Prevalence of tetracycline and rabies virus antibody in raccoons, skunks, and foxes following aerial distribution of V-RG baits to control raccoon rabies in Ontario, Canada

More than 3.6 million baits containing a recombinant vaccinia virus-rabies glycoprotein (V-RG) oral rabies vaccine were aerially or hand-distributed during 1999-2006 in an approximate 4,000-9,000 km(2) area of eastern Ontario, Canada, as part of a multitactic approach to control the raccoon variant of rabies. The efficacy of the program was assessed through the collection and testing of > 6,900 animals for bait acceptance and rabies virus-specific antibodies. Raccoon acceptance of rabies vaccine baits was significantly greater (71-83% ) in areas baited at a density of 150 baits/km(2) compared to areas baited at 75 baits/km(2) (26-58% ), and more raccoons consumed vaccine baits in areas baited with a flight line spacing of 0.75 km (45.3% [321/708]) than with a spacing of 1.5 km (33.8% [108/320]). In addition, greater numbers of raccoons consumed vaccine baits during a drop in September (52.7% [213/404]) as opposed to a June bait drop (34.6% [216/624]). Seropositivity rates for raccoons ranged between 7% and 28% in areas baited at 75/km(2) and 10% to 27% in areas baited at 150/km(2) with statistical differences varying among years and treatments. The last case of raccoon-variant rabies reported in Ontario was in September 2005. The control of raccoon rabies in Ontario has resulted in an estimated $6M to $10 M Cdn annual savings in rabies-associated costs.     

Oral rabies vaccine (ORV) bait uptake by captive striped skunks

Aerial delivery of oral rabies vaccine (ORV) baits has proven effective in large-scale efforts to immunize wildlife against rabies, and in North America this strategy currently is being used to immunize foxes (Urocyon cinereoargenteus and Vulpes vulpes), raccoons (Procyon lotor), and coyotes (Canis latrans). Skunks are also a major reservoir and vector of rabies, but at present oral vaccines for use in skunks are not licensed. Furthermore, given differences in morphology (smaller jaws) and behavior (food handling and consumption), it is unknown if baits currently used in ORV campaigns would be effective for skunks. Because oral vaccine delivery is contingent upon puncture of the vaccine container (VC), baits need to be sufficiently attractive to elicit selection and consumption. Manipulation of the bait to facilitate vaccine ingestion by the target species is a critical element for an effective ORV bait. The objectives of this study were to assess manipulation and consumption of current ORV baits by striped skunks (Mephitis mephitis). We conducted four independent trials with penned animals and various baits to assess bait selection frequency, VC puncture frequency, and consumption. Video recorded trials were used to assess attractiveness of baits and consumption behavior of skunks. Bait characteristics, such as texture, size, and flavor influenced selection and consumption. Fish and chicken flavors were preferred and vaccine containers within selected baits were likely to be punctured. Vaccine ingestion seemed more likely if VCs were directly coated with the bait matrix. To make baits attractive to skunks and to ensure puncture of the VC, modifications to current baits should consider a smaller size, a meat-flavored matrix, a slightly pressurized VC, and a direct coating of matrix on the VC.     

A Behaviorally-Explicit Approach for Delivering Vaccine Baits to Mesopredators to Control Epizootics in Fragmented Landscapes

Despite the widespread use of aerial baiting to manage epizootics among free-ranging populations, particularly in rabies management, bait acceptance and seroconversion rates often are lower than required to eliminate spread of disease. Our objectives in this study, therefore, were to evaluate the performance of stratified bait distribution models derived from resource selection functions (RSF) on uptake of placebo rabies baits by raccoons (Procyon lotor) and Virginia opossums (Didelphis virginiana), as well as the probability of bait uptake as a function of proximity to bait distribution areas in fragmented agricultural ecosystems. Among 478 raccoons and 108 opossums evaluated for presence of Rhodamine B (RB) across 8 sites, only 26% of raccoons and 20% of opossums exhibited marking consistent with bait consumption 14–24 days post-baiting. The effective area treated, based on 90% kernel density estimators of marked individuals, ranged from 99–240 ha larger than bait distribution zones, with RB marked individuals captured up to 753m beyond the bait zone. Despite incorporation of RSF data into bait distribution models, no differences in uptake rates were observed between treatment and control sites. These data likely reflect the underlying constraints imposed by the loss and fragmentation of habitat on animal movement in heterogeneous landscapes, forcing individuals to optimize movements at coarse (i.e., patch-level) rather than fine spatial scales in highly fragmented environments. Our data also confirm that the probability of bait acceptance decreases with increasing distance from bait zone interiors, even within the zone itself. Thus, although bait acceptance was confirmed beyond bait zone boundaries, the proportion of vaccinated individuals may comprise a small minority of the population at increasing distances from baiting interiors. These data suggest focal baiting creates a buffered area of treated individuals around bait zones or bait stations, but repeated treatments may be needed to achieve sufficient uptake to eradicate disease.     

Acceptance of simulated oral rabies vaccine baits by urban raccoons

In summer 1986, a study was conducted to evaluate raccoon (Procyon lotor) acceptance of oral baits that could be used for rabies vaccination. One thousand wax-coated sponge bait cubes were filled with 5 mg of a seromarker (iophenoxic acid), placed in polyethylene bags, and hand-distributed in an 80 ha area within an urban National Park in Washington, D. C. (USA). After 3 wk, target and nontarget animals were trapped and blood samples collected to evaluate bait uptake. Thirty-three of 52 (63%) raccoons had elevated blood iodine levels indicating they had eaten at least one bait, 13 (25%) were negative, and six (12%) had marginal values. These results indicate that sponge baits hand-placed at a density of 12.4/ha can reach a significant proportion of an urban raccoon population. Implications for oral rabies vaccination of raccoons are discussed.     

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.     

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.     

Use of Rhodamine B to Reveal Patterns of Interspecific Competition and Bait Acceptance in Raccoons

Abstract: Passive treatment of raccoons (Procyon lotor) through distribution of vaccine-laden baits recently has emerged as a potential solution to address health and economic conflicts associated with raccoon rabies and may have applications in the management of other pathogens carried by raccoons if frequent bait deployments are used. Consumption of baits by nontarget species reduces the efficiency in which baits can be used to manage wildlife disease, although no study has explicitly evaluated the influence of bait competitor density on the ability to treat raccoons. Our objectives were to use the biomarker Rhodamine B (RB) to 1) evaluate patterns of raccoon bait acceptance as a function of competition with Virginia opossums (Didelphis virginiana), the dominant bait competitor; 2) characterize attributes of opossum bait acceptance to improve efficiency of raccoon treatment; and 3) evaluate the effect of repeated bait exposure on rates of bait acceptance as may be required in the management of wildlife disease issues beyond rabies. Identifying bait consumption by individuals based on the presence of an RB mark in a sample of whiskers, we used logistic regression to model raccoon and opossum bait acceptance as a function of bait availability, previous exposure to baits, demographic attributes, and an index of time spent in the baited area (residency index). For both raccoons and opossums, the best measure of bait availability was the variable number of baits per opossum. The most parsimonious logistic regression model for raccoon bait acceptance included the variables baits per opossum, exposure history, and residency index. The strength of the variable baits per opossum relative to competing measures of bait availability indicated bait consumption by opossums significantly limited the ability to treat raccoons. The most parsimonious model for opossum acceptance was composed of the variables baits per opossum, sex, weight, residency index, baits per opossum X sex, and weight X sex. Patterns of opossum bait acceptance likely were driven by effects of bait availability and sex-dependent differences in movement. Our results call attention to the importance of bait competition in limiting the ability to effectively treat raccoon populations through distribution of baits and suggest managers incorporate information on density of bait competitors, particularly opossums, in allocation of baits.     

A study of techniques for the distribution of oral rabies vaccine to wild raccoon populations

This study evaluates a technique for delivering an oral rabies vaccine to wild raccoon (Procyon lotor) populations. Various baits and attractants were first tested on caged raccoons and baiting trials were then conducted in two distinct physiographic regions of Virginia (USA), the coastal plain and the Piedmont plateau. Raccoon population density studies preceded the field trials. Each polyurethane sponge bait distributed contained approximately 200 mg tetracycline as a tissue biomarker, and was presented in an outer bag with a fish-based attractant. Baits were frozen until used and distributed from an aeroplane throughout two 4-km2 sites in each region. One site received 450 baits/km2 and the other 120 baits/km2. Postbaiting evaluation included the direct observation of baits in the field and the examination of teeth and bone from trapped and hunted animals for evidence of the biomarker. Between 30% and 73% of the captured animals showed evidence of bait consumption. The proportion of animals with evidence of bait uptake changed when areas adjacent to the actual baiting site were included. The percentage of animals taking baits was not related to the density of baits that were distributed.     

Acceptance of baits for delivery of oral rabies vaccine to raccoons.

During 1993-96 the Ontario Ministry of Natural Resources (Canada) implemented a research project to evaluate the efficacy of three candidate baits to deliver oral rabies vaccine to wild raccoons (Procyon lotor). Extensive field testing revealed that raccoon acceptance of Sugar-Vanilla baits (SV) at densities of 200/km2 and 400/km2, hand-placed in urban habitats of Scarborough (Ontario) during 1993, was 74% and 82%, respectively. Raccoon density in those areas averaged 11/km2. Aerial placement of SV baits in rural habitats in Barrie (Ontario) during 1993 and 1994, yielded raccoon acceptance levels of 58% with a density of 100 baits/km2, 59% at 75 baits/km2, and 47% at 50 baits/km2. Raccoon acceptance of SV baits was significantly lower in areas baited at the density of 50/km2. Acceptance of Cheese baits (CH) at a density of 75 baits/km2 was 52%. During 1996 trials in Barrie, modified SV baits with blister packs protruding through the matrix yielded raccoon acceptance values of 51% at a bait density of 54/km2, whereas acceptance of regular SV baits was 39% at a density of 51 baits/km2. Pooling of bait acceptance data for all years revealed that bait acceptance was highest for adult male raccoons. Raccoon density in rural habitats (Barrie, Ontario) where the studies took place, averaged 11-13/km2. Puncture and impact testing of blister packs in baits suggested that they would adequately serve as a vehicle to contain oral rabies vaccine for delivery to raccoons via baits.     

Formulation and evaluation of baits for oral rabies vaccination of raccoons (Procyon lotor)

Captive raccoons were offered a variety of vaccine containers and bait components in a series of three-choice tests. Paraffin wax ampules were the most readily accepted vaccine container. Preferred bait components included corn and shellfish oils, deep fried corn meal batter, and egg, apple and buttermilk flavorings. These results, together with factors including ease of bait formulation, cost, and suitability for field use, were used to develop an experimental delivery system for an oral rabies vaccine. The developed system was composed of a polyurethane sleeve (1.5 x 5.5 cm) dipped in a commercial food batter mix together with corn meal, milk and egg. The sleeve was deep fried in corn oil and a 2.0 ml ampule containing a recombinant rabies vaccine was then inserted into the sleeve bait. These baits were presented to 10 captive raccoons. Nine of the 10 animals developed high levels of rabies virus neutralizing antibodies. Field tests are needed to determine if the delivery system developed also is effective for wild raccoons.     

Comparison of suburban vaccine distribution strategies to control raccoon rabies

Helicopters and hand baiting are commonly used to distribute vaccine-laden baits to help control raccoon (Procyon lotor) rabies in suburban landscapes, but these techniques may be labor intensive, costly, or unavailable in some areas. We tested conventional baiting strategies against polyvinyl-chloride (PVC) bait stations in Erie County (New York, USA) during July and August 2003-05. Hand, helicopter, and bait station treatments were randomly assigned to six 25-km(2) suburban study sites. To estimate the proportion of raccoons that ingested baits, tooth and blood samples from 954 raccoons were collected and examined for tetracycline biomarker and rabies-neutralizing antibodies, respectively. Overall, 38% (358/954) of the raccoons in Erie County tested positive for tetracycline; 16% (155/954) tested seropositive for rabies virus. Year of study significantly impacted biomarker prevalence; fewer raccoons tested positive for tetracycline in 2004. Probability of seropositivity increased with raccoon age. No statistically significant differences existed between baiting strategies and frequencies of biomarker and antibody-positive raccoons across all years combined. Thus, bait stations could be used as part of an integrated rabies control strategy.     

Prerequisites for oral immunization of free-ranging raccoons (Procyon lotor) with a recombinant rabies virus vaccine: study site ecology and bait system development.

A model baiting system suitable for the delivery of an oral rabies vaccine to free-ranging raccoons (Procyon lotor) was developed and tested on barrier islands in South Carolina (USA). Features of barrier island physiography and ecology were studied relative to selective bait deployment and site biosecurity. Capture-mark-recapture data were obtained from 228 raccoons. Raccoon density estimates, using a modified census assessment technique, were one raccoon per 1.8 to 2.7 ha. Mean (+/- SE) and range home area estimates of radio-collared raccoons were 84 (+/- 15.6) ha (27 to 176 ha) by a minimum convex polygon method and 138 (+/- 22.8) ha (43 to 241 ha), by a harmonic mean transformation method. Habitat utilization determinations of radio-collared raccoons were conducted to identify study areas to potentially maximize selectivity of bait towards raccoons and to reduce the absolute number of baits deployed. Island raccoons showed a habitat preference for maritime forest, maritime shrub and marsh areas. Additionally, there was no evidence of inter-island or mainland exchange of ear-tagged or radio-collared raccoons. A disease and mortality survey was conducted to identify baseline pathology and incidental lesions in the target raccoon population, prior to actual vaccination initiation. Thirty-eight percent of 30 clinically suspect raccoons sampled had intracytoplasmic eosinophilic inclusions diagnostic of canine distemper; no other lesions suggestive of viral etiologies were found. Serological surveys for raccoon poxvirus and rabies virus antibodies were negative. Antibody titers to canine adenovirus 1 and 2 indicated a moderate level of exposure (approximately 10 to 16%) in the raccoon population. Overall, 93 to 100% of placebo baits were consistently disturbed by 7 days post-bait deployment, and bait acceptance rates by raccoons ranged from 49 to 85%, by using a modular systems approach to select the optimum combination of bait attractant, biomarker, matrix, density, and distribution. These results suggest that a large proportion (up to 85%) of a free-ranging island raccoon population can be selectively and safely targeted, marked and monitored utilizing a proposed oral bait delivery system for recombinant or other rabies vaccines.     

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.     

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.     

Wild carnivore acceptance of baits for delivery of liquid rabies vaccine

A series of experiments are described on the acceptance, by red foxes (Vulpes vulpes) and other species, of two types of vaccine-baits intended to deliver liquid rabies vaccine. The baits consisted of a cube of sponge coated in a mixture of tallow and wax, or a plastic blister-pack embedded in tallow. All baits contained tetracycline as a biological marking agent: examination of thin sections of carnivore canines under an ultraviolet microscope revealed a fluorescent line of tetracycline if an individual had eaten baits. Baits were dropped from fixed-wing aircraft flying about 100 m above ground at approximately 130 km/h. Flight lines followed the edges of woodlots midway between parallel roads. Baits were dropped at one/sec, resulting in one bait/36 m on the ground, or 17 to 25 baits per km2. Crows (Corvus brachyrhynchos) removed many baits, but did not appear to lower the percent of the fox population which took bait. Dropping baits only into corn and woodland to conceal baits, to reduce depredation by crows, reduced acceptance by foxes. Acceptance by foxes ranged between 37 and 68%. Meat added as an attractant did not raise acceptance. Presence, absence, color and perforations of plastic bags did not alter bait acceptance. Dispersal by juvenile foxes probably lowered the estimates of bait acceptance. It took 7 to 17 days for 80% (n = 330) of foxes to eat their first bait. The rapidity with which foxes picked up their first bait appeared more affected by unknown characteristics of years or study areas than by experimental variables. Skunks (Mephitis mephitis) and raccoons (Procyon lotor) also ate these baits, but acceptance was lower. Small mammals contacted baits, but rarely contacted the vaccine, which had the potential for vaccine-induced rabies in some species. Aerial distribution of baits was more cost-effective than ground distribution as practiced in Europe. This system has potential for field control of rabies, although higher acceptance will be desirable.     

Exposure time of oral rabies vaccine baits relative to baiting density and raccoon population density

Oral rabies vaccination (ORV) baiting programs for control of raccoon (Procyon lotor) rabies in the USA have been conducted or are in progress in eight states east of the Mississippi River. However, data specific to the relationship between raccoon population density and the minimum density of baits necessary to significantly elevate rabies immunity are few. We used the 22-km2 US National Aeronautics and Space Administration Plum Brook Station (PBS) in Erie County, Ohio, USA, to evaluate the period of exposure for placebo vaccine baits placed at a density of 75 baits/km2 relative to raccoon population density. Our objectives were to 1) estimate raccoon population density within the fragmented forest, old-field, and industrial landscape at PBS: and 2) quantify the time that placebo, Merial RABORAL V-RG vaccine baits were available to raccoons. From August through November 2002 we surveyed raccoon use of PBS along 19.3 km of paved-road transects by using a forward-looking infrared camera mounted inside a vehicle. We used Distance 3.5 software to calculate a probability of detection function by which we estimated raccoon population density from transect data. Estimated population density on PBS decreased from August (33.4 raccoons/km2) through November (13.6 raccoons/km2), yielding a monthly mean of 24.5 raccoons/km2. We also quantified exposure time for ORV baits placed by hand on five 1-km2 grids on PBS from September through October. An average 82.7% (SD = 4.6) of baits were removed within 1 wk of placement. Given raccoon population density, estimates of bait removal and sachet condition, and assuming 22.9% nontarget take, the baiting density of 75/ km2 yielded an average of 3.3 baits consumed per raccoon and the sachet perforated.     

Spatial zonation of macrobenthic fauna in Zhanjiang Mangrove Nature Reserve, Guangdong, China

The spatial zonation of macrobenthic fauna in the core region of Zhanjiang Mangrove Nature Reserve was studied with two transects vertical to the shoreline. The first transect was near Deyao Village where three faunal zones of the mangrove swamp could be divided into the following types from the high tide part to the low tide part: the Assiminea lutea-Uca arcuata-Paracleistostoma crassipilum zone, the Cleistostoma dilatatum-Macrophthalmus erato-Littoraria melanostoma zone, and the Paracleistostoma depressum-Cerithidae cingulata zone. Mollusck and crustacean exhibited the highest individual density in this transect. Mollusck mainly influenced the dynamics of community biomass as well as the species diversity index. In the second transect near Hongzhai Village, the following four faunal zones could be determined: the Littoraria melanostoma-Pseudoringicula sinensis-Ceratonereis burmensis zone, the Assiminea lutea-Cleistostoma dilatatum zone with a dominant species belonging to the Ellobiidae, Upogebia sp.-Paracleistostoma depressum zone, and the Metaplax sheni-Cerithidae cingulata zone. The crustacean showed the highest individual density in this transect. Similar to the Deyao transect, dynamics of community biomass and the species diversity index of the Hongzhai transect were mainly influenced by mollusck. By hierarchical clustering and nonmetric multidimensional scaling, the macrobenthic fauna communities could be divided into three and four groups in the Deyao and Hongzhai transects, respectively. These groups corresponded to different types of vegetation of the mangrove swamp. Taken together, our observations indicated that the spatial zonation of the macrobenthic fauna was mainly affected by the characteristics of the mangrove community, sediment characteristics and the tidal line.     

Spatial zonation of macrobenthic fauna in Zhanjiang Mangrove Nature Reserve, Guangdong, China

The spatial zonation of macrobenthic fauna in the core region of Zhanjiang Mangrove Nature Reserve was studied with two transects vertical to the shoreline. The first transect was near Deyao Village where three faunal zones of the mangrove swamp could be divided into the following types from the high tide part to the low tide part: the Assiminea lutea-Uca arcuata-Paracleistostoma crassipilum zone, the Cleistostoma dilatatum-Macrophthalmus erato-Littoraria melanostoma zone, and the Paracleistostoma depressum-Cerithidae cingulata zone. Mollusck and crustacean exhibited the highest individual density in this transect. Mollusck mainly influenced the dynamics of community biomass as well as the species diversity index. In the second transect near Hongzhai Village, the following four faunal zones could be determined: the Littoraria melanostoma-Pseudoringicula sinensis-Ceratonereis burmensis zone, the Assiminea lutea-Cleistostoma dilatatum zone with a dominant species belonging to the Ellobiidae, Upogebia sp.-Paracleistostoma depressum zone, and the Metaplax sheni-Cerithidae cingulata zone. The crustacean showed the highest individual density in this transect. Similar to the Deyao transect, dynamics of community biomass and the species diversity index of the Hongzhai transect were mainly influenced by mollusck. By hierarchical clustering and nonmetric multidimensional scaling, the macrobenthic fauna communities could be divided into three and four groups in the Deyao and Hongzhai transects, respectively. These groups corresponded to different types of vegetation of the mangrove swamp. Taken together, our observations indicated that the spatial zonation of the macrobenthic fauna was mainly affected by the characteristics of the mangrove community, sediment characteristics and the tidal line.     

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.