Street Alabama Dufferin Research Articles

Vaccine-induced Rabies in a Red Fox in Poland.

Rabies as a zoonosis threatens public health worldwide. Several thousand people die each year of infections by the rabies virus (RABV). Oral rabies vaccination (ORV) of wildlife was successfully implemented in many European countries and led to rabies being brought under control there. In Poland, ORV was introduced in 1993 using vaccines containing an attenuated strain of the rabies virus. However, attenuated rabies viruses may have residual pathogenicity and cause the disease in target and non-target animals. A red fox carcass was tested as part of national rabies surveillance, and its brain was screened for RABV infection using two conjugates and a fluorescent antibody test (FAT). The rabies virus was isolated in mouse neuroblastoma cells by rabies tissue culture infection test (RTCIT), and viral RNA was detected by heminested reverse transcriptase PCR (hnRT-PCR) as well as by quantitative real-time RT-PCR (rtRT-qPCR). An amplicon of 600 bp was subjected to Sanger sequencing. To differentiate between vaccine and field RABV strains, PCR-restriction fragment length polymorphism (PCR-RFLP) using the Dra I, Msp I, Nla IV and Mbo II restriction endonucleases was performed. The rabies virus was detected in the fox's brain using FAT, RTCIT and molecular tests. The PCR-RFLP revealed of vaccine-induced rabies, and full-length genome analysis showed 100% nucleotide sequence identity of the isolate with the reference sequences of Street Alabama Dufferin Bern (SAD Bern) vaccine strains and other vaccine-induced rabies virus isolates detected in animals and deposited in GenBank. We detected vaccine-induced rabies for the first time in Poland in a fox during routine rabies surveillance.

The Successful Elimination of Sylvatic Rabies Using Oral Vaccination of Foxes in Slovenia.

Sylvatic rabies was present in Slovenia between 1973 and 2013, with the red fox as the main reservoir of the rabies virus. The first oral rabies vaccination (ORV) control program in foxes started in 1988, using the manual distribution of baits. Significant improvement of fox vaccination was achieved with the aerial distribution of baits, starting in 1995 and successfully finished with the final, fifty-ninth vaccination campaign in 2019. Between 1979 and 2019, a total of 86,471 samples were tested, and 10,975 (12.69%) rabies-positive animals were identified. Within the ORV, two different vaccines were used, containing modified live virus strain Street Alabama Dufferin (SAD) B19 and SAD Bern, while the last ORV campaigns were completed in 2019, with a vaccine containing a genetically modified strain of SPBN GASGAS. Molecular epidemiological studies of 95 rabies-positive samples, originating from red foxes, badgers, cattle, dogs, martens, cats, and horses, revealed a low genetic diversity of circulating strains and high similarity to strains from neighboring countries. During the elimination program, few vaccine-induced rabies cases were detected: three in red foxes and one case in a marten, with no epidemiological relevance. Slovenia has been officially declared a country free of rabies since 2016.

Population- and Variant-Based Genome Analyses of Viruses from Vaccine-Derived Rabies Cases Demonstrate Product Specific Clusters and Unique Patterns.

Rabies in wildlife has been successfully controlled in parts of Europe and North America using oral rabies vaccination, i.e., the distribution of baits containing live-attenuated virus strains. Occasionally, these vaccines caused vaccine virus-induced rabies cases. To elucidate the mechanisms of genetic selection and the effect of viral populations on these rabies cases, a next generation sequencing approach as well as comprehensive data analyses of the genetic diversity of Street Alabama Dufferin (SAD) and ERA vaccine virus strains and vaccine-induced rabies cases from Canada and several European countries were conducted. As a result, twelve newly generated sets of sequencing data from Canada and Poland were added to a pool of previously investigated samples. While the population-based analysis showed a segregation of viruses of ERA vaccine-induced rabies cases from those of SAD Bern original (SAD Bernorig)-derived rabies cases, the in-depth variant analysis revealed three distinct combinations of selected variants for the ERA vaccine-induced cases, suggesting the presence of multiple replication-competent haplotypes in the investigated ERA-BHK21 vaccine. Our findings demonstrate the potential of a deep sequencing approach in combination with comprehensive analyses on the consensus, population, and variant level.

In-depth genome analyses of viruses from vaccine-derived rabies cases and corresponding live-attenuated oral rabies vaccines

Live-attenuated rabies virus strains such as those derived from the field isolate Street Alabama Dufferin (SAD) have been used extensively and very effectively as oral rabies vaccines for the control of fox rabies in both Europe and Canada. Although these vaccines are safe, some cases of vaccine-derived rabies have been detected during rabies surveillance accompanying these campaigns. In recent analysis it was shown that some commercial SAD vaccines consist of diverse viral populations, rather than clonal genotypes. For cases of vaccine-derived rabies, only consensus sequence data have been available to date and information concerning their population diversity was thus lacking.In our study, we used high-throughput sequencing to analyze 11 cases of vaccine-derived rabies, and compared their viral population diversity to the related oral rabies vaccines using pairwise Manhattan distances. This extensive deep sequencing analysis of vaccine-derived rabies cases observed during oral vaccination programs provided deeper insights into the effect of accidental in vivo replication of genetically diverse vaccine strains in the central nervous system of target and non-target species under field conditions. The viral population in vaccine-derived cases appeared to be clonal in contrast to their parental vaccines. The change from a state of high population diversity present in the vaccine batches to a clonal genotype in the affected animal may indicate the presence of a strong bottleneck during infection. In conclusion, it is very likely that these few cases are the consequence of host factors and not the result of the selection of a more virulent genotype. Furthermore, this type of vaccine-derived rabies leads to the selection of clonal genotypes and the selected variants were genetically very similar to potent SAD vaccines that have undergone a history of in vitro selection.

In-Depth Characterization of Live Vaccines Used in Europe for Oral Rabies Vaccination of Wildlife.

Although rabies incidence has fallen sharply over the past decades in Europe, the disease is still present in Eastern Europe. Oral rabies immunization of wild animal rabies has been shown to be the most effective method for the control and elimination of rabies. All rabies vaccines used in Europe are modified live virus vaccines based on the Street Alabama Dufferin (SAD) strain isolated from a naturally-infected dog in 1935. Because of the potential safety risk of a live virus which could revert to virulence, the genetic composition of three commercial attenuated live rabies vaccines was investigated in two independent laboratories using next genome sequencing. This study is the first one reporting on the diversity of variants in oral rabies vaccines as well as the presence of a mix of at least two different variants in all tested batches. The results demonstrate the need for vaccine producers to use new robust methodologies in the context of their routine vaccine quality controls prior to market release.

A strategy to simultaneously eradicate the natural reservoirs of rabies and Ebola virus

Evaluation of: Blaney JE, Wirblich C, Papaneri AB et al. Inactivated or live-attenuated bivalent vaccines that confer protection against rabies and Ebola viruses. J. Virol. 85(20), 10605–10616 (2011).The efficacy of a recombinant live-attenuated or chemically inactivated bivalent vaccine against rabies virus (RABV) and Ebola virus (EBOV) infection was evaluated in a lethal mouse model of infection. The vaccines were derived from the live-attenuated Street Alabama Dufferin B19 RABV platform already approved for veterinary use, where intramuscular, intranasal and intraperitoneal administration of the recombinant vaccines were avirulent in adult mice. Significant levels of serum RABV- and EBOV-specific antibodies were observed postvaccination, with levels that correlated with protection in vaccinated mice post-RABV or -EBOV challenge. These results justify further studies in guinea pigs and nonhuman primates, and highlight a promising strategy to eradicate the natural reservoirs of RABV and EBOV.

Analysis of vaccine-virus-associated rabies cases in red foxes (Vulpes vulpes) after oral rabies vaccination campaigns in Germany and Austria

To eradicate rabies in foxes, almost 97 million oral rabies vaccine baits have been distributed in Germany and Austria since 1983 and 1986, respectively. Since 2007, no terrestrial cases have been reported in either country. The most widely used oral rabies vaccine viruses in these countries were SAD (Street Alabama Dufferin) strains, e.g. SAD B19 (53.2%) and SAD P5/88 (44.5%). In this paper, we describe six possible vaccine-virus-associated rabies cases in red foxes (Vulpes vulpes) detected during post-vaccination surveillance from 2001 to 2006, involving two different vaccines and different batches. Compared to prototypic vaccine strains, full-genome sequencing revealed between 1 and 5 single nucleotide alterations in the L gene in 5 of 6 SAD isolates, resulting in up to two amino acid substitutions. However, experimental infection of juvenile foxes showed that those mutations had no influence on pathogenicity. The cases described here, coming from geographically widely separated regions, do not represent a spatial cluster. More importantly, enhanced surveillance showed that the vaccine viruses involved did not become established in the red fox population. It seems that the number of reported vaccine virus-associated rabies cases is determined predominantly by the intensity of surveillance after the oral rabies vaccination campaign and not by the selection of strains.

Genetic characterisation of attenuated SAD rabies virus strains used for oral vaccination of wildlife

The elimination of rabies from the red fox ( Vulpes vulpes) in Western Europe has been achieved by the oral rabies vaccination (ORV) of wildlife with a range of attenuated rabies virus strains. With the exception of the vaccinia rabies glycoprotein recombinant vaccine (VRG), all strains were originally derived from a common ancestor; the Street Alabama Dufferin (SAD) field strain. However, after more than 30 years of ORV it is still not possible to distinguish these vaccine strains and there is little information on the genetic basis for their attenuation. We therefore sequenced and compared the full-length genome of five commercially available SAD vaccine viruses (SAD B19, SAD P5/88, SAG2, SAD VA1 and SAD Bern) and four other SAD strains (the original SAD Bern, SAD VA1, ERA and SAD 1-3670 Wistar). Nucleotide sequencing allowed identifying each vaccine strain unambiguously. Phylogenetic analysis revealed that the majority of the currently used commercial attenuated rabies virus vaccines appear to be derived from SAD B19 rather than from SAD Bern. One commercially available vaccine virus did not contain the SAD strain mentioned in the product information of the producer. Two SAD vaccine strains appeared to consist of mixed genomic sequences. Furthermore, in-del events targeting A-rich sequences (in positive strand) within the 3′ non-coding regions of M and G genes were observed in SAD-derivates developed in Europe. Our data also supports the idea of a possible recombination that had occurred during the derivation of the European branch of SAD viruses. If confirmed, this recombination event would be the first one reported among RABV vaccine strains.

Humoral and cell-mediated immune responses of foxes ( Vulpes vulpes) after experimental primary and secondary oral vaccination using SAG 2 and V-RG vaccines

Humoral and cell-mediated immune responses of 36 captive foxes to two oral vaccines against rabies currently used for foxes in Europe were studied. The Street Alabama Dufferin (SAD) mutant Gif (SAG 2) vaccine has been selected by double mutation from the SAD virus. The vaccinia recombinant virus (V-RG) expresses the rabies glycoprotein. Both vaccines induce similar humoral and cell-mediated responses after primary and secondary oral administration. We observed a typical anamnestic response, although of a limited duration, after the booster vaccination. Therefore, our results suggested that two successive oral vaccination campaigns should not significantly improve the immunisation of foxes. Lymphocyte in vitro proliferative response to the SAD antigen highlighted the presence in blood of a T-cell specific memory 6 months after vaccination. The synthesis of several vulpine cytokines was detected in peripheral blood mononuclear cells (PBMC) stimulated by SAD antigen via reverse transcription polymerase chain amplification. The data showed a concomitant expression of interleukin (IL)-4 and interferon-γ in PBMC of vaccinated foxes. No change was detected in the level of IL-2, IL-10 and IL-12 synthesis, whereas the pro-inflammatory cytokine tumour necrosis factor-α seemed involved in the activation of naive T lymphocytes.

ELISA test for rabies antibody titration in orally vaccinated foxes sampled in the fields

The assessment of the efficacy of rabies oral vaccination campaigns requires the titration of specific antibodies in the target species. Unfortunately, in Continental Europe, most fox serum samples are in fact “body fluids” taken from cadavers and the lack of a validated titration method for these poor quality sera made it impossible to survey and compare the efficacy of various oral vaccination protocols used by the different European teams. By using ready to use microplates sensitised with rabies virus glycoprotein purchased from a manufacturer and applying a simple and rapid ELISA technique on field fox sera, we obtained antibody quantitation highly correlated with seroneutralising antibody titres measured with a seroneutralisation test on cell culture. We obtained, with fox sera sampled in the same area, the same distribution of high, medium and low titres within all categories of serum quality (from high to very poor quality) and therefore conclude that this ELISA test allows a reliable titration even with highly contaminated body fluids. This test was shown to be equally capable of detecting rabies antibodies in serum samples taken from foxes vaccinated with an highly attenuated rabies virus (the SAG2 double mutant of the Street Alabama Dufferin strain) or with the VRG, the Vaccinia recombinant glycoprotein. Additionally, a strong correlation was demonstrated between titres given by this ELISA (or by the seroneutralisation test) and protection against challenge of foxes orally vaccinated with SAG2 vaccine baits. In view of this validation, this simple and reliable test is proposed for sero-surveying foxes following rabies oral vaccination campaigns.

Oral immunization of wildlife against rabies: concept and first field experiments.

The possibility of immunizing carnivores against rabies with live attenuated vaccine administered by the oral route was raised by North American scientists in the 1960s. Subsequently, several American and European teams tested different vaccine strains in the laboratory for efficacy and safety and studied vaccine stabilization, vaccine delivery systems, bait acceptance by wild animals, and bait distribution schemes. The first field trial of a cloned SAD (Street Alabama Dufferin) strain in baits designed to immunize foxes orally was conducted in an Alpine valley in Switzerland in 1978. A population containing approximately 60% immune foxes at the valley entrance stopped the spread of the disease into untreated upper parts of the valley. The strategic use of oral vaccination of foxes in additional regions of Switzerland resulted in freedom from the zoonosis in four-fifths of the country.

Current oral rabies vaccination in Europe: an interim balance.

The field trial for the oral immunization of foxes against rabies in the Federal Republic of Germany began in 1983 and since the end of 1985 has had the specific goal of the elimination of rabies in large interdependent areas of that country. To meet this goal it was necessary to develop methods for the large-scale production of the SAD (Street Alabama Dufferin) clone B19 vaccine as well as to develop a bait that could be mass-produced (the Tübingen fox bait). It has been shown that after a single vaccination campaign in the field approximately 75% of the fox population is immune to rabies and that after one or two repeated campaigns vaccination in many areas could be discontinued. Participation in the field trial in circumscribed border areas was extended to Italy in 1985 and to Austria, Luxembourg, Belgium, and France in 1986. For the first time, through the use of oral immunization, a method for the elimination of rabies is available that is effective, safe, inexpensive, and practical. Further, this method meets the requirements of animal-protection societies, does not interfere with the preservation of endangered species, and therefore represents a significant political factor.

Evaluation of the single radial-immunodiffusion assay for measuring the glycoprotein content of rabies vaccines

The glycoprotein content of rabies vaccines containing the Pitman—Moore strain of rabies virus was measured by the single radial immunodiffusion assay and correlated with vaccine potency. The variability of this assay was 6·3% for a single vaccine lot tested over a one-year period. Using sera prepared against rabies virus glycoprotein from different strains of virus, the assay gave different values. These differences could be eliminated by using a homologous vaccine strain as an internal reference. Single radial-immunodiffusion values for Pitman—Moore vaccines correlated with the manufacturers' NIH potency assay, but required a mathematical transformation to convert values from one assay to the other. Single radial-immunodiffusion values for Street Alabama Dufferin and Flury-LEP vaccines did not correlate with NIH values. Modification of the single radial immunodiffusion technique and the feasibility of using this assay for the determination of rabies vaccine potency are discussed.