Presence of neutralizing antibodies to rabies virus in striped skunks from areas free of skunk rabies in Alberta

Nine percent of 198 serum samples from striped skunks, Mephitis mephitis (Schreber) from five areas of Alberta were positive for rabies neutralizing antibody. Positive samples were minimal (2%) from specimens sampled in an area enzootic for rabies and occurred at greater rates in areas negative for skunk rabies. Transmission of rabies virus to skunks may have been from a source other than skunks in those areas, most probably from bats.     

Intramuscular vaccination of skunks and raccoons against rabies

Live-captured striped skunks (Mephitis mephitis) and raccoons (Procyon lotor) were immunized with inactivated rabies vaccine by intramuscular injection and released at the point of capture during a rabies control program in Metropolitan Toronto (Ontario, Canada). Serum samples collected prior to and following vaccination revealed that 100% of the skunks and 98% of the raccoons seroconverted. Rabies antibody was still detectable 314 to 757 days postvaccination. Five of six skunks vaccinated in the laboratory survived challenge with rabies virus 90 days postvaccination. To our knowledge, this is the first documentation of the successful seroconversion of skunks and raccoons vaccinated against rabies in the field.     

High-density baiting with ONRAB® rabies vaccine baits to control Arctic-variant rabies in striped skunks in Ontario, Canada

The Arctic variant of rabies virus has been maintained in striped skunks in small foci in southwestern Ontario, Canada, despite the control of the disease in red foxes. To control the disease in skunks, high-density baiting with ONRAB(?) oral rabies vaccine baits was conducted by air and by hand distribution of baits in the vicinity of skunk cases. During 2009, antibody prevalences in skunks were higher in areas baited at a density of 300 baits/km(2) and flight-line spacing of 0.25 km than at 0.5-km spacing. Once an area containing Arctic-variant cases was treated with high densities of ONRAB baits, the disease did not reoccur in skunks in those areas. During 2009, only eight skunks were diagnosed with the Arctic variant of rabies virus in Ontario.     

Oral vaccination of skunks with raccoon poxvirus recombinants expressing the rabies glycoprotein or the nucleoprotein.

Twenty nine skunks (Mephitis mephitis) were vaccinated orally with raccoon poxvirus (RCN) recombinants: 10 with a recombinant expressing the rabies virus glycoprotein (RCNRG), 10 with RCNRG mixed with a recombinant expressing the rabies virus nucleoprotein (RCNRN) and nine with RCN alone. Rabies virus neutralizing antibodies were detected in six of the 20 skunks; five skunks (three given RCNRG, two given a mixture of recombinants) survived a rabies challenge that was lethal for nine skunks vaccinated with RCN alone.     

Rabies in an American bison from North Dakota

In North Dakota (USA) during April 1998, a ranched female bison (Bison bison) was found dead. At gross necropsy, there was profound hair loss and consolidated lung lobes. Intracytoplasmic neuronal inclusions suggestive of Negri bodies were observed in the brain stem and hippocampus, and a diagnosis of rabies was confirmed by the fluorescent antibody test. Antigenic typing demonstrated the occurrence of a rabies virus variant associated with skunks from the upper midwestern USA. This case of a rabid bison was one of only four such instances recorded from the USA over the past 40 yr, and is the first case report of rabies in a bison that reports clinical, pathologic, and antigenic findings. Although rabies in bison is rare, veterinarians and wildlife managers that work closely with such non-traditional species are reminded of the dangers that zoonoses such as rabies present.     

Oral efficacy of an attenuated rabies virus vaccine in skunks and raccoons

Raccoons and skunks are major rabies reservoirs in North America. Oral vaccination is one method to consider for disease control in these carnivores. Under field conditions in the USA, only one oral rabies vaccine has been used. It is efficacious in wildlife such as raccoons (Procyon lotor), coyotes (Canis latrans), and foxes (Vulpes vulpes) but not in skunks (Mephitis mephitis). The objectives of this study were to evaluate an attenuated SAG-2 rabies virus vaccine for safety, immunogenicity, and efficacy by the oral route in skunks and raccoons. Two of five skunks and three of five raccoons developed virus neutralizing antibodies (VNA) by day 14 following oral administration of SAG-2 vaccine. All animals remained healthy. Upon challenge, naive controls succumbed to rabies. Among vaccinated animals, four of five skunks and all five raccoons had VNA on day 7 post-challenge and all survived. Given these results, SAG-2 is a promising candidate vaccine that may satisfy both safety and efficacy concerns for oral rabies immunization of major North American rabies reservoirs.     

Rabies challenge of captive striped skunks (Mephitis mephitis) following oral administration of a live vaccinia-vectored rabies vaccine

Twenty-four adult striped skunks (Mephitis mephitis) were administered the raccoon product formulation of Rabies Vaccine, Live Vaccinia-Vectored (Raboral V-RG, Merial Limited, Athens, Georgia, USA), either by oral instillation or in vaccine-filled coated sachets either as single or multiple doses. A control group remained unvaccinated. Twenty-three of the skunks were challenged 116 days postvaccination with rabies virus (skunk isolate). Six of six naive skunks succumbed to challenge. Four of six skunks that received the vaccine by oral instillation survived challenge. The skunks that did not survive failed to seroconvert following vaccination. None of the skunks that accepted multiple doses of the vaccine offered in coated sachets survived challenge, nor were rabies virus-neutralizing antibodies (VNAs) detected in the sera. Likewise, none of the five skunks ingesting a single sachet developed VNA against rabies. However, in this group one skunk did survive rabies challenge. This preliminary study showed that the vaccinia-vectored oral rabies vaccine Raboral V-RG, as formulated for use in raccoons, is capable of protecting a percentage of skunks against rabies. However, although the fishmeal-coated sachets were readily consumed, subsequent challenge of these animals revealed poor vaccine delivery efficiency.     

Vaccination of free-ranging Pennsylvania raccoons (Procyon lotor) with inactivated rabies vaccine

Thirty-nine free-ranging raccoons (Procyon lotor) in an endemic rabies area of Pennsylvania (USA) were vaccinated with a single intramuscular inoculation of commercial inactivated rabies virus vaccine, 17 June to 23 August 1987. Paired serum samples, pre- and postvaccination, were obtained from eight raccoons and were analyzed in vitro for rabies virus neutralizing antibody using a modified rapid fluorescent focus inhibition test. Seven of eight (88%) recaptured raccoons demonstrated seroconversion within 15 to 26 days of vaccination. At 1 yr postvaccination, three vaccinated raccoons were recaptured and challenged in captivity with street rabies virus, resulting in the death of two of three vaccinates and five of five unvaccinated control raccoons.     

Safety studies of the oral rabies vaccine SAD B19 in striped skunk (Mephitis mephitis)

Safety of the modified live rabies virus vaccine, SAD B19, was studied in striped skunks (Mephitis mephitis). Seven skunks received 10(7.9) foci formatting units by direct oral administration. In four cages, a vaccinated animal was placed with a control animal, the other three vaccinated skunks were housed individually. Saliva and nasal swabs were collected 1, 2, 4, 24, 48, and 72 hr post-vaccination. From all vaccinated and control animals (n = 11) blood samples were collected 0, 28, 56, 84, and 296 days post-vaccination. Three of seven vaccinated skunks seroconverted. None of the control animals had detectable levels of rabies virus neutralizing antibodies. Also no vaccine virus was isolated from the nasal and saliva swabs collected from any animal. Thus, SAD B19 was innocuous for skunks in our study after direct oral administration at field concentration.     

Presence of rabies neutralizing antibodies in wild carnivores following an outbreak of bovine rabies.

In an outbreak of bovine rabies in Argentina, a study was made of vampire bats (Desmodus rotundus) and wild carnivores. Rabies antibody rates of high prevalence were found in the bats, foxes (Dusicyon gymnocercus) and skunks (Conepatus chinga). The outbreak was part of an extensive continuing epizootic of vampire transmitted bovine rabies which may have also involved other vectors in the area of this study. Consumption of dead and dying bats by the carnivores is the suggested means of passage of rabies virus from vampire bats to foxes and skunks. Given optimum conditions it is conceivable that some outbreaks in carnivores may begin in this way.     

Comparing ONRAB® AND RABORAL V-RG® oral rabies vaccine field performance in raccoons and striped skunks, New Brunswick, Canada, and Maine, USA

Control of rabies in mesocarnivore reservoirs through oral rabies vaccination (ORV) requires an effective vaccine bait. Oral rabies vaccine performance in the field may be affected by a variety of factors, including vaccine bait density and distribution pattern, habitat, target species population density, and the availability of competing foods. A field study in which these covariates were restricted as much as possible was conducted along the international border of the state of Maine (ME), USA, and the province of New Brunswick (NB), Canada, to compare the performance of two oral rabies vaccines in raccoons (Procyon lotor) and striped skunks (Mephitis mephitis). RABORAL V-RG(?) (vaccinia-rabies glycoprotein recombinant oral vaccine in fishmeal-coated sachet) or ONRAB(?) (adenovirus-rabies glycoprotein recombinant oral vaccine in Ultralite bait matrix) were distributed in ME and NB, respectively, by fixed-wing aircraft at a density of 75 baits/km(2) along parallel flight lines spaced 1.0 km apart. Sera were collected from live-trapped raccoons and skunks 5-7 wk post-ORV and assayed to determine antibody prevalence in each area. Duplicate serum samples were provided blind to two different laboratories for analyses by rabies virus serum neutralization assays (at both laboratories) and a competitive enzyme-linked immunosorbent assay (at one laboratory). There was no significant difference in the proportion of antibody-positive animals determined by the three serologic methods, nor was there a significant difference between ONRAB and RABORAL V-RG in the proportion of antibody-positive striped skunks observed post-ORV. In contrast, the proportion of antibody-positive raccoons was significantly higher in the ONRAB- versus the RABORAL V-RG-baited areas (74% vs. 30%; χ(2)=89.977, df=5, P<0.0001). These data support that ONRAB may serve as an effective tool for raccoon rabies control.     

Skunk rabies in California (1992-2003)--implications for oral rabies vaccination

Skunk-variant rabies is endemic in California (United States), and the development of oral vaccines and baits to vaccinate skunks is in progress. In 2003, the California Department of Public Health (CDPH) began to quantify the impacts of skunk-variant rabies and to assess the feasibility of using oral rabies vaccination (ORV) as a containment measure. The CDPH rabies case data for skunks were spatially depicted and analyzed using a geographic information system. Statewide, rabid skunks (1992-2003) primarily occurred in seven physiographic regions: Central Coast, North Coast, North Sierra, Sacramento Valley, San Francisco Bay and Delta, San Joaquin Valley, and South Sierra. Detailed analysis of rabid skunks in San Luis Obispo (SLO) and Santa Barbara (SB) counties showed that skunk rabies was endemic in the coastal plain of SLO County between 1992 and 2000, but only became epizootic in SB County during 2002. Despite the widespread distribution of striped skunks (Mephitis mephitis) throughout most of California, the skunk rabies variant has not been found in Los Angeles County since 1979. Results imply that future ORV campaigns for skunk-variant rabies in the Pacific Coastal Plain could deter spread from SLO into SB County, as well as deterring the reintroduction of skunk-variant rabies into southern California.     

Era vaccine-derived cases of rabies in wildlife and domestic animals in Ontario, Canada, 1989-2004

A vaccination program for the control of terrestrial rabies in the province of Ontario, Canada, began in 1989. During the period between 1989 and 2004, over 13 million baits containing the live, attenuated rabies virus ERA-BHK21 were distributed across the province, with the aim of immunizing foxes by the oral route. Animals recovered from bait distribution areas were assayed by fluorescent antibody test for rabies virus infection. Immunoreactivity with a panel of monoclonal antibodies that discriminate between ERA and rabies virus variants known to circulate in Ontario, and molecular genetic analyses were used to identify animals infected with ERA. Nine cases of ERA variant rabies were identified over the 16-yr period of study; these did not appear to be stratified by species, year of discovery, or location of capture. The ERA-positive animals were found across the province in eight counties, all of which had been baited in the year of case discovery. The nine ERA-positive cases included four red foxes (Vulpes vulpes), two raccoons (Procyon lotor), two striped skunks (Mephitis mephitis), and one bovine calf (Bos taurus). Molecular phylogenetic analyses of the partial N gene sequences generated from these isolates indicated that these nine cases were due to infection with the ERA variant. The glycoprotein sequences were predicted from G gene sequencing of all nine field isolates and two laboratory stock ERA viruses. This revealed some heterogeneity at residue 120 (either arginine or histidine) in both field and laboratory stocks as well as a few other mutations in field isolates. The significance of this heterogeneity remains unclear. Our data demonstrate that the ERA vaccine distributed in Ontario carried residual pathogenicity; however, there does not appear to be any evidence of ERA establishment in wildlife populations over the 16-yr period. These results are consistent with previous reports of the rare detection of ERA vaccine-induced rabies and with laboratory studies of ERA pathogenicity.     

Exposure to rabies virus in a population of free-ranging capuchin monkeys (Cebus apella nigritus) in a fragmented, environmentally protected area in southeastern Brazil

The aim of this study is to assess the frequency of rabies antibodies in free-ranging capuchin monkeys (Cebus apella nigritus) in a fragmented, environmentally protected, rural area of southeastern Brazil. Thirty-six free-ranging monkeys were tested by the rapid fluorescent focus inhibition test for detection of antibodies against rabies virus. Four individuals (11.11 %) had neutralizing antibody titers ≥ 0.25 IU/mL, demonstrating rabies virus exposure.     

Rabies in skunks from Mexico.

An enzootic focus of rabies in skunks in Mexico is described. Fifty three wild animals including two badgers (Taxidea taxus), 32 bats (various species), one bobcat (Lynx rufus), two coatis (Nasua narica) three foxes (Urocyon cineroargenteus), one raccoon (Procyon lotor) and 12 skunks (see below) were tested for rabies by direct immunofluorescence assay from 1991 to 1997 in the central part of San Luis Potosi State, Mexico. Rabies occurrence was 21% of all tested mammals, with 19% in skunks and only 2% in other wild species (one bobcat). Skunks represented 23% of all mammals tested and had a rabies prevalence of 83%. Only 10 individuals were identified: three hog-nosed skunks (Conepatus leuconotus) and seven spotted skunks (Spilogale putorius). All were involved in human attacks; the spotted skunk attacks were inside bedrooms while people were sleeping, and the hog-nosed skunk attacks occurred outdoors. Skunk cases of rabies represented 40% of all rabies cases in 1997, and 100% of cases registered for wild animals in San Luis Potosi state. This situation constitutes an important public health problem and requires further epidemiological research to make the human population aware of the problem and to establish measures to limit further human attacks by rabid skunks.     

Emergency response to raccoon rabies introduction into Ontario

During 15 July to 4 October, 1999, rabies control programs were implemented with the objective being to contain the first three confirmed cases of raccoon rabies in Canada. The strategy, called point infection control (PIC) involved the use of three tactics: population reduction (PR), trap-vaccinate-release (TVR) and oral rabies vaccination with baits (ORV), to control the spread of raccoon rabies. A total of 1,202 raccoons (Procyon lotor) and 337 skunks (Mephitis mephitis) were captured and euthanized using 24,719 trap-nights in the three PR zones around the location of the three rabies cases, near Brockville, Ontario. That represented an 83% to 91% reduction in the raccoon populations in an approximate 225 km2 area around the three rabies cases. Raccoon density in the PR zones declined from 5.1-7.1/km2 to 0.6-1.1/km2 following control. All tested specimens were negative for rabies by the fluorescent antibody test (FAT). In addition, 1,759 raccoons and 377 skunks were intramuscularly vaccinated against rabies and released using 27,956 trap-nights in an approximate 485 km2 TVR zone implemented outside of the PR zones. A total of 856 cats from both PR and TVR areas were also captured, vaccinated and released. Cost for the three PIC operations was $363,000.00 Cdn or about $500.00 Cdn/km2. To further contain the outbreak, about 81,300 baits containing Raboral V-RG oral rabies vaccine were aerially distributed on 8 and 27 September 1999, to create an 8 to 15 km wide buffer zone (1,200 km2 area) of vaccinated raccoons immediately beyond the PR and TVR zones. This was the first time that V-RG was used in Canada to orally vaccinate free ranging raccoons against rabies. Baiting costs were $241,000.00 Cdn or about $200.00 Cdn/km2 including post baiting assessment costs. As of 31 August, 2000, thirty-five additional cases (38 in total) of raccoon rabies have occurred in the control and vaccination zones. This number is far below the level of rabies prevalence in USA jurisdictions where raccoon rabies was epizootic. In the future, PIC methodologies will continue to be used in Ontario to contain isolated cases of raccoon rabies.     

Population monitoring in support of a rabies vaccination program for skunks in Arizona

Three population monitoring methods were evaluated in support of a trap/vaccinate/release program for controlling a bat variant of rabies virus in skunks (Mephitis mephitis) in Flagstaff, Arizona (USA). Skunks were the primary species targeted for population monitoring during the program, but feral cats were also monitored as they represented an abundant secondary vector species capable of rabies transmission. Skunks were vaccinated and released, except for a subset tested for rabies. All captured cats were placed in the local animal shelter. Spotlight surveys essentially did not detect skunks, and were not able to detect reductions in the cat population. Catch-per-unit-effort marginally tracked population trends, but a passive track index adapted for an urban setting was most sensitive for detecting changes in skunk and cat populations. Mark-recapture population estimates could not be validly calculated from the data on captures and recaptures due to multiple violations of analytical assumptions.     

Pantropism of rabies virus in free-ranging rabid red fox Vulpes fulva

The fluorescent antibody and mouse inoculation tests were employed to study the pantropism of rabies virus in tissue from free-ranging red fox (Vulpes fulva) submitted for rabies diagnosis. Viral antigen was found in various organs and tissues of the body. The distribution of antigen within tissues is discussed in the light of the pathogenesis and potential excretion of the virus.     

Oral vaccination of captive arctic foxes with lyophilized SAG2 rabies vaccine

Arctic foxes (Alopex lagopus) were immunized with lyophilized SAG2 oral rabies vaccine. The effectiveness of this vaccine was determined by serologic response and survival to challenge by rabies virus isolated from a red fox from Alaska (USA). No vaccine virus was found in saliva 1-72 hr after ingestion. At 2 wk after vaccination, all foxes had seroconverted, with rabies virus neutralizing antibody levels of 0.2-3.1 IU ml(-1). All vaccinated foxes survived to week 17 after challenge, and hippocampus, pons, and cerebellum were free of rabies virus as determined by direct immunofluorescence testing after death. One of four nonvaccinated foxes survived challenge and was free of rabies virus in neural tissue, and no rabies virus neutralizing antibody was detected in blood. Our results suggest that the lyophilized SAG2 oral rabies vaccine could be effective in arctic and subarctic regions, where freezing air and ground temperatures probably would not reduce its immunogenicity.     

Rabies and rabies control in striped skunks (Mephitis mephitis) in three prairie regions of western North America

The number and geographic distribution of rabies cases in striped skunks (Mephitis mephitis) from Saskatchewan (n = 2,506 cases), Montana (n = 1,142), and Alberta (n = 199) since 1963 were reviewed. In Saskatchewan the number of cases increased steadily for 5 yr and then fluctuated consistently in a 4 yr cyclic pattern. Similarly an initial sweep across the province was followed by a cyclic pattern of geographic expansion (3 to 4 yr) and reduction (1 to 2 yr). No organized control efforts were conducted in Saskatchewan. Similar cyclic pattern were not seen in data from Montana or Alberta. In the latter areas, the number and distribution of rabies cases in skunks appeared to reflect efforts to reduce the population of skunks. An integrated program of skunk removal using poison and live-traps in association with research and public education successfully contributed to limiting the spread and establishment of rabies in striped skunks within prairie habitats. Rabies did not persist in skunks in other habitats.