current policy and of public information. In addition, these prevention strategies should be executed over a mid- to long-term period to control rabies.

Costs of raccoon rabies incidents in cattle herds in Hampshire County, West Virginia, and Guernsey County, Ohio

OBJECTIVE

To determine direct and indirect costs associated with raccoon rabies incidents involving cattle herds in Hampshire County, WV, in 2008 and Guernsey County, Ohio, in 2010.

DESIGN

Ex post cost analysis.

ANIMALS

1 cattle herd in Hampshire County, WV, in 2008 and 1 cattle herd in Guernsey County, Ohio, in 2010.

PROCEDURES

Data were collected for each incident through telephone and email interviews with 16 federal, state, and county agency personnel involved in the case investigations and coordinated responses for rabies in the cattle herds. To characterize the economic impact associated with rabies in the 2 cattle herds, cost analysis was conducted with 7 cost variables (salary and benefits for personnel involved in the response, human postexposure prophylaxis, indirect patient costs, rabies diagnostic testing, cattle carcass disposal, market value of euthanized cattle, and enhanced rabies surveillance). Estimates of direct costs were determined on the basis of agency records and other relevant data obtained from notes and reports made by agency staff at the time of the incident and from a review of the literature.

RESULTS

Primary costs included the market value of euthanized cattle ($51,461 in West Virginia; $12,561 in Ohio), human postexposure prophylaxis ($17,959 in West Virginia; $11,297 in Ohio), and salary and benefits for personnel involved in the response ($19,792 in West Virginia; $14,496 in Ohio).

CONCLUSIONS AND CLINICAL RELEVANCE

These results should provide a basis for better characterization of the economic impact of wildlife rabies in cattle in the United States.

Impacts of wildlife baiting and supplemental feeding on infectious disease transmission risk: a synthesis of knowledge

Baiting and supplemental feeding of wildlife are widespread, yet highly controversial management practices, with important implications for ecosystems, livestock production, and potentially human health. An often underappreciated threat of such feeding practices is the potential to facilitate intra- and inter-specific disease transmission. We provide a comprehensive review of the scientific evidence of baiting and supplemental feeding on disease transmission risk in wildlife, with an emphasis on large herbivores in North America. While the objectives of supplemental feeding and baiting typically differ, the effects on disease transmission of these practices are largely the same. Both feeding and baiting provide wildlife with natural or non-natural food at specific locations in the environment, which can result in large congregations of individuals and species in a small area and increased local densities. Feeding can lead to increased potential for disease transmission either directly (via direct animal contact) or indirectly (via feed functioning as a fomite, spreading disease into the adjacent environment and to other animals). We identified numerous diseases that currently pose a significant concern to the health of individuals and species of large wild mammals across North America, the spread of which are either clearly facilitated or most likely facilitated by the application of supplemental feeding or baiting. Wildlife diseases also have important threats to human and livestock health. Although the risk of intra- and inter-species disease transmission likely increases when animals concentrate at feeding stations, only in a few cases was disease prevalence and transmission measured and compared between populations. Mostly these were experimental situations under controlled conditions, limiting direct scientific evidence that feeding practices exacerbates disease occurrence, exposure, transmission, and spread in the environment. Vaccination programs utilizing baits have received variable levels of success. Although important gaps in the scientific literature exist, current information is sufficient to conclude that providing food to wildlife through supplemental feeding or baiting has great potential to negatively impact species health and represents a non-natural arena for disease transmission and preservation. Ultimately, this undermines the initial purpose of feeding practices and represents a serious risk to the maintenance of biodiversity, ecosystem functioning, human health, and livestock production. Managers should consider disease transmission as a real and serious concern in their decision to implement or eliminate feeding programs. Disease surveillance should be a crucial element within the long-term monitoring of any feeding program in combination with other available preventive measures to limit disease transmission and spread.

Vaccines against diseases transmitted from animals to humans: a one health paradigm

This review focuses on the immunization of animals as a means of preventing human diseases (zoonoses). Three frameworks for the use of vaccines in this context are described, and examples are provided of successes and failures. Framework I vaccines are used for protection of humans and economically valuable animals, where neither plays a role in the transmission cycle. The benefit of collaborations between animal health and human health industries and regulators in developing such products is discussed, and one example (West Nile vaccine) of a single product developed for use in animals and humans is described. Framework II vaccines are indicated for domesticated animals as a means of preventing disease in both animals and humans. The agents of concern are transmitted directly or indirectly (e.g. via arthropod vectors) from animals to humans. A number of examples of the use of Framework II vaccines are provided, e.g. against brucellosis, Escherichia coli O157, rabies, Rift Valley fever, Venezuelan equine encephalitis, and Hendra virus. Framework III vaccines are used to immunize wild animals as a means of preventing transmission of disease agents to humans and domesticated animals. Examples are reservoir-targeted, oral bait rabies, Mycobacterium bovis and Lyme disease vaccines. Given the speed and lost cost of veterinary vaccine development, some interventions based on the immunization of animals could lead to rapid and relatively inexpensive advances in public health. Opportunities for vaccine-based approaches to preventing zoonotic and emerging diseases that integrate veterinary and human medicine (the One Health paradigm) are emphasized.

React or wait: which optimal culling strategy to control infectious diseases in wildlife

We applied optimal control theory to an SI epidemic model to identify optimal culling strategies for diseases management in wildlife. We focused on different forms of the objective function, including linear control, quadratic control, and control with limited amount of resources. Moreover, we identified optimal solutions under different assumptions on disease-free host dynamics, namely: self-regulating logistic growth, Malthusian growth, and the case of negligible demography. We showed that the correct characterization of the disease-free host growth is crucial for defining optimal disease control strategies. By analytical investigations of the model with negligible demography, we demonstrated that the optimal strategy for the linear control can be either to cull at the maximum rate at the very beginning of the epidemic (reactive culling) when the culling cost is low, or never to cull, when culling cost is high. On the other hand, in the cases of quadratic control or limited resources, we demonstrated that the optimal strategy is always reactive. Numerical analyses for hosts with logistic growth showed that, in the case of linear control, the optimal strategy is always reactive when culling cost is low. In contrast, if the culling cost is high, the optimal strategy is to delay control, i.e. not to cull at the onset of the epidemic. Finally, we showed that for diseases with the same basic reproduction number delayed control can be optimal for acute infections, i.e. characterized by high disease-induced mortality and fast dynamics, while reactive control can be optimal for chronic ones.

Effects of culling on mesopredator population dynamics

Anthropogenic changes in land use and the extirpation of apex predators have facilitated explosive growth of mesopredator populations. Consequently, many species have been subjected to extensive control throughout portions of their range due to their integral role as generalist predators and reservoirs of zoonotic disease. Yet, few studies have monitored the effects of landscape composition or configuration on the demographic or behavioral response of mesopredators to population manipulation. During 2007 we removed 382 raccoons (Procyon lotor) from 30 forest patches throughout a fragmented agricultural ecosystem to test hypotheses regarding the effects of habitat isolation on population recovery and role of range expansion and dispersal in patch colonization of mesopredators in heterogeneous landscapes. Patches were allowed to recolonize naturally and demographic restructuring of patches was monitored from 2008-2010 using mark-recapture. An additional 25 control patches were monitored as a baseline measure of demography. After 3 years only 40% of experimental patches had returned to pre-removal densities. This stagnant recovery was driven by low colonization rates of females, resulting in little to no within-patch recruitment. Colonizing raccoons were predominantly young males, suggesting that dispersal, rather than range expansion, was the primary mechanism driving population recovery. Contrary to our prediction, neither landscape connectivity nor measured local habitat attributes influenced colonization rates, likely due to the high dispersal capability of raccoons and limited role of range expansion in patch colonization. Although culling is commonly used to control local populations of many mesopredators, we demonstrate that such practices create severe disruptions in population demography that may be counterproductive to disease management in fragmented landscapes due to an influx of dispersing males into depopulated areas. However, given the slow repopulation rates observed in our study, localized depopulation may be effective at reducing negative ecological impacts of mesopredators in fragmented landscapes at limited spatial and temporal scales.

Lack of genetic structure and female-specific effect of dispersal barriers in a rabies vector, the striped skunk (Mephitis mephitis)

Evaluating the permeability of potential barriers to movement, dispersal and gene exchanges can help describe spreading patterns of wildlife diseases. Here, we used landscape genetics methods to assess the genetic structure of the striped skunk (Mephitis mephitis), which is a frequent vector of rabies, a lethal zoonosis of great concern for public health. Our main objective was to identify landscape elements shaping the genetic structure of this species in Southern Québec, Canada, in an area where the raccoon rabies variant has been detected. We hypothesised that geographic distance and landscape barriers, such as highways and major rivers, would modulate genetic structure. We genotyped a total of 289 individuals sampled across a large area (22,000 km²) at nice microsatellite loci. Genetic structure analyses identified a single genetic cluster in the study area. Major rivers and highways, however, influenced the genetic relatedness among sampled individuals. Sex-specific analyses revealed that rivers significantly limited dispersal only for females while highways only had marginal effects. Rivers and highways did not significantly affect male dispersal. These results support the contention that female skunks are more philopatric than males. Overall, our results suggest that the effects of major rivers and highways on dispersal are sex-specific and rather weak and are thus unlikely to prevent the spread of rabies within and among striped skunk populations.

Genetic structure and rabies spread potential in raccoons: the role of landscape barriers and sex-biased dispersal

Identifying natural barriers to movements of hosts associated with infectious diseases is essential for developing effective control strategies. Raccoon rabies variant (RRV) is a zoonosis of concern for humans because its main vector, the raccoon (Procyon lotor), is found near residential areas. In Québec, Canada, all cases of RRV found in raccoons since 2006 were detected on the eastern side of the Richelieu River, suggesting that this river acts as a barrier to gene flow and thus the potential for RRV to spread. The objectives of this study were to characterize the genetic structure of raccoon populations and assess the effect of the Richelieu River on the population structure in southern Québec, Canada. We also evaluated whether RRV spread potential differed between sex and at a larger spatial scale. Our analyses revealed a weak signal of genetic differentiation among individuals located on each side of the Richelieu River. At a larger spatial scale, genetic structuring was weak. Our results suggest that rivers might not always efficiently restrain raccoon movements and spread of RRV. We suggest that the difference in genetic structure found between sexes can be partly explained by male movements during the breeding season in winter, when ice bridges allow passage over most rivers in Québec.

Landscape composition and structure influence the abundance of mesopredators: implications for the control of the raccoon (Procyon lotor) variant of rabies

Rabies propagation in Canada has forced wildlife managers to develop intervention strategies to reduce the risk of rabies epizootics. We assessed whether some landscape characteristics of a corn-dominated region of Quebec in which the raccoon variant of rabies (RVR) has spread were associated with the abundances of raccoons ( Procyon lotor (L., 1758)) and striped skunks (Mephitis mephitis (Schreber, 1776)). We then examined whether landscape variables that best explained spatial variation in raccoon abundance were also good predictors in the detection of rabid raccoons. Between June and September 2007, 9600 raccoons and 1612 skunks were captured from 111 trapping cells. The abundance of captured raccoons, especially that of adult males and juveniles, increased over the summer in trapping cells characterized by a high density of forest edges bordering corn fields. The probability of detecting rabid raccoons also increased with this landscape characteristic, as well as with adult raccoon abundance. No landscape characteristic, however, explained spatial variation in skunk abundance. Efficient RVR control operations in similar landscapes should ideally include widespread distribution of vaccine baits because of the general distribution of skunks, while also focusing on areas where forest patches intersperse with corn fields to target high concentrations of raccoons, particularly in late summer.

Evolution of wildlife rabies control tactics

The development of tactics for the control of rabies in wildlife species has evolved dramatically during the past few decades in part due to research advances. Historically, rabies control measures primarily involved the culling of target species. However, contemporary advances in the research and development of oral rabies vaccines and delivery systems for wildlife have now made it feasible to treat rabies outbreaks over thousands of square kilometers of habitat. Systems have been developed to control rabies in several of the primary wildlife vectors such as raccoon dogs, red foxes, and raccoons, and rabies has been eliminated from many jurisdictions. However, future research is needed to develop cost-effective and efficacious methods to control rabies in species such as striped skunks as well as in nonterrestrial vectors such as bats. As well, cost-effective rabies management techniques need to be adopted by developing nations so that wildlife rabies control is a realistic and achievable goal globally.

Understanding effects of barriers on the spread and control of rabies

This chapter reviews the evidence for the impact of natural and anthropogenic barriers on the spread of rabies using evidence mainly drawn from the epidemics of fox and raccoon variant rabies virus over the past 60 years in North America. Those barriers have both directed and inhibited the spread of rabies and, at a regional scale, have been integrated with rabies control efforts in North America. Few studies have been done, however, to examine how the texture (grain) and configuration of the habitat at finer scales affect rabies control, particularly the massive oral vaccination campaigns in operation along the Atlantic coast and southeastern Canada (Ontario, Québec, New Brunswick). To explore these questions, the authors used stochastic simulation. The model of choice was the Ontario Rabies Model (ORM) adapted for use on the high performance computing resources network in Québec (RQCHP-Réseau québécois de calcul de haute performance; http://rqchp.qc.ca). The combination of the ORM and RQCHP allowed us to run many thousands of experiments to explore interactions between nine landscape grain/configuration combinations and vaccination barriers with varying widths and immunity levels. Our results show that breaches of vaccine barriers increase as the grain size of the landscape increases and as the landscape becomes more structured. We caution that mid levels of vaccination can be counterproductive resulting in rabies persistence rather than control. We also note that our model/computing system has the flexibility and capacity to explore a wide range of questions pertinent to improving the efficacy of rabies control.

Genetic tracking of the raccoon variant of rabies virus in eastern North America

To gain insight into the incursion of the raccoon variant of rabies into the raccoon population in three Canadian provinces, a collection of 192 isolates of the raccoon rabies virus (RRV) strain was acquired from across its North American range and was genetically characterized. A 516-nucleotide segment of the non-coding region between the G and L protein open reading frames, corresponding to the most variable region of the rabies virus genome, was sequenced. This analysis identified 119 different sequences, and phylogenetic analysis of the dataset supports the documented history of RRV spread. Three distinct geographically restricted RRV lineages were identified. Lineage 1 was found in Florida, Alabama and Georgia and appears to form the ancestral lineage of the raccoon variant of rabies. Lineage 2, represented by just two isolates, was found only in Florida, while the third lineage appears broadly distributed throughout the rest of the eastern United States and eastern Canada. In New York State, two distinct spatially segregated variants were identified; the one occupying the western and northern portions of the state was responsible for an incursion of raccoon rabies into the Canadian province of Ontario. Isolates from New Brunswick and Quebec form distinct, separate clusters, consistent with their independent origins from neighboring areas of the United States. The data are consistent with localized northward incursion into these three separate areas with no evidence of east-west viral movement between the three Canadian provinces.

Influence of oral rabies vaccine bait density on rabies seroprevalence in wild raccoons

The effect of different oral rabies vaccine (ORV) bait densities (75, 150, and 300 baits/km(2)) on the seroprevalence of rabies virus neutralizing antibodies (RVNAs) in raccoons (Procyon lotor) was assessed at a 15% seroprevalence difference threshold in rural areas of northeast Ohio. Results (n=588 raccoons) indicated that seropositivity for RVNAs was associated with both bait density and bait campaign frequency. Associations were not detected for raccoon gender, age, or macro-habitat. The odds of being seropositive were greater for raccoons originating from 300 bait/km(2) treatment areas relative to those coming from the 75 bait/km(2) areas (odds ratio [OR]=4.4, probability [P]<0.001, 95% confidence interval [CI]=2.4-7.9), while accounting for cumulative ORV campaigns. No statistical advantage in seroprevalence was detected when comparing 150-75 baits/km(2). These results indicate that a relatively extreme bait density when evenly distributed may be necessary to obtain a significant increase in seroprevalence. Higher bait densities may be more appropriate and less costly to address focused outbreaks than labor intensive trap-vaccinate-release and local population reduction campaigns. Finally, dramatic increases in seroprevalence of RVNA were not observed in raccoons between sequential, semi-annual campaigns, yet cumulative ORV campaigns were associated with gradual increases in seroprevalence.

Oral rabies vaccination in north america: opportunities, complexities, and challenges

Steps to facilitate inter-jurisdictional collaboration nationally and continentally have been critical for implementing and conducting coordinated wildlife rabies management programs that rely heavily on oral rabies vaccination (ORV). Formation of a national rabies management team has been pivotal for coordinated ORV programs in the United States of America. The signing of the North American Rabies Management Plan extended a collaborative framework for coordination of surveillance, control, and research in border areas among Canada, Mexico, and the US. Advances in enhanced surveillance have facilitated sampling of greater scope and intensity near ORV zones for improved rabies management decision-making in real time. The value of enhanced surveillance as a complement to public health surveillance was best illustrated in Ohio during 2007, where 19 rabies cases were detected that were critical for the formulation of focused contingency actions for controlling rabies in this strategically key area. Diverse complexities and challenges are commonplace when applying ORV to control rabies in wild meso-carnivores. Nevertheless, intervention has resulted in notable successes, including the elimination of an arctic fox (Vulpes lagopus) rabies virus variant in most of southern Ontario, Canada, with ancillary benefits of elimination extending into Quebec and the northeastern US. Progress continues with ORV toward preventing the spread and working toward elimination of a unique variant of gray fox (Urocyon cinereoargenteus) rabies in west central Texas. Elimination of rabies in coyotes (Canis latrans) through ORV contributed to the US being declared free of canine rabies in 2007. Raccoon (Procyon lotor) rabies control continues to present the greatest challenges among meso-carnivore rabies reservoirs, yet to date intervention has prevented this variant from gaining a broad geographic foothold beyond ORV zones designed to prevent its spread from the eastern US. Progress continues toward the development and testing of new bait-vaccine combinations that increase the chance for improved delivery and performance in the diverse meso-carnivore rabies reservoir complex in the US.

Tactics and economics of wildlife oral rabies vaccination, Canada and the United States

Economic assessments and modeling studies suggest that these programs yield cost savings and public health benefits.

Progressive elimination of rabies in wildlife has been a general strategy in Canada and the United States; common campaign tactics are trap–vaccinate–release (TVR), point infection control (PIC), and oral rabies vaccination (ORV). TVR and PIC are labor intensive and the most expensive tactics per unit area (≈$616/km² [in 2008 Can$, converted from the reported $450/km² in 1991 Can$] and ≈$612/km² [$500/km² in 1999 Can$], respectively), but these tactics have proven crucial to elimination of raccoon rabies in Canada and to maintenance of ORV zones for preventing the spread of raccoon rabies in the United States. Economic assessments have shown that during rabies epizootics, costs of human postexposure prophylaxis, pet vaccination, public health, and animal control spike. Modeling studies, involving diverse assumptions, have shown that ORV programs can be cost-efficient and yield benefit:cost ratios >1.0.

Safety studies on an adenovirus recombinant vaccine for rabies (AdRG1.3-ONRAB) in target and non-target species

A replication-competent human adenovirus vector in which the rabies virus glycoprotein gene was inserted (AdRG1.3-ONRAB) was given by direct instillation into the oral cavity to representatives of three wildlife vector species of concern in Ontario (red fox, raccoon and striped skunk) and to a variety of non-target wildlife species, domestic and laboratory species. Despite use of a relatively high dose of vaccine, no untoward clinical signs were observed. Subsequent to vaccine exposure, detection of vaccine virus in lung, spleen, intestine, liver, kidney and brain of each animal was attempted using an ONRAB-specific assay combining PCR with Southern blotting (PCR-SB). Of the 1280 tissue samples obtained from vaccinates or contact animals, 18 (1.4%) were found to be PCR-SB positive. Virus isolation attempts were performed utilizing cell culture for all PCR-SB positive tissues and a selection of PCR-SB negative tissues. Histological examination performed on all PCR-SB positive tissues failed to identify lesions attributed to the vaccine. A quantitative real-time PCR was used to determine the excretion of the vaccine in feces and in the oral cavity with 0.8% of oral swabs and 6.8% of fecal specimens found to be positive. The low rates of recovery of vaccine virus from tissues, feces and the oral cavity suggest that the likelihood of ONRAB causing a negative impact on wildlife species is unlikely.

Risk-based cost modelling of oral rabies vaccine interventions for raccoon rabies

Distribution of oral rabies vaccine (ORV) is an effective but costly strategy to control raccoon rabies. Because of high costs, ORV for raccoon rabies in the U.S. has been limited primarily to epizootic areas, leaving extensive raccoon rabies regions without any ORV intervention. Several cost scenarios for ORV application in raccoon rabies enzootic and epizootic regions were modelled in New York State to obtain estimated costs of ORV baits per scenario and potential savings compared with a uniform ORV baiting strategy. These cost scenarios modelled at the census tract, level the application of ORV baits at different densities according to levels of risk defined by the observed number of raccoon rabies cases per km2 and the expected number of cases per km2 estimated with a Poisson regression model. Bait purchase costs were lower using the modelled cost scenarios than a uniform baiting strategy, for both the NYS enzootic region and the Long Island epizootic zone. The proportion of savings for the NYS enzootic region was 29.57%, and the proportion of savings for the Long Island epizootic zone was 38.9%. Use of these cost scenarios to determine bait distribution by rabies risk level should be considered to maximize efficacy and reduce costs of ORV interventions.

Genetic structure of raccoons in eastern North America based on mtDNA: implications for subspecies designation and rabies disease dynamics

Subspecific designations are useful for wildlife management when they represent real barriers to gene flow. In this study, we assess genetic partitioning of mitochondrial DNA control region variation to determine if the structuring is congruent with morphologically defined subspecies of the common raccoon (Procyon lotor (L., 1758)). Mitochondrial control region sequences were analyzed within and among four subspecies ( Procyon lotor elucus Bangs, 1898, Procyon lotor lotor (L., 1758), Procyon lotor hirtus Nelson and Goldman, 1930, and Procyon lotor varius Nelson and Goldman, 1930) that occur along the eastern seaboard of North America through to the central United States. This identified 76 haplotypes, 59 of which were specific to one of the four ranges, while only 1 haplotype was wide-spread. Phylogenetic analysis revealed three distinct lineages: one found primarily in Florida, one along the eastern seaboard, and the third predominantly to the west of the Mississippi River. These lineages likely diverged during the Pleistocene, as a result of rising sea levels creating barriers to gene flow. The range of P. l. elucus is still primarily one lineage supporting the subspecific designation; however, there is considerable lineage mixing across the ranges of P. l. hirtus, P. l. lotor, and P. l. varius, suggesting that they be synonymized to P. l. lotor. While some of these subspecies designations are not supported, we have found that landscape attributes affect gene flow, which can be of use in informing rabies management.

Fishers, farms, and forests in eastern North America

The fisher (Martes pennanti) has recently recovered from historic extirpations across much of its geographic range. There are at least five explanations for the recovery of the fisher, including changes in the amount of habitat, the suitability of habitat, trapping pressure, societal attitudes toward predators, and climate. We evaluated a recovering fisher population in Ontario to test two conditions we viewed as necessary to support the hypothesis that fisher populations have increased due to an increase in the amount of forested land. First, we tested whether the amount of forested land has increased. Second, we tested whether contemporary fisher abundance (and therefore habitat quality) was related to the amount of forest. Topographic maps showed that the proportion of forested land in the study area had increased by 1.9% per decade since 1934 and 3.3% per decade since 1959, likely as a result of land conversion from agricultural uses. Overall the proportion of the study area that was forested increased from 29% to 40% during 1934 to 1995. Census data from the region indicated that there had been a decline in the amount of land area being farmed during the last 50 years. Recent livetrapping data showed that fisher abundance was positively related to the proportion of landscapes that were forested. Based on our results, we could not reject the hypothesis that an increase in the amount of forested land has contributed to the recovery of fisher populations.