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.     

Adult raccoon survival in an enzootic rabies area of Pennsylvania

Twenty-one adult raccoons (Procyon lotor) were radio-marked on each of two areas in Centre County, Pennsylvania from 17 June to 23 August 1987. Raccoons on Area 1 were vaccinated with a commercial inactivated rabies virus vaccine administered intramuscularly, whereas on Area 2 raccoons were not vaccinated. Survival rates were estimated for three periods: pre-season (23 August to 23 October 1987), harvest season (24 October 1987 to 23 January 1988) and post-season (24 January to 26 March 1988). Kaplan-Meier survival rates (+/- SE) were 1.00 +/- 0.00 for both areas during the pre- and post-season periods. Survival rates during the harvest period were 0.67 +/- 0.11 and 0.69 +/- 0.11 for Area 1 and Area 2, respectively. Survival rates between the two areas were not different (P = 0.929). During 23 August 1987 to 26 March 1988, rabies was not an apparent factor in raccoon survival. Conclusions regarding timing an oral rabies vaccination campaign based upon occurrence of rabies-related mortalities could not be presented because of the lack of obvious rabies mortality. However, our findings, combined with information about immunization, vaccine distribution, and peak periods of raccoon rabies, suggest a late winter or early spring vaccination period would be optimum for reducing the number of raccoons susceptible to rabies.     

The elimination of raccoon rabies from Wolfe Island, Ontario: animal density and movements

During 1996 to 1998, an average of 52% to 55% of the raccoon (Procyon lotor) population on Wolfe Island, Ontario was vaccinated against rabies during proactive trap-vaccinate-release (TVR) operations. However, during 1999, the percent of the population vaccinated declined to 39% and an outbreak (6 cases) of raccoon rabies occurred on the island from December 1999 to January 2000. The raccoon population on Wolfe Island declined dramatically (71% reduction) from 1,067 raccoons (mean density = 8.4/km(2) [6.4-12.4, 95% CI]) during 1999 to 305 raccoons (mean density = 2.4/km(2) [0.87-4.1, 95% CI]) in the spring of 2000. Raccoon density immediately following the outbreak was significantly lower in cells with rabies cases, suggesting that rabies had a negative effect on population size. However, raccoon density had doubled by 1 yr following the outbreak. Movement of raccoons on Wolfe Island was as great as 24 km. Male raccoons moved greater distances than females. Movements to surrounding islands were also noted for raccoons ear tagged on Wolfe Island which indicates the island could serve as a focus for greater geographic rabies spread. Point infection control (PIC) during 2000, TVR during 2001-02, and the aerial distribution of Vaccinia-Rabies Glycoprotein (V-RG) baits during 2000 and 2003-05 were used to eliminate rabies from Wolfe Island. No cases have been detected since late January 2000 (to February 2007).     

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.     

Raccoon rabies: the re-emergence of an epizootic in a densely populated area

Investigation of sporadic or isolated cases of rabies was encouraged in the 1950s by the implementation of a national surveillance system for reporting of rabies cases. Low level enzootic disease was recognized in several wild species during this period, including a small focus of rabies in raccoons in Florida. Phylogenetic analysis of the virus transmitted by rabid raccoons and reconstruction of the early history of raccoon rabies in the United States suggests that rabies was present in these animals long before its recognition by the public health community and that the emergence of raccoon rabies as a major threat to public health was the result of several natural and human-mediated events. In recent years, reports of raccoon-human contact and rabies in raccoons have increased as changes in human demographics and land development have concentrated raccoon populations in urban and suburban settings. In addition to the natural spread of rabies from Florida to raccoon populations in Georgia, Alabama, South Carolina and North Carolina, a separate focus in the northeastern states is believed to have been caused by the translocation of raccoons from the southeast to Virginia and West Virginia. Oral vaccination of wild species may be an important adjunct to traditional rabies control measures in the management of this disease in the future.     

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.     

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.     

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.     

Behavior, movements, and demographics of rabid raccoons in Ontario, Canada: management implications

During 1999-2003, 127 cases of raccoon variant rabies were reported in raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) in Ontario, Canada. Raccoons accounted for 98% (125/127) of the reported cases with behaviors/conditions including aggression, fighting with dogs, ataxia, vocalizations, appearance of being sick, and the presence of porcupine (Erethizon dorsatum) quills. Seventy-eight percent of the rabid raccoons were adults. Juveniles were underrepresented (22%) compared with the adult/juvenile ratios found in nonrabid Ontario raccoon populations. Of the known aged raccoons, 83% were < or = 3 yr of age, and 22% of the rabid adult female raccoons had evidence of having had a litter during the year in which they were found to be rabid. The majority of rabid raccoons were reported during the fall, winter, and spring, suggesting a relationship between raccoon behavioral activities such as denning and breeding and the timing of rabies outbreaks. Multiple cases of raccoon rabies occurred at several barns, suggesting that those structures serve as focal points of rabies transmission as a result of denning activities. Movements of five rabid raccoons (range 1,564-4,143 m) were not different from movements of nonrabid raccoons in Ontario. Sixty-six percent of the rabid animals were submitted by government staff, stressing the importance of those agencies in rabies control and surveillance operations. Increased knowledge of the behaviors of rabid raccoons should assist in the development of management strategies for rabies.     

Raccoons (Procyon lotor) in Germany as potential reservoir species for Lyssaviruses

Raccoons can be found almost everywhere in Germany since their first successful introduction in 1934. Although the animal is a well-known reservoir species for rabies in the USA, during the last European fox rabies epizootic, only a few rabid raccoons were reported from Germany. In recent years, the raccoon population density has increased tremendously, especially in (semi) urban settings. Presently, Germany is free of terrestrial wildlife rabies. To assess the potential risk that the raccoon population in Germany could act as a reservoir species upon reemergence of rabies, the susceptibility of the local raccoon population was investigated. Wild-caught animals were inoculated with the most likely lyssavirus variants to infect the local population. It was shown that the raccoons were fully susceptible for a dog and raccoon rabies virus isolate. Also, five of six raccoons inoculated with a fox rabies virus isolate showed clinical signs. However, none of the raccoons infected with European Bat Lyssavirus type 1 succumbed to rabies; meanwhile, all these raccoons seroconverted. It is concluded that the highest risk for the raccoon population in Germany to become infected with lyssaviruses is through the importation of rabies infected dogs.     

Humoral response and protection from experimental challenge following vaccination of raccoon pups with a modified-live canine distemper virus vaccine.

Eight 8-wk-old raccoon pups (Procyon lotor) with maternal canine distemper virus (CDV) neutralizing antibodies (NAb) and 24 8-wk-old seronegative pups were administered a commercial modified-live CDV vaccine (Galaxy, D, Solvay Animal Health, Inc., Kitchener, Ontario, Canada). All 24 seronegative raccoons had detectable serum CDV NAb titers 14 days after the initial dose. Titers rose to maximum levels 4 wk post-vaccination. Mean titers for groups of vaccinated seronegative pups were maintained between 1:256 and 1:2,048 for the remainder of the 3 mo observation period. Geometric means of the serum CDV NAb titer of eight seronegative pups given a single vaccine dose at 8 wk of age did not differ significantly from those of eight pups that were given serial doses at 8, 12, and 16 wk of age, or from those of eight pups vaccinated once at 16 wk of age. Seven unvaccinated 8-wk-old raccoon pups used as controls remained seronegative throughout the trial. Seven out of eight 8-wk-old pups with maternal antibodies, vaccinated at 8, 12, and 16 wk of age, failed to develop a rise in their CDV NAb titers until at least 18 wk of age, 2 wk after the third vaccination. Titers in eight unvaccinated raccoons with maternal antibodies declined steadily to undetectable levels at 20 wk of age. A half-life of 10.55 days was calculated for maternally-derived CDV NAb in raccoon pups. Sixteen vaccinated raccoons were protected from clinical disease following experimental oronasal challenge with a virulent raccoon strain of CDV, 13 to 23 wk after vaccination. Serum CDV NAb titers at the time of challenge ranged from 1:12 to 1:384 and increased during the period of observation. Three of four unvaccinated seronegative raccoons used as controls failed to mount any detectable CDV NAb and were euthanatized after developing clinical signs of canine distemper 26, 29, and 30 days post-challenge (PC). Necropsies confirmed the diagnosis. The fourth control raccoon exhibited transient equivocal clinical signs, mounted a sluggish humoral response, but was clinically normal when euthanatized 42 days PC. In this raccoon, there was focal non-suppurative encephalitis with intranuclear inclusion bodies typical of CDV infection.     

The raccoon an emerging rabies host

The geographic distribution of enzootic rabies in raccoons is currently limited to Florida and Georgia. The enzootic area has steadily expanded northward into Georgia during the 1960's. An epizootic in a population of raccoons closely associated with the human residents of a small, off-shore island was investigated. Forty-seven raccoons from the island were confirmed rabies positive by the State Laboratory from January 22 to May 20, 1969. About 10 percent of the raccoons trapped during the peak of the epizootic were positive and all of these had high titers of virus in their salivary glands but were asymptomatic in behavior. Human exposure typically resulted from close approach to a "sick" raccoon. Similar outbreaks may occur elsewhere when humans live in close contact with a semi-domesticated raccoon population. Rabies vaccination of raccoons should be considered as an alternative to population reduction in such situations.     

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.     

Epidemiology of raccoon rabies in Virginia, 1984 to 1989.

Geographical and temporal trends in reports of rabid raccoons (Procyon lotor) in Virginia were summarized for 1984 to 1989; 3,256 raccoons were submitted for rabies testing, of which 1,053 (32.3%) had rabies. Both the absolute number of rabid raccoons and the percent of rabid raccoons (number rabid divided by number submitted) were examined for seasonal and yearly trends. Geographically, the epidemic moved eastward and southward in the state. The seasonal trend showed bimodal peaks in late winter and early fall and a seasonal low in summer. The percent of rabies positive raccoons peaked 1 mo earlier than the absolute number of rabies positive raccoons. The peak in the number of rabies positive raccoons occurred in 1987, while the percent of rabies positive raccoons peaked in 1986. These trends were used to recommend timing and placement of oral vaccine as one strategy to control raccoon rabies in wildlife.     

Raccoon Density and Movements After Population Reduction to Control Rabies

ABSTRACT Population reduction (PR) and trap-vaccinate-release (TVR) were used to control an outbreak of the raccoon (Procyon lotor) variant of rabies in Ontario, Canada, during 1999. Raccoon density declined significantly following PR; however, density increased significantly 9–10 months post-PR. Recolonization of PR areas with raccoons marked in TVR areas was very low with only 1.8% (32/1,759) of those raccoons dispersing into PR areas during 1999–2000. In addition, the number of raccoons dispersing from TVR areas into PR areas was not significantly greater than the number of raccoons dispersing into treatment areas where population reduction had not been implemented during 1999–2000. Raccoon movements in this study, determined by mark-recapture, averaged < 4.0 km during 1999–2000 and did not differ among treatments (with or without PR). In summary, there was not a mass exodus of raccoons from TVR areas to PR areas during 1999–2000, suggesting there was not an immediate, dramatic, vacuum effect drawing raccoons into areas devoid of raccoons due to PR. However, one year post-PR, raccoon populations were near or above pre-PR densities (due to a high reproductive rate of resident raccoons), suggesting that PR would have to be an annual event if rabies is not eliminated from an area.     

Experimental inoculation of raccoons (Procyon lotor) with rabies virus of skunk origin.

To determine raccoon (Procyon lotor) susceptibility and serum neutralizing antibody response to a skunk salivary gland rabies virus, raccoons were inoculated with a rabies virus isolated from a naturally-infected striped skunk (Mephitis mephitis). Raccoons were divided into four groups of three animals each. A dilution of the rabies virus suspension, 10(2.4), 10(3.4), or 10(4.8), mouse intracerebral lethal dose50 (MICLD50), was administered into the masseter muscles of each animal. Three negative control animals received only diluent. Saliva and sera were collected on post-inoculation days 35, 63 and 92 for virus isolation and determination of serum neutralizing antibody titer. All animals survived the 92 day observation period and none exhibited the behavioral changes classically associated with clinical rabies virus infections. Rabies virus was not detected in the saliva of any raccoon and two of the three animals receiving the highest inoculum developed serum neutralizing antibodies (SNA). On day 92, a challenge suspension of New York City/Georgia (NYC/GA) strain rabies virus in fox salivary glands (10(3.2) MICLD50) was administered to all 12 raccoons. All animals succumbed to rabies virus except the two animals that had earlier developed SNA. The results of this study provided evidence about the susceptibility of raccoons to a skunk rabies virus and demonstrated that exposed raccoons could survive for at least 92 days following exposure. Furthermore, animals developing SNA under such circumstances were capable of withstanding challenge with rabies virus that was fatal for seronegative raccoons.     

Immunogenicity and efficacy of two rabies vaccines in wild-caught, captive raccoons

The immunogenicity and efficacy of two rabies vaccines in wild-caught, captive raccoons (Procyon lotor) were investigated. Raccoons were fed Ontario Slim (OS) baits containing a recombinant vaccinia virus-rabies glycoprotein (VRG) oral rabies vaccine, or they were given an intramuscular (IM) injection of IMRAB(?) 3 rabies vaccine. Blood samples collected before treatment and from weeks 1 to 16 posttreatment were assessed for the presence of rabies virus antibody (RVA). There were significantly more positive responders in the group that received an IM injection of IMRAB 3 (18/27) than in the group that consumed VRG in OS baits (VRG-OS; 4/ 26). There were no significant associations among age, sex, and seroconversion. Of those animals that mounted a humoral immune response to vaccination, RVA was first detected between weeks 1 and 5, with the majority of initial seroconversions detectable at week 2. A subsample of 50 raccoons (19 VRG-OS, 18 IMRAB 3, and 13 controls) from the longitudinal serology study was challenged with live raccoon variant rabies virus 442 days after initial treatment. There were significantly more survivors in the group that received IMRAB 3 (13/18) than in the VRG-OS (5/19) or control (2/13) groups. All 15 raccoons that demonstrated a serologic response survived challenge regardless of treatment. Of the 35 raccoons with no detectable serologic response, 30 (86%) succumbed to rabies virus infection (14/15 VRG-OS, 5/7 IMRAB 3, and 11/13 controls).     

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.     

Oral rabies vaccination of a northern Ohio raccoon population: relevance of population density and prebait serology

Ohio's oral rabies vaccination (ORV) program was established to prevent the westward spread of the raccoon (Procyon lotor) rabies virus (Lyssavirus, Rhabdoviridae) in Ohio, USA. The program, which targets raccoons, distributes vaccine-bait units (VBU) at a target density of 75 units/km2. Few studies have examined the relationship of VBU density and target population density to the prevalence of rabies virus-neutralizing antibodies (RVNA). We conducted experimental VBU distributions in August 2003 and August 2004, 150 km west of the ORV zone where there was no history of raccoon rabies. We measured change in RVNA titers in blood collected from live-trapped raccoons before and after VBU distributions. A closed population mark-recapture estimate of the size of the target population was 91 raccoons/km2, compared to the realized VBU distribution density of 70 units/km2. Surprisingly, 41% of 37 serum samples were RVNA-positive (>or=0.05 IU/ml) before VBU distribution in 2003, but all titers were <0.25 IU/ml. Although viable VBUs were distributed in August 2003, only 21% of 315 samples were RVNA-positive before VBU distribution in 2004, but 9% had titers>or=0.25 IU/ml. Tetracycline (biomarker in bait) prevalence in teeth indicated that 57% of raccoons ingested VBUs after distribution in 2003, and 54% ingested VBUs after distribution in 2004. However, only 8% and 11% of sera were positive for RVNA (>or=0.05 IU/ml) after VBU distribution in 2003 and 2004, respectively. Only 4-5% of sera collected after bait distribution had titers>or=0.25 IU/ml each year. The standard distribution density of 75 VBUs/km2 was insufficient to produce a population-wide immunoprotective response against rabies infection in our high-density target population. Presence of RVNA in a presumed na?ve population before baiting demonstrates that estimating prevalence of RVNA after oral rabies vaccination can be problematic without knowledge of background titers and seasonal changes in prevalence of RVNA before and after baiting.     

Land use associations and changes in population indices of urban raccoons during a rabies epizootic

Land use associations and changes in population indices were assessed for an urban population of raccoons (Procyon lotor) in Baltimore, Maryland (USA), from January 1984 to December 1987. Records were examined for 1,458 raccoons trapped alive and removed dead from city streets during, and after, the peak of a rabies epizootic. The distribution of raccoons was associated with single-unit residential areas primarily along the northern and western perimeter of the city. Beginning in March 1985 an ending in May 1987, an epizootic of raccoon rabies spread through Baltimore, ultimately resulting in the identification of 95 rabid raccoons. Within the study interval, annual numbers of trapped raccoons remained stable from 1984 to 1986, before showing a marked decline in 1987. The number of raccoons removed as vehicle mortalities (road-kills) varied little from 1984-1985 but declined in the last 2 yr of study. Numbers of other road-killed species did not decrease concurrently, suggesting a specific decrease in the urban raccoon population. The rabies epizootic, in conjunction with the increased city and private control, appears to have contributed to a decline in the number of raccoons in Baltimore.