West Nile virus (WNV), a neurotropic arbovirus, has been detected in mosquitos, birds, wildlife, horses, and humans in Malaysia, but limited information is available on WNV infection in Malaysian pigs. We tested 80 archived swine serum samples for the presence of WNV antibody and West Nile (WN) viral RNA using ID Screen West Nile Competition Multi-species enzyme-linked immunosorbent assay kits and WNV-specific primers in reverse transcription polymerase chain reaction assays, respectively. A WNV seroprevalence of 62.5% (50/80) at 95% confidence interval (51.6%-72.3%) was recorded, with a significantly higher seroprevalence among young pigs (weaner and grower) and pigs from south Malaysia. One sample was positive for Japanese encephalitis virus antibodies; WN viral RNA was not detected in any of the serum samples.
Matched MeSH terms: West Nile Fever/blood; West Nile Fever/epidemiology; West Nile Fever/veterinary*; West Nile Fever/virology
Being a tropical country with a conducive environment for mosquitoes, mosquito-borne illnesses such as dengue, chikungunya, lymphatic filariasis, malaria, and Japanese encephalitis are prevalent in Malaysia. Recent studies reported asymptomatic infection of West Nile virus (WNV) in animals and humans, but none of the studies included mosquitoes, except for one report made half a century ago. Considering the scarcity of information, our study sampled mosquitoes near migratory bird stopover wetland areas of West Coast Malaysia located in the Kuala Gula Bird Sanctuary and Kapar Energy Venture, during the southward migration period in October 2017 and September 2018. Our previous publication reported that migratory birds were positive for WNV antibody and RNA. Using a nested RT-PCR analysis, WNV RNA was detected in 35 (12.8%) out of 285 mosquito pools consisting of 2,635 mosquitoes, most of which were Culex spp. (species). Sanger sequencing and phylogenetic analysis revealed that the sequences grouped within lineage 2 and shared 90.12%-97.01% similarity with sequences found locally as well as those from Africa, Germany, Romania, Italy, and Israel. Evidence of WNV in the mosquitoes substantiates the need for continued surveillance of WNV in Malaysia.
West Nile virus (WNV) is a zoonotic single-strand RNA arbovirus (family Flaviviridae: Flavivirus), transmitted among avian hosts in enzootic cycles by a mosquito vector. The virus has a significant disease effect on humans and equines when it bridges into a cycle with various sequelae with epidemic potential. This study was carried out to identify the potential spectrum of WNV hosts in three geographic areas with climatologically distinct features: Malaysia, Qatar, and the United States of America (U.S.). Serum samples were collected from avian and mammal species suspected to be reservoirs for the virus at these areas in a cross-sectional epidemiologic study. The samples were tested for the presence of antibodies against the virus using an enzyme-linked immunosorbent assay. Data on putative risk factors were also collected and analyzed for significance of association with seropositivity using the logistic regression analysis. Among the tested avian and mammalian species, raccoons had the highest seroconversion rate (54%) followed by crows (30%), horses (27%), camels (10%), other avian species (7%), and canine species (3%). It was almost twice as likely to detect seroconversion among these mammalian and avian species in the fall in comparison to other seasons of the year. Only mammalian and avian species and seasons of the year were significantly associated with the likelihood of seroconversion to WNV when we controlled for other factors in the multivariate analysis. Our data from the U.S. showed that raccoons and camels are susceptible to infection by the virus and may play a role in the perpetuation of endemic foci for the disease.
Matched MeSH terms: West Nile Fever/epidemiology; West Nile Fever/veterinary*; West Nile Fever/virology
Over 100 viruses have been associated with acute central nervous system infections. The present review focuses on some of the most common agents of viral encephalitis, as well as important emerging viral encephalitides. In this context, the initial detection of West Nile virus in the Western Hemisphere during the 1999 New York City outbreak, the first description of Nipah virus in Malaysia, and the appearance in Asia of a new neurovirulent enterovirus 71 strain that causes severe neurologic disease are highlighted. In addition, advances regarding diagnosis, neuroimaging and treatment of Japanese and herpes simplex encephalitis are presented.
Matched MeSH terms: West Nile Fever/diagnosis; West Nile Fever/virology
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.
Matched MeSH terms: West Nile Fever/epidemiology*; West Nile Fever/transmission
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.
Matched MeSH terms: West Nile Fever/pathology; West Nile Fever/therapy; West Nile Fever/virology
In Australia, infection of horses with the West Nile virus (WNV) or Murray Valley encephalitis virus (MVEV) occasionally results in severe neurological disease that cannot be clinically differentiated. Confirmatory serological tests to detect antibody specific for MVEV or WNV in horses are often hampered by cross-reactive antibodies induced to conserved epitopes on the envelope (E) protein. This study utilized bacterially expressed recombinant antigens derived from domain III of the E protein (rE-DIII) of MVEV and WNV, respectively, to determine whether these subunit antigens provided specific diagnostic markers of infection with these two viruses. When a panel of 130 serum samples, from horses with known flavivirus infection status, was tested in enzyme-linked immunosorbent assay (ELISA) using rE-DIII antigens, a differential diagnosis of MVEV or WNV was achieved for most samples. Time-point samples from horses exposed to flavivirus infection during the 2011 outbreak of equine encephalitis in south-eastern Australia also indicated that the rE-DIII antigens were capable of detecting and differentiating MVEV and WNV infection in convalescent sera with similar sensitivity and specificity to virus neutralization tests and blocking ELISAs. Overall, these results indicate that the rE-DIII is a suitable antigen for use in rapid immunoassays for confirming MVEV and WNV infections in horses in the Australian context and warrant further assessment on sensitive, high-throughput serological platforms such as multiplex immune assays.
Matched MeSH terms: West Nile Fever/diagnosis; West Nile Fever/veterinary*; West Nile Fever/virology
Kunjin (KUN) is a flavivirus in the Japanese encephalitis antigenic complex that was first isolated from Culex annulirostris mosquitoes captured in northern Australia in 1960. It is the etiological agent of a human disease characterized by febrile illness with rash or mild encephalitis and, occasionally, of a neurological disease in horses. KUN virus shares a similar epidemiology and ecology with the closely related Murray Valley encephalitis (MVE) virus, the major causative agent of arboviral encephalitis in Australia. Based on traditional antigenic methods, KUN was initially found to be similar to, but distinct from, reference strains of West Nile (WN) virus and designated as a new species. However, more recent phylogenic analyses have revealed that some strains of WN virus, including the isolates from New York, are more similar to KUN virus and form a separate lineage to other WN viruses. An unusual KUN isolate from Malaysia and the African virus Koutango appear to form additional lineages within the WN group of viruses. While these findings are in agreement with the Seventh Report of the International Committee for the Taxonomy of Viruses that designates KUN as a subtype of West Nile, they also suggest that the species should be further subdivided into additional subtypes.
Rodent models have been used extensively to study West Nile virus (WNV) infection because they develop severe neurological symptoms similar to those observed in human WNV neuroinvasive disease. Most of this research has focused on old lineage (L) 1 strains, while information about pathogenicity is lacking for the most recent L1 and L2 strains, as well as for newly defined lineages. In this study, 4-week-old Swiss mice were inoculated with a collection of 12 WNV isolates, comprising 10 old and recent L1 and L2 strains, the putative L6 strain from Malaysia and the proposed L7 strain Koutango (KOU). The intraperitoneal inoculation of 10-fold dilutions of each strain allowed the characterization of the isolates in terms of LD50, median survival times, ID50, replication in neural and extraneural tissues and antibody production. Based on these results, we classified the isolates in three groups: high virulence (all L1a strains, recent L2 strains and KOU), moderate virulence (B956 strain) and low virulence (Kunjin and Malaysian isolates). We determined that the inoculation of a single dose of 1000 p.f.u. would be sufficient to classify WNV strains by pathotype. We confirmed the enhanced virulence of the KOU strain with a high capacity to cause rapid systemic infection. We also corroborated that differences in pathogenicity among strains do not correlate with phylogenetic lineage or geographic origin, and confirmed that recent European and African WNV strains belonging to L1 and L2 are highly virulent and do not differ in their pathotype profile compared to the prototype NY99 strain.
West Nile virus (WNV) infection is an emerging zoonotic disease caused by an RNA virus of the genus Flavivirus. WNV is preserved in the environment through cyclic transmission, with mosquitoes, particularly Culex species, serving as a vector, birds as an amplifying host and humans and other mammals as dead-end hosts. To date, no studies have been carried out to determine the prevalence of the WNV antibody in Malaysia. The aim of this study was to screen for the seroprevalence of the WNV in Malaysia's Orang Asli population.
Matched MeSH terms: West Nile Fever/epidemiology*; West Nile Fever/virology
Severe acute respiratory syndrome (SARS) reminds us that sudden disease emergence is a permanent part of our world--and should be anticipated in our planning. Historically the emergence of new diseases has had little or no impact beyond a small, localized cluster of infections. However, given just the right conditions, a highly virulent pathogen can suddenly spread across time and space with massive consequences, as has occurred on several occasions in human history. In the wake of the SARS outbreak, we are now forced to confront the unpleasant fact that human activities are increasing the frequency and severity of these kinds of emergences. The idea of more frequent biological "invasions" with economic and societal impacts comparable to SARS, presents stakeholders in and the global economy with unprecedented new risks, challenges and even opportunities. As a major contributor to economic stability, the insurance industry must follow these trends very closely and develop scenarios to anticipate these events.
Matched MeSH terms: West Nile Fever/epidemiology*; West Nile Fever/prevention & control
Until recently, West Nile (WN) and Kunjin (KUN) viruses were classified as distinct types in the Flavivirus genus. However, genetic and antigenic studies on isolates of these two viruses indicate that the relationship between them is more complex. To better define this relationship, we performed sequence analyses on 32 isolates of KUN virus and 28 isolates of WN virus from different geographic areas, including a WN isolate from the recent outbreak in New York. Sequence comparisons showed that the KUN virus isolates from Australia were tightly grouped but that the WN virus isolates exhibited substantial divergence and could be differentiated into four distinct groups. KUN virus isolates from Australia were antigenically homologous and distinct from the WN isolates and a Malaysian KUN virus. Our results suggest that KUN and WN viruses comprise a group of closely related viruses that can be differentiated into subgroups on the basis of genetic and antigenic analyses.
Matched MeSH terms: West Nile Fever/epidemiology; West Nile Fever/virology*
West Nile virus (WNV) is a zoonotic mosquito-borne flavivirus that is harbored and amplified by wild birds via the enzootic transmission cycle. Wide range of hosts are found to be susceptible to WNV infection including mammals, amphibians and reptiles across the world. Several studies have demonstrated that WNV was present in the Malaysian Orang Asli and captive birds. However, no data are available on the WNV prevalence in wild birds found in Malaysia. Therefore this study was conducted to determine the serological and molecular prevalence of WNV in wild birds in selected areas in the West Coast of Peninsular Malaysia. Two types of wild birds were screened, namely migratory and resident birds in order to explore any possibility of WNV transmission from the migratory birds to the resident birds. Thus, a cross-sectional study was conducted at the migratory birds sanctuary located in Kuala Gula, Perak and Kapar, Selangor by catching 163 migratory birds, and 97 resident birds from Kuala Gula and Parit Buntar, Perak at different time between 2016 and 2017 (Total, n = 260). Blood and oropharyngeal swabs were collected for serological and molecular analysis, respectively. Serum were screened for WNV antibodies using a commercial competitive ELISA (c-ELISA) (ID Screen® West Nile Competition Multi-species ELISA, ID VET, Montpellier, France) and cross-reactivity towards Japanese Encephalitis virus (JEV) was also carried out using the JEV-double antigen sandwich (DAS) ELISA. Oropharyngeal swabs were subjected to one-step RT-PCR to detect WNV RNA, in which positive reactions were subsequently sequenced. WNV seropositive rate of 18.71% (29/155) at 95% CI (0.131 to 0.260) and molecular prevalence of 15.2% (16/105) at 95% CI (0.092 to 0.239) were demonstrated in migratory and resident wild birds found in West Coast Malaysia. Phylogenetic analyses of the 16 WNV isolates found in this study revealed that the local strains have 99% similarity to the strains from South Africa and were clustered under lineage 2. Evidence of WNV infection in resident and migratory birds were demonstrated in this study. As a summary, intervention between migratory birds, resident birds and mosquitoes might cause the introduction and maintenance of WNV in Malaysia, however the assumption could be further proven by studying the infection dynamics in the mosquitoes present in the studied areas.