An assessment of ONRAB oral rabies vaccine persistence in free-ranging mammal populations in Ontario, Canada.

ONRAB is a rabies glycoprotein recombinant human adenovirus type 5 oral vaccine developed for application in baits to control rabies in wildlife populations. Prior to widespread use of ONRAB, both the safety and effectiveness of this vaccine required investigation. While previous research has focused on field performance and the persistence and pathogenicity of ONRAB in captive animals, we sought to examine persistence and shedding of ONRAB in populations of free-ranging target and non-target mammals. We collected oral and rectal swab samples from 84 red foxes, 169 striped skunks, and 116 raccoons during 2007 and 2008 in areas where ONRAB vaccine baits were distributed. We also analyzed 930 tissue samples, 135 oral swab and 138 rectal swab samples from 155 non-target small mammals from 10 species captured during 2008 at sites treated with high densities of ONRAB vaccine baits. Samples were screened for the presence and quantity of ONRAB DNA using quantitative real-time PCR. None of the samples that we analyzed from target and non-target species contained quantities of ONRAB greater than 10(3)EU/mL of ONRAB DNA which is a limit that has previously been applied to assess viral shedding. This study builds on similar research and suggests that replication of ONRAB in animals is short-lived and the likelihood of horizontal transmission to other organisms is low.

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.

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).

Field evaluation of an inactivated vaccine to control raccoon rabies in Ontario, Canada.

Since raccoon rabies first appeared in Ontario in 1999, >90,000 raccoons (Procyon lotor) have received IMRAB3 inactivated rabies vaccine via intramuscular (IM) injection and were released at the point of capture as part of a multiyear rabies control program, trap-vaccinate-release (TVR). Of the 132 confirmed cases infected with raccoon-variant rabies virus in Ontario between 1999 and 2005, two were from that vaccinated group, as indicated by the presence of identifying ear tags. During ongoing rabies control programs in 2003, sera were collected from 172 wild raccoons that had received IMRAB3 and tested for rabies-virus antibodies. Raccoons had one of three histories: 1) vaccinated in the current year only (to examine the response to primary vaccination), 2) vaccinated in the previous year only (to determine the duration of the primary antibody response), and 3) vaccinated in the previous year and current year (to examine antibody response to booster vaccination). Seroconversion in primary vaccinates could be detected as early as 1 wk postvaccination when sera were measured with the use of a competitive enzyme-linked immunosorbent assay (C-ELISA) with a cutoff value established to correspond to a neutralizing titer of 0.5 IU/ml. During weeks three and four postvaccination, 94% of sampled raccoons had detectable antibodies to rabies virus and 31% were still antibody positive the following year. Differences in the kinetics of the immune response were found in raccoons sampled from the two different TVR areas of the province. A strong anamnestic response was detected after booster vaccinations. IMRAB3 by IM injection was found to be an efficacious vaccine for rabies control in raccoons.

The control of raccoon rabies in Ontario Canada: proactive and reactive tactics, 1994-2007.

Proactive and reactive tactics have been utilized in Ontario, Canada, to prevent raccoon rabies from becoming established. A total of 96,621 raccoons (Procyon lotor) and 7,967 striped skunks (Mephitis mephitis) were live captured using 1,221,044 trap nights, vaccinated against rabies by injection, and released, during proactive Trap-Vaccinate-Release (TVR) programs in southern Ontario during 1994-2007. During those years, on average, 43% to 83% of the raccoon populations were vaccinated against rabies. In addition, 20,129 raccoons and 2,735 skunks were vaccinated against rabies, and 8,311 raccoons and 1,449 skunks were euthanized, using 576,359 trap nights, during reactive Point Infection Control (PIC) operations in eastern Ontario during 1999-2005. A significant correlation was detected between trapping effort and the percentage of the raccoon population that was vaccinated. Between 1999 and 2007, 132 cases of raccoon variant rabies (130 raccoons, two striped skunks) were reported in eastern Ontario. The last case occurred on 23 September 2005 with Ontario being free of reported raccoon rabies to 10 November 2008, proving that TVR and PIC are effective tactics for the control of this disease.

Aerial distribution of ONRAB baits as a tactic to control rabies in raccoons and striped skunks in Ontario, Canada.

During August 2006 and 2007, baits containing oral rabies vaccine, live adenovirus vector, known as ONRAB , were aerially distributed in SW Ontario, Canada. Bait acceptance during 2006 was 62 and 74% in raccoons (Procyon lotor) in areas baited at 150 baits/km(2) and 75 and 77% in plots baited at 300 baits/km(2). During 2007, bait acceptance for raccoons ranged between 59% and 80%, and 83% and 87%, in areas baited at 75 and 400 baits/km(2), respectively. Bait acceptance by skunks varied among plots (5-24%). Rabies virus-specific seroconversion during 2006 averaged 66 and 81% in raccoons in areas baited at 150 and 300 baits/km(2), respectively. During 2007, seroconversion by raccoons was 76 and 84% in areas baited at 75 and 400 baits/km(2), respectively. Seroconversion by skunks varied among plots (17-51%). Vaccine efficacy, as judged by the percentage of animals that consumed a bait and seroconverted, averaged 79 and 87% during 2006 for raccoons in areas baited at 150 and 300 baits/km(2), respectively, and 81 and 90% in areas baited during 2007 at 75 and 400 baits/km(2), respectively. Because tetracycline marking was poor in skunks, an estimate of vaccine efficacy was not possible. Aerial distribution of ONRAB vaccine baits seems to be a feasible tactic for controlling rabies in skunks and raccoons.

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.