Rabies Control and Treatment: From Prophylaxis to Strategies with Curative Potential

Rabies is an acute, fatal, neurological disease that affects almost all kinds of mammals. Vaccination (using an inactivated rabies vaccine), combined with administration of rabies immune globulin, is the only approved, effective method for post-exposure prophylaxis against rabies in humans. In the search for novel rabies control and treatment strategies, live-attenuated viruses have recently emerged as a practical and promising approach for immunizing and controlling rabies. Unlike the conventional, inactivated rabies vaccine, live-attenuated viruses are genetically modified viruses that are able to replicate in an inoculated recipient without causing adverse effects, while still eliciting robust and effective immune responses against rabies virus infection. A number of viruses with an intrinsic capacity that could be used as putative candidates for live-attenuated rabies vaccine have been intensively evaluated for therapeutic purposes. Additional novel strategies, such as a monoclonal antibody-based approach, nucleic acid-based vaccines, or small interfering RNAs (siRNAs) interfering with virus replication, could further add to the arena of strategies to combat rabies. In this review, we highlight current advances in rabies therapy and discuss the role that they might have in the future of rabies treatment. Given the pronounced and complex impact of rabies on a patient, a combination of these novel modalities has the potential to achieve maximal anti-rabies efficacy, or may even have promising curative effects in the future. However, several hurdles regarding clinical safety considerations and public awareness should be overcome before these approaches can ultimately become clinically relevant therapies.

Oral Rabies Vaccine Design for Expression in Plants

Vaccination is the sensitization process of the immune system against any pathogen. Generally, recombinant subunit vaccines are considered safer than attenuated vaccines. As whole pathogenic organisms are used in the immunization process, the attenuated vaccines are considered more risky than subunit vaccines. Rabies is the oldest known zoonosis which spreads through a neurotropic Lyssavirus primarily mediated through infected canine bites. Rabies causes worldwide loss of more than 60,000 human lives every year. Animal vaccination is equally important to check the transmission of rabies into humans. Rabies oral vaccination can be a good alternative where multiple booster and priming regimens are required while the painful vaccination process can continue for long durations. Introduction of oral vaccines was made to ease the discomfort associated with the mode of introduction of conventional vaccines into the body. Although the rabies oral vaccine can substantially reduce the cost of vaccination in the developing countries, mass immunization programs need larger quantities of vaccines which should be delivered at nominal cost. Expression of recombinant antigen proteins in E. coli is often not viable because of lack of post-translational modifications and folding requirements. Though yeast and insect cell line expression systems have post-translational processing and modifications, significantly different immunological response against their post-translational modification pattern limits their deployment as an expression system. As an alternative, plants are emerging as a promising system to express and deliver wide range of functionally active biopharmaceutical product at lower cost for mass immunization programs. As generation of vaccine antigenic proteins in plant systems are cheaper, the strategy will benefit developing countries where this disease causes thousands of deaths every year. In this chapter, we will discuss about our efforts toward development of oral rabies vaccine and the methodological steps involved during this procedure in detail.

Immunogenicity and safety of purified chick-embryo cell rabies vaccine under Zagreb 2-1-1 or 5-dose Essen regimen in Chinese children 6 to 17 years old and adults over 50 years: a randomized open-label study

The aim of this Phase IIIb, open-label, randomized study was to demonstrate the non-inferiority of immune responses and to assess the safety of a purified chick-embryo cell rabies vaccine (PCECV) in healthy Chinese children (6 to 17 years) and older adults (≥51 years) following 2 alternative intramuscular (IM) simulated post-exposure prophylaxis (PEP) regimens: 4-dose Zagreb or 5-dose Essen regimen. Serum samples were collected prior to vaccination on Days 1 and 15 and on day 43 to assess immune response by rabies virus neutralizing antibody (RVNA) concentrations. Solicited adverse events (AEs) were recorded for up to 7 days following each vaccine dose, and unsolicited AEs throughout the entire study period. PCECV vaccination induced a strong immune response at Day 15, and the non-inferiority in immune response of the Zagreb vs. the Essen regimen was demonstrated in children and older adults. At Day 15,100% of children (N = 224), and 99% of subjects ≥51 years of age (N = 376) developed adequate RVNA concentrations (≥0.5 IU/mL); at Day 43 all subjects achieved RVNA concentrations ≥0.5 IU/mL, for both PEP regimens. The well-known tolerability and safety profile of the PCECV was again observed in this study following either Zagreb or Essen regimens. Rabies PEP vaccination with PCECV following a Zagreb regimen induced immune responses non-inferior to those of the Essen regimen, and had a similar safety and tolerability profile to the Essen regimen in Chinese children, adolescents, and adults over 51 years. ClinicalTrials.gov identifier: NCT01680016.

Assessing the Safety of Post-exposure Rabies Immunization in Pregnancy

Fourteen pregnant women who received rabies post-exposure prophylaxis (PEP) at the anti-rabies clinic (ARC) of Kempegowda Institute of Medical Sciences (KIMS) were followed up for assessing the safety of modern rabies vaccines and equine rabies immunoglobulin (ERIG) in pregnancy. The women were in the age range of 18-28 years, mostly from urban area (64%) and exposed to suspect rabid dogs (86%). They had received purified vero cell rabies vaccine (Verorab = 8 and Abhayrab = 4), purified chick embryo cell vaccine (Rabipur = 2) by Essen regimen; and equine rabies immunoglobulin (Equirab = 7 and Pasteur anti-rabies serum = 1). None of the pregnant women reported any adverse events to either vaccine or equine rabies immunoglobulin. All had safe vaginal deliveries and in all cases both the mother and the child were found to be healthy and normal.

Safety and Immunogenicity of purified chick embryo cell rabies vaccine (VaxiRab N) administered intradermally as post exposure prophylaxis

The affordability to rabies vaccine for intramuscular administration in post exposure prophylaxis is a major constraint. Therefore, in countries, where there are financial constraints, World Health Organization recommends intradermal rabies vaccination that reduces the quantity and cost of vaccination. This study was done to evaluate the safety and immunogenicity of indigenously developed rabies vaccine (VaxiRab N) in comparison to a WHO recommended rabies vaccine (Rabipur) with demonstrated efficacy when administered by intradermal route using updated Thai Red Cross regimen. Eighty-six dog bite cases were randomly given either VaxiRab N (n = 43) or Rabipur (n = 43) as post exposure prophylaxis. The rabies virus neutralizing antibody concentrations on days 14, 28, 90, and 180 were tested by modified rapid fluorescent focus inhibition test. The geometric mean RVNA concentration of both the groups were compared using t- test and was found that, P value > 0.05 on all days, thus showing no significant difference between the 2 groups. The adverse drug events were also compared using Z-test and was found to be not statistically significant (Z = 1.476, P = 0.139). In conclusion, VaxiRab N was found to be safe and effective in post exposure prophylaxis by intradermal route and was similar to the WHO recommended rabies vaccine (Rabipur) of demonstrated efficacy.

Safety and immunogenicity study of a new purified chick embryo cell rabies vaccine Vaxirab-N (Pitman-Moore strain) manufactured in India

Zydus Cadila Health care, India developed a new purified chick embryo cell rabies vaccine (PCECV, Vaxirab-N; 1 mL) by adapting Pitman-Moore strain of virus on to the chick embryo fibroblast cell line in 2006. During 2007-10, a series of safety and immunogenicity studies were conducted as per ICH-GCP guidelines after obtaining permission from Drug Controller General of India. In the first study, Vaxirab-N was administered to 35 healthy adult volunteers by intramuscular (IM) route using pre exposure regimen. The geometric mean concentration (GMC) of rabies virus neutralizing antibody (RvnAb) of 7.5 IU/mL on day 35. In the second study, Vaxirab-N was administered to 35 healthy adult volunteers using simulated post- exposure prophylaxis regimen by IM route. A GMC of 6.3 IU/mL on day 14, 13.2 IU/mL on day 28 and 8.6 IU/mL on day 90 was obtained. In the third study, Vaxirab-N administered by intradermal (ID) route using Updated Thai Red Cross (TRC) regimen in 36 healthy adult volunteers showed GMC of 7.8 IU/mL on day 14, 11.5 IU/mL on day 28 and 6.0 IU/mL on day 90. The 4th study was multi centric and Vaxirab-N was administered to 129 animal bite cases by IM route using post-exposure Essen regimen. The GMC following this schedule was 8.2 IU/mL on day 14, 13.01 IU/mL on day 28, 7.92 IU/mL on day 90 and 3.72 IU/mL on day 180. Mild to moderate adverse events were reported to Vaxirab-N but no serious adverse events were reported in any of these studies. In conclusion, Vaxirab-N developed by Zydus Cadila was found to be safe and immunogenic by both intramuscular and intradermal route and is recommended for rabies prophylaxis (CTRI No. 2010/091/000055 and 2010/091/000509).

Assessing the relationship between antigenicity and immunogenicity of human rabies vaccines when administered by intradermal route: results of a metaanalysis

The metadata of 10 published studies and 3 vaccine trial reports comprising of 19 vaccine cohorts from four countries conducted over a period of 23 years (1986 - 2009) was used for metaanalysis. The vaccines studied were purified chick embryo cell vaccine (Rabipur, India & Germany), purified vero cell rabies vaccine (Verorab, France; Indirab, India) & human diploid cell vaccine (MIRV, France).The potency of these vaccines varied from 0.55 IU to 2.32 IU per intradermal dose of 0.1 ml per site. The vaccines were administered to 1,011 subjects comprising of 19 cohorts and using five different ID regimens. The immunogenicity was measured by assays of rabies virus neutralizing antibody (RVNA) titres using rapid fluorescent focus inhibition test (RFFIT) [15 cohorts] and mouse neutralization test (MNT) [4 cohorts]. The statistical analysis of the data was done by Karl Pearson's correlation coefficient to measure the relationship between antigenicity and immunogenicity. It was revealed that, there was no significant linear relationship between antigenicity and immunogenicity of rabies vaccines when administered by intradermal route. (p> 0.230 and p>0.568).

Rabies post-exposure prophylaxis vaccination with purified chick embryo cell vaccine (PCECV) and purified vero cell rabies vaccine (PVRV) in a four-site intradermal schedule (4-0-2-0-1-1): An immunogenic, cost-effective and practical regimen

Currently, two intradermal (ID) regimens for rabies post-exposure prophylaxis (PEP) are recommended by WHO and used in countries where approved by national authorities: the Thai Red Cross (TRC) two-site ID regimen and the eight-site ID regimen. Besides these WHO recommended schedules, a new economical four-site ID regimen was evaluated that reduces the cost of PEP by up to 80%, when compared with the standard intramuscular Essen regimen, reduces the number of visits required for the patients when compared with the TRC regimen, and is more convenient than the eight-site regimen. To determine the immunogenicity of the ID four-site PEP regimen (4-0-2-0-1-1), 180 healthy volunteers were randomized to receive 0.1 mL volumes of PCECV or PVRV administered ID over both left and right shoulders and both deltoid regions on day 0, both deltoid regions on day 7 and over one deltoid region on days 30 and 90. Regardless of the vaccine, every subject developed rabies virus neutralizing antibody (RVNA) titers above 0.5 IU/mL by day 14, as determined by rapid fluorescent focus inhibition test (RFFIT) using a homologous test system. Two weeks after the last dose of vaccine, RVNA titers were all above 0.5 IU/mL (day 104). Geometric mean titers were similar throughout the study period. Both vaccines were well tolerated. These results demonstrate that a new four-site ID PEP regimen is a cost-effective and convenient alternative to IM (Essen or Zagreb) or ID (TRC or eight-site) regimens, especially using a 1 mL vial of vaccine (PCECV).

Purification, potency and immunogenicity analysis of Vero cell culture-derived rabies vaccine: a comparative study of single-step column chromatography and zonal centrifuge purification

Continuous Vero cell lines are more suitable for large-scale production of rabies vaccine. The purification of Vero cell-derived rabies vaccine is critical because of the residual cellular DNA and serum proteins. The perfection of techniques using column chromatography with different matrix material, gel filtration and zonal centrifugation is of paramount importance for the optimal purification of rabies vaccine, leaving minimal residual cellular DNA, below the permissible level of 100 pg per dose and serum protein content of 1 ppm. In this study the potency, immunogenicity and safety of Vero cell-derived rabies vaccines were compared following purification by densely or loosely packed DEAE-sepharose CL-6B columns with different bed heights or by zonal centrifugation. The optimal virus recovery and maximum removal of substrate DNA and serum proteins were achieved only when the sepharose CL-6B column bed height was maintained at a thickness of 2-2.5 cm. The rabies virus material was purified by layering over the matrix without applying pressure. DEAE-sepharose CL-6B column purification using a simplified, cost effective technique as described in this study enhances the antigen yield by 50% in comparison with zonal purification.

An immunogenicity study of a newly introduced purified vero cell rabies vaccine (Abhayrab) manufactured in India

Purified Vero cell culture rabies vaccine "Abhayrab" manufactured by Human Biologicals Institute, Ooty, India was subjected for immunogenicity studies. Pre-exposure study was undertaken on 60 healthy volunteers (Group I) with vaccination on days 0, 7 and 21. A group of 75 patients of category II (Group II), 67 of category III (Group III) were given post-exposure prophylaxis and 88 patients of category III were administered with rabies immunoglobulins (Group IV) along with post-exposure prophylaxis as per World Health Organization (WHO) recommendations with a booster on day 90. The volunteers and patients vaccinated showed very few adverse side effects. The blood samples collected from volunteers (Group I) on days 14, 35 and 365 and patients (Group II-IV) on days 14, 30, 90 and 365 showed geometric mean titres (GMT) of >0.5 IU/ml. The study indicated new rabies vaccine manufactured in India was found to be safe and immunogenic.

Antibody response to purified chick embryo cell vaccine in equines for production of equine rabies immune globulin

Rabies is endemic in India. The post exposure treatment of class three bite cases, as recommended by the World Health Organization, must involve the use of rabies immunoglobulin as soon as possible and up to the seventh day of start of anti rabies vaccination. The annual requirement in India as projected by the Ministry of Health, Government of India is about 1500 liters of purified anti rabies serum (ERIG). Central Research Institute (CRI), Kasauli, being the sole producer of ERIG in India, an effort was made to increase the production of ERIG by the use of tissue culture vaccine (Human) for primary immunization of equines. It also involved changing the vaccine from horse brain suspension to tissue culture vaccine by eliminating horse sacrifice for antigen preparation. A better immune response was obtained.

A novel process for the production of a veterinary rabies vaccine in BHK-21 cells grown on microcarriers in a 20-l bioreactor

We studied BHK-21 cells growth in a 2-l bioreactor and investigated the effects of microcarrier concentration, type of growth medium, culture mode and serum concentration. The highest cell density reached was equal to 4x10(6) cells/ml and was achieved in minimum essential medium supplemented with Hanks' salts, non-essential amino acids and 5% fetal calf serum, using a perfusion culture mode and a microcarrier concentration of 4 g Cytodex 3/l. We studied rabies virus production (PV/BHK-21 strain) by BHK-21 cells grown at the optimal conditions determined previously. We analyzed the effects of multiplicity of infection (MOI) and type of medium used for virus multiplication in spinner-flasks and showed that the highest virus titer reached (when the cells were infected at a MOI of 0.3) in M199 medium supplemented with 0.2% of bovine serum albumin was equal to 8.2x10(7) Fluorescent Focus Units (FFU)/ml. When we grew the cells in a 2-l perfused bioreactor, we obtained a maximal virus titer of 3x10(8) FFU/ml. In addition, we scaled-up to a 20-l bioreactor and obtained similar results for cell density and virus titer. The experimental vaccine we developed meets WHO requirements for vaccine potency. Each run yielded about 40,000 doses of potent vaccine.

Expression in plants and immunogenicity of plant virus-based experimental rabies vaccine

A new approach to the production and delivery of vaccine antigens is the use of engineered amino virus-based vectors. A chimeric peptide containing antigenic determinants from rabies virus glycoprotein (G protein) (amino acids 253-275) and nucleoprotein (N protein) (amino acids 404-418) was PCR-amplified and cloned as a translational fusion product with the alfalfa mosaic virus (AlMV) coat protein (CP). This recombinant CP was expressed in two plant virus-based expression systems. The first one utilized transgenic Nicotiana tabacum cv. Samsun NN plants providing replicative functions in trans for full-length infectious RNA3 of AlMV (NF1-g24). The second one utilized Nicotiana benthamiana and spinach (Spinacia oleracea) plants using autonomously replicating tobacco mosaic virus (TMV) lacking native CP (Av/A4-g24). Recombinant virus containing the chimeric rabies virus epitope was isolated from infected transgenic N. tabacum cv. Samsun NN plants and used for parenteral immunization of mice. Mice immunized with recombinant virus were protected against challenge infection. Based on the previously demonstrated efficacy of this plant virus-based experimental rabies vaccine when orally administered to mice in virus-infected unprocessed raw spinach leaves, we assessed its efficacy in human volunteers. Three of five volunteers who had previously been immunized against rabies virus with a conventional vaccine specifically responded against the peptide antigen after ingesting spinach leaves infected with the recombinant virus. When rabies virus non-immune individuals were fed the same material, 5/9 demonstrated significant antibody responses to either rabies virus or AlMV. Following a single dose of conventional rabies virus vaccine, three of these individuals showed detectable levels of rabies virus-neutralizing antibodies, whereas none of five controls revealed these antibodies. These findings provide clear indication of the potential of the plant virus-based expression systems as supplementary oral booster for rabies vaccinations.

Production, purification and analysis of an experimental DNA vaccine against rabies

BACKGROUND

The basic and applied research efforts devoted to the development of DNA vaccines must be accompanied by manufacturing processes capable of being scaled up and delivering a clinical-grade product. This work describes a rapid process of this kind, based on hydrophobic interaction chromatography (HIC) for the production of milligram quantities of an experimental DNA rabies vaccine. Its properties and protective activity are tested in comparison with the same plasmid DNA purified with a commercial kit.

METHODS

The experimental DNA vaccine encoding the rabies virus glycoprotein was amplified in vivo in Escherichia coli. The plasmid was isolated by alkaline lysis, pre-purified and concentrated by isopropanol and (NH4)2SO4 precipitation, and purified by HIC and dialysis. Product quality was controlled by using high-performance liquid chromatography (HPLC), Southern slot blotting, agarose gel electrophoresis, the kinetic-QCL Limulus amoebocyte lysate assay, and protein assays. The expression of the rabies virus glycoprotein was tested in vitro in neuroblastoma cells. The production of rabies-virus-neutralising antibodies and the protection against an intracerebral virus challenge were tested in mice.

RESULTS

One hundred and forty-two milligrams of the plasmid, with an HPLC purity greater than 99% were obtained from 4.5 l medium. Control analysis showed that the vaccine conforms to specifications in terms of impurities (endotoxins, genomic DNA, RNA, proteins). Furthermore, the final experimental vaccine induces rabies-virus-neutralising antibodies and protects mice against a rabies virus challenge.

CONCLUSIONS

This study demonstrates that the method developed for the purification of milligram amounts of plasmid delivers an endotoxin-free, experimental rabies DNA vaccine, with protective activity similar to that obtained with the vaccine purified using a commercial kit.

Immunogenicity, safety and lot consistency in adults of a chromatographically purified Vero-cell rabies vaccine: a randomized, double-blind trial with human diploid cell rabies vaccine

The immunogenicity and safety of a chromatographically purified rabies vaccine (CPRV) was evaluated using US veterinary medical students. In the first study, 242 healthy adults were enrolled in a randomized, modified double-blind, multicenter trial and received five doses of either CPRV or human diploid cell vaccine (HDCV) by intramuscular injection on days 0, 3, 7, 14, and 28 concurrently with human rabies immunoglobulin in a simulated post-exposure prophylaxis regimen. Post-immunization titers in the CPRV and HDCV groups reached 0.5 IU/ml (the WHO-recommended minimally acceptable titer) or greater in all subjects in both vaccine groups by day 14 and remained above that level through day 90. In the second study, 438 healthy adults were enrolled in a randomized, double-blind, multicenter trial and assigned to receive five doses from one of three lots of CPRV by intramuscular injection on days 0, 3, 7, 14, and 28 in a simulated post-exposure prophylaxis regimen to evaluate lot consistency. Post-immunization titers rapidly increased to over 0.5 IU/ml by day 14 for all subjects and remained above that level through day 42 when the study was terminated. The three lots were considered equivalent. The percentage of subjects with at least one local reaction during the five-dose regimen was slightly lower in the CPRV group than in the HDCV group (P=0.06). The most frequently reported local reaction for all doses of vaccine was pain at the injection site. Headache, myalgia, and malaise were the most frequently reported systemic events. The percentage of subjects with at least one systemic event was significantly lower for CPRV (P=0.0084). No vaccine-related serious adverse reaction was reported in these studies. The results of these studies indicate that CPRV administered intramuscularly to healthy adults is immunogenic and is associated with fewer local and systemic reactions than HDCV.

Immunogenicity and effectiveness of post-exposure rabies prophylaxis with a new chromatographically purified Vero-cell rabies vaccine (CPRV): a two-stage randomised clinical trial in the Philippines

Recent improvements in chromatographic purification procedures have made it possible to develop a new chromatographically purified rabies vaccine (CPRV) by further purifying the current rabies vaccine prepared from Vero-cell culture (PVRV) (Verorab; Pasteur Merieux Connaught). The immunogenicity and effectiveness of post-exposure rabies prophylaxis with this new vaccine were evaluated in a two-stage clinical trial conducted in the Philippines. In both study stages. post-exposure treatment consisted of five injections of vaccine [(D)ays 0, 3, 7, 14, 28], together with a dose of rabies immunoglobulin (RIG) of equine or human origin on D0. In stage 1, 231 subjects with low-risk rabies exposure (WHO category I or II), and who had a negative ERIG skin test, were treated with either CPRV (n = 114) or PVRV (n = 117). By D14, all subjects in each group had achieved rabies antibody titres over ten times that recommended by the WHO as indicating seroconversion (> or = 0.5 IU/ml). The kinetics of the immune response to vaccination were very similar in the two groups, and at D28, the immunogenicity of CPRV was equivalent to that of PVRV (one-sided equivalence test). Following these positive results, 132 subjects with severe rabies exposure were included in the second stage of this trial. All were scheduled to receive four vaccine doses with CPRV. After D14, only those 57 patients with confirmed rabies exposure (animal with positive FA test) and seven patients for whom rabies exposure could not be excluded (animal lost or not tested) completed the treatment and were followed for one year to assess survival. After 1 year, 62 patients treated for confirmed or possible severe rabies exposure had been examined and were still alive. Two patients contacted by letter and telephone confirmed good health 7 and 16 months after exposure. No severe local or systemic reactions were reported in either stage of the study, and no treatment-related serious adverse event occurred. This two-stage clinical trial attests to the safety and satisfactory immunogenicity of CPRV in post-exposure rabies treatment, and confirms the effectiveness of a new rabies vaccine in patients with severe confirmed exposure.

A new Vero cell rabies vaccine: results of a comparative trial with human diploid cell rabies vaccine in children

We evaluated the immunogenicity and safety of a chromatographically purified rabies vaccine (CPRV) compared with human diploid cell rabies vaccine (HDCV) after pre-exposure immunizations (both primary and booster). Intramuscular doses of either 0.5 mL of CPRV or 1.0 mL of HDCV were given to 400 schoolchildren on days 0, 7, 28, and 365 (booster). Adequate titers of antibody (> or = 0.15 IU/mL, as defined by the Centers for Disease Control and Prevention) were observed in serum samples from all children 14 days after primary immunization with CPRV and HDCV; the antibodies persisted in all but one child up until 1 year. Fourteen days after the primary immunization series (day 42) and 7 days after booster immunization (day 372), all children had antibody titers of > or = 0.5 IU/mL. Local and systemic reactions after primary and booster immunizations occurred significantly less frequently in the CPRV group. A severe allergic reaction (angioedema) was reported in only one child after booster immunization with HDCV. CPRV has adequate immunogenicity for primary and booster pre-exposure immunizations in children and has a better safety profile than does HDCV.

Immunogenicity and safety in adults of a new chromatographically purified Vero-cell rabies vaccine (CPRV): a randomized, double-blind trial with purified Vero-cell rabies vaccine (PVRV)

Recent improvements in chromatographic purification procedures have made it possible to develop a new chromatographically purified rabies vaccine (CPRV) by further purifying the current rabies vaccine prepared from Vero-cell culture (Verorab; Pasteur Mérieux Connaught). The immunogenicity and safety of primary immunization, followed by a booster at one year, with CPRV was compared to that of the purified Vero cell vaccine (PVRV) in a randomized, double-blind study carried out at four veterinary schools in France. A total of 330 healthy, male and female, first-year veterinary students, aged at least 18 years and who required pre-exposure rabies prophylaxis, were enrolled in this study. Included subjects were randomly assigned either CPRV (n = 163) or PVRV (n = 167) to be given as a primary immunization series of three intramuscular injections (D0, D7, D28), followed by a booster after 1 year (D365). Blood samples for serological analysis were taken at D0 (before first injection), D28, D42, D180, D365 (before booster) and D379. All subjects developed a strong immune response to the primary series, and at D42, all subjects had seroconverted for rabies neutralizing antibody (serum titre > or = 0.5 IU/ml). The rabies virus-neutralizing antibody GMT value at D42 in the CPRV group (23.0 IU/ml) was non-inferior to that in the PVRV group (29.6 IU/ml), according to a one-sided non-inferiority test. While antibody titres tended to decrease over the period of follow-up, at D365 (before booster), 97.5% subjects in the CPRV group and 98.8% of subjects in the PVRV group remained seroconverted. After booster, although the rabies antibody GMT value in the CPRV group was lower than that in the PVRV group, all subjects in both groups were seroconverted, and the difference is probably not clinically important. The incidence of local and systemic reactions tended to decrease with each dose during the primary immunization series, followed by a slight increase after booster (significant time-effect in an exploratory logistic regression analysis). Although mild or moderate local reactions tended to be more frequent after injection with CPRV compared to PVRV, systemic reactions were reported less often (significant group-effects in exploratory logistic regression analyses). One serious adverse event possibly related to vaccine occurred during this study (severe asthenia after the third dose of PVRV). This comparative study in healthy young adults demonstrates that the new chromatographically purified rabies vaccine is as immunogenic as PVRV, and seems to be associated with fewer systemic reactions.

Human rabies: a continuing challenge in the tropical world

More than 99% of all human rabies deaths in the world occur in tropical developing countries. In India alone, 30,000 to 50,000 people may die of rabies each year. The Lyssaviruses (Family Rhabdoviridae) include rabies and rabies-related viruses, 3 of which have caused human disease. Rabies is a zoonosis, principally affecting domestic and stray dogs in most parts of Africa, Asia and Latin America. In North America, southern Africa, parts of the Caribbean and Europe, the principal mammalian reservoir species are wild carnivores. The pathogenesis, clinical features and differential diagnosis of rabies are discussed. The planning of rabies control strategies requires background information on the distribution and incidence of rabies in animals and the species involved. In some parts of the world, such as Latin American cities, most domestic dogs, even apparent strays, have an owner and can be immunized with conventional canine vaccines during well publicized campaigns. However, in areas such as India, where there may be a high proportion of stray domestic dogs without owners, and in those areas where wild mammals are the principal reservoir species, immunization may be possible using live attenuated or recombinant oral vaccines distributed in baits. In the poor tropical developing countries, unsatisfactory nervous tissue vaccines are still widely used. However, economical multisite intradermal regimens using tissue culture vaccines have proved effective and have begun to replace nervous tissue vaccines in some countries.

[The use of rocket immunoelectrophoresis for determining glycoprotein in concentrated rabies vaccines]

Rocket immunoelectrophoresis (RIE) was shown to be useful for the evaluation of glycoprotein (GP) content in concentrated rabies vaccines, and disintegron B., a zwitterionic detergent made in this country, for treatment of the vaccines for these evaluations. The values of GP content obtained by RIE and single radial immunodiffusion test were similar. The highest values were obtained for all the vaccines tested with anti-PM GP serum compared with anti-ERA and Vnukovo-32 GP serum. When anti-PM and anti-Vnukovo-32 GP sera were used for RIE two components were revealed in the vaccines. All the preparations under study contained soluble GP.

Studies on the antigenicity and nucleotide sequence of the rabies virus Nishigahara strain, a current seed strain used for dog vaccine production in Japan

The Nishigahara strain of rabies virus, a current seed strain used for animal vaccine production in Japan, is believed to derived from the original Pasteur strain obtained from Paris in or before 1915. In Japan, the virus was serially passaged through several kinds of animals and cell cultures. Reactions with anti-nucleocapsid protein monoclonal antibodies (MAb-N) indicated the Nishigahara strain had maintained the antigenic profile of the Pasteur virus. Reactions with monoclonal antibodies to the glycoprotein (MAb-G) revealed differences between the Nishigahara strain and the Pasteur strain; however, the Nishigahara strain maintained a closer resemblance to the Pasteur virus than to other Pasteur-related viruses or to rabies strains unrelated to the Pasteur strain. Comparative amino acid sequence analysis of cloned cDNA encoding the G gene confirmed the antigenic differences among these strains and the resemblance of the Nishigahara strain to the original Pasteur strain. Comparative nucleotide sequence analysis of the noncoding pseudogene region (Tordo et al., Proc Natl Acad Sci USA 83, 3914-3918, 1986) revealed different relationships. Unlike the Pasteur strain, which encodes a transcription-terminating signal at the end of the G gene (marking the beginning of the pseudogene), a long G-L intergenic sequence in the Nishigahara strain was connected to the 3' end of the cDNA, and the transcription-terminating signal was present only at the end of, but not before, the pseudogene. These results are not inconsistent with the documented origin of the Nishigahara strain, but the genome structure around the pseudogene region suggests divergence from the Pasteur strain and a closer resemblance to other strains of rabies virus.

Comparative studies on chick embryo cell rabies vaccine and human diploid cell vaccine: pre-exposure use and purity of the vaccines

Neutralizing antibody responses to commercial Japanese-produced chick embryo cell (CEC) vaccines in Japanese and to commercial human diploid cell rabies vaccines (HDCV) in Filipinos were compared by the rapid fluorescent focus inhibition test (RFFIT). Neutralizing antibody titers of the Japanese after subcutaneous (sc) immunization with two doses of the CEC vaccines were not lower than those of the Filipinos with two or three doses of HDCV by intramuscular (i.m.) or intradermal (i.d.) route, respectively. Protein nitrogen content of the CEC vaccine was about 1/300th that of the HDCV. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analysis showed that non-viral protein content in the CEC vaccine was much lower than that in the HDCV. The CEC rabies vaccine seems to be as safe and effective as the HDCV for human pre-exposure immunization.

[The validation of the possibility of obtaining antirabies donor plasma]

The possibility was studied of obtaining of a highly-specific antirabies plasma from donor blood actively immunized with concentrated culture antirabies vaccine and optimal terms were determined for obtaining immunoreactive raw material for manufacturing of antirabies immunoglobulin. Technical aspects of manufacturing antirabies donor plasma are discussed.

Comparisons of nucleotide and deduced amino acid sequences of the glycoprotein genes of a Chinese street strain (CGX89-1) and a Chinese vaccine strain (3aG) of rabies virus

We analyzed the glycoprotein gene sequences of a Chinese street rabies virus strain (CGX89-1) and a Chinese human rabies vaccine strain (3aG). The complete glycoprotein gene sequence of each strain has 1575 nucleotides and encodes a polypeptide of 524 amino acids. The overall nucleotide homology of these glycoprotein genes is 84.5%, and the deduced amino acid homology is 89.5%. Twenty-one percent of the base changes result in amino acid substitutions. Comparison of the homologies of the glycoprotein genes showed that the most conserved region is the ectodomain, whereas the most variable regions are the transmembrane and cytoplasmic domains. The overall nucleotide homologies of the 3aG glycoprotein and the CGX89-1 glycoprotein compared with the Pasteur virus glycoprotein are 91.2% and 84.1% respectively. The glycoprotein gene sequences presented here, the first from isolates of Chinese origin, provide insights into the biologically significant regions of this rabies gene.

Beta-propiolactone treatment impairs the biological activity of residual DNA from BHK-21 cells infected with rabies virus

The effects of beta-propiolactone (BPL), an alkylating and virus inactivating agent, on the structural and in vitro biological properties of different DNA preparations from BHK-21 cells were investigated. Both uninfected and rabies virus-infected cells were used. Purified cellular DNA (celDNA) was used as the reference, and supernatants from infected cells were treated with BPL. For structural and biological studies three types of DNA preparation were tested: celDNA; purified DNA from cell (infected or uninfected) supernatant (pcsDNA) with or without BPL treatment; and residual cell DNA present in purified rabies virus (inactivated or not) preparations. Rabies infection and BPL (diluted 1:4000) treatment induced modifications in the structure of the three DNA types, including strand breaks and nicks. The damage to the DNA structure by BPL modifies the biological properties of the pcsDNA appraised by its ability to serve as the template in vitro for different polymerases. When rabies virus was inactivated with BPL diluted 1:1000 the DNA damage increased dramatically: small double-stranded DNA fragments (50-200 base pairs) were generated which could not function as templates for polymerases.

Rabies vaccine standardization: International Collaborative Study for the Characterization of the fifth International Standard for Rabies Vaccine

A collaborative study was carried out to establish a replacement for the International Standard for Rabies Vaccine, the stocks of which are exhausted. Three rabies vaccines for human use derived from different rabies virus strains and prepared on different cell culture substrates were compared with the International Standard for Rabies Vaccine using in vivo and in vitro assay methods in a collaborative study involving 14 participants. The proposed fifth International Standard (PISRAV) which was derived from the same virus strain as the present international standard preparation, the Pitman Moore (PM) strain, was found to be approximately twice as potent relative to the International Standard in immunogenicity assays as in antigenicity assays. On the other hand another vaccine, derived from the LEP strain, was considerably more potent in antigenicity assays than in immunogenicity assays. The glycoprotein of the proposed replacement standard measured in antigenicity assays appeared to be stable at +37 degrees C for 245 days, whereas the immunogenicity of the proposed replacement vaccine was sensitive to this heat treatment and the vaccine lost 66% of its immunogenic potency. The results of this study indicate that the NIH protection test should continue to form the primary basis for potency assay of rabies vaccine as glycoprotein content does not appear to correlate with immunogenic potency for different types of vaccine. The vaccine coded PISRAV has been established as the fifth International Standard for Rabies Vaccine and a potency of 16 International Units of Rabies Vaccine (based on the immunogenicity assays) assigned to the contents of each ampoule. Each ampoule has also been assigned a unitage of 10 IU of PM Rabies Virus Glycoprotein and 135 IU of PM Rabies Virus Ribonucleoprotein.

Rabies neutralizing antibody in serum of children compared to adults following post-exposure prophylaxis

Rabies neutralizing antibody concentrations in serum (SRNA) elicited by experimental post-exposure prophylaxis (PEP) regimens are used to assess their potential clinical efficacy. Although PEP with human rabies immunoglobulin (HRIG) plus human diploid-cell culture vaccine (HDCV) is almost completely protective, the limited availability of these components has stimulated the search for alternative regimens. Since 33% to over 60% of PEP is administered to children, a need exists for data on the SRNA response to HRIG plus HDCV in children, to be used to assess the potential value of alternative PEP treatments. We measured SRNA by the rapid fluorescent focus inhibition test on days 0, 1, 3, 7, 14, 28, 56 and 90 after initiation of PEP with HRIG (20 IU/kg) and HDCV (1.0 ml on day 0, 3, 7, 14, 28) in 10 children [8 +/- 4 (mean +/- SD) years of age] and 32 adult control patients (38 +/- 16 years of age). Early, uniform appearance of SRNA was observed with no differences between groups. These data are consistent with the demonstrated efficacy of PEP with HRIG plus HDCV in children as in adults and provide results that can be used for initial evaluation of experimental pediatric PEP regimens in the future.

Effect of one booster dose in antirabies vaccination

The antibody response obtained after one booster dose of rabies vaccine prepared in suckling mice brains at Serviço de Saúde Pública da Cidade do Rio de Janeiro is described. Four prime vaccinal groups were used: group I, persons who had received 16 doses 10 years before this investigation; group II, persons who had received 5 doses of the vaccine 10 years before; group III, persons who had received 9 doses 5 years before; and group IV, persons who had received 16 doses 5 years before. One booster dose of the vaccine was administered to all persons involved in the study. Blood samples were collected before vaccination (day 0), then 7 and 30 days after vaccination. Antibody titres were determined by seroneutralization test in mice (SWM). The results demonstrated that all persons who had been treated with 5, 9 or 16 doses of the vaccine 5 to 10 years before had their antibody titres increased on the 7th and 30th days after one booster dose.

Immunization of monkeys with rabies ribonucleoprotein (RNP) confers protective immunity against rabies

The ability of rabies virus ribonucleoprotein (RNP) to induce protective immunity against rabies and to prime for production of virus-neutralizing antibodies (VNA) was studied in monkeys. Following two immunizations with RNP, monkeys developed a strong anti-RNP response and were protected against a challenge infection with a lethal dose of street rabies virus. Monkeys that were primed with RNP and then immunized with a single dose of human diploid cell vaccine (HDCV) developed VNA titres comparable to the VNA titres in non-primed monkeys after a second HDCV immunization. The utility of rabies RNP for the pre-exposure prophylaxis of human rabies is discussed.

In vitro rabies vaccine potency appraisal by ELISA: advantages of the immunocapture method with a neutralizing anti-glycoprotein monoclonal antibody

The replacement of the in vivo potency test (NIH test) for rabies vaccine evaluation by in vitro methods is at present discussed in many reports and also by WHO expert working groups. For this purpose, in vitro glycoprotein titration has been proposed. Among the different glycoprotein assays, we have studied two ELISA methods (immunocapture and direct plate coating with the antigen to be tested) using neutralizing mono- and polyclonal antibodies. In our view, the immunocapture method based on the use of a neutralizing monoclonal anti-glycoprotein antibody seems to be a convenient tool for the determination of the in vitro potency of rabies vaccine and of the products corresponding to the different steps of their production process.

Rabies Vaccine Adsorbed: neutralizing antibody titers after three-dose pre-exposure vaccination

Field trials at several schools of veterinary medicine showed that three-dose pre-exposure rabies vaccination with Rabies Vaccine Adsorbed developed by the Michigan Department of Health elicited neutralization antibody in practically all recipients two to three weeks after immunization. Titers declined during the first six months after vaccination. However, by 18 to 24 months, 98 percent of recipients still had titers equal or greater than a 1:5 dilution of serum.

The protective effect of the large-scale use of PHKC rabies vaccine in humans in China

Reported are the results obtained with different immunization schedules of adjuvant or freeze-dried concentrated (FDC) primary hamster kidney cell (PHKC) rabies vaccine on volunteers. The FDC vaccine (potency, 4.5 IU), which was inoculated in six doses, on days 0, 3, 7, 14, 30 and 90, and the adjuvant vaccine (potency 2.5 IU), which was inoculated in five doses, on days 0 and 7 (double dose), 14, 30 and 90, induced earlier, higher, and more persistent neutralizing antibody titres than the adjuvant vaccine which was inoculated in five doses on days 0, 3, 7, 14 and 30. The persistence of the neutralizing antibody titres induced by three intradermal doses of vaccine administered on days 0 (4 sites), 7 (2 sites), and 28 (1 site) was lower than that induced by six intramuscular doses administered on days 0, 3, 7, 14, 30, and 90. A cell-mediated immunity (CMI) was also induced in vaccinees who received the adjuvant vaccine. The protective effect of the adjuvant vaccine was better than that of the previously used Semple vaccine and has had a positive effect on the epidemiology of human rabies in China.

Human diploid cell rabies vaccine purified by zonal centrifugation: a controlled study of antibody response and side effects following primary and booster pre-exposure immunizations

Systemic allergic reactions following booster immunizations have complicated rabies pre-exposure prophylaxis with the human diploid cell rabies vaccine licensed in the US (conventional HDCV). We conducted two studies comparing an HDCV purified by zonal centrifugation to conventional HDCV. In a study of primary pre-exposure immunization, volunteers received one of four regimens: three 1.0-ml intramuscular (i.m.) or 0.1-ml intradermal (i.d.) doses of conventional or purified HDCV over 28 days. Although volunteers vaccinated i.m. had significantly greater rabies neutralizing antibody titres (VNA) 49 days, 91 days and 26 months after immunization began than volunteers vaccinated i.d. (p less than 0.005-p less than 0.05), there were no significant differences between vaccines. In a study of booster immunizations, 77 volunteers immunized with conventional HDCV 2 years earlier received a 0.1-ml i.d. booster with either conventional or purified HDCV. VNA was significantly greater with the conventional HDCV on days 7 and 28 after booster, but not on day 365. A moderate or severe reaction was reported by 5 (13%) of the 40 persons who received boosters with conventional HDCV, versus none of 37 who received the purified HDCV (p = 0.03). Purified HDCV appears to be preferable to conventional HDCV for booster vaccination.

[A new rabies vaccine in public health practice in the USSR]

A new antirabies vaccine prepared on the basis of virus grown in the ovine brain, purified from 85-90% of brain-tissue ballast substances and inactivated with beta-propilactone has been developed at the Moscow Research Institute of Viral preparations (USSR Acad. Med. Sci.). The preparation produces no neuro-allergenic effect in tests on guinea pigs. When injected to humans, the vaccine shows much lower reactogenicity than Fermi vaccine. High antigenic and immunogenic activity of the new vaccine has made it possible to work out a less intensive immunization schedule in comparison with that used for immunization with Fermi vaccine and nonconcentrated tissue-culture vaccine, viz. doses of 3 ml for 12 days or doses of 3 ml for 20 days with two booster immunizations. The preparation has been introduced into medical practice.

[Specific activity of a concentrated, chromatography-purified cultured rabies vaccine]

Animal experiments and trials on humans have shown that purified and concentrated chromatographic tissue-culture rabies vaccine is safe and essentially more potent than commercial tissue-culture rabies vaccine.

Resolution of conformation equilibria in linear peptides by circular dichroism in cryogenic solvents

The circular dichroism spectra of the synthetic peptide antigen, 209-222 of the surface glycoprotein of the rabies virus were recorded as a function of solvent composition and over the temperature range of +60 degrees C to -135 degrees C; beta-III and beta-II reverse turn conformations were found to exist in TFE/H2O (3:1) at room temperature and in ethanediol/H2O (2:1) below -110 degrees C respectively. Evidence, from comparison of observed and calculated spectra, is given to support the existence of a conformational equilibrium between a beta-II and a beta-III reverse turn. These data can serve as a basis for synthetic vaccine development and understanding the nature of polypeptide chain folding.

Rhesus diploid rabies vaccine (adsorbed): neurological safety in guinea pigs and Lewis rats

Rabies vaccine produced in rhesus diploid cells (RDRV) and adsorbed on aluminium phosphate was evaluated for its neurological safety in guinea pigs and Lewis rats. The vaccine (as well as aluminium phosphate itself) in combination with myelin basic protein did not induce experimental allergic encephalomyelitis (EAE) when injected into either species. RDRV combined with complete Freund's adjuvant still failed to induce any signs of EAE. In contrast, basic protein combined with complete Freund's adjuvant induced severe EAE in both guinea pigs and rats. No experimental evidence was obtained to indicate adverse neuroimmunological activity of RDRV.

Oral vaccination of the fox against rabies using a live recombinant vaccinia virus

Rabies, a viral disease affecting all warm-blooded animals, is prevalent in most parts of the world, where it propagates amongst wild animals, particularly the fox and dog. The public health and economic consequences of infection in man and livestock are well known. Attempts to control the disease by vaccinating wild carnivores with inactivated or attenuated rabies virus remain controversial, and we have instead evaluated here the potential of a recombinant vaccinia virus to protect foxes against the disease. We have found that the administration of vaccinia virus (VV) or a recombinant harbouring the rabies surface antigen gene (VVTGgRAB) is innocuous to foxes. The recombinant virus can elicit the production of titers of rabies-neutralizing antibodies equal or superior to those obtained with conventional vaccine, and 10(8) plaque-forming units (PFU) of VVTGgRAB administered subcutaneously, intradermally or orally confers complete protection to severe challenge infection with street rabies virus.

Immune complex-like disease in 23 persons following a booster dose of rabies human diploid cell vaccine

Following a routine 0.1 ml booster dose of Merieux rabies human diploid cell vaccine (HDCV), administered intradermally, 23(10.2%) of 226 persons had signs and symptoms compatible with an immune complex-like disease. The disease had its onset from 3-13 days after the injection, lasted 1-5 days, and consisted primarily of urticaria (78.3%), macular rash (65.2%), angiooedema (39.1%), and arthralgia (17.4%). None of the cases were considered severe, and all recovered with no sequelae. There were significant differences in attack rates between men (78.3% of all cases) and women, and between those receiving vaccinations on different days. Similar reactions have been reported following intramuscular booster doses of HDCV. Since the Merieux HDCV is used worldwide, physicians administering HDCV must be aware of these adverse reactions and warn patients. Appropriate therapy should be instituted as warranted by severity of reactions.

Rabies immunosome (subunit vaccine) structure and immunogenicity. Pre- and post-exposure protection studies

Rabies immunosomes (glycoprotein anchored on pre-formed liposomes) have been prepared in order to study their structural, biological and immunological properties. The glycoprotein molecules appear to have the same orientation on the immunosome as on the viral particle: (1) electron microscopy analysis shows particles of 40 to 70 nm with spikes protruding outward, (2) one particular epitope shows the same accessibility to a neutralizing monoclonal antibody as on the viral particle. When injected into animals, rabies immunosomes are cleared from the organism by a process different from that for the liposomes used to anchor the glycoprotein: a higher rate of transition through the spleen is observed with immunosomes than with purified glycoprotein or liposomes. Immunosomes induce high levels of neutralizing antibodies and protect animals against challenge with virulent strains. This protective activity is not altered after several months of storage at 4 degrees C. Furthermore, rabies immunosomes were shown to be efficient in post-exposure treatment of laboratory animals that had been experimentally infected with a lethal dose of a rabies wild strain.

[Pre-exposure rabies vaccination using a new duck embryo vaccine]

An economical, highly purified and concentrated duck embryo rabies vaccine (PDEV) was investigated in relation to pre-exposure rabies prophylaxis. The vaccine was injected subcutaneously according to the then prescribed scheme for human diploid cell rabies vaccines (HDCV). Additionally, a third dose was given on day 120. Serum anti-rabies antibody levels were determined on days 0, 56, 120, und 170. On day 56 all volunteers showed an anti-rabies antibody level of at least 1.0 IU/ml, indicating that PDEV is sufficiently immunogenic to allow its use according to the pre-exposure schedules for HDCV. Some rather low titers noted on day 120 indicate that an early booster dose or a third primary immunization dose is justified, as recently recommended by the WHO.

Purified chick embryo cell (PCEC) rabies vaccine for human use. Laboratory data

A new inactivated rabies vaccine (Purified Chick Embryo Cell vaccine) for use in humans has been developed. The FLURY-LEP C25 strain of rabies virus was adapted to propagate in primary chick embryo cell cultures. The antigen was purified and concentrated by continuous density gradient centrifugation and inactivated by Betapropiolactone. The PCEC-rabies vaccine was tested for innocuity, tolerability and protective capacity in a series of laboratory tests and compared with Human Diploid Cell Strain rabies vaccine (HDCSV) of similar antigenicity. The results of the laboratory tests indicated that this new vaccine was excellently tolerated and that its protective activity met the high standard of HDCS-vaccine, conditions which were imposed on the PCEC-vaccine before clinical trials in man were initiated.