Immunogenicity and safety of recombinant rabies viruses used for oral vaccination of stray dogs and wildlife

A VSV-based oral rabies vaccine was sentineled by Peyer's patches and induced a timely and durable immune response

The global eradication of canine-mediated human rabies remains an ongoing public health priority. While conventional oral rabies vaccines (ORVs) have demonstrated partial success in interrupting zoonotic transmission, current formulations necessitate improvements in both immunogenic profiles and mechanistic clarity. Herein, we present a recombinant vesicular stomatitis virus (VSV)-vectored vaccine candidate (rVSVΔG-ERA-G) engineered to express the glycoprotein of the rabies virus (RABV) ERA strain, substituting the native VSV glycoprotein. Preclinical evaluation across multiple mammalian species (Mus musculus, Canis lupus familiaris, Felis catus, Vulpes lagopus, and Nyctereutes procyonoides) revealed rapid seroconversion and sustained neutralizing antibody responses. Challenge experiments demonstrated 100% survival efficacy in pre-exposure prophylaxis models, with partial protection observed in post-exposure scenarios. Safety assessments confirmed significant attenuation of neurotropism and absence of horizontal transmission or environmental shedding. Furthermore, evidence showed that rVSVΔG-ERA-G is recognized by Peyer's patches (PPs), where a cascade activation of immune cells occurred. From another perspective, the absence of functional microfold cells in PPs hampered the initiation and progression of immune responses. This proof-of-concept study establishes rVSVΔG-ERA-G as an ORV candidate with enhanced biosafety and cross-species immunogenicity. The elucidation of M cell-dependent mucosal priming mechanisms provides a rational framework for optimizing the targeted delivery of ORVs.

Recent Advances in Oral Vaccines for Animals

Compared to traditional injected vaccines, oral vaccines offer significant advantages for the immunization of livestock and wildlife due to their ease of use, high compliance, improved safety, and potential to stimulate mucosal immune responses and induce systemic immunity against pathogens. This review provides an overview of the delivery methods for oral vaccines, and the factors that influence their immunogenicity. We also highlight the global progress and achievements in the development and use of oral vaccines for animals, shedding light on potential future applications in this field.

A Global Perspective on Oral Vaccination of Wildlife against Rabies

The long-term mitigation of human-domestic animal-wildlife conflicts is complex and difficult. Over the last 50 yr, the primary biomedical concepts and actualized collaborative global field applications of oral rabies vaccination to wildlife serve as one dramatic example that revolutionized the field of infectious disease management of free-ranging animals. Oral vaccination of wildlife occurred in diverse locales within Africa, Eurasia, the Middle East, and North America. Although rabies is not a candidate for eradication, over a billion doses of vaccine-laden baits distributed strategically by hand, at baiting stations, or via aircraft, resulted in widespread disease prevention, control, or local disease elimination among mesocarnivores. Pure, potent, safe, and efficacious vaccines consisted of either modified-live, highly attenuated, or recombinant viruses contained within attractive, edible baits. Since the late 1970s, major free-ranging target species have included coyotes (Canis latrans), foxes (Urocyon cinereoargenteus; Vulpes vulpes), jackals (Canis aureus; Lupulella mesomelas), raccoons (Procyon lotor), raccoon dogs (Nyctereutes procyonoides), and skunks (Mephitis mephitis). Operational progress has occurred in all but the latter species. Programmatic evaluations of oral rabies vaccination success have included: demonstration of biomarkers incorporated within vaccine-laden baits in target species as representative of bait contact; serological measurement of the induction of specific rabies virus neutralizing antibodies, indicative of an immune response to vaccine; and most importantly, the decreasing detection of rabies virus antigens in the brains of collected animals via enhanced laboratory-based surveillance, as evidence of management impact. Although often conceived mistakenly as a panacea, such cost-effective technology applied to free-ranging wildlife represents a real-world, One Health application benefiting agriculture, conservation biology, and public health. Based upon lessons learned with oral rabies vaccination of mesocarnivores, opportunities for future extension to other taxa and additional diseases will have far-reaching, transdisciplinary benefits.

Immune response after oral immunization of goats and foxes with an NDV vectored rabies vaccine candidate

Vaccination of the reservoir species is a key component in the global fight against rabies. For wildlife reservoir species and hard to reach spillover species (e. g. ruminant farm animals), oral vaccination is the only solution. In search for a novel potent and safe oral rabies vaccine, we generated a recombinant vector virus based on lentogenic Newcastle disease virus (NDV) strain Clone 30 that expresses the glycoprotein G of rabies virus (RABV) vaccine strain SAD L16 (rNDV_GRABV). Transgene expression and virus replication was verified in avian and mammalian cells. To test immunogenicity and viral shedding, in a proof-of-concept study six goats and foxes, representing herbivore and carnivore species susceptible to rabies, each received a single dose of rNDV_GRABV (108.5 TCID50/animal) by direct oral application. For comparison, three animals received the similar dose of the empty viral vector (rNDV). All animals remained clinically inconspicuous during the trial. Viral RNA could be isolated from oral and nasal swabs until four (goats) or seven days (foxes) post vaccination, while infectious NDV could not be re-isolated. After four weeks, three out of six rNDV_GRABV vaccinated foxes developed RABV binding and virus neutralizing antibodies. Five out of six rNDV_GRABV vaccinated goats displayed RABV G specific antibodies either detected by ELISA or RFFIT. Additionally, NDV and RABV specific T cell activity was demonstrated in some of the vaccinated animals by detecting antigen specific interferon γ secretion in lymphocytes isolated from pharyngeal lymph nodes. In conclusion, the NDV vectored rabies vaccine rNDV_GRABV was safe and immunogenic after a single oral application in goats and foxes, and highlight the potential of NDV as vector for oral vaccines in mammals.

Emergency response using oral rabies vaccination of dogs -field data from Namibia demonstrate high efficiency

Dog-mediated rabies is responsible for tens of thousands of human deaths annually, and in resource-constrained settings, vaccinating dogs to control the disease at source remains challenging for various reasons. Currently, rabies elimination efforts rely on mass dog vaccination by the parenteral route. While oral rabies vaccination (ORV) of dogs is primarily considered a tool to increase herd immunity, particularly by targeting free-roaming and stray dogs, here, we are showcasing an ORV-only approach as an emergency response model. Using a third-generation vaccine and a standardized egg-flavored bait, we assessed the effectiveness and vaccination under field conditions in the Zambezi region of Namibia. During this trial, with four teams and within four working days, 3097 dogs were offered a bait, of which 88,0% were considered vaccinated. Teams managed to vaccinate, on average, over 20 dogs/h, despite using a door-to-door vaccination approach. The favorable results both in terms of bait acceptance and successful vaccination as well as field applicability and effectiveness further support the great potential of ORV in dog rabies control programmes.

Efficacy of Oral Rabies Vaccine Baits Containing SPBN GASGAS in Domestic Dogs According to International Standards

(1) Background: The oral vaccination of free-roaming dogs against rabies has been developed as a promising complementary tool for mass dog vaccination. However, no oral rabies vaccine has provided efficacy data in dogs according to international standards. (2) Methods: To test the immunogenicity and efficacy of the third-generation oral rabies virus vaccine strain, SPBN GASGAS, in domestic dogs, dogs were offered an egg-flavoured bait containing 3.0 mL of the vaccine (10^7.5 FFU/mL) or a placebo egg-flavoured bait. Subsequently, these 25 vaccinated and 10 control animals were challenged approximately 6 months later with a dog rabies virus isolate. Blood samples were collected at different time points postvaccination and examined by ELISA and RFFIT. (3) Results: All but 1 of the 25 vaccinated dogs survived the challenge infection; meanwhile, all 10 control dogs succumbed to rabies. The serology results showed that all 25 vaccinated dogs seroconverted in ELISA (>40% PB); meanwhile, only 13 of the 25 vaccinated dogs tested seropositive ≥ 0.5 IU/mL) in RFFIT. (4) Conclusions: The SPBN GASGAS rabies virus vaccine meets the efficacy requirements for live oral rabies vaccines as laid down by the European Pharmacopoeia and the WOAH Terrestrial Manual. SPBN GASGAS already fulfilled the safety requirements for oral rabies vaccines targeted at dogs. Hence, the egg-flavoured bait containing SPBN GASGAS is the first oral vaccine bait that complies with WOAH recommendations for the intended use of oral vaccination of free-roaming dogs against rabies.

The Raccoon (Procyon lotor) as a Neozoon in Europe

The raccoon (Procyon lotor) is a North American half-bear that is present in much of Europe and Asia as a result of both accidental and planned releases. In Europe, raccoons were introduced primarily as a source of fur for the fur industry. In the 1930s, raccoons were released into the wild in Central Europe. At the same time, animals from fur farms and private holdings continued to enter the wild. In the following decades, the raccoon spread over large parts of Europe. In addition to the invasive spread of the Central European initial population, individual releases of raccoons occurred frequently, mainly in Southern Europe. The high adaptability of the raccoon favors its expansion into new habitats. It has a high reproductive rate, is very mobile, and encounters few predators in Europe. Raccoons have recently become a topic of interest when large raccoon populations have colonized suburban and urban areas. Despite the proximity of raccoons and humans, however, there have been hardly any conflicts to date, unlike in North America. A significant negative impact on the native fauna has been suspected but not proven. Raccoons have been identified as vectors of zoonotic diseases. Nevertheless, monitoring of the increasing numbers of raccoons in Europe seems advisable.

Oral Rabies Vaccine Strain SPBN GASGAS: Genetic Stability after Serial In Vitro and In Vivo Passaging

Oral vaccination of wildlife has shown to be a very effective management tool in rabies control. Evaluation of the genetic stability of vaccine viruses before distributing vaccine baits in the environment is essential because all available oral rabies vaccines, including the genetically engineered rabies virus vaccine strain SPBN GASGAS (Rabitec), are based on replication-competent viruses. To evaluate the genetic stability of this vaccine strain, five serial passages of the Master Seed Virus (MSV) in the production cell line BHK21 Cl13 were performed. Furthermore, to test possible reversion to virulence, a back-passage study in suckling mouse brain (SMB) was performed. Subsequently, the pooled 5th SMB passage was inoculated intracerebrally (i.c.) in adult and suckling mice. The full genome sequences of the isolated 5th passage, in vivo and in vitro, were compared at both the consensus and the quasispecies level with the MSV. Additionally, the full genome sequence of the 6th SMB passage from the individual animals was determined and compared. Full-length integration of the double glycoprotein and modified base substitutions at amino acid position 194 and 333 of the glycoprotein could be verified in all 5th and 6th passage samples. Overall, 11 single nucleotide polymorphisms (SNPs) were detected in the 5th pooled SMB passage, 4 with frequency between 10 and 20%, and 7 with between 2.5 and 10%. SNPs that resulted in amino acid exchange were found in genes: N (one SNP), G (four SNPs), and L (three SNPs). However, none of these SNPs were associated with reversion to virulence since all adult mice inoculated i.c. with this material survived. In the individual samples of the 6th SMB passage 24 additional SNPs (>2.5%) were found, of which only 1 SNP (L-gene, position 6969) had a prevalence of >50% in 3 of 17 samples. The obtained results confirmed the stable expression of genetic modifications and the genetic stability of the consensus strain after serial in vivo and in vitro passaging.

Oral rabies vaccination of dogs-Experiences from a field trial in Namibia

Dog-mediated rabies is responsible for tens of thousands of human deaths annually, and in resource-constrained settings, vaccinating dogs to control the disease at source remains challenging. Currently, rabies elimination efforts rely on mass dog vaccination by the parenteral route. To increase the herd immunity, free-roaming and stray dogs need to be specifically addressed in the vaccination campaigns, with oral rabies vaccination (ORV) of dogs being a possible solution. Using a third-generation vaccine and a standardized egg-flavoured bait, bait uptake and vaccination was assessed under field conditions in Namibia. During this trial, both veterinary staff as well as dog owners expressed their appreciation to this approach of vaccination. Of 1,115 dogs offered a bait, 90% (n = 1,006, 95%CI:91-94) consumed the bait and 72.9% (n = 813, 95%CI:70.2-75.4) of dogs were assessed as being vaccinated by direct observation, while for 11.7% (n = 130, 95%CI:9.9-17.7) the status was recorded as "unkown" and 15.4% (n = 172, 95%CI: 13.4-17.7) were considered as being not vaccinated. Smaller dogs and dogs offered a bait with multiple other dogs had significantly higher vaccination rates, while other factors, e.g. sex, confinement status and time had no influence. The favorable results of this first large-scale field trial further support the strategic integration of ORV into dog rabies control programmes. Given the acceptance of the egg-flavored bait under various settings worldwide, ORV of dogs could become a game-changer in countries, where control strategies using parenteral vaccination alone failed to reach sufficient vaccination coverage in the dog population.

Review of Oral Rabies Vaccination of Dogs and Its Application in India

Oral rabies vaccines (ORVs) have been in use to successfully control rabies in wildlife since 1978 across Europe and the USA. This review focuses on the potential and need for the use of ORVs in free-roaming dogs to control dog-transmitted rabies in India. Iterative work to improve ORVs over the past four decades has resulted in vaccines that have high safety profiles whilst generating a consistent protective immune response to the rabies virus. The available evidence for safety and efficacy of modern ORVs in dogs and the broad and outspoken support from prominent global public health institutions for their use provides confidence to national authorities considering their use in rabies-endemic regions. India is estimated to have the largest rabies burden of any country and, whilst considerable progress has been made to increase access to human rabies prophylaxis, examples of high-output mass dog vaccination campaigns to eliminate the virus at the source remain limited. Efficiently accessing a large proportion of the dog population through parenteral methods is a considerable challenge due to the large, evasive stray dog population in many settings. Existing parenteral approaches require large skilled dog-catching teams to reach these dogs, which present financial, operational and logistical limitations to achieve 70% dog vaccination coverage in urban settings in a short duration. ORV presents the potential to accelerate the development of approaches to eliminate rabies across large areas of the South Asia region. Here we review the use of ORVs in wildlife and dogs, with specific consideration of the India setting. We also present the results of a risk analysis for a hypothetical campaign using ORV for the vaccination of dogs in an Indian state.

Research Advances on the Interactions between Rabies Virus Structural Proteins and Host Target Cells: Accrued Knowledge from the Application of Reverse Genetics Systems

Rabies is a lethal zoonotic disease caused by lyssaviruses, such as rabies virus (RABV), that results in nearly 100% mortality once clinical symptoms appear. There are no curable drugs available yet. RABV contains five structural proteins that play an important role in viral replication, transcription, infection, and immune escape mechanisms. In the past decade, progress has been made in research on the pathogenicity of RABV, which plays an important role in the creation of new recombinant RABV vaccines by reverse genetic manipulation. Here, we review the latest advances on the interaction between RABV proteins in the infected host and the applied development of rabies vaccines by using a fully operational RABV reverse genetics system. This article provides a background for more in-depth research on the pathogenic mechanism of RABV and the development of therapeutic drugs and new biologics.

Oral vaccination of foxes and raccoon dogs against rabies with the 3rd generation oral rabies virus vaccine, SPBN GASGAS, in Finland

Background

To prevent re-emergence of wildlife-mediated rabies in Finland, oral rabies vaccine baits are distributed every year during autumn in southern Finland in a vaccination zone bordering Russia. Recently, Finland introduced a 3rd generation oral rabies virus vaccine bait. By analysing bait uptake and seroconversion in red foxes and raccoon dogs, the field efficacy of this new vaccine strain, SPBN GASGAS, was compared with the originally used highly efficacious 1st generation vaccine SAD B19.

Results

Overall, 74.6% and 53.9% of the animals submitted from the vaccination area after the campaigns (2017–2019) tested positive for the presence of the bait marker and anti-rabiesvirus antibodies, respectively. No significant difference was observed between years, species and vaccine.

Conclusions

The field performance of the highly attenuated 3rd generation oral rabies vaccine, SPBN GASGAS, in terms of bait uptake and seroconversion was similar to the 1st generation vaccine, SAD B19, and therefore offers a suitable alternative.

Long-Term Immunogenicity and Efficacy of the Oral Rabies Virus Vaccine Strain SPBN GASGAS in Foxes

To evaluate the long-term immunogenicity of the live-attenuated, oral rabies vaccine SPBN GASGAS in a full good clinical practice (GCP) compliant study, forty-six (46) healthy, seronegative red foxes (Vulpes vulpes) were allocated to two treatment groups: group 1 (n = 31) received a vaccine bait containing 1.7 ml of the vaccine of minimum potency (10^6.6 FFU/mL) and group 2 (n = 15) received a placebo-bait. In total, 29 animals of group 1 and 14 animals of group 2 were challenged at 12 months post-vaccination with a fox rabies virus isolate (10^3.0 MICLD₅₀/mL). While 90% of the animals offered a vaccine bait resisted the challenge, only one animal (7%) of the controls survived. All animals that had seroconverted following vaccination survived the challenge infection at 12 months post-vaccination. Rabies specific antibodies could be detected as early as 14 days post-vaccination. Based on the kinetics of the antibody response to SPBN GASGAS as measured in ELISA and RFFIT, the animals maintained stable antibody titres during the 12-month pre-challenge observation period at a high level. The results indicate that successful vaccination using the oral route with this new rabies virus vaccine strain confers long-term duration of immunity beyond one year, meeting the same requirements as for licensure as laid down by the European Pharmacopoeia.

Codon optimization of G protein enhances rabies virus-induced humoral immunity

Rabies, caused by rabies virus (RABV), is a fatal zoonosis, which still poses a threat to public health in most parts of the world. Glycoprotein of RABV is the only viral surface protein, which is critical for the induction of virus-neutralizing antibodies (VNA). In order to improve the production of VNA, recombinant RABVs containing two copies of G gene and codon-optimized G gene were constructed by using reverse genetics, named LBNSE-dG and LBNSE-dOG, respectively. After being inoculated into the mouse brains, LBNSE-dOG induced more apoptosis and recruited more inflammatory cells than LBNSE-dG and LBNSE, resulting in reduced virulence in vivo. After intramuscular (im) immunization in mice, LBNSE-dOG promoted the formation of germinal centres (GCs), the recruitment of GC B cells and the generation of antibody-secreting cells (ASCs) in the draining lymph nodes (LNs). Consistently, LBNSE-dOG boosted the production of VNA and provided better protection against lethal RABV challenge than LBNSE-dG and LBNSE when it was used as both live and inactivated vaccines. Our results demonstrate that the codon-optimized RABV LBNSE-dOG displays attenuated pathogenicity and enhanced immunogenicity, therefore it could be a potential candidate for the next generation of rabies vaccines.

Clearance of attenuated rabies virus from brain tissues is required for long-term protection against CNS challenge with a pathogenic variant

Rabies virus is a neurotropic lyssavirus which is 100% fatal in its pathogenic form when reaching unprotected CNS tissues. Death can be prevented by mechanisms delivering appropriate immune effectors across the blood-brain barrier which normally remains intact during pathogenic rabies virus infection. One therapeutic approach is to superinfect CNS tissues with attenuated rabies virus which induces blood-brain barrier permeability and immune cell entry. Current thinking is that peripheral rabies immunization is sufficient to protect against a challenge with pathogenic rabies virus. While this is undoubtedly the case if the virus is confined to the periphery, what happens if the virus reaches the CNS is less well-understood. In the current study, we find that peripheral immunization does not fully protect mice long-term against an intranasal challenge with pathogenic rabies virus. Protection is significantly better in mice that have cleared attenuated virus from the CNS and is associated with a more robust CNS recall response evidently due to the presence in CNS tissues of elevated numbers of lymphocytes phenotypically resembling long-term resident immune cells. Adoptive transfer of cells from rabies-immune mice fails to protect against CNS challenge with pathogenic rabies virus further supporting the concept that long-term resident immune cell populations must be established in brain tissues to protect against a subsequent CNS challenge with pathogenic rabies virus.

Efficacy of the oral rabies virus vaccine strain SPBN GASGAS in foxes and raccoon dogs

To test the immunogenicity and efficacy of a new oral rabies virus vaccine strain SPBN GASGAS in wildlife target species, one group of foxes and two groups of raccoon dogs were offered a bait containing 1.7 ml of the vaccine (10^6.6 FFU/ml; 10^6.8 FFU/dose) and subsequently challenged approximately 180 days later with a fox rabies virus isolate. One group of raccoon dogs (n=30) received the same challenge dose (10^0.7 MICLD₅₀/ml) as the red foxes (n=29). The other group with raccoon dogs (n=28) together with 8 animals that received the vaccine dose by direct instillation into the oral cavity (DIOC) were infected with a 40-fold higher dose of the challenge virus (10^2.3 MICLD₅₀/ml). All but one of the 29 vaccinated foxes survived the challenge infection; meanwhile all 12 control foxes succumbed to rabies. Twenty-eight of 30 vaccinated raccoon dogs challenged with the same dose survived the infection, however only six of 12 control animals succumbed. When the higher challenge dose was administered, all 12 control animals died from rabies and all 36 vaccinated animals (28 baited plus 8 DIOC) survived. Blood samples were collected at different time points post vaccination and examined by both RFFIT and ELISA. The kinetics of the measured immune response was similar for both species, although in RFFIT slightly higher values were observed in foxes than in raccoon dogs. However, the immune response as measured in ELISA was identical for both species. The oral rabies virus vaccine SPBN GASGAS meets the efficacy requirements for live rabies virus vaccines as laid down by the European Pharmacopoeia.

Protective immune response of oral rabies vaccine in stray dogs, corsacs and steppe wolves after a single immunization

In this study the safety and protective immunity of an oral rabies vaccine, based on the live, modified rabies virus strain VRC-RZ2, was examined in stray dogs (Canis Sp.), corsacs (Vulpes corsac) and steppe wolves (Canis lupus campestris). In the safety group (dogs, n=6; corsacs, n=3; wolves, n=3) which was vaccinated with a 10-times field dose/animal, no animals showed any signs of disease or changes in behavior or appetite during the period of clinical observation, similar to the animals in the negative control group. Saliva samples taken from animals prior and post (5^th and 10^th days) vaccination failed to demonstrate rabies virus antigen. Observations of immunogenicity in vaccinated carnivores (dogs, corsacs and wolves) during a 180 day period showed the titers of virus neutralizing antibodies (VNA) in the blood sera of vaccinated dogs to be within 0.59-1.37 IU/mL. On 14 days post vaccination (dpv), all the wild carnivores had detectable levels of neutralizing antibodies, with mean titers ranging from 0.50 ± 0.07 IU/mL (for wolves) to 0.59 ± 0.10 IU/mL (for corsacs). Weeks after vaccination, all the vaccinated wolves and corsacs had higher levels of neutralizing antibodies: 0.70 ± 0.10 - 0.71 ± 0.08 IU/mL at 30 dpv, 1.06 ± 0.08 - 1.28 ± 0.21 IU/mL at 60 dpv and 0.41 ± 0.09 - 047 ± 0.06 at 180 dpv. The highest level of VNA (˃1.0 IU/ml) was detected at 60 dpv, in all vaccinated animals. After challenge all vaccinated dogs remained healthy for 180 days. Control animals (unvaccinated dogs) developed symptoms of rabies on day 6 post administration of a virulent virus and died of rabies on days 11-13. Of note, the VNA titers in all the wild carnivores (corsacs and wolves) immunized with VRC-RZ2 were higher than 0.5 IU/ml (0.59 ± 0.11 IU/ml), even as early as 14 days post vaccination. These, presumably protective, titers of antibodies to rabies virus were present in the dogs and wild carnivores examined in this study for at least 180 days.

Feasibility and efficacy of oral rabies vaccine SAG2 in endangered Ethiopian wolves

Diseases are a major cause of population declines in endangered populations of several canid species. Parenteral vaccination efforts to protect Ethiopian wolves (Canis simensis) from rabies have targeted the domestic dog reservoir, or the wolves themselves in response to confirmed outbreaks. Oral vaccination offers a more cost-efficient, safe and proactive approach to protect Ethiopian wolves and other threatened canids from rabies. Field trials of the oral vaccine Rabigen® SAG2Dog were undertaken in the Bale Mountains of southeastern Ethiopia. Four different bait types and three delivery methods were tested in twelve Ethiopian wolf packs, and the oral vaccine (using the preferred bait) was trialled in three packs. Vaccine uptake and immunization rates were measured through direct observations and in live-trapped animals through the assessment of biomarker levels and serological status. Commercial baits were never taken by wolves; goat meat baits had the highest uptake, compared to rodent and intestine baits. Targeted delivery from horseback and nocturnal delivery within a pack's territory performed favourably compared to random bait distribution. Bait uptake by non-target species was lowest during the nocturnal blind distribution. Of 21 wolves trapped after vaccination, 14 were positive for the biomarker iophenoxic acid (i.e. ingested the bait and most likely pierced the sachet with the vaccine). Of these, 86% (n=12/14) had levels considered sufficient to provide protective immunity to wildlife (⩾0.20IU/ml), and 50% (n=7/14) demonstrated antibody titres above the universally recognised threshold (⩾0.5IU/ml) -the baseline average was 0.09IU/ml (n=12 wolves). All but one of the wolves vaccinated in 2014 were alive 14months later. Our trials confirm the potential for SAG2, delivered in a goat meat bait, to effectively protect Ethiopian wolves against rabies, supporting the initiative for a more efficient and proactive approach to manage and eventually eliminate rabies in Ethiopian wolf populations.

A recombinant rabies virus (ERAGS) for use in a bait vaccine for swine

Purpose

Rabies viruses (RABV) circulating worldwide in various carnivores occasionally cause fatal encephalitis in swine. In this study, the safety and immunogenicity of a recombinant rabies virus, the ERAGS strain constructed with a reverse genetics system, was evaluated in domestic pigs.

Materials and Methods

Growing pigs were administered 1 mL (10^8.0 FAID₅₀/mL) of the ERAGS strain via intramuscular (IM) or oral routes and were observed for 4 weeks' post-inoculation. Three sows were also inoculated with 1 mL of the ERAGS strain via the IM route. The safety and immunogenicity in swine were evaluated using daily observation and a virus-neutralizing assay (VNA). Fluorescent antibody tests (FAT) for the RABV antigen and reverse transcriptase-polymerase chain reaction (RT-PCR) assays for the detection of the nucleocapsid (N) gene of RABV were conducted with brain tissues from the sows after necropsy.

Results

The growing pigs and sows administered the ERAGS strain did not exhibit any clinical sign of rabies during the test period test and did develop VNA titers. The growing pigs inoculated with the ERAGS strain via the IM route showed higher VNA titers than did those receiving oral administration. FAT and RT-PCR assays were unable to detect RABV in several tissues, including brain samples from the sows.

Conclusion

Our results suggest that the ERAGS strain was safe in growing pigs and sows and induced moderate VNA titers in pigs.

Safety and immunogenicity of recombinant rabies virus (ERAGS) in mice and raccoon dogs

Purpose

The development of a genetically modified live rabies vaccine applicable to wild raccoon dogs is necessary for the eradication of rabies in Korea. Thus, we constructed a recombinant rabies virus (RABV) called the ERAGS strain, using a reverse genetic system and evaluated its safety and efficacy in mice and its safety and immunogenicity in raccoon dogs.

Materials and Methods

ERAGS, which has Asn194Ser and Arg333Glu substitutions in the glycoprotein, was constructed using site-directed mutagenesis. Mice were inoculated with the ERAGS strain (either 10^5.0 or 10^7.0 FAID₅₀/mL) via intramuscular (IM) or intracranial injections and then challenged with a virulent RABV. Raccoon dogs were administered the ERAGS strain (10^8.0 FAID₅₀/mL) either orally or via the IM route and the immunogenicity of the strain was evaluated using fluorescent antibody virus neutralization tests.

Results

The ERAGS strain inoculated into murine neuroblastoma cells reached 10^7.8 FAID₅₀/mL at 96-hour post-inoculation. The virus was not pathogenic and induced complete protection from virulent RABV in immunized 4- and 6-week-old mice. Korean raccoon dogs immunized with the ERAGS strain via IM or oral route were also safe from the virus and developed high titer levels (26.4-32.8 IU/mL) of virus-neutralizing antibody (VNA) at 4 weeks post-inoculation.

Conclusion

The ERAGS RABV strain was effectively protective against rabies in mice and produced a high VNA titer in raccoon dogs.

Genetically modified rabies virus ERA strain is safe and induces long-lasting protective immune response in dogs after oral vaccination

Oral immunization in free-roaming dogs is one of the most practical approaches to prevent rabies for developing countries. The safe, efficient and long-lasting protective oral rabies vaccine for dogs is highly sought. In this study, rabies virus (RABV) Evelyn-Rokitnicki-Abelseth (ERA) strain wild-type (rERA) and a genetically modified type (rERAG333E) containing a mutation from arginine to glutamic acid at residue 333 of glycoprotein (G333E) were generated by reverse genetic. The recombinant virus rERAG333E retained growth properties of similar to the parent strain rERA in BHK-21 cell culture. The G333E mutation showed genetic stability during passage into neuroblastoma cells and in the brains of suckling mice and was significantly reduced the virulence of rERA in mice. rERAG333E was immunogenic in dogs by intramuscular inoculation. Mice orally vaccinated with rERAG333E induced strong and one year longer virus neutralizing antibodies (VNA) to RABV, and were completely protected from challenge with lethal street virus at 12months after immunization. Dogs received oral vaccination with rERAG333E induced strong protective RABV VNA response, which lasted for over 3years, and moderate saliva RABV-specific IgA. Moreover, sizeable booster responses to RABV VNA were induced by a second oral dose 1year after the first dose. These results demonstrated that the genetically modified ERA vaccine strain has the potential to serve as a safe and efficient oral live vaccine against rabies in dogs.

Oral immunization of mice with recombinant rabies vaccine strain (ERAG3G) induces complete protection

PURPOSE

New rabies vaccine bait for both pets and raccoon dogs residing in Korea is needed to eradicate rabies infection among animals. In this study, we constructed a recombinant rabies virus (RABV), the ERAG3G strain, using a reverse genetics system. Then we investigated the efficacy of this strain in mice after oral administration and the safety of this strain in cats after intramuscular administration.

MATERIALS AND METHODS

The ERAG3G strain was rescued in BHK/T7-9 cells using the full-length genome mutated at the amino acid position 333 of the glycoprotein gene of RABV and helper plasmids. Four-week-old mice underwent one or two oral administrations of the ERAG3G strain and were challenged with the highly virulent RABV strain CVSN2c 14 days after the second administration. Clinical symptoms were observed and body weights were measured every day after the challenge.

RESULTS

All mice showed complete protection against virulent RABV. In addition, cats intramuscularly inoculated with the ERAG3G strain showed high antibody titers ranging from 2.62 to 23.9 IU/mL at 28-day postinoculation.

CONCLUSION

The oral immunization of the ERAG3G strain plays an important role in conferring complete protection in mice, and intramuscular inoculation of the ERAG3G strain induces the formation of anti-rabies neutralizing antibody in cats.

Molecular detection and genetic diversity of Babesia gibsoni in dogs in Bangladesh

Babesia gibsoni is a tick-borne hemoprotozoan parasite of dogs that often causes fever and hemolytic illness. Detection of B. gibsoni has been predominantly reported in Asian countries, including Japan, Korea, Taiwan, Malaysia, Bangladesh and India. The present study shows the first molecular characterization of B. gibsoni detected from dogs in Bangladesh. Blood samples were collected on FTA® Elute cards from 50 stray dogs in Mymensingh District in Bangladesh. DNA eluted from the cards was subjected to nested PCR for the 18S rRNA gene of Babesia species. Approximately 800bp PCR products were detected in 15 of 50 dogs (30%). Based on restriction fragment length polymorphism (RFLP) and direct sequencing of the PCR products, all parasite isolates were identified as B. gibsoni. Furthermore, the BgTRAP (B. gibsoni thrombospondin-related adhesive protein) gene fragments were detected in 13 of 15 18S rRNA gene PCR positive blood samples. Phylogenetic analysis of the BgTRAP gene revealed that B. gibsoni parasites in Bangladesh formed a cluster, which was genetically different from other Asian B. gibsoni isolates. In addition, tandem repeat analysis of the BgTRAP gene clearly showed considerable genetic variation among Bangladeshi isolates. These results suggested that B. gibsoni parasites in a different genetic clade are endemic in dogs in Bangladesh. Further studies are required to elucidate the origin, distribution, vector and pathogenesis of B. gibsoni parasites circulating in dogs in Bangladesh.

Genetic characterisation of the rabies virus vaccine strains used for oral immunization of foxes in Poland to estimate the effectiveness of vaccination

The main reservoir of rabies virus in Poland has been the red fox. To control rabies in wildlife, oral immunization of foxes was introduced in 1993. The vaccine is effective when it confers immunity against the virus circulating in the environment. To assess the above issue, a study of the molecular characteristics of 570-bp fragments of the N and G genes of vaccine strains SAD B19 and SAD Bern against street virus strains was performed. The results confirmed the similarity of the vaccine strains and rabies virus strains circulating in the environment and also demonstrate the genetic stability of vaccine strains that have been distributed in Poland for 20 years.

Prophylaxis of human hydrophobia in South Korea

Domestic human hydrophobia has not been reported since the one case of 2004 in South Korea, but still a few animal rabies occur persistently since the reemerging stage of rabies from 1993. The government has made efforts to control animal rabies in many aspects, but whether prophylactic strategy for human hydrophobia is performed adequately is in question. The rate of proper post-exposure prophylaxis for animal bite case in 'high-risk region' of rabies is very low with 20% between 2011 and 2013. The National Animal Bite Patient Surveillance targeting 'high-risk region' is missing out animal bite cases who visit directly to hospitals in 'suspect-risk region' of rabies. Little data seems to exist for pre-exposure prophylaxis of domestic hydrophobia. Danger of reoccurrence of human hydrophobia always remain in South Korea. The medical personnel needs to have greater interest on the matter and the government strengthen the management system.

A single immunization with recombinant rabies virus (ERAG3G) confers complete protection against rabies in mice

Purpose

New alternative bait rabies vaccines applicable to pet dogs and wild animals are needed to eradicate rabies in Korea. In this study, recombinant rabies virus, ERAG3G strain was constructed using reverse genetic system and the safety, efficacy and immunogenicity of the ERAG3G strain was evaluated in mice and dogs.

Materials and Methods

Using the full-length genome mutated amino acid at position 333 of glycoprotein of rabies virus (RABV) and helper plasmids, the ERAG3G strain was rescued in BHK/T7-9 cells successfully. Mice were inoculated with the ERAG3G strain for safety and efficacy. Safety and immunogenicity of the dog inoculated with the ERAG3G strain (1 mL, 10^8.0 FAID₅₀/mL) via intramuscular route was evaluated for 28 days after inoculation.

Results

The ERAG3G strain rescued by reverse genetic system was propagated well in the mouse neuroblastoma cells revealing titer of 10^8.5 FAID₅₀/mL and was not pathogenic to 4- or 6-week-old mice that received by intramuscular or intracranical route. Immunization with the ERAG3G strain conferred complete protection from lethal RABV in mice. Dogs inoculated with the vaccine candidate via intramuscular route showed high neutralizing antibody titer ranging from 2.62 to 23.9 IU/mL at 28 days postinoculation.

Conclusion

Our findings suggest that the ERAG3G strain plays an important role in inducing protective efficacy in mice and causes to arise anti-rabies neutralizing antibody in dogs.

Limited brain metabolism changes differentiate between the progression and clearance of rabies virus

Central nervous system (CNS) metabolic profiles were examined from rabies virus (RABV)-infected mice that were either mock-treated or received post-exposure treatment (PET) with a single dose of the live recombinant RABV vaccine TriGAS. CNS tissue harvested from mock-treated mice at middle and late stage infection revealed numerous changes in energy metabolites, neurotransmitters and stress hormones that correlated with replication levels of viral RNA. Although the large majority of these metabolic changes were completely absent in the brains of TriGAS-treated mice most likely due to the strong reduction in virus spread, TriGAS treatment resulted in the up-regulation of the expression of carnitine and several acylcarnitines, suggesting that these compounds are neuroprotective. The most striking change seen in mock-treated RABV-infected mice was a dramatic increase in brain and serum corticosterone levels, with the later becoming elevated before clinical signs or loss of body weight occurred. We speculate that the rise in corticosterone is part of a strategy of RABV to block the induction of immune responses that would otherwise interfere with its spread. In support of this concept, we show that pharmacological intervention to inhibit corticosterone biosynthesis, in the absence of vaccine treatment, significantly reduces the pathogenicity of RABV. Our results suggest that widespread metabolic changes, including hypothalamic-pituitary-adrenal axis activation, contribute to the pathogenesis of RABV and that preventing these alterations early in infection with PET or pharmacological blockade helps protect brain homeostasis, thereby reducing disease mortality.

A recombinant rabies virus encoding two copies of the glycoprotein gene confers protection in dogs against a virulent challenge

The rabies virus (RABV) glycoprotein (G) is the principal antigen responsible for the induction of virus neutralizing antibodies (VNA) and is the major modality of protective immunity in animals. A recombinant RABV HEP-Flury strain was generated by reverse genetics to encode two copies of the G-gene (referred to as HEP-dG). The biological properties of HEP-dG were compared to those of the parental virus (HEP-Flury strain). The HEP-dG recombinant virus grew 100 times more efficiently in BHK-21 cell than the parental virus, yet the virulence of the dG recombinant virus in suckling mice was lower than the parental virus. The HEP-dG virus can improve the expression of G-gene mRNA and the G protein and produce more offspring viruses in cells. The amount of G protein revealed a positive relationship with immunogenicity in mice and dogs. The inactivated HEP-dG recombinant virus induced higher levels of VNA and conferred better protection against virulent RABV in mice and dogs than the inactivated parental virus and a commercial vaccine. The protective antibody persisted for at least 12 months. These data demonstrate that the HEP-dG is stable, induces a strong VNA response and confers protective immunity more effectively than the RABV HEP-Flury strain. HEP-dG could be a potential candidate in the development of novel inactivated rabies vaccines.

Intramuscular inoculation of mice with the live-attenuated recombinant rabies virus TriGAS results in a transient infection of the draining lymph nodes and a robust, long-lasting protective immune response against rabies

A single intramuscular application of the live but not UV-inactivated recombinant rabies virus (RABV) variant TriGAS in mice induces the robust and sustained production of RABV-neutralizing antibodies that correlate with long-term protection against challenge with an otherwise lethal dose of the wild-type RABV. To obtain insight into the mechanism by which live TriGAS induces long-lasting protective immunity, quantitative PCR (qPCR) analysis of muscle tissue, draining lymph nodes, spleen, spinal cord, and brain at different times after TriGAS inoculation revealed the presence of significant copy numbers of RABV-specific RNA in muscle, lymph node, and to a lesser extent, spleen for several days postinfection. Notably, no significant amounts of RABV RNA were detected in brain or spinal cord at any time after TriGAS inoculation. Differential qPCR analysis revealed that the RABV-specific RNA detected in muscle is predominantly genomic RNA, whereas RABV RNA detected in draining lymph nodes is predominantly mRNA. Comparison of genomic RNA and mRNA obtained from isolated lymph node cells showed the highest mRNA-to-genomic-RNA ratios in B cells and dendritic cells (DCs), suggesting that these cells represent the major cell population that is infected in the lymph node. Since RABV RNA declined to undetectable levels by 14 days postinoculation of TriGAS, we speculate that a transient infection of DCs with TriGAS may be highly immunostimulatory through mechanisms that enhance antigen presentation. Our results support the superior efficacy and safety of TriGAS and advocate for its utility as a vaccine.

The present and future of rabies vaccine in animals

An effective strategy for preventing rabies consists of controlling rabies in the host reservoir with vaccination. Rabies vaccine has proven to be the most effective weapon for coping with this fatal viral zoonotic disease of warm-blooded animals, including human. Natural rabies infection of an individual is always associated with exposure to rabid animals, and the duration of clinical signs can vary from days to months. The incubation period for the disease depends on the site of the bite, severity of injury, and the amount of infecting virus at the time of exposure. The mortality of untreated cases in humans is 100%. Over the last 100 years, various rabies vaccines have been developed and used to prevent or control rabies in animals, such as modified live vaccine, inactivated rabies vaccine, and oral modified live vaccine. These have proved safe and efficacious worldwide. New-generation rabies vaccines, including recombinant rabies virus-based vaccines, vectored vaccines, DNA-based vaccines, and plant vaccines, have been explored to overcome the limitations of conventional rabies vaccines. This article discusses current and next-generation rabies vaccines in animals.

A novel rabies vaccine based on a recombinant parainfluenza virus 5 expressing rabies virus glycoprotein

Untreated rabies virus (RABV) infection leads to death. Vaccine and postexposure treatment have been effective in preventing RABV infection. However, due to cost, rabies vaccination and treatment have not been widely used in developing countries. There are 55,000 human death caused by rabies annually. An efficacious and cost-effective rabies vaccine is needed. Parainfluenza virus 5 (PIV5) is thought to contribute to kennel cough, and kennel cough vaccines containing live PIV5 have been used in dogs for many years. In this work, a PIV5-vectored rabies vaccine was tested in mice. A recombinant PIV5 encoding RABV glycoprotein (G) (rPIV5-RV-G) was administered to mice via intranasal (i.n.), intramuscular (i.m.), and oral inoculation. The vaccinated mice were challenged with a 50% lethal challenge dose (LD(50)) of RABV challenge virus standard 24 (CVS-24) intracerebrally. A single dose of 10(6) PFU of rPIV5-RV-G was sufficient for 100% protection when administered via the i.n. route. The mice vaccinated with a single dose of 10(8) PFU of rPIV5-RV-G via the i.m. route showed very robust protection (90% to 100%). Intriguingly, the mice vaccinated orally with a single dose of 10(8) PFU of rPIV5-RV-G showed a 50% survival rate, which is comparable to the 60% survival rate among mice inoculated with an attenuated rabies vaccine strain, recombinant LBNSE. This is first report of an orally effective rabies vaccine candidate in animals based on PIV5 as a vector. These results indicate that rPIV5-RV-G is an excellent candidate for a new generation of recombinant rabies vaccine for humans and animals and PIV5 is a potential vector for oral vaccines.

Developments in rabies vaccines

The development of vaccines that prevent rabies has a long and distinguished history, with the earliest preceding modern understanding of viruses and the mechanisms of immune protection against disease. The correct application of inactivated tissue culture-derived vaccines is highly effective at preventing the development of rabies, and very few failures are recorded. Furthermore, oral and parenteral vaccination is possible for wildlife, companion animals and livestock, again using inactivated tissue culture-derived virus. However, rabies remains endemic in many regions of the world and causes thousands of human deaths annually. There also remain no means of prophylaxis for rabies once the virus enters the central nervous system (CNS). One reason for this is the poor immune response within the CNS to infection with rabies virus (RABV). New approaches to vaccination using modified rabies viruses that express components of the innate immune system are being applied to this problem. Preliminary reports suggest that direct inoculation of such viruses could trigger an effective anti-viral response and prevent a fatal outcome from RABV infection.

6th International Conference on Emerging Zoonoses

The 6th International Conference on Emerging Zoonoses, held at Cancun, Mexico, 24-27 February 2011, offered 84 participants from 18 countries, a snapshot of current research in numerous zoonoses caused by viruses, bacteria or prions. Co-chaired by Professors Heinz Feldmann and Jürgen Richt, the conference explored 10 topics: (i) The ecology of emerging zoonotic diseases; (ii) The role of wildlife in emerging zoonoses; (iii) Cross-species transmission of zoonotic pathogens; (iv) Emerging and neglected influenza viruses; (v) Haemorrhagic fever viruses; (vi) Emerging bacterial diseases; (vii) Outbreak responses to zoonotic diseases; (viii) Food-borne zoonotic diseases; (ix) Prion diseases; and (x) Modelling and prediction of emergence of zoonoses. Human medicine, veterinary medicine and environmental challenges are viewed as a unity, which must be considered under the umbrella of 'One Health'. Several presentations attempted to integrate the insights gained from field data with mathematical models in the search for effective control measures of specific zoonoses. The overriding objective of the research presentations was to create, improve and use the tools essential to address the risk of contagions in a globalized society. In seeking to fulfil this objective, a three-step approach has often been applied: (i) use cultured cells, model and natural animal hosts and human clinical models to study infection; (ii) combine traditional histopathological and biochemical approaches with functional genomics, proteomics and computational biology; and (iii) obtain signatures of virulence and insights into mechanisms of host defense response, immune evasion and pathogenesis. This meeting review summarizes 39 of the conference presentations and mentions briefly the 16 articles in this Special Supplement, most of which were presented at the conference in earlier versions. The full affiliations of all presenters and many colleagues have been included to facilitate further inquiries from readers.