The prion protein gene is dispensable for the development of spongiform myeloencephalopathy induced by the neurovirulent Cas-Br-E murine leukemia virus

The Cas-Br-E murine leukemia virus (MuLV) induces paralysis in susceptible mice that is accompanied by a severe spongiform myeloencephalopathy. These neurodegenerative lesions are very similar to those observed in prion diseases. To determine whether the prion protein gene (Prn-p) product was a downstream effector of this neurovirulent MuLV, we inoculated Prn-p(-/-) knockout homozygote and control heterozygote or wild-type mice with this retrovirus. All groups developed typical paralysis and spongiform encephalopathy, and no differences in clinical or histological phenotypes were observed between these groups. These results indicate that the Cas-Br-E MuLV does not require the prion protein to induce lesions. Thus, MuLV and prion proteins may induce a very similar disease through distinct pathways, or the viral Env protein, which harbors the primary determinant of pathogenicity, may act in a common pathway but downstream of the prion protein.

Isolation of poliovirus from cases of acute flaccid paralysis

OBJECTIVE

To evaluate the frequency of isolation of polio and other viruses from fecal samples in subjects with acute flaccid paralysis in northern parts of India.

SETTING

Rural and Urban Immunization Centers used for Expanded Programme on Immunization.

METHODS

219 fecal samples were collected by anal tube in 1992 from Punjab, Haryana, Himachal Pradesh and Chandigarh and processed for virus isolation.

RESULTS

Of 219 fecal samples, 103 (47%) were positive for viruses in the age group of 3 mo to 5 yr. Amongst the positive samples, the predominant isolated was poliovirus type 1 (70.9%) from all the States. Non polio enteroviruses were isolated from 20.4% of fecal samples.

CONCLUSION

Even though poliovirus is still the most common etiologic agent for acute flaccid paralysis in northern India, non polio enteroviruses are also emerging as important causal pathogens in this condition.

Current status of poliovirus infections

Two scientists who played leading roles in the conquest of poliomyelitis died recently. In 1954, Jonas Salk provided the first licensed polio vaccine, the formalin (and heat)-inactivated virus. Albert Sabin gave us the attenuated live virus vaccine, which was licensed in 1962. This paper takes the reader through the history of the disease, including its pathogenesis, epidemiology, vaccines, and future directions. The emphasis is on vaccines, for it seems that with proper vaccination the number of new cases is falling dramatically. It is hoped that by the year 2000, we will accomplish the goal of the World Health Organization of "a world without polio." Then, because there is no animal reservoir, we can seriously discuss when and how to eliminate the need for vaccination and ultimately destroy our stocks of poliovirus.

Factors affecting induction of neurological disorders in mice by paralysis-inducing Friend-related PVC viruses

Our previous studies showed that the passage of the Friend virus complex through rats generated variant MuLVs, designated PVC111, PVC211, PVC321 and PVC441, that induced neurological disorders associated with tremor and paralysis. In this study, we tested the pathogenicity of four different PVC viruses in mice. Although histopathological studies revealed spongiform degeneration in the spinal cords of NFS mice infected with each PVC virus, only PVC441 frequently induced tremor and paralysis. After a long latency, all of these viruses induced leukemia associated with severe anemia. Further studies with PVC441 revealed dose- and age-dependence for tremor induction. In contrast to NFS mice, BALB/c, DBA/2 and C57BL/6 mice infected with PVC441 virus showed no neurological symptoms, although the virus could be isolated from the tissues of central nervous system. Despite the absence of neurological symptoms, a high degree of neuronal degeneration in the lumbar spinal cord was found in PVC441-infected BALB/c mice. A low degree of neuronal degeneration was found in PVC441-infected DBA/2 or C57BL/6 mice. Genetic crosses of these resistant mice with susceptible NFS mice indicated that resistance to tremor induction by PVC441 was dominant in all mouse strains and suggested that various host genes may control the susceptibility of mice to tremor induction by PVC441 virus.

ts1-Induced spongiform encephalomyelopathy: physical forms of high-mobility DNA in spinal cord tissues of paralyzed mice are products of premature termination of reverse transcription

ts1 is a temperature-sensitive mutant of Moloney murine leukemia virus that causes hind-limb paralysis in mice. In tissues of the central nervous systems of paralyzed moribund FVB/N mice, a major component of the unintegrated viral DNA of ts1 consists of highly mobile physical forms of viral-specific DNA (HM DNA). Previous studies with ecotropic virus-specific polarity probes showed that the gp70-coding region of the env gene in the HM DNA was minus-sense single-stranded DNA. The physical forms of the HM DNA have now been characterized in more detail with additional ecotropic virus-specific probes that hybridized to the p15E-coding region of the env gene and two locations within the U3 region of the long terminal repeat. Two major classes of HM DNA were found: class I molecules consist of short minus-sense single-stranded DNA; class II molecules are partial DNA duplexes that are longer than the class I molecules. The two classes of HM DNA molecules are intermediate products of reverse transcription of the viral RNA of ts1. Since tissues that are infected with cytopathic retroviruses may contain high levels of unintegrated viral DNA, the HM DNA may have a role in inducing neurodegeneration in the central nervous systems of mice that are infected with ts1.

Distribution of viral RNA in the spinal cord of DBA/2 mice developing biphasic paralysis following infection with the D variant of encephalomyocarditis virus (EMC-D)

DBA/2 mice infected with the D variant of encephalomyocarditis virus (EMC-D) (10(1) PFU/head) developed biphasic hind limb paralysis. As a first step in clarifying its pathogenesis, we examined the distribution of viral RNA in the spinal cord using in situ hybridization. At 3 days post inoculation (DPI), in the spinal cord of mice showing slight paralysis, viral RNA was observed in capillary endothelial cells and a few adjacent glia cells in the funiculus lateralis from thoracic to lumbar enlargement. At 7 DPI, in the spinal cord of mice showing apparent paralysis, viral RNA was observed in a larger number of glia cells in the demyelinated lesion associated with infiltration of macrophages in the funiculus lateralis and in a small number of degenerated neurons in the cornu ventrale. In the funiculus lateralis, viral RNA could not be observed after 28 DPI. On the other hand, viral RNA was observed in degenerated neurons in the cornu ventrale of mice showing the second phase paralysis at 42 DPI. Many CD4+T cells infiltrated around these degenerated neurons. These results suggest that: (1) the viral entry zone was the capillary endothelial cells in the funiculus lateralis; (2) first phase paralysis was due to demyelination caused by EMC-D and associated with macrophage infiltration; (3) second phase paralysis was due to degeneration of motor neurons bearing viral RNA associated with infiltration by CD4+T cells.

Analyses of restriction fragment patterns (RFPs) and pathogenicity in baby mice of equine herpesvirus 1 and 4 (EHV-1 and EHV-4) strains circulating in Danish horses

Twenty-five strains of equine herpesvirus 1 (EHV-1) and one strain of equine herpesvirus 4 (EHV-4) isolated from material from various clinical cases in Denmark, together with reference EHV-1 and EHV-4 strains, were compared by restriction fragment pattern (RFP) analysis and inoculation of baby mice. The RFP analyses revealed that all EHV-1 strains belonged to genome type Ip. Four fetal isolates exhibited genomic characteristics that have been suggested as specific markers of the attenuated strain Rac H, widely used as a live vaccine. As the use of five vaccines against EHV-1 and EHV-4 has never been allowed in Denmark, it is assumed that Rac H derivatives have been acquired from visiting horses and thus are now circulating in the horse population. Baby mice inoculation revealed that four biotypes could be distinguished on the basis of pathogenicity. However, no strict correlation with pathogenicity in the natural host was seen.

Biological characterization and molecular cloning of murine C-type retroviruses derived from the TSZ complex from mainland China

Characterization of the SRS murine retrovirus complex, derived from the TSZ system of murine leukemia developed in China, was carried out. The initial stock contained XC+, NB-tropic virus (and possibly other viruses), and induced several neoplastic diseases in neonatally inoculated NIH Swiss mice: erythroid leukemia, myeloid leukemia (acute myeloblastic leukemia), and lymphoblastic lymphoma (both B- and T-lymphoid). In addition, approximately 30% of inoculated animals developed central nervous system disease--hindlimb paralysis or semilateral paralysis. Rescue of virus from the spleen of an animal with combined erythroid/myeloid leukemia, followed by endpoint dilution gave two stocks: 19-6 (XC+, NB-tropic) and 19-7 (XC-, NB-tropic). Both stocks induced erythroid and myeloid leukemia, and 19-6 induced CNS symptoms as well. Southern blot analysis indicated that the predominant viruses from the 19-6 and the 19-7 cultures were related, but different in the env region. An infectious virus molecular clone of provirus from 19-6 cells was obtained. The resulting cloned virus [SRS 19-6 murine leukemia virus (MuLV)] induced four kinds of leukemia: erythroid, myeloid, B-lymphoma, and T-lymphoma; in many cases, more than one tumor type was identified in the same animal. Such a broad spectrum of leukemias induced by a cloned MuLV is unusual. Flaccid hindlimb paralysis induced by SRS 19-6 MuLV could be attributed to meningeal B-lymphoma. Immunofluorescent staining with a panel of env-specific monoclonal antibodies confirmed that the 19-6 and 19-7 viral stocks contained different viruses, which differed from previously characterized MuLVs. The viruses of the SRS complex may provide interesting reagents for investigations of MuLV-induced disease.

Paralysis caused by acute myelitis in Theiler's murine encephalomyelitis virus strain GD VII infection is induced by CD4+ lymphocytes infiltrating the spinal cord

Intravenous infection by Theiler's murine encephalomyelitis virus strain GD VII causes acute encephalomyelitis and paralysis in infected mice. However, nude mice and cyclophosphamide-treated ddY mice did not show paralysis when they were able to survive until day 20 post-infection (p.i.). Of ddY mice infected with 5 x 10(7) p.f.u./mouse, 70-80% showed symptoms of paralysis on day 20 p.i. The viral titres in the brain and spinal cord in infected mice were not significantly different between paralytic and non-paralytic mice. In all of the mice infected with the virus, CD4+ lymphocytes and CD8+ lymphocytes had infiltrated the brain on days 10, 12, 14 and 20 p.i. as demonstrated by flow cytometric analysis. In contrast, few T lymphocytes infiltrated the spinal cord in the non-paralytic mice. Administration of an anti-CD4 monoclonal antibody (MAb) or anti-T cell receptor-alpha beta MAb on day 6 p.i. inhibited paralysis until day 20 p.i., though 20% of the MAb-treated mice and 80% of the control mice showed paralysis. Administration of anti-CD8 MAb was not effective in the suppression of paralysis. The MAb treatment did not significantly augment viral replication in the spinal cord, although the viral titres in the brain of the MAb-treated mice increased significantly. After the transfer of spleen cells from infected C3H mice, the recipient mice infected with a small amount of the virus showed paralysis, though uninfected mice did not. This transfer could be blocked by CD4+ lymphocyte depletion of the donor mice. These results indicate that paralysis caused by acute myelitis in Theiler's virus strain GD VII infection is induced by CD4+ lymphocytes infiltrating the spinal cord.

Infection of central nervous system cells by ecotropic murine leukemia virus in C58 and AKR mice and in in utero-infected CE/J mice predisposes mice to paralytic infection by lactate dehydrogenase-elevating virus

Certain mouse strains, such as AKR and C58, which possess N-tropic, ecotropic murine leukemia virus (MuLV) proviruses and are homozygous at the Fv-1n locus are specifically susceptible to paralytic infection (age-dependent poliomyelitis [ADPM]) by lactate dehydrogenase-elevating virus (LDV). Our results provide an explanation for this genetic linkage and directly prove that ecotropic MuLV infection of spinal cord cells is responsible for rendering anterior horn neurons susceptible to cytocidal LDV infection, which is the cause of the paralytic disease. Northern (RNA) blot hybridization of total tissue RNA and in situ hybridization of tissue sections demonstrated that only mice harboring central nervous system (CNS) cells that expressed ecotropic MuLV were susceptible to ADPM. Our evidence indicates that the ecotropic MuLV RNA is transcribed in CNS cells from ecotropic MuLV proviruses that have been acquired by infection with exogenous ecotropic MuLV, probably during embryogenesis, the time when germ line proviruses in AKR and C58 mice first become activated. In young mice, MuLV RNA-containing cells were found exclusively in white-matter tracts and therefore were glial cells. An increase in the ADPM susceptibility of the mice with advancing age correlated with the presence of an increased number of ecotropic MuLV RNA-containing cells in the spinal cords which, in turn, correlated with an increase in the number of unmethylated proviruses in the DNA extracted from spinal cords. Studies with AKXD recombinant inbred strains showed that possession of a single replication-competent ecotropic MuLV provirus (emv-11) by Fv-1n/n mice was sufficient to result in ecotropic MuLV infection of CNS cells and ADPM susceptibility. In contrast, no ecotropic MuLV RNA-positive cells were present in the CNSs of mice carrying defective ecotropic MuLV proviruses (emv-3 or emv-13) or in which ecotropic MuLV replication was blocked by the Fv-1n/b or Fv-1b/b phenotype. Such mice were resistant to paralytic LDV infection. In utero infection of CE/J mice, which are devoid of any endogenous ecotropic MuLVs, with the infectious clone of emv-11 (AKR-623) resulted in the infection of CNS cells, and the mice became ADPM susceptible, whereas littermates that had not become infected with ecotropic MuLV remained ADPM resistant.

Epidemiology and clinical characteristics of acute flaccid paralysis associated with non-polio enterovirus isolation: the experience in the Americas

The Pan American Health Organization adopted as a goal the interruption of transmission of wild poliovirus from the americas by 1990. Collection and processing of stool specimens from patients with acute flaccid paralysis (AFP) to identify wild poliovirus is critical for monitoring the success of the eradication programme. In the study described, cases of AFP in children less than 15 years of age reported in the Americas from 1989 to 1991 were evaluated to investigate the epidemiology of AFP associated with the isolation of non-polio enterovirus (NPEV), to characterize their clinical presentation, and to compare their clinical characteristics with those of AFP cases associated with the isolation of wild poliovirus (confirmed as poliomyelitis). The results show that the notification pattern for AFP associated with NPEV isolates is similar to that for all AFP cases. While AFP associated with NPEV isolates generally differs clinically from confirmed poliomyelitis, 2-21% of cases met one of three case definitions for poliomyelitis. Following the eradication of poliomyelitis, countries can therefore anticipate the continued reporting of cases of AFP that clinically mimic poliomyelitis but which are associated with NPEV. The study also confirms that NPEV circulation is common and that most isolates were from cases that did not resemble poliomyelitis. It is therefore questionable whether characterization of NPEV isolates is essential for global eradication of poliomyelitis and consequently whether allocation of resources for that purpose can be justified.

Development of physical forms of unintegrated retroviral DNA in mouse spinal cord tissue during ts1-induced spongiform encephalomyelopathy: elevated levels of a novel single-stranded form in paralyzed mice

ts1 is a murine leukemia virus that causes rapidly evolving hindlimb paralysis in susceptible strains of mice. Following perinatal infection, three physical forms of unintegrated viral DNA were detected in the spinal cord by Southern blot hybridization. Linear and supercoiled closed-circle viral double-stranded DNAs were detected in both the central nervous system and non-central nervous system tissues. An elevated level of a novel minus-sense single-stranded form of viral DNA, which had a very high mobility in agarose gels, was correlated with the onset of symptoms of paralysis. As the severity of paralysis progressed, the level of this single-stranded form increased rapidly, with the highest level in the spinal cords of moribund mice. Since the virulence of a number of cytopathic retroviruses has been associated with the presence of increased amounts of unintegrated viral DNA in the tissues of the infected hosts, this novel form of highly mobile unintegrated single-stranded DNA may have a role in the neuropathogenesis of ts1.

Paralytic poliomyelitis in Romania, 1984-1992. Evidence for a high risk of vaccine-associated disease and reintroduction of wild-virus infection

Although poliomyelitis due to wild-virus infection has virtually disappeared from Romania, with no cases having been documented between 1984 and 1989, vaccine-associated paralytic poliomyelitis has been reported at very high rates for over two decades. In November 1990, to decrease the risk of vaccine-associated paralytic poliomyelitis, oral poliovirus vaccine produced in Romania was replaced by imported oral vaccine made by a Western European manufacturer. To better quantify the risk of vaccine-associated paralytic poliomyelitis and the impact of the change in vaccine manufacturer, the authors reviewed clinical, epidemiologic, and laboratory data on poliomyelitis cases that occurred in Romania from 1984 to 1992. Poliovirus isolates were characterized at the US Centers for Disease Control and Prevention. During the period 1984-1992, 132 confirmed cases of paralytic poliomyelitis were reported in Romania, of which 13 were classified as wild-virus-associated, 93 as vaccine-associated, and 26 as "of unknown origin." Wild type 1 poliovirus was isolated during 1990-1992 from nine of 13 (69%) cases in an outbreak that occurred primarily among undervaccinated gypsy children. Vaccine-associated cases were epidemiologically and virologically distinct from wild-virus cases. Of the 93 vaccine-associated cases, 45 children were recipients and 48 were contacts. The overall risk of vaccine-associated paralytic poliomyelitis in Romania (1 case per 183,000 doses of oral poliovirus vaccine distributed) was 14-fold higher than the risk in the United States. The risks of recipient vaccine-associated paralytic poliomyelitis related to the first dose of oral vaccine were similar for Romanian and imported vaccine (1 case per 95,000 doses and 1 case per 65,000 doses, respectively), as were the total risks of vaccine-associated paralytic poliomyelitis. These findings definitively demonstrate a substantially elevated risk of vaccine-associated paralytic poliomyelitis in Romania which was not affected by a change in oral poliovirus vaccine manufacturer.