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.     

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.     

Husbandry,overwinter care,and reproduction of captive striped skunks (Mephitis mephitis)

The striped skunk (Mephitis mephitis) is the focus of research interest for a variety of reasons, including its roles as a rabies reservoir, urban pest, predator of bird eggs, and parasite host. Some research programmes may require husbandry and breeding of captive animals, and because skunks are inactive in the winter in northern environments, special methods are needed to maintain the animals over winter. We report on the establishment of a colony of striped skunks kept in captivity in the northern part of their range. Our goals were to develop simple and effective methods to keep skunks in captivity over winter, and successfully breed skunks in a manner that resembles conditions in the wild. In the spring of 2002, three wild‐caught, pregnant females gave birth in captivity (mean litter size=7). During the first year, 11 of 12 females kept in captivity over winter reproduced successfully in the spring of 2003, with a mean litter size of 5.5 (range=4–8, n=11). In the summer of 2003, 91 of 93 juveniles (97.9%) survived >60 days past weaning. Our high survival and reproduction rates testify to the success of this program, and provide insights into the husbandry of a species that is inactive during winter. Zoo Biol 24:83–91, 2005. © 2005 Wiley‐Liss, Inc.     

Care, management, and biology of captive striped skunks (Mephitis mephitis).

The striped skunk has a number of characteristics that make it one of the most desirable wild carnivores for scientific study. This paper described in detail the care and management of this species in captivity. Reproduction and factors which may affect productivity were discussed, including: duration of mating period, experience, and age of the female. Two optimal mating periods resulted in the greatest productivity and survival of young: (1) 24 hours and (2) 24 hours followed by another mating of equal duration 2 or 3 da later. Experienced females required fewer matings, conceived earlier, and had larger litters than their inexperienced counterparts. Captive skunks conceived as early as mid-February; births occurred in May or June with litters averaging 4.17 pups per litter. Females produced their maximum number of young at age 2 and had a progressive decline in mean litter size after this age. Measurements of growth and development of the young up to 32 da were included. A descenting method used in descenting nearly 300 pups was described. Mortality was high during the first 2 mo of life, with only 59.81% (192/321) of the pups surviving until weaning. Sixteen different pathologic conditions confirmed by necropsy were listed. The signs of canine distemper in the striped skunk were described.     

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.     

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.     

Streptococcus equisimilis infection in striped skunks (Mephitis mephitis) in Saskatchewan

Three radio-collared striped skunks (Mephitis mephitis) found dead during a field study of winter ecology of striped skunks near Willowbrook, Saskatchewan, Canada were examined. Streptococcus equisimilis was identified as the primary agent causing necrotizing purulent pneumonia in one skunk and suppurative meningoencephalitis in another. Both Streptococcus equisimilis and Streptococcus canis were isolated from lesions of purulent myocarditis and pyothorax in the third skunk. These are apparently the first reported cases of S. equisimilis infection in striped skunks and suggest that this opportunistic pathogen may be a significant cause of mortality under some conditions.     

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.     

Oral tool use by captive orangutans (Pongo pygmaeus)

Eight captive orangutans (Pongo pygmaeus) were given wooden blocks embedded with raisins and bamboo as raw material for tool making in a study of manual laterality. In about three quarters of the raisin extraction bouts, the orangutans held the tool in the lips or teeth rather than in their hands. Three adult males and 2 adult females showed extreme (> or =92%) preference for oral tool use, a subadult male and an adult female used oral tools about half the time, and 1 adult female preferred manual tool use. Most oral tool users made short tools (approx. 4-10 cm long) that were held in the lips and (probably) supported by the tongue. Preference for oral tool use does not correlate with body weight, age or sex, but it may be related to hand size or individual preference. This is the first report of customary oral tool use as the norm in captive orangutans; it resembles the behavioral patterns reported by van Schaik et al. and Fox et al. in nature.     

Weather dependent behaviour of captive striped hyaenas (Hyaena hyaena)

The frequencies of 4 behaviour patterns (lying down, comfort movements, scent-marking and social time) of two captive striped hyaenas collected by the one-zero-sampling method on 16 observations between May and December 1974 at the Zurich Zoological Garden were correlated with the local equivalent temperature (T_eq). The frequencies of lying down and comfort movements increased with higher T_eq (positive correlation), while scent-marking decreased (negative correlation). Social time was not affected by the prevailing thermal conditions.     

Oral vaccination of raccoons (Procyon lotor) with an attenuated (SAD-B19) rabies virus vaccine

Unlike previous reports to the contrary, raccoons (Procyon lotor) were successfully vaccinated against rabies with a liquid SAD-B19 attenuated virus vaccine administered per os and given in vaccine-laden baits. There was neither evidence of vaccine-induced rabies in raccoons nor in a limited safety trial with opossums (Didelphis virginiana) given SAD-B19. Protection from lethal street rabies virus infection was not absolute: only three of nine raccoons given 1 x 10(6.0) TCID/ml were protected versus five of 10 raccoons given 1 x 10(7.0) TCID/ml of SAD-B19 and challenged 4 mo after consumption of vaccine-laden baits. Six of eight raccoons consuming 1 x 10(8.8) TCID/ml of SAD-B19 vaccine in baits survived street rabies virus challenge 2 mo postvaccination. Raccoon survivorship was not wholly dependent upon rabies virus-neutralizing antibody titer on the day of challenge. Vaccinated raccoons demonstrated a prominent anamnestic response within 1 wk following challenge. Surviving raccoons were observed for a minimum of 3 mo following street rabies virus challenge with neither clinical nor pathologic evidence of rabies. The SAD-B19 rabies vaccine administered within baits in captivity appears less effective for raccoons than for its demonstrated efficacy in the immunization of free-ranging foxes (Vulpes vulpes) in Europe.     

Oral vaccination against raccoon rabies: landscape heterogeneity and timing of distribution influence wildlife contact rates with the ONRAB vaccine bait

Aerial distribution of oral vaccine baits is one of the available strategies for controlling the spread of infectious wildlife diseases. This technique has commonly been used to control rabies in wild carnivores and, together with other techniques, was used to immunize wild populations of raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) after the detection of the first rabid raccoon in the province of Quebec, Canada, in 2006. Vaccine bait distribution was conducted over large areas where agricultural land is dominant but interspersed with residual forest patches. Our objective was to evaluate the effect of habitat (forest vs. agricultural crops) in space and time on the contact rate between wildlife and the ONRAB(?) vaccine bait, a recent alternative to the V-RG(?). Four transects of eight vaccine baits each were installed parallel to, and at different distances from, the forest's edge (under forest cover, at field-forest edge, and at 50 and 200 m from forest edge in agricultural crops) at three sites composed of various crop types interspersed with forest patches. This experiment was conducted during three periods (late spring, 1-7 June; summer, 27 July-2 August; and fall, 24-30 October) in 2009. Contact rates with vaccine baits were monitored for 7 days in each period to evaluate the potential temporal variations generated within the habitat types. Contact rates with ONRAB vaccine baits were highest under forest cover and in the fall. Of 13 species observed in proximity to the vaccine baits, raccoons were the most frequent (49.5%, n=55 visits). Our study underlines the importance of taking into account landscape heterogeneity and timing of distribution when planning the distribution of vaccine baits to control rabies in raccoons.     

Seasonal and daily activity patterns of striped skunks (Mephitis mephitis) in the Canadian prairies

We investigated the hypothesis that the daily and seasonal activity patterns of female and male striped skunks ( Mephitis mephitis ) vary with reproductive constraints. Four biological periods were identified: pre-parturition (1 April–14 May), parturition and rearing (15 May–30 June), pre-dispersal (1–31 July), and dispersal (1–31 August). Tracking data (1873h) indicated that activity (percentage time active) of female skunks varied among seasons, being lowest during the pre-parturition period (34 ± 10%), and highest during the pre-dispersal period (66 ± 4%). Male activity did not vary among seasons (55 ± 3%). Animals of both sexes were mostly nocturnal, and had similar patterns of daily activity. Onset and cessation of activity were highly variable, but were not affected by season or sex. Daily activity typically started 13 ± 10 min before sunset, and was terminated 35 ± 8min before sunrise. Night-time activity periods of both sexes were often (57%, n = 108) interrupted by at least one resting period (median = 1, range = 0–4). However, females rarely (5%, n = 89) returned to the maternal den to rest. We hypothesize that the nocturnal activity of adults is linked to prey activity and reduced predation risk, whereas apparent diurnal activity of juveniles represents an adaptation to daily fasting periods caused by the nocturnal foraging trips of females.     

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.     

A new flavor-coated sachet bait for delivering oral rabies vaccine to raccoons and coyotes

Research was conducted during 1996-2000 to develop baits for delivering an oral rabies vaccine to raccoons (Procyon lotor) and coyotes (Canis latrans). A bait was sought that: (1) was attractive to the target species, (2) could be distributed by aircraft, (3) was as effective (or more so) than the currently used fish meal polymer bait, and (4) could be produced in large numbers by automated procedures and could be purchased by user groups at substantially lower cost. Ten field trials were conducted to document raccoons' bait flavor preferences, evaluate a new vaccine sachet bait coated with various attractants, and determine if the sachet bait would effectively deliver Raboral V-RG oral rabies vaccine (Merial Limited, Athens, Georgia, USA) to this species. Raccoons preferred fish and crustacean-based flavors over those derived from plant materials. Raccoon visits to tracking stations, frequency of bait removals, and percent of sachets discarded by this species that were emptied of placebo vaccine indicated efficacy of the new bait was equal or superior to the currently used fish meal polymer bait. A field trial conducted in fall 1998 compared aerially distributed vaccine-laden sachet and polymer baits and showed there was no difference between the percent of raccoons from the test and reference areas subsequently found positive for rabies antibody. Four bait trials to determine coyote response to sachet baits were conducted in 1997-98. The propensity for canids to gulp or bolt smaller food items is well known. Thus, a first trial involved offering fish-flavored sachet baits of different sizes to 30 captive coyotes to determine if smaller size baits were more frequently swallowed intact. Two field trials were also conducted in fall 1997 to determine if free-ranging coyotes discriminated among sachet baits coated with different attractants. Finally, Raboral V-RG-laden poultry-flavored sachet baits were aerially dropped and the percent of seropositive coyotes was compared with coyotes from surrounding areas where fish meal polymer vaccine baits had been distributed. Captive coyotes did not swallow sachet baits intact, regardless of size. Bait preference field trials indicated that coyotes preferred poultry, cheese/beef tallow, and fish-flavored sachet baits and that such baits were taken at the same rate as polymer baits. A sample of coyotes from the area baited with vaccine-laden sachet baits had a markedly higher (P = 0.01) seropositivity rate than coyotes from areas where vaccine was distributed in polymer baits. Sachet bait production could be facilitated by automated technology and sachet baits used either as an alternative vaccine delivery device or in combination with the fish meal polymer bait.     

Energetic consequences and ecological significance of heterothermy and social thermoregulation in striped skunks (Mephitis mephitis)

We assessed patterns and energetic consequences of different overwintering strategies, torpor, and social thermoregulation in the striped skunk (Mephitis mephitis) under natural ambient temperature and photoperiod. Striped skunks entered spontaneous daily torpor, with the lowest torpid body temperature (T(b)) reaching 26.0 degrees C, the lowest recorded T(b) for a carnivore. Patterns of daily torpor differed between solitary and grouped skunks: all solitary skunks regularly entered daily torpor, but only some individuals in communal dens employed torpor. When they did, it was shallow and infrequent. Solitary skunks entered torpor on average 50 times (in 120 d) compared with 6 times for grouped skunks. During torpor, solitary skunks had average minimum T(b) of 26.8 degrees C and bout duration of 7.8 h, whereas grouped skunks had average minimum T(b) of 30.9 degrees C and bout duration of 5.4 h. Torpor by solitary skunks occurred during their activity phase, but grouped skunks' shallow torpor bouts were restricted to their diurnal resting phase. On average, grouped skunks experienced lower percent daily fat loss, and they emerged in spring with higher percent body fat of 25.5%. In contrast, solitary skunks emerged in spring with only 9.3% body fat. In conclusion, the use of daily torpor and social thermoregulation in northern populations of striped skunks represent two strikingly different mechanisms to minimize energetic costs and increase individual fitness in response to unfavorable environmental conditions.     

Rotavirus-associated diarrhea in young raccoons (Procyon lotor), striped skunks (Mephitis mephitis) and red foxes (Vulpes vulpes)

Electron microscopy and a commercial ELISA test for rotavirus antigen were used to diagnose rotavirus infection in diarrheic raccoons (Procyon lotor), striped skunks (Mephitis mephitis) and red foxes (Vulpes vulpes). Gross and histopathological changes in two raccoons and two red foxes were found to be very similar to those described previously in rotavirus mediated diarrhea in other animals. While an etiology for the diarrhea is not definitively established, it would appear to involve rotavirus alone or possibly in concert with enteropathogenic coliform bacteria, overfeeding of a commercial kitten milk replacer and the stresses of captivity.     

Development of a bait and baiting system for delivery of oral rabies vaccine to free-ranging African wild dogs (Lycaon pictus)

The objective of the study was to develop a bait and baiting system capable of delivering one effective dose of oral rabies vaccine to each member of a free-ranging African wild dog (Lycaon pictus) pack. Trials were conducted between June and October 2000. The results of cafeteria-style bait preference trials testing seven candidate baits in captive wild dogs revealed a significant preference for chicken heads (June trials: P = 0.023, September trials: P = 0.021). Trials using a topical biomarker (rhodamine B) showed that chicken head baits were sufficiently chewed on most occasions to rupture the vaccine container. Free-ranging wild dogs and young pups ingested chicken head baits. Significant dominance of bait intake by a single individual was seen in four of six study packs and in the three packs in which an alpha pair could be distinguished, the dominant feeder was an alpha animal. Pattern of bait distribution and degree of satiation had no effect on pack coverage (proportion of pack ingesting at least one bait). Pack coverage was significantly related to trial number (r = 0.71, P < 0.001), with pack coverage increasing with increased exposure of the pack to the baits. During 46 hr of diurnal observations of free-ranging wild dogs only two baits were lost to non-target species. A baiting system for the oral vaccination of captive and free-ranging wild dogs is proposed.     

Oral rabies vaccine contact by raccoons and nontarget species in a field trial in Florida

Rabies is enzootic in raccoons (Procyon lotor) in the eastern United States. Oral vaccination of free-ranging raccoons against rabies has the potential to control the disease in a principal reservoir and reduce the risk of rabies exposure among domestic animals and humans. Free-ranging animal contact with baits containing a vaccinia virus recombinant vaccine expressing the rabies glycoprotein gene (V-RG) was monitored in Pinellas County (Florida, USA) from February through May 1997. Bait contact was assessed with 423 tracking plate nights; conducted in four land use zones: single residential, multiple residential, industrial-commercial, and undeveloped. The undeveloped land use zone was further described by six vegetation communities: mangrove swamp, red maple swamp, beach dune, pine forest, mixed oak hammock, and cabbage palm hammock. Seven animal taxa contacted the baited tracking plates across the four land use zones: raccoons, opossums (Didelphis virginiana), cats (Felis catus), dogs (Canis familiaris), rabbits (Sylvilagus sp.), unidentified rodents, and birds. A total of 252/413 (61%) of the baits was contacted by animals; 95 (38%) of these were specifically by the raccoon, the target species. Overall bait contact by all animals was significantly different among the four land use zones, being highest in the undeveloped zone (82%) and lowest in the industrial-commercial zone (34%). Bait contact by raccoons also was significantly different among the undeveloped and pooled urban zones. Among the six vegetation communities, bait contact by all animals was significantly different ranging from 95% in the mangrove to 50% in the cabbage palm hammock. Among the four vegetation communities tested, bait contact by raccoons also was significantly different.