Oral rabies vaccine: evaluation of its infectivity in three species of rodents

Recombinant rabies viruses expressing GM-CSF or flagellin are effective vaccines for both intramuscular and oral immunizations

Our previous studies indicated that recombinant rabies viruses (rRABV) expressing chemokines or cytokines (including GM-CSF) could enhance the immunogenicity by recruiting and/or activating dendritic cells (DC). In this study, bacterial flagellin was cloned into the RABV genome and recombinant virus LBNSE-Flagellin was rescued. To compare the immunogenicity of LBNSE-Flagellin with recombinant virus expressing GMCSF (LBNSE-GMCSF), mice were immunized with each of these rRABVs by intramuscular (i.m.) or oral route. The parent virus (LBNSE) without expression of any foreign molecules was included for comparison. The i.m.-immunized mice were bled at three weeks after the immunization for the measurement of virus neutralizing antibody (VNA) and then challenged with 50 LD50 challenge virus standard (CVS-24). Orally immunized mice were boosted after three weeks and then bled and challenged one week after the booster immunization. It was found that both LBNSE-GMCSF and LBNSE-Flagellin recruited/activated more DCs and B cells in the periphery, stimulated higher levels of adaptive immune responses (VNA), and protected more mice against challenge infection than the parent virus LBNSE in both the i.m. and the orally immunized groups. Together, these studies suggest that recombinant RABV expressing GM-CSF or flagellin are more immunogenic than the parent virus in both i.m. and oral immunizations.

Oral vaccination of dogs with recombinant rabies virus vaccines

Oral rabies virus (RV) vaccines are used to immunize a diversity of mammalian carnivores, but no single biological is effective for all major species. Recently, advances in reverse genetics have allowed the design of recombinant RV for consideration as new vaccines. The objective of this experiment was to examine the safety, immunogenicity and efficacy of recombinant RV vaccines administered to captive dogs by the oral route, compared to a commercial vaccinia-rabies glycoprotein (V-RG) recombinant virus vaccine. Animals consisted of naive purpose-bred beagles of both sexes, and were 6 months of age or older. Dogs were randomly assigned to one of six groups, and received either diluent or vaccine (PBS; V-RG; RV SN10-333; RV SPBN-Cyto c; RV SPBNGA; RV SPBNGAGA), with at least six animals per group. On day 0, 1 ml of each vaccine (or PBS) was administered to the oral cavity of each dog, at an approximate concentration of 10(8) to 10(9) TCID50. After vaccination, dogs were observed daily and bled weekly, for 5 weeks, prior to RV challenge. No signs of illness related to vaccination were detected during the observation period. Excluding the controls, RV neutralizing antibodies were detected in the majority of animals within 1-2 weeks of primary vaccination. Thereafter, all dogs were inoculated in the masseter muscle with a street virus of canine origin. All control animals developed rabies, but no vaccinates succumbed, with the exception of a single dog in the V-RG group. Review of these preliminary data demonstrates the non-inferiority of recombinant RV products, as concerns both safety and efficacy, and supports the suggestion that these vaccines may hold promise for future development as oral immunogens for important carnivore species, such as dogs.

A recombinant vaccinia-rabies virus in the immunocompromised host: oral innocuity, progressive parenteral infection, and therapeutics

With the emergence of raccoons (Procyon lotor) as the primary rabies reservoir in the United States of America, a recombinant vaccinia-rabies glycoprotein (V-RG) virus vaccine was developed that protected raccoons by the oral route from rabies infection. Despite extensive laboratory evaluation, vaccine safety concerns remained about free-choice distribution for wildlife rabies control. In this study, the oral innocuity of V-RG virus was demonstrated in immunodeficient mice but parenteral exposure resulted in systemic and progressive infection, albeit significantly abrogated in severity in comparison to vaccinia virus. Treatment with vaccinia immune globulin and hydroxyphosphonylmethoxy-propyl-cytosine resulted in significantly longer survival and minimized V-RG viral gross lesions.

Serological survey for orthopoxvirus infection of wild mammals in areas where a recombinant rabies virus is used to vaccinate foxes

Several fox vaccination campaigns against rabies have been undertaken in Belgium by using a vaccinia-rabies recombinant virus distributed in baits in the field. However, foxes and other wild animals that may ingest the baits could be infected at the same time by another orthopoxvirus, such as cowpox virus, which circulates in wildlife. Recombination between the two viruses could therefore occur. A serological survey for antibodies to orthopoxvirus, and particularly to cowpox virus, was undertaken in foxes and in several other wild species. Antibodies were detected only in two rodent species, in 16 of 25 bank voles (64 per cent) and in two of 29 woodmice (7 per cent). The risk of virus recombination in wildlife can therefore be considered to be extremely low.

Evaluation of the safety of two attenuated oral rabies vaccines, SAG1 and SAG2, in six Arctic mammals

The safety of two attenuated oral rabies vaccines was evaluated in mink and in five species of rodents which occur in the Arctic. A 0.03 ml sample of liquid vaccine was installed directly into the mouth of voles and lemmings and 0.1 ml into the mouth of Arctic ground squirrels and mink. Animals were euthanized at 36 and 46 days postexposure; brain tissue was analyzed by FAT and serum by RFFIT. No rabies deaths occurred in 47 animals tested. Four animals representing three rodent species seroconverted, the highest titer being 0.5 IU ml-1. The absence of rabies virus in brain tissue indicates the safety of these vaccines in these species. The replacement of arginine with glutamic acid at position 333 reduces the pathogenicity of these vaccines, thereby presumably preventing the deleterious effect of viral entry into CNS neurons.

Comparison of the susceptibility of the red fox (Vulpes vulpes) to a vaccinia-rabies recombinant virus and to cowpox virus

Sylvatic rabies can be efficiently controlled by vaccination of foxes with a vaccinia-rabies recombinant virus. However, the risk of recombination between the engineered vaccine virus and other orthopoxviruses endemic in wildlife, such as cowpox virus, still needs to be investigated. In this study, foxes inoculated orally and intradermally with cowpox virus were found to be not very susceptible to cowpox virus, which was isolated from only the oropharynx and tonsils, at low titre and for only five days after inoculation. Thus the risk of recombination between these viruses in foxes is very low.

Potential pathogenicity for rodents of vaccines intended for oral vaccination against rabies: a comparison

Different oral vaccines intended to control fox rabies were administered to 271 wild rodents. Vaccines were administered orally or by the mucosal route to four different European species belonging to the genera Apodemus, Arvicola, Clethrionomys and Microtus. These rodents are likely to consume baits and to have contact with the vaccine. Two genetically engineered vaccines were tested: SAG1 (an avirulent mutant of the rabies virus) and V-RG (vaccinia recombinant virus expressing the rabies glycoprotein gene). Both were found to be completely innocuous when administered orally or by the mucosal route. The residual pathogenicity of conventional modified live vaccines derived from the SAD strain was confirmed.

Effectivity of oral vaccination of foxes against rabies with Flury HEP strain 675

A group of 14 adult foxes was orally vaccinated with 2 ml Flury HEP strain 675, titre 10(8.2 TCID50. Each fox seroconverted neutralizing antibody titres ranging between 1:40 and 1:640. These foxes survived an intramuscular challenge with 8000 mouse LD50 pathogenic rabies virus, whereas six out of seven unprotected control foxes died within 28 days. This study was accompanied by virus isolation, fluorescence microscopic examination and neutralization tests.

Enteric inoculation with ERA rabies virus: evaluation of a candidate wildlife vaccine in laboratory rodents

A series of experiments on the safety and efficacy of enteric vaccination was carried out in laboratory rodents using the ERA strain of rabies virus both live and inactivated. In the first and second experiments in white Norway rats, several methods of inoculation were compared for the development of rabies neutralizing antibody. In later experiments, the potential for disease transmission through salivary excretion of ERA strain, or through scavenging, or cannibalism were evaluated. Enteric inoculation of rats with high doses of live ERA virus often failed to give an antibody response yet would occasionally kill adult animals. Rabies antigen was demonstrable in the trigeminal ganglion and tongue of one of these rats, and 14 of 65 (21.5 percent) adult mice died from rabies after eating infants infected with the ERA strain.