Sickness and recovery of dogs challenged with a street rabies virus after vaccination with a vaccinia virus recombinant expressing rabies virus N protein

Risks related to a possible reduction of the waiting period for dogs after rabies antibody titration to 30 days compared with 90 days of the current EU legislative regime

EFSA received a mandate from the European Commission to assess the risks related to a possible reduction of the waiting period after rabies antibody titration test to 30 days compared with 90 days of the current EU legislation, for dogs moving from certain non-EU countries to the EU. This Scientific Report assessed the probability of introduction of rabies into the EU through commercial and non-commercial movements of vaccinated dogs with a positive titration test (≥ 0.5 IU/mL) if the waiting period decreases from 90 to 30 days. Assuming that all the legal requirements are complied with, the risk of transmission of rabies through the movement of a vaccinated dog is related to the risk of introducing an animal incubating rabies that was infected before the day of vaccination or shortly after vaccination but before the development of immunity (21 days post-vaccination). Using published data on the incubation period for experimental and field cases in dogs and considering the rabies incidence data in certain countries, the aggregated probability for the annual introduction of rabies through dogs was assessed. Considering the uncertainty related to the duration of the incubation period, the number of imported dogs, and the disease incidence in some countries it was concluded with a 95% certainty that the maximum number of rabies-infected imported dogs complying with the regulations in a 20-year period could increase from 5 to 20 when decreasing the waiting period from 90 to 30 days. Nevertheless, the potential impact of even a small increase in probability means the risk is increased for a region like the EU where rabies has long been a focus for eradication, to protect human and animal health.

Modelling the factors affecting the probability for local rabies elimination by strategic control

Dog rabies has been recognized from ancient times and remains widespread across the developing world with an estimated 59,000 people dying annually from the disease. In 2011 a tri-partite alliance consisting of the OIE, the WHO and the FAO committed to globally eliminating dog-mediated human rabies by 2030. Regardless of global support, the responsibility remains with local program managers to implement successful elimination programs. It is well known that vaccination programs have a high probability of successful elimination if they achieve a population-coverage of 70%. It is often quoted that reducing population turnover (typically through sterilizations) raises the probability for local elimination by maintaining herd immunity for longer. Besides this, other factors that affect rabies elimination are rarely mentioned. This paper investigates the probability for local elimination as it relates to immunity, fecundity, dog population size, infectivity (bite rates), in-migration of immune-naïve dogs, and the initial incidence. To achieve this, an individual-based, stochastic, transmission model was manipulated to create a dataset covering combinations of factors that may affect elimination. The results thereof were analysed using a logistic regression model with elimination as the dependent variable. Our results suggest that smaller dog populations, lower infectivity and lower incidence (such as when epidemics start with single introductions) strongly increased the probability for elimination at wide ranges of vaccination levels. Lower fecundity and lower in-migration had weak effects. We discuss the importance of these findings in terms of their impact and their practical application in the design of dog-mediated rabies control programs.

Most guidelines for rabies control call for at least 70% vaccination coverage of dogs. This level of immunity has a very high probability for the local elimination of rabies, but it is often not an achievable ideal due to resource constraints. Campaign managers can be strategic on how they allocate their resources. Lower infectivity rates are present in areas with more restricted dog movements and have higher probabilities for elimination at lower vaccination rates. Smaller sub-populations have higher probabilities for elimination at the same vaccination coverage levels compared to larger sub-populations. Vaccinating immune corridors can divide meta-populations into smaller sub-populations that are likely to result in elimination either due to their small size or due to the local low infectivity. Areas already free of rabies require lower vaccination levels to maintain freedom compared to endemic areas. Where donors do not specifically require sterilization campaigns, funds meant for rabies control should not be diverted to sterilizations.

A next generation vaccine against human rabies based on a single dose of a chimpanzee adenovirus vector serotype C

Rabies, caused by RNA viruses in the Genus Lyssavirus, is the most fatal of all infectious diseases. This neglected zoonosis remains a major public health problem in developing countries, causing the death of an estimated 25,000-159,000 people each year, with more than half of them in children. The high incidence of human rabies in spite of effective vaccines is mainly linked to the lack of compliance with the complicated administration schedule, inadequacies of the community public health system for local administration by the parenteral route and the overall costs of the vaccine. The goal of our work was the development of a simple, affordable and effective vaccine strategy to prevent human rabies virus infection. This next generation vaccine is based on a replication-defective chimpanzee adenovirus vector belonging to group C, ChAd155-RG, which encodes the rabies glycoprotein (G). We demonstrate here that a single dose of this vaccine induces protective efficacy in a murine model of rabies challenge and elicits strong and durable neutralizing antibody responses in vaccinated non-human primates. Importantly, we demonstrate that one dose of a commercial rabies vaccine effectively boosts the neutralizing antibody responses induced by ChAd155-RG in vaccinated monkeys, showing the compatibility of the novel vectored vaccine with the current post-exposure prophylaxis in the event of rabies virus exposure. Finally, we demonstrate that antibodies induced by ChAd155-RG can also neutralize European bat lyssaviruses 1 and 2 (EBLV-1 and EBLV-2) found in bat reservoirs.

Comparison of the protective efficacy between single and combination of recombinant adenoviruses expressing complete and truncated glycoprotein, and nucleoprotein of the pathogenic street rabies virus in mice

Background

Rabies is an important viral zoonosis that causes acute encephalitis and death in mammals. To date, several recombinant vaccines have been developed based on G protein, which is considered to be the main antigen, and these vaccines are used for rabies control in many countries. Most recombinant viruses expressing RABV G protein retain the G gene from attenuated RABV. Not enough is currently known about the protective effect against RABV of a combination of recombinant adenoviruses expressing the G and N proteins of pathogenic street RABV.

Methods

We constructed a recombinant adenovirus (Ad-0910Gsped) expressing the signal peptide and ectodomain (sped) of G protein of the Korean street strain, and evaluated the immunological protection conferred by a single and combination of three kinds of recombinant adenoviruses (Ad-0910Gsped and Ad-0910G with or without Ad-0910 N) in mice.

Results

A combination of Ad-0910G and Ad-0910 N conferred improved immunity against intracranial challenge compared to single administration of Ad-0910G. The Ad-0910G virus, expressing the complete G protein, was more immunogenic than Ad-0910Gsped, which expressed a truncated G protein with the transmembrane and cytoplasmic domains removed. Additionally, oral vaccination using a combination of viruses led to complete protection.

Conclusions

Our results suggest that this combination of viruses is a viable new intramuscular and oral vaccine candidate.

Differential Host Immune Responses after Infection with Wild-Type or Lab-Attenuated Rabies Viruses in Dogs

METHODOLOGY/PRINCIPAL FINDINGS

The experimental infection of dogs with TriGAS induced high levels of VNA in the serum, whereas wt RABV infection did not. Dogs infected with TriGAS developed antibodies against the virus including its glycoprotein, whereas dogs infected with DRV-NG11 only developed rabies antibodies that are presumably specific for the nucleoprotein, (N) and not the glycoprotein (G). We show that infection with TriGAS induces early activation of B cells in the draining lymph nodes and persistent activation of DCs and B cells in the blood. On the other hand, infection with DRV-NG11 fails to induce the activation of DCs and B cells and further reduces CD4 T cell production. Further, we show that intrathecal (IT) immunization of TriGAS not only induced high levels of VNA in the serum but also in the CSF while intramuscular (IM) immunization of TriGAS induced VNA only in the serum. In addition, high levels of total protein and WBC were detected in the CSF of IT immunized dogs, indicating the transient enhancement of blood-brain barrier (BBB) permeability, which is relevant to the passage of immune effectors from periphery into the CNS.

CONCLUSIONS/SIGNIFICANCE

IM infection of dogs with TriGAS induced the production of serum VNA whereas, IT immunization of TriGAS in dogs induces high levels of VNA in the periphery as well as in the CSF and transiently enhances BBB permeability. In contrast, infection with wt DRV-NG11 resulted in the production of RABV-reactive antibodies but VNA and antibodies specific for G were absent. As a consequence, all of the dogs infected with wt DRV-NG11 succumbed to rabies. Thus the failure to activate protective immunity is one of the important features of RABV pathogenesis in dogs.

Confirmation of a new conserved linear epitope of Lyssavirus nucleoprotein

Bioinformatics analysis was used to predict potential epitopes of Lyssavirus nucleoprotein and highlighted some distinct differences in the quantity and localization of the epitopes disclosed by epitope analysis of monoclonal antibodies against Lyssavirus nucleoprotein. Bioinformatics analysis showed that the domain containing residues 152-164 of Lyssavirus nucleoprotein was a conserved linear epitope that had not been reported previously. Immunization of two rabbits with the corresponding synthetic peptide conjugated to the Keyhole Limpe hemocyanin (KLH) macromolecule resulted in a titer of anti-peptide antibody above 1:200,000 in rabbit sera as detected by indirect enzyme-linked immunosorbent assay (ELISA). Western blot analysis demonstrated that the anti-peptide antibody recognized denatured Lyssavirus nucleoprotein in sodium dodecylsulfonate-polyacrylate gel electrophoresis (SDS-PAGE). Affinity chromatography purification and FITC-labeling of the anti-peptide antibody in rabbit sera was performed. FITC-labeled anti-peptide antibody could recognize Lyssavirus nucleoprotein in BSR cells and canine brain tissues even at a 1:200 dilution. Residues 152-164 of Lyssavirus nucleoprotein were verified as a conserved linear epitope in Lyssavirus.

Molecular epidemiology and a loop-mediated isothermal amplification method for diagnosis of infection with rabies virus in Zambia

The National Livestock Epidemiology and Information Center (NALEIC) in Zambia reported over 132 cases of canine rabies diagnosed by the direct fluorescent antibody test (DFAT) from 2004 to 2009. In this study, the lineage of rabies virus (RABV) in Zambia was determined by phylogenetic analysis of the nucleoprotein (N) and glycoprotein (G) gene sequences. Total RNA was extracted from 87-DFAT brain specimens out of which only 35 (40%) were positive on nested reverse transcription polymerase chain reaction (RT-PCR) for each gene, and 26 being positive for both genes. Positive specimens for the N (n=33) and G (n=35) genes were used for phylogenetic analysis. Phylogenetic analysis of the N gene showed two phylogenetic clusters in Zambia belonging to the Africa 1b lineage present in eastern and southern Africa. While one cluster exclusively comprised Zambian strains, the other was more heterogeneous regarding the RABV origins and included strains from Tanzania, Mozambique and Zambia. Phylogenetic analysis of the G gene revealed similar RABV strains in different hosts and regions of Zambia. We designed primers for reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay from the consensus sequence of the N gene in an attempt to improve the molecular diagnosis of RABV in Zambia. The specificity and reproducibility of the RT-LAMP assay was confirmed with actual clinical specimens. Therefore, the RT-LAMP assay presented in this study may prove to be useful for routine diagnosis of rabies in Zambia.

Post-exposure prophylaxis (PEP) of rabies-infected Indian street dogs

A rabies post-exposure prophylaxis study was carried out to examine the efficacy of two commercially available rabies vaccines and the efficacy of a 5- or 3-dose vaccination regime. Healthy, native breed dogs (N = 40), seronegative for rabies antibody, were challenged intramuscularly with virulent rabies virus brain suspension (10(4.4) MLD50) by direct inoculation into the masseter muscle. The dogs were divided into four equal groups and injected intramuscularly with either Nobivac Rabies (Intervet), Rabisin (Merial) or placebo on multiple occasions (3 or 5-times) over the next 28 days. All dogs were confined in their respective groups for 90 days post-challenge and observed for the development of any clinical signs. Serum samples were assayed for rabies antibody using both the Rapid Fluorescent Focus Inhibition Test (RFFIT) and the Enzyme Linked Immunosorbent Assay (ELISA). None of the vaccinated dogs showed any clinical signs of rabies at any stage of the study. All of their brain tissue samples taken at the end of the study were found negative for rabies viral antigen. Six of the dogs in the control group showed signs of either furious or dumb rabies and died before the end of the study. In all these dogs the diagnosis of rabies was confirmed by means of a specific fluorescent antibody test (FAT) and by the presence of Negri-bodies in brain smears. Four control dogs survived after mild and transient clinical signs showing protective titers at the end of the trial (day 90). Their brain samples were negative for Negri-bodies and in the FAT. Both vaccines were found to be safe and effective in preventing rabies when inoculated intramuscularly applying the 5-dose regime (0, 3, 7, 14 and 28 days). Limited by space only one vaccine could also be tested in a 3-dose schedule. Using this 3-dose regime (0, 5 and 28 days) Nobivac Rabies was also found to be safe and effective in preventing rabies. All vaccinated dogs responded with antibody titers > 0.5 IU by 7 days.

Localization of the antigenic sites of newcastle disease virus nucleocapsid using a panel of monoclonal antibodies

A panel of six monoclonal antibodies (mAbs) against the nucleocapsid (NP) protein of Newcastle disease virus (NDV) was produced by immunization of Balb/c mice with purified recombinant NP protein. Western Blot analysis showed that all the mAbs recognized linearized NP epitopes. Three different NP antigenic sites were identified using deleted truncated NP mutants purified from Escherichia coli. One of the antigenic sites was located at the C-terminal end (residues 441 to 489) of the NP protein. Two other antigenic sites were located within the N-terminal end (residues 26-121 and 122-375). This study demonstrates that the N- and C-terminal ends of the NP proteins are responsible in eliciting immune response, thus it is most likely that these ends are exposed on the NP.

Expression of the rabies virus nucleoprotein in plants at high-levels and evaluation of immune responses in mice

Transgenic plants have been employed successfully as a low-cost system for the production of therapeutically valuable proteins including antibodies, antigens and hormones. Here, we report expression of a full-length nucleoprotein gene of rabies virus in transgenic tomato plants. The nucleoprotein was also transiently expressed in Nicotiana benthamiana plants by agroinfiltration. In both cases, the nucleoprotein was expressed at high levels, 1-5% of total soluble protein in tomato and 45% in N. benthamiana. Previously, only epitopes of the nucleoprotein had been expressed in plants. The presence and expression of the transgene was verified by PCR, Southern, northern and western blots. Mice were immunized both intraperitoneally (i.p.) and orally with tomato protein extracts containing the N protein induced the production of antibodies. The antibody titer of mice immunized i.p., was at least four times higher than that of mice immunized orally. These results were reflected in the challenge experiments where i.p.-immunized mice were partially protected against a peripheral virus challenge whereas orally immunized mice were not. This protection was comparable to that obtained in previous experiments employing different expression systems. Work is in progress to express both G and N proteins in transgenic plants and evaluate protection in mice.

Live vaccinia-rabies virus recombinants, but not an inactivated rabies virus cell culture vaccine, protect B-lymphocyte-deficient A/WySnJ mice against rabies: considerations of recombinant defective poxviruses for rabies immunization of immunocompromised individuals

Presently, commercially available cell culture rabies vaccines for humans and animals consist of the five inactivated rabies virus proteins. The vaccines elicit a CD4+ helper T-cell response and a humoral B-cell response against the viral glycoprotein (G) resulting in the production of virus neutralizing antibody. Antibody against the viral nucleoprotein (N) is also present, but the mechanism(s) of its protection is unclear. HIV-infected individuals with low CD4+ T-lymphocyte counts and individuals undergoing treatment with immunosuppressive drugs have an impaired neutralizing antibody response after pre- and post-exposure immunization with rabies cell culture vaccines. Here we show the efficacy of live vaccinia-rabies virus recombinants, but not a cell culture vaccine consisting of inactivated rabies virus, to elicit elevated levels of neutralizing antibody in B-lymphocyte deficient A/WySnJ mice. The cell culture vaccine also failed to protect the mice, whereas a single immunization of a vaccinia recombinant expressing the rabies virus G or co-expressing G and N equally protected the mice up to 18 months after vaccination. The data suggest that recombinant poxviruses expressing the rabies virus G, in particular replication defective poxviruses such as canarypox or MVA vaccinia virus that undergo abortive replication in non-avian cells, or the attenuated vaccinia virus NYVAC, should be evaluated as rabies vaccines in immunocompromised individuals.

Cross-reactive antigenicity of nucleoproteins of lyssaviruses recognized by a monospecific antirabies virus nucleoprotein antiserum on paraffin sections of formalin-fixed tissues

Diagnosis of rabies is routinely confirmed by detection of rabies virus antigens in acetone-fixed frozen brain tissues or imprint smears using an immunofluorescence method with commercial antirabies virus antibodies. Since recent molecular analyses disclosed wide heterogeneity in the genome sequences of rabies virus strains and related lyssaviruses, it is necessary to confirm the presence of common epitopes in these lyssaviruses. In this study we confirmed the presence of cross-reactive antigens of various lyssaviruses in paraffin sections of formalin-fixed tissue using a monospecific rabbit antiserum prepared by immunization with a recombinant nucleoprotein of rabies virus. By immunohistochemical application, the antigen was detected predominantly in the cytoplasm of neurons in the brains of mice infected with rabies virus, Duvenhage virus, Mokola virus and European bat lyssavirus-1, while no cross-reaction was observed in uninfected humans and animals including dogs, bats, and raccoons. In addition, we examined one autopsy case that was infected in a rabies-endemic nation and developed the clinical manifestation of rabies after returning to Japan in 1970, and found that the antigen was well preserved in paraffin sections of formalin-fixed tissues. Thus, this suggests that the lyssavirus-specific antigen is recognized by the monospecific antibody against rabies virus nucleoprotein, and that this cross-reactive antigen is detectable on formalin-fixed paraffin-embedded tissues by immunohistochemical analysis.

Rabies DNA vaccination of non-human primates: post-exposure studies using gene gun methodology that accelerates induction of neutralizing antibody and enhances neutralizing antibody titers

Pre-exposure DNA vaccination protects non-human primates against rabies virus. Post-exposure protection of monkeys against rabies virus by DNA vaccination has not been attempted. Presumably, post-exposure experiments have not been undertaken because neutralizing antibody is usually slow to be induced after DNA vaccination. In this study, we initially attempted to accelerate the induction of neutralizing antibody by varying the route and site of DNA vaccination and booster frequency. Gene gun (GG) vaccinations above axillary and inguinal lymph nodes or in ear pinnae generated higher levels of neutralizing antibody than intradermal (ID) needle vaccinations in the pinnae. Concurrent GG booster vaccinations above axillary and inguinal lymph nodes and in ear pinnae, 3 days after primary vaccination, accelerated detectable neutralizing antibody. GG booster vaccinations also resulted in higher neutralizing antibody levels and increased the durability of this response. Post-exposure vaccination with DNA or the human diploid cell vaccine (HDCV), in combination with an one-time treatment with human rabies immune globulin (HRIG), protected 50 and 75% of the monkeys, respectively, as compared to 75% mortality of the controls. These data will be useful for the refinement, development, and implementation of future pre- and post-exposure rabies DNA vaccination studies.

Rabies vaccines: from the past to the 21st century

Since the first development of a rabies vaccine by Pasteur in the late 19th century, second- and third-generation vaccines with improved efficacy and less reactogenicity have been developed for use in humans and animals. Despite the availability of safe but rather expensive vaccines based on inactivated virus propagated in diploid cell cultures, much of the human vaccinations worldwide are still carried out with nerve tissue-containing vaccines, which have various side effects. A number of experimental vaccines are under development that may provide alternative safe and potent but less expensive vaccine options. These include DNA vaccines, recombinant viral vaccines, and recombinant protein vaccines. Further testing is needed to determine if and which one of these novel vaccines will make their way into mass production and application in the future.

One-time gene gun or intramuscular rabies DNA vaccination of non-human primates: comparison of neutralizing antibody responses and protection against rabies virus 1 year after vaccination

We have previously shown that Macaca fascicularis (Cynomologus) monkeys receiving a primary and either one or two booster rabies DNA vaccinations are protected against rabies virus. In this study, we determined whether monkeys that had been vaccinated only once via gene gun or intramuscularly (i.m.) with different concentrations of DNA would be protected against rabies virus challenge. Neutralizing antibody responses were assayed for 1 year before the monkeys were challenged. Neutralizing antibody was detected at least 50 days earlier in gene gun vaccinated as compared to i.m. vaccinated animals. Prior to viral challenge, all (6/6, 100%) gene gun vaccinated animals, but only 3/6 (50%) i.m. vaccinated animals seroconverted. In general, antibody titers of the gene gun vaccinated animals were higher than the titers of the i.m. vaccinated animals. There was no correlation between the concentration of DNA used for vaccination, the neutralizing antibody responses elicited and protection against viral challenge. Seven days after viral challenge, a rapid and strong anamnestic antibody response was elicited in 100% of the gene gun vaccinated monkeys and in four i.m. vaccinated monkeys. Neutralizing antibody remained undetectable in two i.m. vaccinated monkeys. Overall, 60% (3/5) of the gene gun vaccinated animals and 87% (5/6) of the i.m. vaccinated monkeys survived viral challenge. This study is the first, to our knowledge, to show long-term protection of non-human primates against a human viral pathogen using a DNA vaccination protocol that did not include a booster immunization.

A recombinant rabies virus expressing vesicular stomatitis virus glycoprotein fails to protect against rabies virus infection

To investigate the importance of the rabies virus (RV) glycoprotein (G) in protection against rabies, we constructed a recombinant RV (rRV) in which the RV G ecto- and transmembrane domains were replaced with the corresponding regions of vesicular stomatitis virus (VSV) glycoprotein (rRV-VSV-G). We were able to recover rRV-VSV-G and found that particle production was equal to rRV. However, the budding of the chimeric virus was delayed and infectious titers were reduced 10-fold compared with the parental rRV strain containing RV G. Biochemical analysis showed equal replication rates of both viruses, and similar amounts of wild-type and chimeric G were present in the respective viral particles. Additional studies were performed to determine whether the immune response against rRV-VSV-G was sufficient to protect against rabies. Mice were primed with rRV or rRV-VSV-G and challenged with a pathogenic strain of RV 12 days later. Similar immune responses against the internal viral proteins of both viruses indicated successful infection. All mice receiving the rRV vaccine survived the challenge, whereas immunization with rRV-VSV-G did not induce protection. The results confirm the crucial role of RV G in an RV vaccine.

Mapping of epitopes and structural analysis of antigenic sites in the nucleoprotein of rabies virus

Linear epitopes on the rabies virus nucleoprotein (N) recognized by six MAbs raised against antigenic sites I (MAbs 6-4, 12-2 and 13-27) and IV (MAbs 6-9, 7-12 and 8-1) were investigated. Based on our previous studies on sites I and IV, 24 consecutively overlapping octapeptides and N- and C-terminal-deleted mutant N proteins were prepared. Results showed that all three site I epitopes studied and two site IV epitopes (for MAbs 8-1 and 6-9) mapped to aa 358-367, and that the other site IV epitope of MAb 7-12 mapped to aa 375-383. Tests using chimeric and truncated proteins showed that MAb 8-1 also requires the N-terminal sequence of the N protein to recognize its binding region more efficiently. Immunofluorescence studies demonstrated that all three site I-specific MAbs and one site IV-specific MAb (7-12) stained the N antigen that was diffusely distributed in the whole cytoplasm; the other two site IV-specific MAbs (6-9 and 8-1) detected only the N antigen in the cytoplasmic inclusion bodies (CIB). An antigenic site II-specific MAb (6-17) also detected CIB-associated N antigen alone. Furthermore, the level of diffuse N antigens decreased after treatment of infected cells with cycloheximide. These results suggest that epitopes at site I are expressed on the immature form of the N protein, but epitope structures of site IV MAbs 6-9 and 8-1 are created and/or exposed only after maturation of the N protein.

Rabies vaccine. Developments employing molecular biology methods

Rabies vaccines produced by means of molecular biology are described. Recombinant vaccines employing either viruses as vectors (vaccinia, adenovirus, poxvirus, baculovirus, plant viruses) or a plasmid vector carrying the rabies virus glycoprotein gene are discussed. Synthetic peptide technology directed to rabies vaccine production is also presented.

Field evaluation of two bait delivery systems for the oral immunization of dogs against rabies in Tunisia

Two bait delivery systems for the oral immunization of dogs against rabies were tested in small scale field trials in a semi-rural area in Tunisia: bait delivery to owned dogs during door to door visits of households (door to door baiting) and distribution of baits on transect lines (transect line baiting). A prototype bait (DBL2) configured for industrial production and containing either sulfadimethoxine (SDM) as a systemic marker or Rhodamine B as a topical marker was used. The overall proportion of dogs which took a bait and presented topical marker staining after door to door baiting was 59.1%. The total time and costs spent per bait accepting dog averaged 34 person minutes and US$4, respectively. Unconsummated baits were readily recovered. No unprotected human contacts with baits were recorded. Door to door baiting is a very specific but time-consuming method that enables a safe administration of vaccine baits to owned dogs. For transect line baiting, baits were distributed at a density of ca 3000 baits per km2 along double transect lines. Baits were recovered after 20 h. According to the proportion of SDM positive serum samples, 24.1% of owned dogs in the baiting area had consumed baits. Of all owned and ownerless dogs, presumably free-roaming during transect line baiting, > 40% had consumed baits. The total time and costs spent per bait accepting dog averaged 48 person minutes and ca US$20, respectively. The household census revealed 32 direct human contacts with the bait matrix which corresponds to 1.4% of inhabitants. Placing baits on transect lines gives the possibility to vaccinate dogs not accessible by vaccination systems which base on dog owner participation. However, the method is not specific, less safe than other systems, not easily accepted by the human population, and costly.

Characterization of T-cell response to woodchuck hepatitis virus core protein and protection of woodchucks from infection by immunization with peptides containing a T-cell epitope

Specific activation of T cells appears to be a prerequisite for viral clearance during hepatitis B virus (HBV) infection. The T-cell response to HBV core protein is essential in determining an acute or chronic outcome of HBV infection, but how this immune response contributes to the course of infection remains unclear. This is due to results obtained from humans, which are restricted to phenomenological observations occurring during the clinical onset after HBV infection. Thus, a useful animal model is needed. Characterization of the T-cell response to the core protein (WHcAg) of woodchuck hepatitis virus (WHV) in woodchucks contributes to the understanding of these mechanisms. Therefore, we investigated the response of woodchuck peripheral blood mononuclear cells (PBMCs) to WHcAg and WHcAg-derived peptides, using our 5-bromo-2'-deoxyuridine assay. We demonstrated WHcAg-specific proliferation of PBMCs and nylon wool-nonadherent cells from acutely WHV-infected woodchucks. Using a cross-reacting anti-human T-cell (CD3) antiserum, we identified nonadherent cells as woodchuck T cells. T-cell epitope mapping with overlapping peptides, covering the entire WHcAg, revealed T-cell responses of acutely WHV-infected woodchucks to peptide1-20, peptide100-119, and peptide112-131. Detailed epitope analysis in the WHcAg region from amino acids 97 to 140 showed that T cells especially recognized peptide97-110. Establishment of polyclonal T-cell lines with WHcAg or peptide97-110 revealed reciprocal stimulation by peptide97-110 or WHcAg, respectively. We vaccinated woodchucks with peptide97-110 or WHcAg to prove the importance of this immunodominant T-cell epitope. All woodchucks immunized with peptide97-110 or WHcAg were protected. Our results show that the cellular immune response to WHcAg or to one T-cell epitope protects woodchucks from WHV infection.

Immunogenicity and relative attenuation of different vaccinia-rabies virus recombinants

Immunogenicity and relative attenuation were examined for the following Tian Tan strain vaccinia-rabies recombinant viruses: 1) NGc-1, which coexpresses the glycoprotein (G) and nucleocapsid protein (N) of the rabies virus Challenge Virus Standard (CVS) strain; 2) Nc-1, which expresses the CVS N; 3) Gc-2, Gc-3, Gc-4, and Gc-5, which express CVS G via promoters from different vaccinia strains or from different vaccinia genome loci; 4) Ga-1, which expresses the G of rabies virus strain aG; and 5) Gas-1; which expresses the carboxyltruncated G ectodomain (Gs) of strain aG. All but Nc-1 and Gas-1 induced rabies virus neutralizing antibodies (VNAs) and protected groups of mice at very high frequencies from intramuscular (IM) or intracranial (IC) challenge with CVS or SW1 Shanghai dog street rabies virus (SRV); Nc-1 and Gas-1 were partly protective, more frequently against IM challenge. NGc-1 and Gc-5 appeared to induce high levels of VNAs sooner after immunization than the other constructs in mice. Relative attenuation assessed by IM infection of neonatal mice, IC infection of adult mice, and intradermal infection of rabbits with varying doses was best for NGc-1. All the recombinants were at least 100-fold more attenuated than the parent, Tian Tan vaccinia virus. Gc-2, Gc-3, Gc-4, Gc-5, and NGc-1 induced VNAs after immunization of dogs, and a subset of VNA-positive animals vaccinated with NGc-1 or Gc-3 were protected against an otherwise lethal IM injection of SRV at 21 days after vaccination.

Rabies and African wild dogs in Kenya

Three packs of African wild dogs (Lycaon pictus) ranging to the north of the Masai Mara National Reserve in southwestern Kenya were monitored from 1988 to 1990. During a six week period (August 2-September 14, 1989), 21 of 23 members of one of these packs died. Histological examination of two brain samples revealed eosinophilic intracytoplasmic inclusions (Negri bodies), supporting a diagnosis of rabies viral encephalitis. An additional brain sample tested positive for rabies with a fluorescent antibody test. Nucleotide sequence of the rabies viral N and G genes from isolates of four African wild dogs (including an individual from Tanzania) indicated that infection was with a viral variant common among domestic dogs in Kenya and Tanzania. A hypothesis linking African wild dog rabies deaths to researcher handling is evaluated and considered implausible.

Expression of the nucleoprotein of rabies virus in Escherichia coli and mapping of antigenic sites

Investigations were performed to delineate the antigenic sites I and IV of rabies virus nucleoprotein (N), the former of which is well conserved among the rabies and rabies-related viruses. The N cDNA of the RC-HL strain was inserted into an expression vector pET3a, with which the E. coli BL21(DE3) was transformed. Upon induction with isopropyl-1-thio-beta-D-galactoside, the transformants produced a protein with a size (56 k-Da) almost identical to that of the authentic N protein. The protein also reacted with a panel of our N protein-specific monoclonal antibodies (N-MAbs) including the antibodies against the antigenic sites I and IV. By using the cDNA, various deletion mutants were generated and expressed in E. coli to examine the reactivity of mutant proteins with N-MAbs by Western blot analysis. Deletion of the C-terminal 67 amino acid residues did not abolish their reactivity with any of the N-MAbs specific for the sites I and IV. When 91 residues or more were deleted from the C-terminus, however, the protein lost the reactivity, indicating that the antigenic sites I and IV are mapped to a small region which is comprised of at most 24 amino acid residues from positions 360 to 383. Comparison of the 24-amino acid sequence with the corresponding region of N protein of several other Lyssavirus strains suggests that the antigenic site I is mapped to positions 360 to 369.

The glycoprotein G of rhabdoviruses

Rhabdoviruses show an RNA-containing helically-wound nucleocapsid either enclosed by or enclosing a membrane M protein, surrounded by a lipid bilayer through which dynamic protein trimers made up of non-covalently associated monomers of glycoprotein G (G) project outside. Mature monomeric rhabdoviral G has more than 500 amino acids, 2-6 potential glycosylation sites, 12-16 highly conserved cysteine residues, 2-3 stretches of a-d hydrophobic heptad-repeats, a removed amino terminal hydrophobic signal peptide, a close to the carboxy terminal hydrophobic transmembrane sequence and a carboxy terminal short hydrophylic cytoplasmic domain. Association-dissociation between monomers-trimers and displacement of the trimers along the plane of the lipid membrane, are induced by changes in the external conditions (pH, temperature, detergents, etc.). Throughout conformational changes the G trimers are responsible for the virus attachment to cell receptors, for low-pH membrane fusion and for reacting with host neutralizing monoclonal antibodies (MAbs). Antigenic differences could exist between monomers and trimers, which may have implications for future vaccine developments. The family Rhabdoviridae is made up of the Lyssavirus (rabies), the Vesiculovirus (vesicular stomatitis virus, VSV) and many rhabdoviruses infecting fish, plants, and arthropod insects. All these reasons make the G of rhabdoviruses an ideal subject to study comparative virology and to investigate new vaccine technologies.

Target cells of cytotoxic T lymphocytes directed to the individual structural proteins of rabies virus

Target cells of cytotoxic T lymphocytes (CTL) directed to the individual structural proteins (except for the large polymerase (L) protein) of rabies virus were established by expressing only the respective protein in murine neuroblastoma (NA) and murine macrophage (J774-1) cell lines. Mice infected with the ERA strain of rabies virus developed CTL responses to all of these rabies virus proteins. The cytotoxic activity was abrogated by pretreatment of the effector cells with anti-CD8 monoclonal antibody (MAb) and complement but not with anti-CD4 MAb. Cell lysis by CTL was blocked in the presence of anti-major histocompatibility complex (MHC) class 1 antibodies in J774-1 cell lines. Rabies virus-infected cells express these proteins at the surface, which can be recognized and lysed by the respective CTL. Mice immunized with beta-propiolactone-inactivated virus induced a CTL response against glycoprotein but not against internal viral components. This assay system might be useful for further analysis of the possible contribution of these proteins in the cell-mediated immune protection against rabies.

Rabies virus antinucleoprotein antibody protects against rabies virus challenge in vivo and inhibits rabies virus replication in vitro

We previously reported that A/WySnJ mice vaccinated via a tail scratch with a recombinant raccoon poxvirus (RCN) expressing the rabies virus internal structural nucleoprotein (N) (RCN-N) were protected against a street rabies virus (D. L. Lodmell, J. W. Sumner, J.J. Esposito, W.J. Bellini, and L. C. Ewalt, J. Virol. 65:3400-3405, 1991). To improve our understanding of the mechanism(s) of this protection, we investigated whether sera of A/WySnJ mice that had been vaccinated with RCN-N but not challenged with street rabies virus had anti-rabies virus activity. In vivo studies illustrated that mice inoculated in the footpad with preincubated mixtures of anti-N sera and virus were protected. In addition, anti-N sera inoculated into the site of virus challenge protected mice. The antiviral activity of anti-N sera was also demonstrated in vitro. Infectious virus was not detected in cultures 24 h following infection with virus that had been preincubated with anti-N sera. At later time points, infectious virus was detected, but inhibition of viral production was consistently > or = 99% compared with control cultures. The protective and antiviral inhibitory activity of the anti-N sera was identified as anti-N antibody by several methods. First, absorption of anti-N sera with goat anti-mouse immunoglobulin serum, but not normal goat serum, removed the activity. Second, radioimmuno-precipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of sucrose density gradient-fractionated anti-N sera showed that antiviral activity was present only in the fraction containing anti-N antibody. Finally, absorption of anti-N sera with insect cells infected with a baculovirus expressing the N protein removed the protective activity. These data indicate that anti-N antibody is a component of the resistance to rabies virus infections.

Resistance of mice vaccinated with rabies virus internal structural proteins to lethal infection

Mice were vaccinated with recombinant vaccinia virus (rVac) expressing the glycoprotein (G), nucleoprotein (N), phosphoprotein (NS) or matrix protein (M) of rabies virus and their resistance to peripheral lethal infection with street rabies virus was examined. Mice vaccinated with rVac-G or rVac-N developed strong antibody responses to the corresponding proteins and essentially all mice survived challenge infection. Mice vaccinated with rVac-NS or rVac-M developed only a slight antibody response, however, a significant protection (59%) was observed in the rVac-NS-vaccinated mice, whereas rVac-M-vaccinated mice were not protected. No anti-G antibodies were detected in the sera of mice which has been vaccinated with rVac-N or rVac-NS and survived challenge infection. Passive transfer of anti-N monoclonal antibodies (MAbs) recognizing an epitope located on amino acids 1-224 of the protein prior to challenge resulted in significant protection, although the protection was not complete even with a high amount of antibodies. In contrast, none of the mice given MAbs recognizing an epitope of amino acids 247-415 or F(ab')2 fragments from a protective MAb IgG were protected. Administration of anti-CD 8 MAb to rVac-N-vaccinated mice showed no significant effect on protection. Our observations suggest that a considerable part of the protection achieved by the vaccination with rVac-N can be ascribed to the intact anti-N antibodies recognizing an epitope located on amino acids 1-224 of the protein.