Detection of rabies virus RNA in the central nervous system of experimentally infected mice using in situ hybridization with RNA probes

Rabies virus is usually demonstrated in human or animal tissues using antigen-detection or viral isolation techniques. Rabies virus RNA can be demonstrated in paraffin-embedded tissues using in situ hybridization. Negative (-) sense 35S- and 3H-labeled RNA probes, specific for rabies virus nucleocapsid protein mRNA, were used for the detection of rabies virus RNA in the nervous system of mice experimentally infected with fixed and street strains of rabies virus. In situ hybridization signals were compared with rabies virus antigen demonstrated with immunoperoxidase staining. Rabies virus RNA and antigen were also demonstrated in the same neurons using a double-labeling technique. In situ hybridization has potential applications as a diagnostic test for rabies and in studies of rabies pathogenesis.

[Rabies as a public health problem]

Rabies virus belong to the family Rhabdoviridae; it has a coiled RNA core surrounded by a bullet-shaped envelop, covered with glycoproteins surface projections. After entry into a new host in the bite site, the virus multiplies in muscle cells and it spreads through neural pathways, without stimulating a protective host immune-response. Transmission depends on simultaneous delivery of virus to the salivary gland and the limbic system of the brain, which is the cause of the animal fury and biting tendency. In México, rabies continues to be a serious health and economic problem, and urban rabies still predominates with a large number of human and animal cases recorded yearly. A total of 426 human deaths were reported between 1978 and 1983. Over 9,069 cases of animal rabies were reported in 1986 and 50,000 patients required antirabies postexposure vaccinations. Infected animals can be identified by demonstration of specific fluorescence in brain tissue. A dog or cat which has bitten a human should be captured and observed by a veterinarian for 15 days. The immediate objective of postexposure treatment is to prevent virus from entering and damaging neural tissue, therefore, promptness is essential. All wounds should be thoroughly cleared with soap and water concurrent use of both passive and active immunization provides optimal therapy. Wherever possible, human rather than equine products should be used for passive immunization, and Fuenzalida's nerve tissue rabies vaccine should be used for active protection. Paediatricians should urge parents to caution children attempting to get stray or wild animals as pets. Domestic dogs and cats should be thoroughly vaccinated.

Interferon induced within the central nervous system during infection is inconsequential as a mechanism responsible for murine resistance to street rabies virus

SJL/J mice are resistant, whereas A/WySnJ mice are susceptible to intraperitoneally (i.p.) inoculated street rabies virus (SRV). In this report we determine whether interferon (IFN) induced within the central nervous system (CNS) of these mice during infection is associated with resistance. We show that the high concentration of type 1 interferon (IFN-alpha/beta) within the CNS of A/WySnJ mice is ineffective in inhibiting SRV replication in these tissues, and is unimportant in ameliorating disease. More importantly, the 100% survival of SRV-infected SJL/J mice following neutralization of IFN within the CNS with anti-IFN-alpha/beta suggests that protection of target cells by this minimal amount of IFN is not the mechanism responsible for the innate resistance of SJL/J mice to i.p. inoculated SRV.

Ecology and epidemiology of fox rabies

Although fox rabies has been reported in every country that has foxes, current foci of fox rabies are limited to Europe and North America. The fox rabies virus has unique characteristics that seem to be the result of adaptation through successive passages, i.e., high pathogenicity for the fox, excretion in saliva of a high proportion of infected animals, and low frequency of postinfection immunity. The spread of fox rabies is greatly favored by the characteristics of the genus Vulpes--ubiquity, broad diet, prolific nature, and its particular ethology and ecology. Animals may be immunized by oral vaccination, but natural mechanisms that also can terminate outbreaks are discussed.

Skunk rabies

In North America, the number of cases of rabies diagnosed in skunks generally exceeds that in either raccoons or foxes. Enzootic skunk rabies occurs mainly in four geographic regions: (1) southern Ontario and Quebec and upper New York State; (2) the north central United States and the Canadian provinces of Manitoba, Saskatchewan, and Alberta; (3) California; and (4) south central United States (Texas and several adjacent states). Rabies in these areas (in skunks and, to a large extent, in other terrestrial mammals) is caused mainly by three street virus variants, as determined by monoclonal antibody testing (one variant for areas 2 and 3 and separate variants for each of areas 1 and 4). Experimental studies suggest that the species specificity (e.g., raccoon vs. skunk) of enzootic rabies is due, at least partly, to differences in the pathogenicity of variants of rabies virus.

Pathogenesis of rabies virus infection in dogs

Most dogs experimentally infected with street rabies virus showed clinical signs of rabies before death, but up to 18% of the dogs died without showing detectable signs of illness. In dogs showing signs, rabies was not invariably fatal. Up to 20% of dogs recovered without any supportive treatment. Some dogs inoculated with American (southern Texas) or Ethiopian canine street virus excreted virus in their saliva up to 14 days before signs appeared. There was no relation between the time of excretion of virus in the saliva and the titer of virus in the salivary glands at death. One dog that recovered from rabies intermittently excreted rabies virus in its saliva for a long time. The carrier state in rabies may play a significant role in the perpetuation and survival of the virus and may become a source for rabies outbreaks whenever a new generation of rabies susceptibles reaches critical density.

Failure to thrive, wasting syndrome, and immunodeficiency in rabies: a hypophyseal/hypothalamic/thymic axis effect of rabies virus

Studies of rabies virus in several animal models consistently showed hypothalamic infection, hypophyseal infection, dramatic growth impairment (in the form of failure to thrive), wasting syndrome, and immune depletion. Rabies virus infection was studied through routine monoclonal antinucleocapsid antibody immunofluorescence and through a peroxidase-antiperoxidase immunoperoxidase method. The latter was modified to detect the in situ production of growth hormone by uninfected and rabies virus-infected adeno-a-pituicytes (with confirmation of the results both in vivo and in vitro). Infection with rabies virus made the specialized pituicytes produce less growth hormone. Growth before rabies virus infection and its reduction due to infection were investigated in a linear regression model. The fit was statistically significant (P less than .05) in all species studied: mouse, rat, rabbit, cow, and cat. Immune depression was studied in terms of alterations in the immunotopography of the thymus and also the specific T- and B-cell homing areas of the spleen (although spleen data are not presented here). On the basis of these results and a thorough review of wasting syndromes encountered in other diseases, a primary failure to thrive and an ensuing wasting syndrome were described and characterized for rabies, and their origin was assigned to a dysfunction of the hypophyseal/hypothalamic/thymic axis associated with at least (but not necessarily only) one of the centrally controlled growth hormones.

[Evaluation of 3 antigenically different strains of rabies virus, in mice. I. Study of the clinical observation periods]

Estudou-se, comparativamente, o comportamento de três cepas de vírus rábico, duas de origem de cão, Jales e Nigéria, e uma de origem de morcego, DR 19, com perfis antigênicos do nucleocapside distintos. Estas cepas foram inoculadas por via intramuscular, na face interna da coxa, em dois grupos de camundongos, com 21 e 28 dias de idade. Os animais foram observados durante 30 dias, levando-se em consideração os períodos de observação clínica (incubação e duração da doença), determinando-se os coeficientes de mortalidade para cada grupo etário e para cada uma das cepas virais, bem como o título infectante de pool de cérebros de cada sub-grupo experimental. Os resultados obtidos permitiram constatar comportamento semelhante entre as cepas Jales e Nigéria, notadamente em relação aos períodos de observação clínica e mortalidade, para ambos os grupos etários, diferindo, todavia, quando comparados aos da cepa DR 19.

[Biological properties of variants of the rabies street virus]

Experiments in dogs inoculated intracerebrally with biological variants of paralytic (PRV) and convulsive (CRV) rabies virus isolated from the Yak strain population of street rabies virus demonstrated distinct differences in the biological properties of the variants PRV induced in dogs paralytic rabies with a short incubation period (average 6.4 days) and CRV induced an atypical convulsive form characterized by attacks of tonic convulsions of the body, legs, and head twitching, and a longer incubation period (18.5 and 9.6 days, respectively). This explains a wide variability of the biological properties of street rabies virus strains.

Morphologic appearance of inclusion bodies and their association with the antigenic composition of naturally occurring rabies viruses

A total of 112 rabies virus-infected skunk brain samples from naturally occurring cases (64 from Missouri, 48 from Kentucky) were code labeled and grouped into two morphologic categories according to the appearance and size of the discrete particles observed by immunofluorescent-antibody staining. The reactivity of the blind-labeled samples was then determined using a panel of 23 antinucleocapsid monoclonal antibodies to test whether morphologic appearance was associated with antigenicity. Two categories were defined and designated; they were morphologic type I (MO-I) and morphologic type II (MO-II). MO-I viruses produced granular-type fluorescing aggregates with no evidence of inclusions compatible in appearance with Negri bodies. MO-II viruses produced at least one and usually many large, round, or oval fluorescing inclusion bodies. No viruses categorized as MO-I reacted with antinucleocapsid monoclonal antibodies 103-7, 239-10, and 120-2; all MO-II viruses reacted positively to these three antibodies, with one exception involving antinucleocapsid monoclonal antibody 239-10. The results indicate a strong association between the reactivity of these antibodies and the morphologic appearance of the aggregates of antigen.

[The Italian experience in the control of rabies. II. Laboratory research]

Diagnoses of rabies have been performed at the Zooprophylactic Institutes of Brescia and Padua since 1977, 5,765 foxes have been examined and 1,805 (31.30%) resulted positive. The same Institutes have performed also the laboratory tests in order to control the presence of Tetracycline, the serum conversion and the presence of wild or attenuated viruses in the nervous tissue of foxes and other wild animals in occasion of the oral vaccination campaigns of foxes.

Growth characteristics in cell culture and pathogenicity in mice of two terrestrial rabies strains indigenous to Canada

Two strains of street rabies virus from striped skunks (Mephitis mephitis) were used to infect either a murine neuroblastoma (NA 1300) or a baby hamster kidney (BHK-21/C13) cell culture and the cell infection rates were noted during 4 days postinfection. These cultures were then passaged for four consecutive passages, and the viruses obtained in the supernatant fluids of passage 4 were then treated as original isolates and used to infect both neuroblastoma and baby hamster kidney cells. The mortality period in Swiss white mice caused by the various virus suspensions was noted. The virus strain from the brain of skunks from Saskatchewan infected neuroblastoma and baby hamster kidney cells equally well, produced similar virus titres in supernatant fluids after four subcultures in both cell types, and appeared to produce similar mortality periods in mice from either the original brain tissue or from cell culture supernatant fluids. On the other hand, the virus from the brains of skunks from Ontario readily infected neuroblastoma but poorly infected baby hamster kidney cell cultures. Passage of this strain through four subcultures in both cell types produced virus titres in the supernatant fluids of equal magnitude. However, reisolation of the virus from the supernatant fluid of passage 4 in neuroblastoma cell cultures showed a similar pattern to that from the original brain, while the virus from baby hamster kidney cell passage supernatant fluid was considerably altered. Although the mortality period in mice was similar with virus from the brain and neuroblastoma cell cultures, this period was shortened when mice were inoculated with baby hamster kidney culture supernatant virus.(ABSTRACT TRUNCATED AT 250 WORDS)

Is there a risk to contacts of patients with rabies?

The number of persons in the United States potentially in contact with rabid humans has increased in recent years because of labor-intensive medical care, longer survival times, and care in two or more hospitals. Many of these persons request rabies prophylaxis, and their physicians prescribe it because of their insecurity, a situation that is expensive and often unnecessary. Records of the Centers for Disease Control and the literature were reviewed to examine the current practice of prophylaxis of contacts and the actual need for it. Rabies virus is present in a variety of human fluids and tissues during the first five weeks of illness, but there are only four well-documented reports of human-to-human transmission--all in corneal transplant recipients. Prophylaxis of contacts of 14 rabid patients was predominantly for saliva exposure to open wounds or mucous membranes and was given most often to medical personnel having the greatest contact with the patient. Although it has never been documented, human-to-human transmission of rabies following saliva exposure remains a theoretical possibility. Virus shedding by rabid patients should be studied thoroughly in the future. Recommendations for managing contacts of rabid patients are presented.

Experimental rabies in skunks: immune response and salivary gland infection

Groups of striped skunks (Mephitis mephitis) were inoculated intramuscularly with graded doses of street rabies virus. At various intervals after inoculation, saliva and sera were tested for rabies virus and neutralizing antibodies, respectively. Skunks that developed rabies were killed in terminal stages of the disease and the following examinations were made: titers of virus and antibody in submandibular salivary glands and brain, extent of immunofluorescence in submandibular salivary glands, and histologic examination of various tissues. Skunks that received inocula containing 4 x 10(4) to 4 x 10(5) mouse intracerebral lethal dose50 (MICLD50) had detectable serum neutralizing antibodies by 7-12 days postinoculation; however, most of the skunks that received lower doses (40 to 4 x 10(3) MICLD50) did not have detectable serum neutralizing antibodies until clinical signs began. In the salivary glands, slight and extensive immunofluorescence corresponded to high and low titers of tissue neutralizing antibody. Also low viral titers were associated with high tissue neutralizing antibody titers. There was a close correlation between viral titers in right and left submandibular salivary glands. The results suggest that the immune response can impede the process of infection of the salivary glands resulting in lack of antigen or low amounts of antigen in this tissue. This could occur through interference with centrifugal neural transport of virus and/or neutralization of virus during transfer from neural elements to epithelial cells. Lack of infectious virus or low viral titers in salivary glands containing antigen and high levels of tissue neutralizing antibodies can be caused partly by postmortem virus neutralization (during viral titration).

Electrophysiological and sleep alterations in experimental mouse rabies

Changes in the spontaneous brain electrical activity and sleep organization were investigated in 5 mice strains during the evolution of experimental fixed rabies infection. Cortical electrodes were chronically implanted for continuous EEG recording and spectral analysis until death. Three evolutionary phases were individualized. The initial phase exhibited alterations of sleep stages, REM sleep disappearance, pseudoperiodic facial myoclonus and first clinical signs. The mature phase was characterized by a generalized EEG slowing (2-4 cycles/s). The terminal phase occurring with extinction of hippocampal rhythmic slow activity showed a flattening of cortical activity. The brain electrical activity ceased about 30 min before the cardiac arrest. Paroxysmal activities appeared during the course of the disease as bursts of rhythmic slow waves, pseudoperiodic spikes or occasionally ictal epileptic discharges. Spectral analysis revealed a progressive and characteristic clustering of the EEG frequency band power values. The spread of infection in the CNS was monitored by specific immunofluorescence studies which revealed the presence of rabies virus antigen in the pons, the cerebellum, the thalamus and the cortex during the initial phase. The pyramidal field of the hippocampus was infected during the mature phase but the gyrus dentatus was never infected even at the terminal phase. These studies show that particular neuronal functions are impaired during rabies virus infection suggesting that neuronal alterations may be involved in the pathogenic mechanisms leading to lethality.

Axonal transport of rabies virus in the central nervous system of the rat

Stereotaxic inoculation of rabies virus into specific nuclei in the central nervous system has been used for the investigation of the central neural transport mechanisms of viral information. The infection was monitored by specific fluorescence and peroxidase studies and the titration of viral infectivity in dissected brain areas. Twenty-four hours after inoculation into the striatum, cortex, or substantia nigra, infected neurons were detected only in cells from areas and nuclei which were related to the site of inoculation. The distribution of infected neurons showed that retrograde axoplasmic flow plays a determining role in the transport of rabies virus 24 hours after delivery of virus to specific target nuclei. Local destruction of neurons by kainic acid at the site of viral inoculation did not prevent the uptake and subsequent retrograde axonal transport of virus. There was an overall correlation between the major neural connections of the inoculated areas (e.g. the striatum) and the infected areas 24 hours later (e.g. the substantia nigra).

Demonstration of antigenic variation among rabies virus isolates by using monoclonal antibodies to nucleocapsid proteins

Rabies virus isolates from terrestrial animals in six areas of the United States were examined with a panel of monoclonal antibodies to nucleocapsid proteins. Characteristic differences in immunofluorescence reactions permitted the formation of four antigenically distinct reaction groups from the 231 isolates tested. The geographic distribution of these groups corresponded well with separate rabies enzootic areas recognized by surveillance of sylvatic rabies in the United States. Distinctive reaction patterns were also identified for viral proteins from four infected bat species, and identical patterns were found in eight isolated cases of rabies in terrestrial animals. These findings suggest that monoclonal antibodies can be used to study the prevalence, distribution, and transmission of rabies among wildlife species.

[Comparative assessment of the neurovirulence of vaccinal strains of the rabies virus]

Neurovirulence of three vaccine strains of rabies virus ("Moscow", "Vnukovo-32", and "MIVP-74") was studied in mice using pathomorphology data. After intracerebral inoculations changes in the CNS were similar. The presence and the degree of the involvement of the Ammon horn is the main indicator of the infectious activity of the strain. The disease and death of the animals after inoculation with an attenuated strain may be due to the damage of intermediate neurons of descending projection tracts of the brain stem and cerebellum. Differences between strains in neurovirulence were most clearly observed after peripheral inoculation, when the "MIVP-74" strain, unlike the other two, proved to be apathogenic. Neurovirulent properties should be evaluated by characteristics of the CNS pathomorphology after intracerebral and peripheral inoculations.

Experimentally induced rabies in four cats inoculated with a rabies virus isolated from a bat

Four cats were inoculated IM with rabies virus isolated from the salivary gland of a naturally infected big brown bat (Eptesicus fuscus). The 4 cats developed clinical signs of rabies after a median incubation period of 42 days. The median duration of clinical illness was 5 days. Results of fluorescent antibody evaluation, mouse inoculation, and tissue culture isolation indicated large differences in virus concentrations in various areas of the CNS of individual cats. These differences also were observed between cats. Rabies virus was isolated from the salivary glands and saliva of 2 cats; urinary bladder was the only other nonneural tissue found infected. Our observations indicated that cat rabies can be caused by bat rabies virus; that cats thus infected have infectious saliva during aggressive behavior and can therefore transmit the disease; and that adequate specimens of hippocampus, cerebellum, and brain stem are essential for reliable determination of rabies infection. The findings support recommendations for regular rabies vaccination of cats, even in areas of rabies-free terrestrial mammals.

Rabies encephalitis: immunohistochemical investigations

Three cases of human rabies encephalitis were studied immunohistochemically using a specific antiserum to rabies ribonucleoprotein (RNP) and the peroxidase-antiperoxidase method. In this way, RNP could be specifically demonstrated in all cerebral regions and the spinal cord with a predilection for virus attack on the diencephalon and the brain stem according to the clinical course of the disease, and possibly reflecting the phenomenon of pathoclisis. Virus antigen was mainly present in the nerve cell bodies and processes, and in glial cells, especially in the interfascicular oligodendroglia, which seems to be a route of rabies virus infection in the later course of this fatal disease. Immunohistochemically, virus antigen was not limited to the Negri bodies: it was also traceable in the cytoplasm. Altogether, many more virus infected cells were established by immunostaining than were to be expected by the presence of Negri bodies in hematoxylin-eosin stained sections.

Pathways of the early propagation of virulent and avirulent rabies strains from the eye to the brain

Penetration of the central nervous system of the adult rat by the CVS strain of rabies virus and its two avirulent derivatives Av01 and Av02 has been studied by inoculation of the virus into the anterior chamber of the eye. The primary sites of penetration of CVS were (i) the intraocular parasympathetic oculomotor fibers, (ii) the retinopetal fibers of pretectal origin, and (iii) the intraocular fibers of the ophthalmic nerve. The mutant strains, however, lost the capacity to invade the two former groups of fibers, although their penetration into the trigeminal system was not impaired. Neither strain CVS nor the mutants infected primarily the intraocular adrenergic terminals and the optic nerve. Mutant strains, but not CVS, were able to infect the lens. These results indicate that the cholinergic receptor may not be the only receptor for rabies virus and that rabies virus is conveyed in the nervous system by retrograde axoplasmic flow. Strain CVS spread throughout the brain and propagated eventually back to the retina. The mutants penetrated the brain as well, but the infection was slow, involved different cerebral structures, and cleared up completely in 3 weeks, probably because of an efficient immune response.

Rabies virus in different segments of brain and spinal cord of naturally and experimentally infected dogs

In order to determine the presence of rabies virus in different segments of Central nervous system (CNS) of rabid animals, 31 naturally infected dogs and 6 experimentally injected ones by masseter inoculation were studied by means of Fluorescent Antibody (FA) technique and mouse intracerebral inoculation (MI) test. In the naturally infected group, the positivity by FA technique was 100.0% for the segments of Ammon's horn, cerebellum, bulb and for cervical, lumbar and sacral cord and 96.7%; for thoracic cord. Mouse inoculation test of corresponding materials was 100.0% positive for Ammon's horn, cerebellum, bulb and lumbar cord; 96.7% for cervical cord; and 93.5% for sacral cord. All examined segments of experimentally infected animals were 100.0% positive for both FA and MI tests. No clear-cut relationship could be found between the site of virus inoculation and the presence of the virus in the spinal cord. The results presented in this paper corroborate previous suggestions for the use of the spinal cord as one of the alternative laboratory diagnostic specimens for the canine rabies diagnosis.

Antigenic variants of rabies virus in isolates from eastern, central and northern Canada

Street rabies virus isolated from 51 specimens from Ontario, Quebec, Manitoba and the Northwest Territories have been typed by a panel of 36 antinucleocapsid monoclonal antibodies. Three main groups were found. The first group comprised those terrestrial mammals originating in Ontario, Quebec and the Northwest Territories. The second group was found in terrestrial mammals from Manitoba. The third heterogenous group was made up of bats from Ontario.

On the replication and spread of rabies virus in the human central nervous system

Ultrastructural and immunohistochemical studies on the brains of two autopsy cases of human rabies revealed: By the peroxidase-antiperoxidase method, viral antigens were present in all eosinophilic inclusions detected in formalin fixed paraffin sections. Numerous antigenic masses, which apparently corresponded to the matrices and cylindrical particles in neurites revealed by electron microscopy, were present in the neuropil remote from neuronal perikarya. There were virions in the intercellular spaces and virus-budding from the plasma membrane into the extracellular space in the absence of a matrix, strongly indicating that rabies virus in the human central nervous system could spread through the intercellular spaces and that the replication of the virus was not necessarily accompanied by the formation of inclusion bodies. The synapse was involved in rabies as indicated by virions in the synaptic terminals. The implications of these observations are discussed in conjunction with the results of previous in vitro and animal experiments.

[Excretion of the rabies virus in foxes after experimental infection]

Fourteen foxes (Vulpes vulpes crucigera) were experimentally infected with rabies. The excretion of the virus in saliva was subjected to qualitative study. Three different street strains isolated in the territory of the Czech Socialist Republic were used for the intramuscular infection at the doses of 50 or 5000 MICLD50. The presence of the virus in saliva was demonstrated in 12 animals (86%). Post-mortal examination revealed the virus in the salivary gland of 13 animals (93%). The virus started to be excreted in saliva maximally two days before the onset of the clinical signs of the disease and it lasted maximally six days. The affinity of the virus for the salivary gland was related to the strain used, and increased when a lower infection dose had been administered.

Rabies virus in the salivary glands and nasal mucosa of naturally infected skunks

Several salivary glands and the nasal mucosa of rabid skunks (Mephitis mephitis) contained rabies virus. Generally titers were high in the submandibular, moderate in the parotid and low to moderate in the zygomatic, molar and sublingual salivary glands. The nasal mucosa (glands and epithelium) contained virus at low to moderate titers that occasionally were equal to titers in brain.

Antigenic characteristics of isolates associated with a new epizootic of raccoon rabies in the United States

A panel of 23 monoclonal antibodies to the nucleocapsid protein of rabies virus was used to study the antigenic character of isolates of rabies virus from raccoons in the mid-Atlantic region of the United States. Comparison of the reaction pattern of these isolates with that of isolates of rabies virus collected from areas of major rabies outbreaks (skunk rabies in the midwestern United States, fox rabies in the northeastern United States, and raccoon rabies in the southeastern United States) suggests that this new epizootic originated with the transportation of rabid raccoons from the southeastern United States.

Distribution of rabies virus, interferon and interferon-mediated enzymes in the brains of virus-infected rats

The distribution of rabies virus, interferon and interferon-mediated enzymes, pppA(2'p5'A)n synthetase (2-5A synthetase) and poly(rI) . poly(rC)-Sepharose-bound protein kinase, was studied in different regions of the brains of rabies virus-infected rats. A broad range of virus infectivity was found in the brain stem, cerebellum, cortex, hippocampus and striatum. Similarly, the levels of interferon were variable (2500 to 60 000 units/mg protein in tissue extracts) in the different brain regions studied but were unrelated to the corresponding infectivities . The level of 2-5A synthetase and protein kinase was enhanced several-fold in the individual brain regions and the degree of such enhancement was correlated with the level of interferon.

Murine resistance to street rabies virus: genetic analysis by testing second-backcross progeny and verification of allelic resistance genes in SJL/J and CBA/J mice

Intraperitoneal challenge with street rabies virus of second-backcross offspring produced from susceptible females mated with either randomly selected or rabies-resistant first-backcross males indicated that murine resistance is under the influence of the concurrent presence of each of two segregating genes. Furthermore, the greater than or equal to 96% resistance of offspring produced from (SJL X CBA)F1 and (CBA X SJL)F1 hybrids crossed to susceptible A.SW or A/WySn mice demonstrated that resistance genes of SJL/J and CBA/J mice are allelic.

Peripheral distribution of virus in dogs inoculated with two strains of rabies virus

Forty-seven Beagles were inoculated IM with an Ethiopian strain or a Mexican strain of rabies virus to study the pathogenesis of street rabies virus in dogs. Thirty-nine dogs died of rabies, with incubation periods lasting 9 to 69 days. Of the dogs that died, 82% had shown typical signs of rabies, but 18% died without any noticeable signs of illness. Eight dogs that remained healthy during an observation period lasting more than 2 years did not produce detectable amounts of rabies virus-neutralizing antibodies; however, when challenge exposed with a large dose of the homologous rabies virus inoculum, these 8 dogs responded with high antibody titers, but challenge-exposed control dogs died of rabies. Infective virus was isolated from the saliva and cerebrospinal fluid of dogs before any signs of rabies were noticed; rabies virus-neutralizing antibodies were not detected in the serum and cerebrospinal fluid before illness. In this study, viral antigen was not detected in the skin biopsy specimens taken before signs of rabies were noticed. At necropsy of the 39 dogs, rabies virus was detected in most tissues examined. Viral antigen was detected in the skin tissues of 14 (36.8%) of the 38 dogs examined. The presence of viral antigen in the skin seemed to correlate with the presence of virus in the salivary glands, but virus in the salivary glands did not indicate the presence of virus in the skin. Eleven (44%) of the 25 dogs which had virus in the salivary glands did not have any detectable amount of viral antigen in the skin.(ABSTRACT TRUNCATED AT 250 WORDS)

Naturally acquired rabies in an eastern chipmunk (Tamias striatus)

Rabies in an Eastern chipmunk was detected by fluorescent-antibody testing and mouse inoculation. The results were independently confirmed, and the virus was recovered from tissue culture.

Rabies in the Federal Republic of Germany, 1950-81: the influence of landscape

Rabies statistics for 1950-81 were studied to investigate regional differences in the occurrence of rabies in the Federal Republic of Germany. At the level of Landkreis (administrative unit with a mean area of 1013 km(2)), four basic patterns of rabies incidence were identified: insignificant occurrence, low undulations, intermittent peaks, and high oscillations. The distribution of these four epidemiological patterns of rabies was geographically localized. Insignificant occurrence of rabies was found almost exclusively on land under 100 m above sea level with less than 10% forest cover. High oscillations in rabies occurrence were found most often in areas over 200 m above sea level with an average of at least 35% forest cover.

Immunohistological demonstration of serum proteins and structural and viral antigens in paraffin sections of nervous tissues

A brief outline is given of applications of immunohistological techniques to the study of normal and diseased nervous tissue. Protease treatment of paraffin sections usually enhances sensitivity and reliability both of IF and PAP techniques. Sensitivity of immunohistological examination of paraffin sections is comparable to that of virus detection by normal virological techniques in animal rabies and slightly superior to EM search for virions in SSPE and PML. Immunostaining for MBP appears to be the most sensitive method for myelin, especially for demonstration of very thin myelin sheaths, which are important in studies of myelogenesis and cortical myeloarchitecture. Prolonged fixation in formalin clearly diminishes or abolishes immunoreactivity. Compacted myelin stains less well for MBP than preparative myelin artefacts and the surface of myelinated fibers. GFAP production is enhanced when glioma cells invade surrounding mesenchymal structures. The chance finding of GFAP-like immunoreactivity in a cancer metastasis casts doubt on the astroglial specificity of GFAP.

An in vivo and in vitro study of rabies virus infection of the rat superior cervical ganglia

In the attempt to develop a homogeneous neuronal model to study rabies pathogenesis in vivo and in vitro, the superior cervical ganglia (SCG) were chosen because of their unique features. In vivo infection of the SCG was attempted by inoculation of fixed rabies virus into the anterior eye chamber. However, viral by this route as well as intracerebrally failed to infect this neuronal organ in adult rats whereas the infection was poorly efficient in 24 hours newborn rats. Dissociated cell cultures from the rat embryo SCG were infected in vitro and examined for the presence of rabies specific antigen and release of virus particles in the supernatant. Despite the presence of rabies nucleoprotein in the cytoplasm and the presence of typical Negri bodies, neurons from the rat SCG produced few particles as observed by electron microscopy and no increase in virus yields could be detected by titration of viral infectivity during the infectious cycle. Our observations indicate that although rabies virus is neurotropic as shown in previous studies, all neuronal tissues are not equally susceptible to this viral infection. The resistance of the SCG to rabies virus infection in vivo does not seems to be a lack of accessibility of this organ to infection since other authors had shown that it could be infected by herpes virus. Both in vitro and in vivo experiments show that although neurons from the SCG are susceptible to rabies virus infection, infected cells do not produce rabies infectious virions efficiently.

Neurotropism of rabies virus. An in vitro study

The relative susceptibility of neurons and glia, grown as monolayers in vitro, to rabies virus infection was explored. Established cell lines of neuronal or glial phenotype and primary cultures of cells derived from mouse dorsal root ganglia (DRC) or brain were used as homologues of the targets of rabies virus in the nervous system. Fixed rabies virus (CVS) strain was used in most experiments; other fixed rabies strains (PV, HEP, ERA) and a street rabies virus isolate were used in some. Virus-cell tropism was determined by immunofluorescence assay for rabies nucleocapsid antigen and cell permissivity was assessed by titration of virus yields. Neuronal cells always exhibited a much greater susceptibility to infection and a greater propensity to sustain viral growth. By immunofluorescence, 90-100% of neurons commonly had viral inclusion bodies, while doses of the virus three to four orders of magnitude higher still left greater than 99% of astrocytes, in brain cell cultures and 90 +/- 5% of the non-neuronal cells in DRG cultures without any obvious signs of rabies virus. Neuroblastoma cells (95 +/- 5% with viral antigens) produced viral yields about four orders of magnitude higher than glioma cells (10 +/- 5% with viral antigens). Though the overall infectivity of street virus was lower than that of fixed virus strains, a significantly higher viral tropism for neurons than for glia was maintained. Thus, primary neuronal cultures offer a means of exploring molecular events in rabies virus infection and their role in pathogenesis.