Oral vaccination of raccoons (Procyon lotor) with genetically modified rabies virus vaccines

Abstract

Oral vaccination is an important tool currently in use to control the spread of rabies in wildlife populations in various programs around the world. Oral rabies vaccination (ORV) of raccoons represents the largest targeted program to control wildlife rabies in the United States. Currently, the vaccinia-rabies glycoprotein recombinant virus vaccine (V-RG) is the only licensed oral rabies vaccine in the US. In the current study, captive raccoons were used to evaluate two previously described constructs of a rabies virus vaccine developed by reverse genetics (SPBNGAS and SPBNGAS-GAS) for immunogenicity and efficacy compared to the V-RG vaccine. Four of five control animals succumbed to rabies virus after severe challenge, while three of five animals vaccinated orally with SPBNGAS succumbed. No mortality was observed for animals administered SPBNGAS-GAS or the V-RG vaccine. The results of this preliminary study suggest that SPBNGAS-GAS provides comparable efficacy to V-RG. Additional studies will be needed to determine the duration of immunity and optimal dosage of SPBNGAS-GAS and to examine its efficacy in other reservoir species.

Immunogenicity and Efficacy of Two Rabies Vaccines in Wild-Caught, Captive Raccoons

“…Although we cannot rule out the contribution of other factors, such as cell-mediated immune responses (Nathanson and Gonzalez-Scarano, 1991;Lambot et al, 2001), to survival of some animals in the absence of a strong humoral immune response, the fact that a similar proportion of control animals also survived suggests that survival of these vaccinates was not due to immunization. The challenge virus dose was chosen to result in a minimum of 80% mortality in the nonvaccinated group as per Title 9, Part 113 of the Code of Federal Regulations (CFR, 2010); therefore, the presence of survivors in the control group was not unexpected and also has been reported in other studies (Black and Lawson, 1970;Rupprecht et al, 1988Rupprecht et al, , 1993Sé tien et al, 1998;Blanton et al, 2007;Henderson et al, 2009;Mü ller et al, 2009). Despite clear differences between the vaccines in composition and route of administration, the effect of the humoral immune response, once initiated, was similar with respect to protection from disease.…”

“…Different study environments (laboratory and field), experimental designs, and vaccine presentation methods (bait vs. oral) are also complicating factors. Laboratory studies of VRG immunogenicity reporting seroconversion rates approaching 100% involved either direct instillation of the vaccine into the oral cavity (Blanton et al, 2007) or ingestion of vaccine via polyurethane sponge baits (Rupprecht et al, 1986(Rupprecht et al, , 1988. Seroconversion rates of 60-70% were reported in field studies when VRG was dispensed in a wax ampule inserted into a fishmeal polymer (FP) bait (Hanlon et al, 1998;Roscoe et al, 1998).…”

Oral Vaccination of Captive Small Indian Mongoose (Herpestes auropunctatus) against Rabies

“…Previous studies in mongooses using very similar constructs showed that the presence of VNA was indicative for protective immunity (Blanton et al, 2006). SPBN GASGAS has been tested in other species such as raccoons, and animals with VNA were consistently protected against a relevant rabies infection (Blanton et al, 2007). Therefore, no challenge infection was performed.…”

Ecology of Rabies Virus Exposure in Colonies of Brazilian Free-Tailed Bats (Tadarida brasiliensis) at Natural and Man-Made Roosts in Texas

“…Positive VNA titers (!0.06 IU=mL) were demonstrated by complete neutralization of the challenge virus dose (50 focus forming doses) at a 1:4 serum dilution. The choice of this cutoff value follows previous studies for Lyssavirus surveillance using bat and nonbat sera (Shankar et al 2004, Lumlertdacha et al 2005, Blanton et al 2007, Jackson et al 2008. A previous study has demonstrated that the immunoglobulin G fraction of the bat serum is responsible for neutralization activity against RABV (Shankar et al 2004).…”