Short report: isolation and partial characterization of a Puumala virus from a human case of nephropathia epidemica in France

Puumala (PUU) virus (Bunyaviridae: Hantavirus), the etiologic agent of nephropathia epidemica (NE), the mid form of hemorrhagic fever with renal syndrome, is enzootic in Europe and has been known to occur in France since 1983. We report the first isolation of PUU virus in France and western Europe from a case of NE acquired in France. The virus was isolated from a serum collected in the acute phase of the clinical course by successive blind passages in Vero E6 cells. Serologic typing using monoclonal antibodies confirmed the identity of the virus as PUU. The sequence of an 832-nucleotide fragment of the virus medium RNA segment obtained by the polymerase chain reaction (PCR) also classified it as a PUU virus. The sequence of this isolate from a human case in France is closely related to the sequence of a PUU virus obtained by the PCR from a German patient.

[Post-exposure antirabies vaccination. Early serological response to vaccine cultivated on VERO cells using a reduced 2-1-1 schedule]

OBJECTIVES

An abbreviated 2-1-1 schedule for post-exposure rabies vaccination would theoretically lead to more rapid production of specific antibodies than the classical schedule. We measured early serological response to the 2-1-1 schedule.

METHODS

Patients consulting the antirabies centre of the Epinal hospital from June 1992 to June 1993 who had never been vaccinated and whose exposure history justified antirabies vaccination were included in this study. Fifty subjects were vaccinated with PVRV (purified vero rabies vaccine, Pasteur Institute) cultured on VERO (vervet monkey origin) cells using the abbreviated 2-1-1 schedule of 2 doses (0.5 ml = 2.5 IU/dose) on day 0 and 1 dose on days 7 and 21. Antirabies antibodies were assayed using the Platelia Rage immunoenzyme method (Diagnostic Pasteur) on day 21. Titres above 0.5 IU were considered to give protection and non-protected subjects were seen again on day 28 for a supplementary dose.

RESULTS

Only 34 subjects (68%) had protective antibody titres on day 21, but by day 28, 48 (96%) had acquired immunity. In this study population, the age range was from 1 to 83 years and age over 30 years appeared to delay antibody formation.

CONCLUSION

These findings emphasize the importance of initial antirabies immunoglobulins if short incubation in suspected and the need for serological follow-up if delayed antibody formation is suspected (subjects over 30).

Contribution to rabies prevention

After the end of the Second World War, an outbreak of fox rabies invaded Europe. For the immunization of human populations and domestic animals against the risk of rabies transmitted by infected wild animals, it appeared necessary to replace the first generation of rabies vaccines (nerve tissue vaccines) by more potent and safer vaccines. The European vaccine manufacturers, in close collaboration with the research institutes engaged in rabies research, soon and quickly developed a second generation of rabies vaccines, produced in cell cultures including continuous cell lines grown in bioreactors of industrial scale. The third generation of rabies vaccines is already available: the vaccinia-rabies glycoprotein recombinant vaccine is presently applied on a large scale in some European countries for immunization of wildlife. The canarypox recombinant vaccine has already been considered and successfully tested for human immunization.

Safety and immunogenicity of combined rabies and typhoid fever immunization

The prevalence of rabies and typhoid fever in many developing countries poses a serious health hazard to travellers. The development of a combined immunization schedule would be advantageous. A study was performed on 104 adult volunteers using purified Vero cell rabies vaccine and Typhim Vi, a purified capsular polysaccharide, either separately or in combination. No significant difference was observed in immunogenicity or tolerance between the two groups. A 3-year follow-up study is planned.

Rabies-specific production of interleukin-2 by peripheral blood lymphocytes from human rabies vaccinees

Cell-mediated immunity induced by rabies vaccination was studied in humans by the determination of specific interleukin-2 (IL-2) production in a large number of donors (postexposure immunized patients and pre-exposure immunized laboratory workers). Peripheral blood lymphocytes (PBL) from 35 donors were tested for IL-2 production after in vitro stimulation by different rabies and rabies-related viruses. IL-2 responses were compared to antibody recognition of these different virus serotypes by sera from the same individuals. IL-2 was produced by PBL from more than 85% of donors after stimulation with inactivated and purified rabies viruses (IPRV) prepared from either Pittman Moore (PM) or Pasteur Virus (PV) strains. IL-2 was also produced by 65 and 45% of donor PBL stimulated with IPRV from the European Bat Lyssavirus (EBL) and Mokola (Mok) rabies-related virus strains respectively. No correlation was found between the production of IL-2 by PBL and the levels of virus neutralizing antibody (VNAb). Moreover, 50, 25 and 35% of donors produced IL-2 after stimulation of their PBL with ribonucleoprotein (RNP) from PV-, EBL- and Mok-viruses, respectively. These results obtained with a large number of human rabies vaccinees and using an assay specific to T-cell activation confirm the significant cross-reactivity of T-cell responses directed against rabies and rabies-related viruses. This study shows that IL-2 production could be used for the study of cell-mediated immunity and T-cell memory induced in humans by rabies vaccination.

Appraisal of rabies vaccine potency by determination of in vitro, specific interleukin-2 production

The potency of different rabies vaccines was measured via cell mediated immunity (CMI) assessed by the production of interleukin-2 (IL-2) by CD4+CD8- lymphocytes. IL-2 production by splenocytes from mice immunized with various vaccines was measured following in vitro stimulation with antigens from different rabies and rabies-related strains. IL-2 production was specific, reproducible and correlated with the vaccine protective activity as determined by the pre-exposure NIH test. Our results suggest that measurement of IL-2 production could be used for the appraisal of rabies vaccine potency.

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.

Enhancement of interleukin-2 activity by liposomes

The present report demonstrates that liposomes increase the interleukin-2 (IL-2) dependent proliferation of cytotoxic T-lymphocyte line (CTLL) cells used for the measurement of IL-2 activity. This effect was better observed with suboptimal doses of IL-2 and low concentrations of lipids. The increased IL-2 dependent proliferation is not due to a direct effect of liposomes on CTLL cells but rather to an interaction between IL-2 and liposomes. An interaction between IL-2 and components of fetal calf serum is also demonstrated. The results indicate that liposomes may interfere with IL-2 bioassay but also show the possibility of potentiating IL-2 activity for therapeutic purposes.

From rabies to rabies-related viruses

Antigenic differences between rabies virus strains characterized with monoclonal antibodies presently define at least four serotypes within the Lyssavirus genus of the Rhabdoviridae family: classical rabies virus strains (serotype 1), Lagos bat virus (serotype 2), Mokola virus (serotype 3) and Duvenhage virus (serotype 4). The wide distribution of rabies-related virus strains (serotypes 2, 3 and 4) and above all, the weak protection conferred by rabies vaccines against some of them (principally Mokola virus) necessitates the development of new specific vaccines. We first determined the complete nucleotide sequence of a rabies virus strain of serotype 1 (Pasteur virus) and characterized the structure of the viral genes and their regulatory sequences. We then extended this study to the Mokola virus genome. Five non-overlapping open reading frames were found in both viruses and had similar sizes and positions in both. Similarities were also found in the mRNA start and stop sequences and at the genomic extremities. Comparison of both genomes helps to analyze the basis of the particular antigenicity of these two serotypes. The sequence homology in the region coding for the viral glycoprotein was only 58% between the two viruses, compared with 94% between different rabies virus strains within serotype 1. This comparison, extended to other unsegmented negative strand RNA viruses, gives new insight into the understanding of rhabdoviruses and paramyxoviruses. Furthermore, molecular cloning provides a rationale for the genetic engineering of a future vaccine.

Recent data on the epidemiology and prophylaxis of human rabies in France

Rabies is an animal disease which is transmitted to man only by accident, most often through the bite (more rarely after scratches or licks of mucosa) of a rabid animal, domestic or wild. A good knowledge of the epizootiology of animal rabies is therefore necessary to establish, on solid grounds, the prophylaxis of human rabies. Inter-human transmission of rabies being an exceptional event which will be considered separately, the epidemiology of human rabies mainly studies the sources and circumstances of human exposure to rabid animals, which differ according to the epizootiology of animal rabies in a given country: either enzootic (or hyperenzootic) canine rabies, or enzootic selvatic rabies. It appears that the risk of human rabies is higher in the first situation for two reasons: (i) rabies viruses show an increased virulence due to numerous serial passages in dogs (viruses with short incubation period) and (ii) high frequency of dog-man contacts due to the high density of both populations.

[Antigenic variants of rabies virus isolated in the northeast and southeast of Brazil. Preliminary study]

To help identify the different strains of rabies virus existing in Brazil, the antigenic profile of 13 virus isolates from humans and animals was determined. The indirect immunofluorescence technique was used, with monoclonal antibodies targeted at the viral nucleocapsid. In the northeast of the country five different viral strains were identified, and in the southeast, two. A rhabdovirus isolated from a fox could not be characterized as a rabies virus. Previously, only two antigenic variants had been identified in Brazil. It would appear that distribution of the strains is not related to the species from which they are isolated or to their geographical origin, a finding that differs from previous observations. These preliminary results underscore the need for further research in order to identify the existence and distribution of different strains of rabies virus in Brazil, which would help to prevent rabies vaccination failures.

[The efficacy of the ERA rabies vaccine, in mice against 4 antigenic variants of rabies virus]

ERA anti-rabies vaccine prepared in kidney tissue culture was evaluated against four different antigenic strains of rabies virus in mice: two of them dog strains, C/SP and C/NG, another a bat vampire strain, DR-19, and the CVS strain. The CVS antigenic characteristics were determined by means the antinucleocapsid monoclonal antibodies technique. Twenty one days old mice were vaccinated, intramuscularly, in the inner side of the thigh, with 0.05 ml of vaccine and challenged at 42 days old, together with those of the control group, intramuscularly, in the inner side of the thigh, with 0.05 ml of the corresponding viral strain dilution. The ERA anti-rabies vaccine protected 100% of all the mice challenged with C/SP, C/NG and DR-19 strains and 83% of those challenged with CVS. The control groups mortality rate varied between 70 and 90%.

The use of immunosome technology for vaccines against rabies and other viral diseases

Subunit viral vaccines present several advantages. They are free of nucleic acids (of viral and/or cellular origin) and proteins of cellular and/or serum origin; they contain only the relevant antigen. For rabies virus, the antigen which induces the virus-neutralizing antibody (VNAb) is the glycoprotein (GP), which is anchored, in form of spikes, to the viral membrane. The GP may be extracted from the virion but, after solubilization and purification, it appears to be poorly immunogenic. In order to restore its immunogenicity, GP molecules are anchored to preformed liposomes (unilamellar phospholipid vesicles) to mimic their native structure and environment. The subunit vaccine obtained by this technique is called an "immunosome" (IMS). Rabies immunosomes exhibit structural and immunological properties very similar to those of the viral particle. The rabies glycoprotein molecules, anchored to the lipid bilayer of the liposome, correctly expose the immunodominant epitope involved in VNAb induction and induce a strong specific humoral immune response. They also induce a specific cellular immune response. As a result IMS have a highly protective activity when tested with either pre- or post-exposure potency tests. Immunosome technology may be applied to other purified membrane proteins or amphiphilic peptides to restore their immunogenicity.

Complete cloning and molecular organization of a rabies-related virus, Mokola virus

Mokola virus is a rabies-related virus responsible for both animal and human encephalitis cases in Africa. We report here the construction of a genomic library containing overlapping cDNA clones encompassing the entire genome. Five overlapping clones were sufficient to cover the genome (about 12 kb in size). Mokola virus was shown to share the same genomic organization as the rabies virus genome and also identical transcription signals. cDNA probes characterized six different transcripts by Northern blotting experiments; five of them corresponded in size and location to rabies virus mRNAs, and one of particular interest corresponded to a bicistronic RNA which included the genes for the phosphoprotein and the matrix protein. Comparison of the 3' and 5' end sequences of the Mokola genome with those of other members of the Lyssavirus genus showed a high homology and led us to propose a genus-specific consensus sequence. However, the latter appeared to vary widely throughout the Rhabdoviridae family.

Trial of economical regimens of suckling mouse brain rabies vaccine for postexposure prophylaxis in Lagos, Nigeria

The suckling mouse brain rabies vaccine, recommended for production and routine use in Nigeria from our previous study, was investigated in the present study in an effort to reduce the cost of antirabies treatment in the country. This is needed for economic reasons. Instead of seven daily doses followed by three boosters, we tried five daily doses followed by three boosters, with or without equine hyperimmune serum given on day 0 (40 IU per kg body weight). Fifty dog-bite, victims, aged 3-81 years, were placed on this regimen, 25 with serum and 25 without serum, according to the history of the case. The serum had no effect on the kinetics of antibody development and both serum and vaccine were well tolerated. The geometric mean titres (GMTs) of antirabies antibodies in the sera of recipients of vaccine alone on days 10, 28 and 90 were 3.05 equivalent units ml-1 (EU ml-1), 4.35 EU ml-1 and 2.54 EU ml-1 respectively. Among those who had received antiserum and vaccine the titres were respectively 3.19 EU ml-1, 4.35 EU ml-1 and 3.02 EU ml-1. Of the 50 subjects, 49 showed detectable antibodies by day 28, and all the 50 survived. This regimen is therefore recommended for further trial in countries where rabies is endemic but potent antirabies vaccines are scarce and expensive. Another 23 subjects, considered not to be at risk of rabies, were given a one-tenth dose, two-site intradermal inoculation of the same vaccine on days 0, 3, 7, 14, 28 and 90.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the induction of specific cytotoxic T lymphocytes following immunization of F1 hybrid mice with rabies antigens

The measurement of the production of cytotoxic T lymphocytes (CTL) induced in mice by rabies antigens currently uses spleen cells from immunized A/J mice as effector cells and infected neuroblastoma syngeneic cells as target cells. For several reasons, including difficulties in obtaining A/J mice, as well as genetic analysis of immune responses, it would be advantageous to use strains of mice other than the A/J mice. However, cell lines other than the neuroblastoma Neuro-2a line are difficult to infect by the rabies virus. Therefore, using the same target cells expressing the major histocompatibility complex H-2kd, we have developed an experimental system based on the induction of CTL in F1 BALB/c X C3H/HeJ hybrid H-2kd mice. Splenocytes from F1 hybrid mice primed with inactivated purified rabies virus (IPRV) exhibited cytotoxic activity specific for syngeneic infected target cells (Neuro-2a). High amounts of IPRV were required for the induction of CTL following in vivo priming. The antigen dose required for CTL induction was reduced by in vitro restimulation. In addition to specific CTL, a high level of natural killer cell activity was induced in F1 hybrid mice by priming with IPRV. Among rabies antigen preparations tested (IPRV, purified glycoprotein and ribonucleoprotein), only IPRV induced strong CTL stimulation.

[A simplified method of vaccination against rabies after exposure]

Vaccination against rabies after exposure to the risk of contamination is currently performed according to the WHO recommendations: 6 injections in 6 visits. We have studied the serological effectiveness of a simplified method using the human diploid-cell rabies vaccine: the vaccine is injected subcutaneously at the rate of 2 doses on day 0, then one dose on day 7 and one dose on day 21. Fifty subjects were vaccinated, and antiglycoprotein antibodies were assayed in serum by the immunoenzymatic technique (EU/ml). Seroconversion with titres above 0.5 EU/ml was observed in all subjects. The antibody titres were 0.127 +/- 1.57, 11.31 +/- 8.87, 10.2 +/- 7.55, and the numbers of subjects with protective titres were 0/50, 11/50, 46/47 and 36/37 on days 0, 7, 21 and 90 respectively. No undesirable side-effect was recorded. The good results obtained with this 2+1+1 vaccination schedule (4 injections in 3 visits) suggest that the recommended method of post-exposure vaccination could be replaced by this simplified method.

Comparative field evaluation of the fluorescent-antibody test, virus isolation from tissue culture, and enzyme immunodiagnosis for rapid laboratory diagnosis of rabies

The rabies tissue culture infection test (RTCIT) and rapid rabies enzyme immunodiagnosis (RREID) were compared to the fluorescent-antibody test (FAT) with field specimens. At the French National Reference Center for Rabies, 15,248 specimens were analyzed by FAT and RTCIT, and 2,290 of those specimens were also tested by RREID; 818 other specimens were tested by FAT and RREID in 12 laboratories located in Africa, Asia, and Latin America. The sensitivities and specificities of RREID and RTCIT were comparable. This study showed that both tests can be used as backup procedures to confirm FAT. RREID is also strongly recommended for epidemiological studies and for laboratories which are not equipped for performing FAT.

Comparative study of two human diploid rabies vaccines administered with antirabies globulin

The association of human rabies immune globulin (HRIG) to the vaccine is recommended for postexposure rabies treatment in cases of severe exposure. In a previous study using an abbreviated postexposure vaccination schedule it was observed that passive immunization could partially inhibit the active immune response, with three cell-culture purified vaccines but not with the concentrated human diploid cell vaccine (HDCV). In order to see if this difference was related to the purification process, the present study was designed comparing two HDCV, one concentrated and the other concentrated and purified, both of them administered in association with HRIG. The neutralizing antibody response in the vaccines was found to be identical with both vaccines, ruling out the role of the purification and confirming the excellent immunogenicity of both human diploid cell vaccines and the absence of inhibition of the active immune response by the association of HRIG to HDCV.

Monoclonal antibodies to Mokola virus for identification of rabies and rabies-related viruses

Rabies and rabies-related virus strains were studied by using a panel of monoclonal antibodies directed against either nucleocapsid proteins or cell surface antigens of Mokola virus (Mok-3). Each strain was used in parallel to infect cultured cells and mice. Then, the patterns of reactivity of the different monoclonal antibodies were determined by the immunofluorescent-antibody staining procedure. On cells, the monoclonal antibodies differentiated fixed rabies virus strains (serotype 1) from rabies-related virus strains. The seven fixed strains (CVS, PV4, PM, Flury LEP and HEP, ERA, and SAD) reacted identically. The previous serotype groupings (serotype 2, Lagos-bat virus; serotype 3, Mokola virus; serotype 4, Duvenhage virus) established with anti-rabies monoclonal antibodies were confirmed, except for that of Lagos-bat Kindia, which appeared to be related to the African subtype of the Duvenhage serotype (Duv-2). Within the Mokola (Mok-1, -2, -3, and -5 and Umhlanga) and the Lagos-bat (Lag-1 and -2, Zimbabwe, Pinetown, and Dakar) serotypes, each strain appeared to be distinct. The African subtype of the Duvenhage serotype reacted differently from the European subtype. Within the Duvenhage serotype, subtypes Duv-4, -5, and -6 and Denmark reacted identically, while subtypes Duv-1, -2, and -3 and German Democratic Republic appeared to be distinct. The monoclonal antibodies specific for the cell surface antigens were also used in neutralization tests with all the strains. Two of them neutralized the infectivity of Mokola virus.

History of rabies: advances in research towards rabies prevention during the last 30 years

The great amount of basic research on rabies virus in the last 30 years has led to important improvements in the methods used for the prevention of rabies--methods that include rapid laboratory diagnosis, production of cell culture vaccine, and the means for controlling wildlife rabies. These advances are briefly reviewed.

A rabies agglutination test (RAT) for rabies antibody detection

An agglutination test has been developed for the detection of rabies antibodies after human vaccination. The rabies agglutination test (RAT) is based on the capability of specific antibody to agglutinate sensitized polystyrene (or latex) beads. In the RAT, latex beads were coated, in a first step, with inactivated and purified rabies virus (PV strain adapted and propagated on BHK-21 cells) and, in a second step, with bovine serum albumin. Negative control beads were coated with bovine serum albumin (BSA) only. To test for human antibody, several microliters of serum were mixed on a glass slide with an equal volume of virus-sensitized beads and the mixture was gently agitated. After a few minutes, agglutination was visible with sera which had been characterized as positive by the virus neutralization antibody (VNAb) technique. No agglutination was observed with negative sera tested with virus-coated beads or with positive sera tested with BSA-coated beads. Virus-sensitized beads were agglutinated when the virus neutralizing antibody titres were equal to or greater than 2.5 international units per ml (IU/ml) in human sera. The concordance between the RAT results and VNAb titres was about 97% when 2.5 IU/ml was taken as the cut off value for determining the positive sera with the VNAb technique. The possibility that clinicians might use the RAT as a simple means to determine sero-conversion at the end of the post-exposure treatment of patients is discussed.

Immunity against the European bat rabies (Duvenhage) virus induced by rabies vaccines: an experimental study in mice

Protection experiments were performed in mice with different inactivated vaccines prepared with the fixed rabies virus strains: PM (Pitman-Moore), PV4 (Pasteur virus) and LEP (Flury LEP) against an intracerebral challenge with a European bat virus (Duvenhage, strain Hamburg, DUV3). All vaccines protected mice against challenge with CVS (Challenge virus standard). Vaccines prepared with PV4 protected mice against a DUV3 challenge. On the contrary, PM or LEP vaccines did not protect mice against a DUV3 infection. The protection conferred by PV4 vaccines against Duvenhage could be due to the antigenic relationship which seems to exist between PV4 and European bat virus as revealed by serum-virus neutralization, absorption experiments and CTL crossreactivity. The four virus strains PAS, PV4, PM and CVS, originated from the Pasteur virus isolated in 1882 from the brain of a rabid cow, were classified in two groups on the basis of reactivity with neutralizing anti-glycoprotein monoclonal antibodies. One group contained the L. Pasteur (PAS) and the PV4 strains, the second contained PM and CVS strains. The divergence between the two virus groups possibly resulted from distinct passage histories.

Interleukin-2 production in vitro: a new approach to the study of rabies vaccine immunogenicity as appraised by testing different glycoprotein presentations

When injected as an immunosome presentation (molecules anchored to preformed liposome), rabies glycoprotein (GP) is capable of protecting animals against rabies either before or after viral infection. The presentation of the GP molecules in the correct form seems to be essential for the induction of antirabies protection. This condition must be taken in account in the making-up of a rabies subunit vaccine. In order to study the relationship between the immune responses induced by the rabies GP and its protective activity, different presentations of the GP were prepared. Purified glycoprotein molecules were associated under different physical forms: liposome-anchored, self-aggregated (rosettes) and associated with the viral lipids (virosomes). These presentations appeared different on electron microscopy. They also exhibited differences in the expression of an immunodominant epitope and in their protective activity. The non-specific immune response, as appraised by interferon production and natural cytotoxicity, was induced at a high level only by the purified viral particles. Specific immune responses (namely virus neutralizing antibody and interleukin-2 production) was induced at high levels only by the viral particle and by the liposome-anchored glycoprotein. A parallelism has previously been established between protection by glycoprotein preparations and interleukin-2 production in primed mice splenocytes. This suggests that the measure of interleukin-2 production in vitro could be used to evaluate the capability of a rabies antigen to induce a T-cell response and to confer protection.

Interaction of rabies vaccine with human rabies immunoglobulin and reliability of a 2-1-1 schedule application for postexposure treatment

Five commercially available rabies vaccines (HDCV, FBKC vaccine, PCEC vaccine, PVRV and PDEV) applied alone or combined with human rabies immunoglobulin (HRIG) were administered, by random allocation, to 161 volunteer vaccinees, using the abbreviated 2-1-1 postexposure immunization schedule. Protective levels of rabies antibody were demonstrated in all vaccinees by day 14, and in all but one vaccinee from day 21 to day 90. Partial inhibition of the antibody response due to HRIG was observed for three vaccines (PCEC vaccine, PVRV and PDEV). In terms of economy, reliability and rapid antibody induction, the 2-1-1 schedule proves superior to the presently recommended regimen for postexposure rabies prophylaxis.

Enhancement of antigen-specific interleukin 2 production by adding liposomes to rabies antigens for priming

Antigen-specific IL-2 production was assessed, using splenocytes from rabies immune mice incubated for 24 h with rabies virus antigen. The antigenic material used for in vivo priming was either purified glycoprotein from rabies virus, or the inactivated virus. The time between priming, harvesting and restimulation of the splenocytes was 7 days. It was found that when antigenically inert liposomes were injected, together with antigenic material, to the prospective splenocyte donor mice, IL-2 production was enhanced. This augmentation was observed particularly when priming was performed with the inactivated rabies virus.

Interleukin 2 increases protection against experimental rabies

Vaccination with either whole inactivated rabies virus or immunosome (rabies glycoprotein anchored on liposomes) induces a high level of interleukin 2 (IL 2) production after in vitro specific stimulation of splenocytes from primed mice (9). On the contrary, infection with a live rabies virus does not specifically induce the production of IL 2: splenocytes from ill mice previously infected with wild rabies virus cannot be specifically stimulated by rabies antigens, whereas they can be non-specifically stimulated by a mitogen (Concanavalin A (Con A]. When injected in mice, exogenous IL 2 (purified rat IL 2 or human recombinant IL 2) exhibits an adjuvant effect on rabies virus vaccine or subunit vaccine tested in a pre-exposure potency test (NIH test). When injected in hamsters, according to a post-exposure potency test (infection with a wild rabies virus followed by vaccination), IL 2 has no adjuvant effect on the rabies vaccine. Nevertheless, when injected alone, IL 2 protects thirty to fifty percent of the infected animals treated (1 hour, 3 and 7 days post-infection) with 10 international units of human recombinant IL 2.

Immunological relationships between rabies virus and rabies-related viruses studied with monoclonal antibodies to Mokola virus

Specific monoclonal antibodies (mAb) were prepared against a rabies-related lyssavirus, Mokola virus. A strain isolated in the Central African Republic, Mok-3, was used as immunogen. After 3 fusions more than 90 hybridoma cultures secreting mAb were identified. According to their different patterns of reactivity against rabies and rabies-related viruses, 61 ascites fluids were obtained. The antibody class was IgM for 2 of them and IgG for 59. They were specific for one of the 4 major viral proteins, as determined by immunofluorescence, neutralization and immunoblotting tests. Their patterns of reactivity were determined against 6 different strains of rabies-related viruses: Lagos-bat virus from Nigeria (Lag-1) and the Central African Republic (Lag-2), Duvenhage virus from the Republic of South Africa (Duv-1) and Federal Republic of Germany (Duv-3), Mokola virus from Nigeria (Mok-1) and Cameroon (Mok-2) and a fixed strain of rabies virus, the challenge virus strain (CVS). According to their reactivities with these strains and the pattern of fluorescence, the mAb were classified into 11 different groups with intracytoplasmic fluorescence and 7 groups with cell surface fluorescence. A differential diagnosis of these lyssaviruses is possible in tissue culture using some of these mAb.

Treatment of rabies in mice and foxes with antiviral compounds

Thirty four chemical compounds were injected into rabies infected mice by intramuscular (i.m.) route. Twenty four compounds such as well known therapeutic agents: amantadine, lipacids, phenol compounds, didemnin-B, procaine, nucleosides analogues (ribavirin, tiazofurin, pyrazofurin) had no effect. Two compounds had a slight effect not justifying to consider them as possible therapeutic agents: selenazofurin and an analogue of ribavirin (RTA). Eight heteropolyanions (HPA), which have a related chemical structure, were efficient providing 100% protection. Nineteen compounds were injected into rabies infected mice by the intracerebral (i.c.) route. Fourteen compounds such as ribavirin, RTA, selenazofurin, tiazofurin and 9 HPA compounds had no effect. Five other HPA compounds (HPA 23-39-46-51-56) were efficient preventing the development of clinical infection in some mice. Whatever was the treatment route, treated surviving mice developed rabies neutralizing antibodies. No proof of viral multiplication was found in their brains. As some HPA compounds did produce a therapeutic effect in mice, two of them HPA 23 and HPA 39 were administered to rabies-infected foxes. In foxes the compounds prolonged the mean survival time and increased the number of survivors. These data suggest that chemotherapy might be worthwhile when vaccination was impossible.

New vaccines for immunization of man: new approaches towards the prevention of rabies in man

Cell culture rabies vaccines for human use, highly immunogenic and well tolerated, are now used for pre-exposure immunization as well as for post-exposure treatment. Presently available cell culture rabies vaccines induce immunity against the SAD modified live rabies virus used for oral immunization of foxes. They also induce immunity against the newly identified European bat rabies virus (Duvenhage).

The association of the rabies glycoprotein with liposome (immunosome) induces an in vitro specific release of interleukin 2

BALB/c mice were primed by receiving a unique intraperitoneal injection of rabies virus antigens presented as complete inactivated virus (P.V. strain) or as purified glycoproteins either in the aggregated form or in physical combination with liposomes (i.e., in the form of "immunosomes"). The splenocytes of these mice were restimulated, 6-15 days after priming, in culture with rabies virus antigens, and antigen-specific IL-2 production was measured. It was found that rabies antigens presented as immunosomes were as active as the inactivated virus, whereas equivalent amounts of purified glycoproteins were inactive. The optimal amounts of rabies immunosomes used for priming was found to be 0.5 to 0.05 micrograms per mouse.