Pathogenesis of rabies in dogs inoculated with an Ethiopian rabies virus strain. Immunofluorescence, histologic and ultrastructural studies of the central nervous system

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.

Rabies in Our Neighbourhood: Preparedness for an Emerging Infectious Disease

Emerging infectious disease (EID) events have the potential to cause devastating impacts on human, animal and environmental health. A range of tools exist which can be applied to address EID event detection, preparedness and response. Here we use a case study of rabies in Southeast Asia and Oceania to illustrate, via nearly a decade of research activities, how such tools can be systematically integrated into a framework for EID preparedness. During the past three decades, canine rabies has spread to previously free areas of Southeast Asia, threatening the rabies-free status of countries such as Timor Leste, Papua New Guinea and Australia. The program of research to address rabies preparedness in the Oceanic region has included scanning and surveillance to define the emerging nature of canine rabies within the Southeast Asia region; field studies to collect information on potential reservoir species, their distribution and behaviour; participatory and sociological studies to identify priorities for disease response; and targeted risk assessment and disease modelling studies. Lessons learnt include the need to develop methods to collect data in remote regions, and the need to continuously evaluate and update requirements for preparedness in response to evolving drivers of emerging infectious disease.

Virulence mismatches in index hosts shape the outcomes of cross-species transmission

Emerging disease epidemics often result from a pathogen establishing transmission in a novel host species. However, for reasons that remain poorly understood, most cross-species transmissions fail to establish in the newly infected species. Examining experimental cross-species inoculations of rabies virus, we show that host and viral factors predict differences in disease progression in ways that are expected to impact the likelihood of onward transmission. Disease progression was accelerated and virus excretion decreased when the reservoir and novel host were physiologically or genetically more dissimilar. These insights may help to explain and predict host shifts in rabies and other zoonotic viruses and highlight meta-analyses of experimental inoculation data as a powerful and generalizable approach for understanding the dynamics of index infections.

Whether a pathogen entering a new host species results in a single infection or in onward transmission, and potentially an outbreak, depends upon the progression of infection in the index case. Although index infections are rarely observable in nature, experimental inoculations of pathogens into novel host species provide a rich and largely unexploited data source for meta-analyses to identify the host and pathogen determinants of variability in infection outcomes. We analyzed the progressions of 514 experimental cross-species inoculations of rabies virus, a widespread zoonosis which in nature exhibits both dead-end infections and varying levels of sustained transmission in novel hosts. Inoculations originating from bats rather than carnivores, and from warmer- to cooler-bodied species caused infections with shorter incubation periods that were associated with diminished virus excretion. Inoculations between distantly related hosts tended to result in shorter clinical disease periods, which are also expected to impede onward transmission. All effects were modulated by infection dose. Taken together, these results suggest that as host species become more dissimilar, increased virulence might act as a limiting factor preventing onward transmission. These results can explain observed constraints on rabies virus host shifts, describe a previously unrecognized role of host body temperature, and provide a potential explanation for host shifts being less likely between genetically distant species. More generally, our study highlights meta-analyses of experimental infections as a tractable approach to quantify the complex interactions between virus, reservoir, and novel host that shape the outcome of cross-species transmission.

SNAP25 regulates the release of the Rabies virus in nerve cells via SNARE complex-mediated membrane fusion

Recent studies have reported that host proteins regulate Rabies virus (RABV) infection via distinct mechanisms. The abnormal neural function caused by RABV infection is related to the abnormal synaptic signal transmission in which the RABV glycoprotein (G) is involved. In the present study, two recombinant Rabies viruses (rRABVs), namely rSAD-SAD-Flag-G and rSAD-CVS-Flag-G, were established and rescued based on rSAD and verified by indirect fluorescence assay (IFA), and western blotting (WB). To investigate how the G protein interacts with synaptosomal-associated protein 25 (SNAP25), primary neuronal cells (PNC) of embryonic mice were cultured and infected with rRABVs. Immunoprecipitation (IP) and LC-MS/MS analysis of glycoprotein-binding proteins, which were flag tagged, were carried out to determine the interaction of G protein and soluble N-ethylmaleimide-sensitive factor attachment protein receptor proteins (SNARE) complex in PNC. G protein and the SNARE member SNAP25 were co-expressed in HEK293 cells or primary neuronal cells to investigate their colocalization. Knockdown of SNAP25 with small interfering RNA (siRNA) was conducted on mNA cells, and rRABV replication was observed by IFA, qRT-PCR, and virus titration. The results indicated that rRABVs were successfully rescued and grew well in PNC. Flag-tag IP and confocal microscopy demonstrated that SNAP25 works together with G protein and colocalizes with G on the cytomembrane of HEK293 cells. The downregulation of SNAP25, using RNA interference, resulted in a significant decrease in the number of viral mRNAs, viral proteins, and virus particles. Furthermore, the regression of SNAP25 did not affect the initial infection of the virus but reduced the infectivity of progeny virions.

Association between RABV G Proteins Transported from the Perinuclear Space to the Cell Surface Membrane and N-Glycosylation of the Sequon Asn(204)

In this study, G proteins of the rabies virus (RABV) Kyoto strain were detected in the cytoplasm but not distributed at the cell membrane of mouse neuroblastoma (MNA) cells. G proteins of CVS-26 were detected in both the cell membrane and perinuclear space of MNA cells. We found that N-glycosylation of street RABV G protein by the insertion of the sequon Asn(204) induced the transfer of RABV G proteins to the cell surface membrane. Fixed RABV budding from the plasma membrane has been found to depend not only on G protein but also on other structural proteins such as M protein. However, the differing N-glycosylation of G protein could be associated with the distinct budding and antigenic features of RABV in street and fixed viruses. Our study of the association of N-glycan of G protein at Asn(204) with the transport of RABV G protein to the cell surface membrane contributes to the understanding of the evolution of fixed virus from street virus, which in turn would help for determine the mechanism underlying RABV budding and enhanced host immune responses.

Lyssaviruses and bats: emergence and zoonotic threat

The continued detection of zoonotic viral infections in bats has led to the microbial fauna of these mammals being studied at a greater level than ever before. Whilst numerous pathogens have been discovered in bat species, infection with lyssaviruses is of particular significance from a zoonotic perspective as, where human infection has been reported, it is invariably fatal. Here we review the detection of lyssaviruses within different bat species and overview what is understood regarding their maintenance and transmission following both experimental and natural infection. We discuss the relevance of these pathogens as zoonotic agents and the threat of newly discovered viruses to human populations.

Lyssavirus infection: 'low dose, multiple exposure' in the mouse model

The European bat lyssaviruses (EBLV-1 and EBLV-2) are zoonotic pathogens present within bat populations across Europe. The maintenance and transmission of lyssaviruses within bat colonies is poorly understood. Cases of repeated isolation of lyssaviruses from bat roosts have raised questions regarding the maintenance and intraspecies transmissibility of these viruses within colonies. Furthermore, the significance of seropositive bats in colonies remains unclear. Due to the protected nature of European bat species, and hence restrictions to working with the natural host for lyssaviruses, this study analysed the outcome following repeat inoculation of low doses of lyssaviruses in a murine model. A standardized dose of virus, EBLV-1, EBLV-2 or a 'street strain' of rabies (RABV), was administered via a peripheral route to attempt to mimic what is hypothesized as natural infection. Each mouse (n=10/virus/group/dilution) received four inoculations, two doses in each footpad over a period of four months, alternating footpad with each inoculation. Mice were tail bled between inoculations to evaluate antibody responses to infection. Mice succumbed to infection after each inoculation with 26.6% of mice developing clinical disease following the initial exposure across all dilutions (RABV, 32.5% (n=13/40); EBLV-1, 35% (n=13/40); EBLV-2, 12.5% (n=5/40)). Interestingly, the lowest dose caused clinical disease in some mice upon first exposure ((RABV, 20% (n=2/10) after first inoculation; RABV, 12.5% (n=1/8) after second inoculation; EBLV-2, 10% (n=1/10) after primary inoculation). Furthermore, five mice developed clinical disease following the second exposure to live virus (RABV, n=1; EBLV-1, n=1; EBLV-2, n=3) although histopathological examination indicated that the primary inoculation was the most probably cause of death due to levels of inflammation and virus antigen distribution observed. All the remaining mice (RABV, n=26; EBLV-1, n=26; EBLV-2, n=29) survived the tertiary and quaternary inoculations although the serological response did not necessarily reflect the repeated exposure. We conclude that despite repeated exposure, neither clinical disease nor serological response can be predicted and that further studies are required to understand the mechanisms behind survival following multiple exposures to lyssaviruses.

Differential chemokine responses in the murine brain following lyssavirus infection

The hallmark of lyssavirus infection is lethal encephalomyelitis. Previous studies have reported distinct lyssavirus isolate-related differences in severity of cellular recruitment into the encephalon in a murine model of infection following peripheral inoculation with rabies virus (RABV) and European bat lyssavirus (EBLV)-1 and -2. In order to understand the role of chemokines in this process, comparative studies of the chemokine pattern, distribution and production in response to infection with these lyssaviruses were undertaken. Expression of CCL2, CCL5 and CXCL10 was observed throughout the murine brain with a distinct caudal bias in distribution, similar to both inflammatory changes and virus antigen distribution. CCL2 immunolabelling was localized to neuronal and astroglial populations. CCL5 immunolabelling was only detected in the astroglia, while CXCL10 labelling, although present in the astroglia, was more prominent in neurons. Isolate-dependent differences in the amount of chemokine immunolabelling in specific brain regions and chemokine production by neurons in vitro were observed, with a greater expression of CCL5 in vivo and CXCL10 production in vitro after EBLV infection. Additionally, strong positive associations between chemokine immunolabelling and perivascular cuffing and, to a lesser extent, virus antigen score were also observed. These differences in chemokine expression may explain the variation in severity of encephalitic changes observed in animals infected with different lyssavirus isolates.

Postexposure treatment with the live-attenuated rabies virus (RV) vaccine TriGAS triggers the clearance of wild-type RV from the Central Nervous System (CNS) through the rapid induction of genes relevant to adaptive immunity in CNS tissues

Postexposure treatment (PET) of wild-type rabies virus (RV)-infected mice with a live-attenuated triple-glycoprotein RV variant (TriGAS) promotes survival but does not prevent the pathogenic RV from invading and replicating in the brain. Successful PET is associated with the induction of a robust virus-neutralizing antibody response and clearance of the wild-type RV from brain tissues. Comparison of the transcriptomes of normal mouse brain with those of wild-type-RV-infected mice that had received either mock or TriGAS PET treatment revealed that many of the host genes activated in the mock-treated mice represent type I interferon (IFN) response genes. This indicates that RV infection induces an early type I IFN response that is unable to control the infection. In contrast, most of the activated genes in the brain of the RV-infected, TriGAS-treated mouse play a role in adaptive immunity, including the regulation of T cell activation, T cell differentiation, and the regulation of lymphocyte and mononuclear cell proliferation. These findings were confirmed by quantitative PCR (qPCR) array studies, which showed that 3 genes in particular, encoding chemokine ligand 3 (Ccl3), natural killer cell activator 2 (interleukin 12B [IL-12B]), and granzyme A (GzmA), were activated earlier and to a greater extent in the brains of RV-infected mice treated with TriGAS than in the brains of mock-treated mice. The activation of these genes, known to play key roles in the regulation of lymphocyte and mononuclear cell proliferation, is likely an important part of the mechanism by which TriGAS mediates its PET activity.

Serial passage of a street rabies virus in mouse neuroblastoma cells resulted in attenuation: potential role of the additional N-glycosylation of a viral glycoprotein in the reduced pathogenicity of street rabies virus

Street rabies viruses are field isolates known to be highly neurotropic. However, the viral elements related to their pathogenicity have yet to be identified at the nucleotide or amino acid level. Here, through 30 passages in mouse neuroblastoma NA cells, we have established an attenuated variant of street rabies virus strain 1088, originating from a rabid woodchuck followed by 2 passages in the brains of suckling mice. The variant, 1088-N30, was well adapted to NA cells and highly attenuated in adult mice after intramuscular (i.m.) but not intracerebral (i.c.) inoculations. 1088-N30 had seven nucleotide substitutions, and the R196S mutation of the G protein led to an additional N-glycosylation. Street viruses usually possess one or two N-glycosylation sites on the G protein, 1088 has two, while an additional N-glycosylation site is observed in laboratory-adapted strains. We also established a cloned variant 1088-N4#14 by limiting dilution. Apart from the R196S mutation, 1088-N4#14 possessed only one amino acid substitution in the P protein, which is found in several field isolates. 1088-N4#14 also efficiently replicated in NA cells and was attenuated in adult mice after i.m. inoculations, although it was more pathogenic than 1088-N30. The spread of 1088-N30 in the brain was highly restricted after i.m. inoculations, although the pattern of 1088-N4#14's spread was intermediate between that of the parental 1088 and 1088-N30. Meanwhile, both variants strongly induced humoral immune responses in mice compared to 1088. Our results indicate that the additional N-glycosylation is likely related to the reduced pathogenicity. Taken together, we propose that the number of N-glycosylation sites in the G protein is one of the determinants of the pathogenicity of street rabies viruses.

Assessing the risks of intervention: immobilization, radio-collaring and vaccination of African wild dogs

Controversy has surrounded the role of intervention in studies of African wild dogs Lycaon pictus. Following the death or disappearance of all wild dogs under study in the Serengeti ecosystem, it was suggested that immobilization, radio-collaring or administration of rabies vaccines might have caused high mortality by compromising wild dogs′ immune response to rabies virus. Planning future management and research on wild dogs and other species demands an assessment of the risks associated with such intervention. This paper critically reviews the available evidence and concludes that it is extremely unlikely that intervention contributed to the extinction of wild dogs in the Serengeti ecosystem. A more likely scenario is that vaccination failed to protect wild dogs exposed to rabies virus. Radio-collaring is an important component of wild dog research; hence, the benefits of immobilization appear to outweigh the risks, as long as (i) research is orientated towards wild dog conservation, (ii) radiocollaring is followed up by efficient monitoring, (iii) the number of animals immobilized is kept to the minimum necessary to maintain scientific rigour, and (iv) full data on disease and genetics are collected from all immobilized animals. By contrast, rabies vaccination currently seems to confer few benefits, at least when a single dose of vaccine is given. Further research, on captive animals, is in progress to establish more effective protocols, and to assess the role that vaccination might play in future management of wild dog populations.

Detection of rabies virus antigen in dog saliva using a latex agglutination test

Dog bites are responsible for more than 90% of human rabies deaths in Asia. We developed a simple and inexpensive test based on latex agglutination (LA) for rabies virus antigen detection in dog saliva. Rabies virus antigen could be detected by agglutination on a glass slide using latex particles coated with gamma globulin. By evaluation of paired saliva-brain specimens from 238 dogs, the LA test using saliva was 99% specific and 95% sensitive compared to the fluorescent antibody test (FAT) on brain smears. The advantages of the LA test over the standard FAT are that it is comparatively simple and there is no need to kill the animal before examination.

Characterization of Sendai virus M protein mutants that can partially interfere with virus particle production

Substitution of Val(113) in Sendai virus (SeV) M protein generates non-functional polypeptides, characterized by their exclusion from virus particles and by their ability to interfere with virus particle production. These phenotypic traits correlate with a single-band PAGE migration profile, in contrast to wild-type M (M(wt )), which separates into two species, one of which is a phosphorylated form. The single-band migration is likely to result from a conformational change, as evidenced by the lack of maturation of a native epitope and by a particular tryptic digestion profile, and not from the phosphorylation of all M molecules, an assumption consistent with the PAGE migration feature. One of the M mutants (HA-M(30 ), an M protein carrying Thr(112)Met and Val(113) Glu substitutions tagged with an influenza virus haemagglutinin epitope) was characterized further in the context of SeV infection, i.e. under conditions of co-expression with M(wt). HA-M (30) is shown (i) to bind mainly to membrane fractions, (ii) not to co-precipitate M(wt), as HA-M(wt) does, (iii) to interfere with the binding of nucleocapsids to membranes and (iv) to accumulate in perinuclear regions, in contrast to HA-M(wt ), which is also found at the cell periphery. Such mutants constitute potential tools for the identification of critical steps in paramyxovirus assembly and budding.

Morphometric analysis of McCoy cells inoculated with cerebrospinal fluid from patients with rabies

To demonstrate the potential of McCoy cells for the isolation of rabies virus from the cerebrospinal (CSF) fluid of a patient with a diagnosis of rabies, McCoy cells were inoculated with CSF from a patient with a clinical diagnosis of rabies and investigated in terms of morphometric aspect using the JAVA analysis system for the quantification of the increased size of infected cells compared to noninfected cells. The cells were also examined in terms of specific staining for the diagnosis of rabies by the method of Sellers for the observation of intracytoplasmic inclusions and by specific immunofluorescence staining for rabies virus. Infected cells showed changes in cell permeability and morphologic modifications which differed significantly compared to normal cells (P < 0.001) when analyzed by the Mann-Whitney and Kruskal-Wallis tests. Intense activity of the endoplasmic reticulum was also observed, as indicated by the presence of intracytoplasmic inclusions visualized by specific staining. The present study demonstrated the isolation of rabies virus from the CSF of a patient with rabies, showing that McCoy cells can be used for the laboratory diagnosis of patients suspected to have rabies.

Molecular characterization of carrier rabies isolates

We compared the genomes of nine dog rabies virus isolates using two molecular methods. The viruses used in the comparison included three Ethiopian rabies strains from carrier dogs, a street strain from a rabid dog from the same geographic area, two saliva isolates made from an experimentally infected carrier dog, the virus isolated from the tonsil of this carrier dog at necropsy, and two laboratory strains. We produced overlapping polymerase chain reaction (PCR) segments spanning 97% of the genome. Restriction analysis of these PCR products with AvaII, Bcll, and BamHI detected 39 variable sites representing 668 nucleotides (nt) or 5.5% of the genome. We also compared the DNA and the deduced peptide sequences of a 200-nt segment of the 3' end of the rabies nucleoprotein gene. Previous work with these Ethiopian carrier viruses and the endemic street strain had failed to show any differences among them. Both restriction mapping and sequence analysis of 200 nt of the nucleoprotein gene allowed us to individually identify these isolates. Phylogenetic analyses of these data sets showed only the two saliva isolates of the experimentally infected carrier dog to be identical. Each of the viruses in this study, including the one isolated from the tonsil of the experimentally infected carrier dog, could be distinguished by these techniques.

Structures associated with the expression of rabies virus structural genes in insect cells

When rabies virus structural genes were expressed in insect cells, major observed alterations were a high level of cytoplasmic vacuolization caused by the matrix protein M2 and the glycoprotein G. Ring-like structures, 16 nm in diameter, were observed in cell-free extracts from insect cells that expressed the N protein alone. Hexagonally shaped structures, 16-20 nm in diameter, and regular lattice aggregates of the same structures appeared on co-expression of N and M1 proteins. Co-expression of the four structural proteins led to the formation of cell surface blebs containing the structures corresponding to N and M1 proteins.

Experimental rabies infection of non-nervous tissues in skunks (Mephitis mephitis) and foxes (Vulpes vulpes)

Non-neural tissues, from three male and four female stripped skunks (Mephitis mephitis), 5 to 7 months old, and one male and two female red foxes (Vulpes vulpes), 12 to 16 months old, experimentally infected with street rabies virus, were examined by light microscopic immunohistochemical and electron microscopic methods. This is the first report of ultrastructural lesions in rabies-infected adrenal medulla, cornea, and nasal glands. Using the streptavidin biotin peroxidase technique, antigen was detected in mucous cells and interstitial neurons and their processes in the submandibular salivary gland, in chromaffin cells of the adrenal medulla, in epidermal cells of the skin, in external root sheath cells of hair follicles, and in corneal epithelial cells. Electron microscopically, matrix (viral nucleocapsid), virions, and anomalous viral products were common in most tissues examined, but their relative proportions varied. The results suggested that replication with minimal accumulation of matrix and anomalous viral growth products was characteristic of growth in tissues (submandibular salivary gland) that frequently produce high titers of virus, whereas replication with large amounts of matrix and anomalous structures occurred in tissues (adrenal gland and nasal gland) that generally contained low or moderate titers of virus. Novel findings included viral budding into secretory granules, increase in microfilaments in infected mucogenic cells, and continuity of viral convoluted membranous profiles with rough endoplasmic reticulum of chromaffin cells and nasal glandular cells. The presence of viral antigen and developing virus in extra-neural tissues constitutes a potential risk of non-bite exposure to people in certain groups/occupations.

The distribution of Challenge virus standard rabies virus versus skunk street rabies virus in the brains of experimentally infected rabid skunks

The proposal that the bizarre behavioral changes which occur during rabies infection are due to selective infection of limbic system neurons was further studied in skunks (a species important in naturally occurring disease). A detailed immunohistochemical study of brains of skunks experimentally infected with either Challenge virus standard (CVS) or street rabies virus revealed only trace amounts of viral antigen in many limbic system neurons and marked differences in viral distribution between street and CVS virus. These data were collected during early stage rabies when behavioral changes occur. Areas which contained heavy accumulations of street rabies virus but low amounts of CVS rabies virus were the neuronal perikarya and processes of the dorsal motor nucleus of the vagus, midbrain raphe, hypoglossal and red nuclei. In contrast, large accumulations of CVS virus were found in the Purkinje cells of the cerebellum, the habenular nuclei and in pyramidal cells throughout the cerebral cortex, while corresponding areas in all street virus-infected skunks contained minimal antigen. These findings were very consistent for animals of the same experimental group and between skunks inoculated both intramuscularly and intranasally with skunk street virus. Skunks inoculated intramuscularly with CVS rabies virus failed to develop rabies. Since, in this model, street virus infection generally produces furious rabies and CVS infection results in dumb rabies, we speculate that the behavioral changes which occur in these two different clinical syndromes are due to the heavy and specific accumulation of virus in different regions of the CNS. These results show that regions other than those of the limbic system may also be involved in the pathogenesis of behavior changes in rabid animals.

Paralysis of street rabies virus-infected mice is dependent on T lymphocytes

Street rabies virus (SRV)-infected T-lymphocyte-deficient (nude) mice, in contrast to euthymic mice, did not develop hindlimb paralysis prior to death. To document the role of T lymphocytes in rabies virus-associated paralysis, 10(8) spleen cells from normal immunocompetent euthymic mice were transferred to nude mice and the recipient mice were challenged with SRV. One hundred percent of the reconstituted mice developed paralysis and died. Depletion of T cells from the donor spleen suspension prior to transfer abrogated the development of paralysis but did not prevent the deaths of the recipient animals. Mice receiving 10(8) rabies virus-immune spleen cells did not become paralyzed and did not die. Nude mice inoculated with either rabies virus-immune or normal mouse serum prior to and following SRV inoculation did not develop paralysis. Immune serum protected the mice, whereas animals inoculated with normal serum died. Central nervous system inflammatory responses in nude mice immunologically reconstituted with normal spleen cells were characterized by diffuse cellular infiltrates in the parenchyma and extensive perivascular cuffing. Perivascular infiltrates included CD8+ and CD4+ T lymphocytes and Mac-1+ macrophage-microglial cells. Inflammatory cells in the parenchyma were limited to CD8+ lymphocytes and Mac-1+ cells. These observations indicate that paralysis of SRV-infected mice is dependent on T lymphocytes. Whether injury leading to paralysis is mediated by T lymphocytes or by an influence of T lymphocytes on macrophage-microglial cells or other cells remains to be determined.

Protection of mice with vaccinia virus recombinants that express the rabies nucleoprotein

The role of rabies virus nucleoprotein (N) in protection against rabies was examined with recombinant vaccinia viruses expressing the N of the Challenge Virus Standard strain. Two chimeric plasmids were constructed with the open reading frame of the N gene placed downstream of the vaccinia P7.5 promoter (early/late class) or the vaccinia P11 promoter (late class), with each expression cassette flanked by vaccinia thymidine kinase (TK) sequences to enable marker rescue by TK insertional inactivation. Two recombinants were isolated that expressed the rabies N in infected cells as determined by radioimmunoprecipitation and immunofluoresence microscopy with an anti-N monoclonal antibody. Two groups of 25 ICR mice inoculated intradermally with the recombinants and challenged with 75 MFPLD50 of street rabies virus showed high survival ratios (22/25 and 21/25). Intramuscular inoculation, however, was not protective against 25 MFPLD50. The intradermally vaccinated mice developed non-neutralizing antibodies against rabies N.

Further studies on rabies virus isolated from healthy dogs in Nigeria

Rabies viruses isolated from healthy dogs, were passaged in mice and adapted to cell culture. After 5-7 passages, isolated viruses were subjected to monoclonal antibody (Mab) characterization with a panel of 36 anti-nucleocapsid (NC) and 40 anti-glycoprotein (G) MAbs. The four viruses showed positive fluorescence with all NC hybridomas except MAb 422-5, confirming them as true rabies virus isolates. The anti-G MAb reactivity pattern was the same in the four isolates indicating that they belong to the same antigenic group, but were antigenically distinct from the Flury LEP rabies vaccine virus which is widely used throughout Nigeria for canine vaccination, and from other previously characterized street lyssaviruses from Nigeria.

Astrocytic reaction predominance in chronic encephalitis of Junin virus-infected rats

Junin virus antigen distribution and astrocytic reaction to prolonged infection were characterized in rat brain by the PAP technique. During the acute stage of neurologic disease following intracerebral inoculation, Junin antigen was detected in 100% of animals, strongly in most neurons but also to a much lesser degree in scattered astrocytes, dropping to 20% of rats at 540 days postinfection. Initially labeled in all brain areas, viral antigen gradually disappeared from hippocampus but persisted irregularly in cerebral cortex, basal ganglia, Purkinje cells, pons, and medulla oblongata. Such a pattern suggests that specific neuronal subpopulations, in spite of apparently unaltered cell morphology, may persistently harbor the virus, leading on occasion to a delayed neurologic syndrome. During both the acute and chronic stages of disease, a mild inflammatory exudate was observed, characterized by the presence of T and B lymphocytes, as well as macrophages and unidentified round cells. GFAP immunostaining showed increased astrocytic reaction as infection lapsed into chronicity. Corpus callosum, hippocampus, and cerebellum exhibited the sharpest reactive astrocytosis, followed by basal ganglia, pons, and medulla oblongata, whereas in cerebral cortex it was considerably less. Astrocyte activation, which failed to correlate with viral antigen presence in neurons, seems to result from a generalized condition, possibly including diffusible brain factors triggered by viral infection. Such widespread astroglial reaction may thus contribute to the outcome of the late neurologic syndrome.

Pathogenesis of rabies virus from a Danish bat (Eptesicus serotinus): neuronal changes suggestive of spongiosis

Rabies virus strains isolated from a European bat (Eptesicus serotinus) in Denmark (DBV), a North American big brown bat (Eptesicus fuscus) in New York State (NY-bat), and a human in South Africa (Duvenhage strain (DUV-1) were studied by using a panel of monoclonal antibodies and by inoculating mice, cats, and dogs. The ten Danish virus isolates from the same bat species reacted identically with a panel of monoclonal antibodies. Immunofluorescence, monoclonal antibody, and histopathologic studies showed that the Danish bat isolates were similar to Duvenhage, and to some degree, to classical rabies virus. All isolates produced fatal infections in mice when inoculated by the intracerebral, footpad, and oral routes. Dogs and cats inoculated intracerebrally with the DBV and DUV-1 virus strains died of rabies-like illnesses within 10 days. Although no dogs that were inoculated intramuscularly or intravenously showed signs of disease, all developed neutralizing antibodies and resisted challenge with lethal dose of street rabies virus. All dogs inoculated with the NY-bat virus, with the exception of those inoculated intravenously, showed classical signs of rabies and one of the intramuscularly inoculated dogs recovered. Cats inoculated intramuscularly also died of rabies-like illness within 15 days. At necropsy, rabies antigen was detected by immunofluorescence in frozen sections of several organs, including brain and salivary glands. Histopathologic and electron microscopic studies of the central nervous system of mice, dogs and cats that died of DBV infection showed neuronal cytoplasmic changes considered to be a form of spongiosis.

Rabies virus in the tonsils of a carrier dog

A female dog, inoculated with a rabies isolate from the saliva of an apparently healthy Ethiopian dog, developed rabies but later recovered without supportive treatment. Rabies virus was isolated from the saliva collected 42, 169 and 305 days after recovery. Sixteen months after it recovered, the dog suddenly died after giving birth to two stillborn puppies. At necropsy, viral antigen could be detected in the tonsils and the brain tissue, but viable virus was isolated from the Palatine tonsils only.