Japanese encephalitis virus (JEV) and West Nile virus (WNV) provide some of the most important examples of emerging zoonotic viral encephalitides. For these flaviviruses, only a small proportion of those infected develop clinical features, and these may range from a non-specific flu-like illness to a severe fatal meningoencephalitis, often with Parkinsonian features, or a poliomyelitis-like flaccid paralysis. The factors governing the clinical presentations, and outcome of flavivirus infections are poorly understood, but studies have looked at viral virulence determinants and the host immune response. Previous studies on JEV have suggested that the distribution of the four genotypes across Asia may relate to the differing clinical epidemiology (epidemic disease in the north, endemic disease in the south). However, new data based on the complete nucleotide sequence of a virus representing one of the oldest lineages, and phylogenetic analyses of all JEV strains for which genetic data are available, suggest that the distribution is best explained in terms of the virus' origin in the Indonesia-Malaysia region (where all genotypes have been found), and the spread of the more recent genotypes to new geographical areas. Clinical studies have shown that innate immunity, as manifested by interferon alpha levels, is important in JEV and other flaviviruses, but treatment with interferon alpha did not improve the outcome. A failure of the humoral immune response, is associated with death from encephalitis caused by JEV and WNV. Cellular immunity has been less well characterized, but CD8+ and CD4+ T cells are thought to be important.
The role of the cytoskeleton, actin, and microtubules were examined during the process of Japanese encephalitis (JEV) infection in a human neuroblastoma cell line, IMR32. Cytochalasin D and nocodazole were used to depolymerise the cellular actin and microtubules, respectively, in order to study the effect of JEV infection in the cell. This study shows that depolymerisation of the actin cytoskeleton at early process of infection inhibits JEV infection in the cell; however infection was not inhibited when depolymerisation occurred at the later stage of infection. The microtubules, on the other hand, are required at 2 points in infection. The antigen production in the cells was inhibited when the infected cells were treated at time up to 2 hours after inoculation and there was no significant effect at later times, while the viable virus released continued to be affected until 10 hours after inoculation. In conclusion, infection of JEV in IMR32 cells required actin to facilitate early process in infection and the microtubular network is utilised as the transport system to the virus replication site and the release of mature virus.
Since it emerged in Japan in the 1870s, Japanese encephalitis has spread across Asia and has become the most important cause of epidemic encephalitis worldwide. Four genotypes of Japanese encephalitis virus (JEV) are presently recognized (representatives of genotypes I to III have been fully sequenced), but its origin is not known. We have determined the complete nucleotide and amino acid sequence of a genotype IV Indonesian isolate (JKT6468) which represents the oldest lineage, compared it with other fully sequenced genomes, and examined the geographical distribution of all known isolates. JKT6468 was the least similar, with nucleotide divergence ranging from 17.4 to 19.6% and amino acid divergence ranging from 4.7 to 6.5%. It included an unusual series of amino acids at the carboxy terminus of the core protein unlike that seen in other JEV strains. Three signature amino acids in the envelope protein (including E327 Leu-->Thr/Ser on the exposed lateral surface of the putative receptor binding domain) distinguished genotype IV strains from more recent genotypes. Analysis of all 290 JEV isolates for which sequence data are available showed that the Indonesia-Malaysia region has all genotypes of JEV circulating, whereas only more recent genotypes circulate in other areas (P < 0.0001). These results suggest that JEV originated from its ancestral virus in the Indonesia-Malaysia region and evolved there into the different genotypes which then spread across Asia. Our data, together with recent evidence on the origins of other emerging viruses, including dengue virus and Nipah virus, imply that tropical southeast Asia may be an important zone for emerging pathogens.
The exotic and emerging viral encephalitides are caused by animal or human viruses and characterised by sudden unexpected outbreaks of neurological disease, usually in tropical and sub-tropical regions, but sometimes spreading to temperate areas. Although a wide range of viruses come within this label, as this review highlights, there are common research questions as to the origin and spread of the viruses, the contribution of viral and host factors to the clinical presentations and outcome, and the possibilities for treatment and vaccination.
The Sarawak strain of Japanese encephalitis virus (JE-Sar) is virulent in 3-week-old mice when inoculated intraperitoneally. The nucleotide sequence for the envelope glycoprotein (E) of this virus was determined and compared with the published sequences of four other strains. There were several silent nucleotide differences and five codon changes. Monoclonal antibodies (MAbs) against the E protein of JE-Sar virus were prepared and characterized. MAb-resistant mutants of JE-Sar were selected to determine if mutations in the E protein gene could affect its virulence for mice. Eight mutants were isolated using five different MAbs that identified virus-specific or group-reactive epitopes on the E protein. The mutants lost either complete or partial reactivity with selecting MAb. Several showed decreased virulence in 3-week-old mice after intraperitoneal inoculation. Two (r27 and r30) also showed reduced virulence in 2-week-old mice. JE-Sar and the derived mutants were comparable in their virulence for mice, when inoculated intracranially. Mutant r30 but not r27 induced protective immunity in adult mice against intracranial challenge with parent virus. However, r27-2 did induce protective immunity against itself. Nucleotide sequencing of the E coding region for the mutants revealed single base changes in both r30 and r27 resulting in a predicted change from isoleucine to serine at position 270 in r30 and from glycine to aspartic acid at position 333 in r27. The altered capacity of the mutants to induce protective immunity is consistent with the immunogenicity changes predicted by computer analysis using the Protean II program.
The last decade of the 20th Century saw the introduction of an unprecedented number of encephalitic viruses emerge or spread in the Southeast Asian and Western Pacific regions (Mackenzie et al, 2001; Solomon, 2003a). Most of these viruses are zoonotic, either being arthropod-borne viruses or bat-borne viruses. Thus Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, has spread through the Indonesian archipelago to Papua New Guinea (PNG) and to the islands of the Torres Strait of northern Australia, to Pakistan, and to new areas in the Indian subcontinent; a strain of tick-borne encephalitis virus (TBEV) was described for the first time in Hokkaido, Japan; and a novel mosquito-borne alphavirus, Me Tri virus, was described from Vietnam. Three novel bat-borne viruses emerged in Australia and Malaysia; two, Hendra and Nipah viruses, represent the first examples of a new genus in the family Paramyxoviridae, the genus Henipaviruses, and the third, Australian bat lyssavirus (ABLV) is new lyssavirus closely related to classical rabies virus. These viruses will form the body of this brief review.
Japanese encephalitis (JE) is a neurotropic flavivirus that causes inflammation in central nervous system (CNS), neuronal death and also compromises the structural and functional integrity of the blood-brain barrier (BBB). The aim of this study was to evaluate the BBB disruption and apoptotic process in Japanese encephalitis virus (JEV)-infected transfected human brain microvascular endothelial cells (THBMECs). THBMECs were overlaid by JEV with different MOIs (0.5, 1.0, 5.0 and 10.0) and monitored by electrical cell-substrate impedance sensing (ECIS) in a real-time manner in order to observe the barrier function of THBMECs. Additionally, the level of 43 apoptotic proteins was quantified in the virally infected cells with different MOIs at 24h post infection. Infection of THBMEC with JEV induced an acute reduction in transendothelial electrical resistance (TEER) after viral infection. Also, significant up-regulation of Bax, BID, Fas and Fasl and down-regulation of IGFBP-2, BID, p27 and p53 were observed in JEV infected THBMECs with 0.5 and 10 MOIs compared to uninfected cells. Hence, the permeability of THBMECs is compromised during the JEV infection. In addition high viral load of the virus has the potential to subvert the host cell apoptosis to optimize the course of viral infection through deactivation of pro-apoptotic proteins.