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At least 19 recordsLinked to original sources
PubMed1991

Persistent infection of Vero cells by the flavivirus Murray Valley encephalitis virus.

Murray Valley encephalitis (MVE) virus strain OR2 was serially passaged on Vero cells to establish a persistent infection which was maintained for over 300 days. Supernatants from infected cells protected Vero cells from c.p.e. and caused up to a 95% reduction of wild-type virus yield. These protective and interfering effects suggest that defective interfering (DI) particles are responsible for the establishment and maintenance of the MVE virus persistent infection. The persistently infected cell supernatant preparations shared several features with DI particle preparations from other viral systems, such as their amplification to detectable levels after two to four passages of virus. However, results from this study suggest that DI particles of MVE virus differ from other studied systems in that they are able to affect only moderately the yield of infectious wild-type virus. The genetic drift of the parental virus during the course of a long term persistent infection in vitro appears to be minimal.

Animals↗
PubMed2002

Mechanism of virulence attenuation of glycosaminoglycan-binding variants of Japanese encephalitis virus and Murray Valley encephalitis virus.

The in vivo mechanism for virulence attenuation of laboratory-derived variants of two flaviviruses in the Japanese encephalitis virus (JEV) serocomplex is described. Host cell adaptation of JEV and Murray Valley encephalitis virus (MVE) by serial passage in adenocarcinoma cells selected for variants characterized by (i) a small plaque phenotype, (ii) increased affinity to heparin-Sepharose, (iii) enhanced susceptibility to inhibition of infectivity by heparin, and (iv) loss of neuroinvasiveness in a mouse model for flaviviral encephalitis. We previously suggested that virulence attenuation of the host cell-adapted variants of MVE is a consequence of their increased dependence on cell surface glycosaminoglycans (GAGs) for attachment and entry (E. Lee and M. Lobigs, J. Virol. 74:8867-8875, 2000). In support of this proposition, we find that GAG-binding variants of JEV and MVE were rapidly removed from the bloodstream and failed to spread from extraneural sites of replication into the brain. Thus, the enhanced affinity of the attenuated variants for GAGs ubiquitously present on cells and extracellular matrices most likely prevented viremia of sufficient magnitude and/or duration required for virus entry into the brain parenchyma. This mechanism may also account, in part, for the attenuation of the JEV SA14-14-2 vaccine, given the sensitivity of the virus to heparin inhibition. A pronounced loss of the capacity of the GAG-binding variants to produce disease was also noted in mice defective in the alpha/beta interferon response, a mouse strain shown here to be highly susceptible to infection with JEV serocomplex flaviviruses. Despite the close genetic relatedness of JEV and MVE, the variants selected for the two viruses were altered at different residues in the envelope (E) protein, viz., Glu(306) and Asp(390) for JEV and MVE, respectively. In both cases the substitutions gave the protein an increased net positive charge. The close spatial proximity of amino acids 306 and 390 in the predicted E protein structure strongly suggests that the two residues define a receptor-binding domain involved in virus attachment to sulfated proteoglycans.

Amino Acid Substitution↗
PubMedDate not supplied

Polymerase chain reaction tests for the identification of Ross River, Kunjin and Murray Valley encephalitis virus infections in horses.

OBJECTIVE: To develop and validate specific, sensitive and rapid diagnostic tests using RT-PCR for the detection of Ross River virus (RRV), Kunjin virus (KV) and Murray Valley encephalitis virus (MVEV) infections in horses. METHODS: Primer sets based on nucleotide sequence encoding the envelope glycoprotein E2 of RRV and on the nonstructural protein 5 (NS5) of KV and MVEV were designed and used in single round PCRs to test for the respective viruses in infected cell cultures and, in the case of RRV, in samples of horse blood and synovial fluid. RESULTS: The primer pairs designed for each of the three viruses amplified a product of expected size from prototype viruses that were grown in cell culture. The identity of each of the products was confirmed by nucleotide sequencing indicating that in the context used the RT-PCRs were specific. RRV was detected in serums from 8 horses for which there were clinical signs consistent with RRV infection such that an acute-phase serum sample was taken and submitted for RRV serology testing. The RRV RT-PCR was analytically sensitive in that it was estimated to detect as little as 50 TCID50 of RRV per mL of serum and was specific in that the primer pairs did not amplify other products from the 8 serum samples. The RRV primers also detected virus in three independent mosquito pools known to contain RRV by virus isolation in cell culture. Samples from horses suspected to be infected with KV and MVEV were not available. CONCLUSION: Despite much anecdotal and serological evidence for infection of horses with RRV actual infection and associated clinical disease are infrequently confirmed. The availability of a specific and analytically sensitive RT-PCR for the detection of RRV provides additional opportunities to confirm the presence of this virus in clinical samples. The RT-PCR primers for the diagnosis of KV and MVEV infections were shown to be specific for cell culture grown viruses but the further validation of these tests requires the availability of appropriate clinical samples from infected horses.

Alphavirus Infections↗
PubMed2000

Immunisation with gamma globulin to murray valley encephalitis virus and with an inactivated Japanese encephalitis virus vaccine as prophylaxis against australian encephalitis: evaluation in a mouse model.

In northwestern Australia, the flavivirus Murray Valley encephalitis (MVE) poses a significant health risk to infants in some aboriginal communities, particularly during each wet season. While there are too few cases to warrant the development of a vaccine against MVE, a safe, effective prophylaxis for these children is still urgently required. The use of passive transfer of human gamma globulin to MVE or immunisation with a vaccine to the closely related Japanese encephalitis (JE) virus were investigated as potential strategies. When 40 microg of IgG was purified from MVE-immune human sera and transferred to 3-week-old mice, the animals were protected from lethal IP inoculation with MVE virus while still producing a detectable immune response to the virus. Similarly, sera from adult mice infected sublethally with MVE or JE virus provided significant protection against MVE infection. However, sera from mice sublethally infected with the related Kunjin or immunised with the inactivated JE vaccine (Biken) provided no protection against MVE challenge. In fact, mice immunised passively with the latter appeared to succumb to MVE challenge more rapidly than mice that received serum from unimmunised animals, suggesting that antibody to the vaccine had accelerated the progression of disease. These preliminary trials in mice indicate that passive immunisation with human gamma globulin has the greatest potential as a strategy for MVE prophylaxis, whilst the apparent enhancement of MVE by antibodies to the JE vaccine requires further investigation, with particular reference to current vaccination programs in areas of Australia and Papua New Guinea, where both JE and MVE occur.

Animals↗
PubMed2002

Murray Valley encephalitis virus recombinant subviral particles protect mice from lethal challenge with virulent wild-type virus.

We report on the development and characterisation of a recombinant Murray Valley encephalitis virus (MVE) envelope glycoprotein expression system that results in the secretion of subviral particles (SVPs) upon transfection of the murine fibroblast (COS-7) cell line. Initially, aspects of the physical and antigenic structure of cell-associated and secreted forms of the MVE envelope glycoproteins (prM and E) are presented. We then show that BALB/c mice inoculated with SVPs purified from pcDNA(3)-prM/E-transfected COS-7 cell supernatants are protected from lethal challenge with the virulent prototype strain MVE-1-51 and that this protection correlates with the development of a neutralising humoral immune response by the host. By contrast, prior immunisation with cell-associated, recombinant MVE envelope glycoproteins did not protect mice from challenge with MVE-1-51 and this was associated with the development of antibody that was unable to neutralise virus infectivity in vitro. These studies demonstrate that SVPs derived from the in vitro expression of recombinant MVE prM and E genes are an effective candidate vaccine for the prevention of encephalitis in the mouse model.

Animals↗
PubMed2002

Reappearance of human cases due to Murray Valley encephalitis virus and Kunjin virus in central Australia after an absence of 26 years.

Murray Valley encephalitis (MVE) and Kunjin virus disease are endemic in the tropical parts of the Northern Territory and Western Australia, but have been absent from Central Australia since 1974. In 2000, 5 laboratory-confirmed cases of encephalitis occurred over a short period in the normally dry inland region of Central Australia. The sudden occurrence of cases in March and April 2000 followed unusually high rainfall in the preceding months and evidence of flavivirus activity in the endemic areas in the Kimberley region of Western Australia. Further cases were reported in the following wet season, without preceding human cases in known endemic areas. These findings indicate the reintroduction of these viruses into Central Australia and establishment of local cycles of infection with an ongoing risk to the local population. This area may also act as a potential source for reintroduction of MVE into south-eastern Australia.

Adult↗