Outbreak Of Viral Encephalitis Research Articles

The reemerging and outbreak of genotypes 4 and 5 of Japanese encephalitis virus.

The Japanese encephalitis virus (JEV) is classified into five distinct genotypes, with genotypes 1 and 3 historically showing higher activity. These genotypes are the primary agents of viral encephalitis in the Asian continent. Genotypes 4 and 5 have remained silent in low-latitude tropical regions since their discovery. From 2009, the hidden genotype 5 suddenly emerged simultaneously in mosquitoes from the Tibetan region of China and those from South Korea in East Asia. The detection of genotype 5 of JEV in these mosquitoes was associated with cases of viral encephalitis in the local population. Similarly, in 2022, the long-silent genotype 4 of JEV emerged in Australia, resulting in a local outbreak of viral encephalitis that primarily affected adults and caused fatalities. The emergence and outbreaks of genotypes 4 and 5 of JEV present new challenges for the prevention and control of Japanese encephalitis (JE). This study not only analyzes the recent emergence of these new genotypes but also discusses their implications in the development of JE vaccines and laboratory tests for newly emerging JEV infections.

Re-Emerged Genotype IV of Japanese Encephalitis Virus Is the Youngest Virus in Evolution.

An outbreak of viral encephalitis caused by a Japanese encephalitis virus (JEV) genotype IV infection occurred in Australia between 2021 and 2022. A total of 47 cases and seven deaths were reported as of November 2022. This is the first outbreak of human viral encephalitis caused by JEV GIV since it was first isolated in Indonesia in the late 1970s. Here, a comprehensive phylogenetic analysis based on the whole genome sequences of JEVs revealed it emerged 1037 years ago (95% HPD: 463 to 2100 years). The evolutionary order of JEV genotypes is as follows: GV, GIII, GII, GI, and GIV. The JEV GIV emerged 122 years ago (95% HPD: 57-233) and is the youngest viral lineage. The mean substitution rate of the JEV GIV lineage was 1.145 × 10-3 (95% HPD values, 9.55 × 10-4, 1.35 × 10-3), belonging to rapidly evolving viruses. A series of amino acid mutations with the changes of physico-chemical properties located in the functional important domains within the core and E proteins distinguished emerging GIV isolates from old ones. These results demonstrate the JEV GIV is the youngest JEV genotype at a rapid evolution stage and has good host/vector adaptability for introduction to non-endemic areas. Thus, surveillance of JEVs is highly recommended.

West Nile Virus Induced Cell Death in the Central Nervous System.

West Nile virus (WNV), a mosquito-borne, single-stranded flavivirus, has caused annual outbreaks of viral encephalitis in the United States since 1999. The virus induces acute infection with a clinical spectrum ranging from a mild flu-like febrile symptom to more severe neuroinvasive conditions, including meningitis, encephalitis, acute flaccid paralysis, and death. Some WNV convalescent patients also developed long-term neurological sequelae. Neither the treatment of WNV infection nor an approved vaccine is currently available for humans. Neuronal death in the central nervous system (CNS) is a hallmark of WNV-induced meningitis and encephalitis. However, the underlying mechanisms of WNV-induced neuronal damage are not well understood. In this review, we discuss current findings from studies of WNV infection in vitro in the CNS resident cells and the in vivo animal models, and provide insights into WNV-induced neuropathogenesis.

Estimating biologically relevant parameters under uncertainty for experimental within-host murine West Nile virus infection.

West Nile virus (WNV) is an emerging pathogen that has decimated bird populations and caused severe outbreaks of viral encephalitis in humans. Currently, little is known about the within-host viral kinetics of WNV during infection. We developed mathematical models to describe viral replication, spread and host immune response in wild-type and immunocompromised mice. Our approach fits a target cell-limited model to viremia data from immunocompromised knockout mice and an adaptive immune response model to data from wild-type mice. Using this approach, we first estimate parameters governing viral production and viral spread in the host using simple models without immune responses. We then use these parameters in a more complex immune response model to characterize the dynamics of the humoral immune response. Despite substantial uncertainty in input parameters, our analysis generates relatively precise estimates of important viral characteristics that are composed of nonlinear combinations of model parameters: we estimate the mean within-host basic reproductive number,R0, to be 2.3 (95% of values in the range 1.7-2.9); the mean infectious virion burst size to be 2.9 plaque-forming units (95% of values in the range 1.7-4.7); and the average number of cells infected per infectious virion to be between 0.3 and 0.99. Our analysis gives mechanistic insights into the dynamics of WNV infection and produces estimates of viral characteristics that are difficult to measure experimentally. These models are a first step towards a quantitative understanding of the timing and effectiveness of the humoral immune response in reducing host viremia and consequently the epidemic spread of WNV.

Evaluation of vector competence for West Nile virus in Italian Stegomyia albopicta (=Aedes albopictus) mosquitoes.

West Nile virus (WNV) is a zoonotic arboviral pathogen transmitted by mosquitoes in a cycle that involves wild birds as reservoir hosts. The virus is responsible for outbreaks of viral encephalitis in humans and horses. In Europe, Culex pipiens (Diptera: Culicidae) is considered to be the main vector of WNV, but other species such as Stegomyia albopicta (=Aedes albopictus) (Diptera: Culicidae) may also act as competent vectors of this virus. Since 2008 human cases of WNV disease have been reported in northeast Italy. In 2011, new areas of southern Italy became involved and a first outbreak of WNV lineage 1 occurred on the island of Sardinia. On the assumption that a potential involvement of St. albopicta in WNV transmission cannot be excluded, and in order to evaluate the competence of this species for the virus, an experimental infection of an St. albopicta laboratory colony, established from mosquitoes collected in Sardinia, was carried out. The results were compared with those obtained in a colony of the main vector Cx. pipiens. The study showed St. albopicta collected on Sardinia to be susceptible to WNV infection, which suggests this Italian mosquito species is able to act as a possible secondary vector, particularly in urban areas where the species reaches high levels of seasonal abundance.

The Australian Public is Still Vulnerable to Emerging Virulent Strains of West Nile Virus.

The mosquito-borne West Nile virus (WNV) is responsible for outbreaks of viral encephalitis in humans and horses with particularly virulent strains causing recent outbreaks in Eastern Europe, the Middle East, and North America. In Australia, a strain of WNV, Kunjin (WNVKUN), is endemic in the north and infection with this virus is generally asymptomatic. However, in early 2011, following extensive flooding, an unprecedented outbreak of WNVKUN encephalitis in horses occurred in South-Eastern Australia, resulting in more than 1,000 cases and a mortality of 10–15%. Despite widespread evidence of equine infections, there was only a single mild human case reported during this outbreak. To understand why clinical disease was seen in horses without similar observations in the human population, a serosurvey was conducted using blood donor samples from areas where equine cases were reported to assess level of flavivirus exposure. The seroprevalence to WNVKUN in humans was low before the outbreak (0.7%), and no significant increase was demonstrated after the outbreak period (0.6%). Due to unusual epidemiological features during this outbreak, a serosurvey was also conducted in rabbits, a potential reservoir host. Out of 675 animals, sampled across Australia between April 2011 and November 2012, 86 (12.7%) were seropositive for WNVKUN, with the highest prevalence during February of 2012 (28/145; 19.3%). As this is the first serological survey for WNVKUN in Australian feral rabbits, it remains to be determined whether wild rabbits are able to develop a high enough viremia to actively participate in WNV transmission in Australia. However, they may constitute a sentinel species for arbovirus activity, and this is the focus of on-going studies. Collectively, this study provides little evidence of human exposure to WNVKUN during the 2011 outbreak and indicates that the Australian population remains susceptible to the emergence of virulent strains of WNV.

The Changing Epidemiology of Kunjin Virus in Australia

West Nile virus (WNV) is a mosquito-borne virus responsible for outbreaks of viral encephalitis in humans and horses, with particularly virulent strains causing recent outbreaks of disease in Eastern Europe, the Middle East and North America. A strain of WNV, Kunjin (WNVKUN), is endemic in northern Australia and infection with this virus is generally asymptomatic. However in early 2011, an unprecedented outbreak of encephalitis in horses occurred in south-eastern Australia, resulting in mortality in approximately 10%–15% of infected horses. A WNV-like virus (WNVNSW2011) was isolated and found to be most closely related to the indigenous WNVKUN, rather than other exotic WNV strains. Furthermore, at least two amino acid changes associated with increased virulence of the North American New York 99 strain (WNVNY99) compared to the prototype WNVKUN were present in the WNVNSW2011 sequence. This review summarizes our current understanding of WNVKUN and how the epidemiology and ecology of this virus has changed. Analysis of virulence determinants of contemporary WNVKUN isolates will provide clues on where virulent strains have emerged in Australia. A better understanding of the changing ecology and epidemiology associated with the emergence of virulent strains is essential to prepare for future outbreaks of WNV disease in Australia.

Recombination in human coxsackievirus B5 strains that caused an outbreak of viral encephalitis in Henan, China

In 2011, human coxsackievirus B5 (CVB5) caused an outbreak of viral encephalitis in Henan, China. Complete genome sequence analysis based on two isolates showed that the 5' half of the genome (nt 1-4540) had high similarity (>97%) to that of CVB5 strain GU376747, and the 3' half (nt 4700-7402) showed high similarity (>96%) to that of human coxsackievirus B3 (CVB3) strain GQ141875. These isolates had the highest similarity (97.7%) to the Changchun strain, based on the complete genome, rather than to other CVB5 strains isolated from Henan in recent years. There were therefore at least two groups of CVB5 circulating in Henan Province, which evolved at different rates.

Neurological infections: risks of globalisation and new drugs

Each year, the highest incidence of microbial infections in the nervous system is caused by pathogens such as meningococcus, toxoplasmosis, and Cryptococcus, and by encephalitic viruses such as those that cause Japanese encephalitis. For example, this year an outbreak of viral encephalitis in northern India resulted in 2300 hospital admissions and over 400 deaths.1 The herpes virus family also accounts for many cases of encephalitic infections, as does influenza virus, with the likelihood of encephalitic infections relating each year to the severity of the pandemic.

Etiology survey on an outbreak of viral encephalitis

To isolate and identify the pathogen that caused an outbreak of viral encephalitis in Henan province in 2010; and to analyze the genetic characteristic of gene viral protein1(VP1) on the viral strains isolated. During the period of the outbreak of viral encephalitis in Lushan county, Pingdingshan city, Henan province, eight hospitalized patients were recruited in the study. All the patients' feces samples were collected. Three patients' cerebrospinal fluids samples and another four patients' serum samples were collected separately. The virus in the samples were isolated and identified by enterovirus (EV) combined serum. The VP1 gene of the positive isolate was amplified by reverse transcriptase PCR method, and its nucleotide sequence was detected and the genetic evolution was analyzed. Fifteen samples were collected in total, including 8 feces samples, 3 cerebrospinal fluids samples and 4 serum samples. The results of Fluorescence Quota PCR detection showed that 11 out of 15 samples were positive; 2 strains of virus were isolated from 2 feces samples and the serotype were all Coxsackie-positive identified by the EV combined serum. The full-length VP1 genetic sequences were all 849 bp, and showed 77.1% - 96.9% similar to the nucleotide and 95.8% - 100% similar to the amino acid of CoxB5. The analysis showed that the genetic evolution tree was just the same with Genotype-D. CoxB5 whose genotype was Genotype-D, was the pathogen that caused the outbreak of viral encephalitis in Lushan county, Pingdingshan city, Henan province.

Escalation of Japanese encephalitis in India: Evidence from 2005 viral encephalitis outbreak and appraisal of niceties

Escalation of Japanese encephalitis in India: Evidence from 2005 viral encephalitis outbreak and appraisal of niceties

Promising Antibody Fights Lethal Viruses

LITTLE MORE THAN A DECADE AGO, Nipah virus was not even a blip on the world’s infectious diseases radar. But all that changed in 1999. Nipah emerged as a newly discovered pathogen in a Malaysian outbreak of viral encephalitis among pigs and pig farmers that claimed 105 human lives. Nipahanditscloserelative,Hendravirus,stillaresomewhatobscureorganisms. But their highly pathogenic nature— Nipah’shumanmortalityratereaches75% and,insmalloutbreaks,hasbeen100%— has put researchers on a fast track to developatherapeuticagentcapableof treating infection with both viruses. In October, researchers working collaboratively in the United States and Australia announced a major step forward in combating these viruses. They demonstrated for the first time that a neutralizing human monoclonal antibody known as m102.4 is capable of protecting against disease in ferrets when given 10 hours after exposure to Nipah virus (Bossart KN et al. PloS Pathog. 2009;5[10]:e1000642). The findings have bolstered hopes that safe, effective postexposure treatment for use in humans infected with Nipah or Hendra virus can be developed. “We’ve been working with this monoclonal for years,” said Christopher Broder, PhD, professor of microbiology at the Uniformed Services University of the Health Sciences in Bethesda, Md, and a study coauthor. “It’s cross-reactive, it neutralizes all known isolates of Nipah and Hendra, and it’s fully human.” The ferret studies were conducted at the Commonwealth Scientific and Industrial Research Organization’s Australian Animal Health Laboratory, a biosecurity facility inGeelong,Victoria,Australia. Of 8 ferrets inoculated with doses of Nipah virus 10 times higher than the minimum needed to cause infection, 6 received m102.4—3 got the antibody 24 hours before inoculation and 3 received it 10 hours afterward.

Enteroviruses in Patients with Acute Encephalitis, Uttar Pradesh, India

An outbreak of viral encephalitis occurred in northern India in 2006. Attempts to identify an etiologic agent in cerebrospinal fluid by using reverse transcription–PCR showed positivity to enterovirus (EV) in 66 (21.6%) of 306 patients. Sequencing and phylogenetic analyses of PCR products from 59 (89.3%) of 66 specimens showed similarity with EV-89 and EV-76 sequences.

Nipah virus encephalitis.

Nipah virus was first discovered in 1999, after a severe outbreak of viral encephalitis among pig farm workers in Malaysia. The disease is thought to spread from Pteropus bats to pigs and then to humans following close contact. The reported mortality rate in this outbreak was 40%. The main necropsy finding in patients with Nipah virus encephalitis was disseminated microinfarction associated with vasculitis and direct neuronal involvement. Relapse of encephalitis was seen in 10% of those who survived the initial illness. Since that initial report, recurrent outbreaks of Nipah virus encephalitis have been seen in Bangladesh and West Bengal, India. These outbreaks occurred between January and May, with Pteropus giganteus as a reservoir of the virus. In Bangladesh, the virus probably spread directly from bats to humans-with human to human spread as another important mode of infection-and the mortality rate was 70%.

Molecular-biological identification of pathogens which caused an outbreak of viral encephalitis in Jinan area

To investigate the etiology of the outbreak of viral encephalitis in Jinan area in 2003. Virus-specific nucleic acid fragments were amplified by random PCR and RT-PCR using specific primers to enterovirus. After sequencing, the gene sequence was handled by the program BLAST for homologous analysis and the software Clustal W 1.82 for multiple sequence alignment to identify the etiology and its genotype. Five strains were isolated from clinical specimens. A gene fragment for one strain was acquired using random PCR, which was highly homologous to enterovirus. Then, the 5' non-translated region and partial VP1 region were amplified and sequenced. The five isolated strains were all identified as Coxsackievirus B5, and what was more, they were most homologous to the strain isolated during the outbreak of aseptic meningitis and encephalitis in Zhejiang province from 2002 to 2004. Coxsackievirus B5 is closely associated with the outbreak of viral encephalitis in Jinan area in 2003. It is an important etiology but other viruses may also played a role which remains to be clarified.

Japanese Encephalitis Outbreak, Yuncheng, China, 2006

To the Editor: Japanese encephalitis (JE) epidemics have occurred only in Asia. More than 50,000 cases of JE with ≈10,000 deaths have been reported since 1998 (1,2). The People’s Republic of China reported 5,104 cases and 214 deaths in 2005. Most of these deaths occurred in infants (3,4). During July and August 2006, an outbreak of viral encephalitis occurred in Yuncheng, Shanxi Province, People’s Republic of China. A total of 66 cases (1.32/100,000 population) were reported, including 19 deaths (case-fatality rate 28.8%). The cases had a widespread distribution over 9 counties and involved 37 towns and 61 administrative villages. The ratio of male-to-female patients was 1:0.89. A distinct clinical feature of this outbreak was the age distribution. More than 86% of the patients were >30 years of age, with only 10% of patients 50 years of age (5). We report serologic and virologic findings for the 2006 outbreak of viral encephalitis. Forty-six clinical specimens collected from 34 patients who had a diagnosis of viral encephalitis, including 33 serum samples and 13 cerebrospinal fluid (CSF) samples, were studied. All serum samples were screened for immunoglobulin M (IgM) to West Nile virus (WNV) by using the WNV IgM-capture ELISA kit (PanBio, Brisbane, Queensland, Australia) and for IgM to dengue virus or Japanese encephalitis virus (JEV) by using the JE-Dengue IgM Combination ELISA kit (PanBio). Results for JEV were confirmed by using the JE Virus IgM-Capture ELISA kit (Shanghai B & C Enterprise Development Co. Ltd, Shanghai, People’s Republic of China). WNV-specific or dengue virus–specific IgM was not detected in any samples. JEV-specific IgM was detected in 27 (80%) patients, which indicated recent JEV infections. The other 7 patients were negative for JEV by ELISA and reverse transcription–PCR (RT-PCR). Increases >4-fold in neutralizing antibodies were detected in acute- and convalescent-phase serum samples from 9 patients (10 serum pairs were collected during the outbreak). Attempts were made to detect virus in CSF of patients and in 2,400 mosquitoes. Mosquitoes (mainly Culex spp.) were collected in cow sheds and hog pens around houses and processed into pools of 100. Total RNA was extracted from CSF or mosquito homogenate by using the QIAamp viral RNA extraction kit (QIAGEN, Valencia, CA, USA) according to the manufacturer’s specifications. RT was performed by using Ready-To-Go-You Prime First Strand Beads (Amersham Pharmacia Biotech, Piscatawy, NJ, USA) and a seminested PCR to amplify 492-bp gene fragments of the premembrane (PrM) sequence of JEV by using the Takara LA Taq PCR kit (Takara Bio Inc., Shiga, Japan). The primers were derived from Ishikawa strain genome sequences (GenBank accession no. {type:entrez-nucleotide,attrs:{text:AB051292,term_id:12082323,term_text:AB051292}}AB051292). Primers PrMF: 5′-CGT TCT TCA AGT TTA CAG CAT TAG C-3′ (251–275), PrMR1: 5′-CGY TTG GAA TGY CTR GTC CG-3′ (724–743), and PrMR2: 5′-CCY RTG TTY CTG CCA AGC ATC CAM CC-3′ (901–925) were used. JEV PrM gene was amplified from CSF of 6 (46%) of 13 patients and 10 of 24 pools of mosquitoes by using the same seminested RT-PCR. To identify JEV genotype(s) involved in this outbreak, PCR products were sequenced. Eleven sequences (GenBank accession nos. {type:entrez-nucleotide-range,attrs:{text:EF434264-EF434274,start_term:EF434264,end_term:EF434274,start_term_id:148925198,end_term_id:148925218}}EF434264-EF434274) were obtained from 6 patients and 5 pools of mosquitoes. The 11 sequences were compared phylogenetically with17 known JEV strains of the 4 recognized genotypes (classified on the basis of a 240-nt region of the prM gene). As shown in the Figure, the 11 sequences were those of JEV. Figure Phylogenetic analysis of Japanese encephalitis virus strains predicted from premembrane gene sequences. Neighbor-joining tree was generated by using MEGA 3.1 software (www.megasoftware.net) and rooted with Murray Valley encephalitis (MVE) virus sequence ... Further analysis showed that these 11 sequences can be grouped into genotypes I and III. Both genotypes were found in patient and mosquito samples, indicating that these genotypes co-circulated during this JE outbreak. JE has been endemic in Yuncheng for many years (6). A vaccine against JE (SA14–14–2) has been used in this area in infants, but not in adults. This might be 1 reason why a higher adult incidence was found in this outbreak. JEV genotype III had been the predominant genotype in previous years, but genotype I has been recently detected at increased frequencies (7–10). Detection of 2 JEV genotypes in 1 epidemic has not been reported. Whether simultaneous circulation of >1 genotype during an outbreak indicates a new type of emergence of JEV or that this has occurred and not been detected is unknown.

Why the West in West Nile Virus Infections?

West Nile virus (WNV) was initially isolated and identified in 1937 in Uganda (Africa). Over the ensuing decades, outbreaks of WNV were infrequent, usually associated with mild febrile illnesses, and most commonly found in west Asia, Africa and the Middle East (1,2). However, WNV was identified in North America in 1999 following an outbreak of viral encephalitis in New York City (USA) that resulted in 62 confirmed human cases with seven deaths (3). Within the next five years, WNV emerged as an important human, avian and equine disease in the United States (2–7). Following this outbreak in New York City, several Canadian provinces implemented enhanced surveillance for human cases of WNV encephalitis, but none were detected. The first WNV-infected bird was detected in Ontario in 2001, and the first confirmed human cases of WNV infection endemic to Canada occurred in Quebec and Ontario in 2002 (8). During the summer of 2003, WNV became firmly established within the Canadian ecology and a total of 1493 human cases of illness (14 deaths) due to WNV infection were reported, with the majority occurring in western Canada (9). The ensuing three years were relatively quiet with only 26 cases reported in 2004, 225 cases in 2005 and 151 cases in 2006. However, 2007 has seen a record 2035 human cases reported in Canada as of September 15, with more than 99% of the cases occurring in the three Prairie provinces (9).

Japanese Encephalitis Outbreak, India, 2005

An outbreak of viral encephalitis occurred in Gorakhpur, India, from July through November 2005. The etiologic agent was confirmed to be Japanese encephalitis virus by analyzing 326 acute-phase clinical specimens for virus-specific antibodies and viral RNA and by virus isolation. Phylogenetic analysis showed that these isolates belonged to genogroup 3.

Nipah Encephalitis Outbreak in Malaysia

Introduction: Between September 1998 and June 1999, there was a severe outbreak of viral encephalitis among the pig farm workers in Malaysia. Methods: This is a review of the published literature related to the outbreak with the focus on human diseases. Results: The encephalitis was caused by a newly discovered paramyxovirus related to Hendra virus, later named Nipah virus. There were 265 patients with acute encephalitis. The disease is thought to spread from pig to man through close contact. The risk of human-to-human spread is thought to be low. The disease affected mainly adult Chinese males, half of whom had affected family members. The disease presented mainly as acute encephalitis with a short incubation period of less than two weeks, with the main symptoms of fever, headache, and giddiness followed by coma. Distinctive clinical signs include segmental myoclonus, areflexia and hypotonia, hypertension, and tachycardia. Initial cerebrospinal fluid was abnormal in 75% of patients. Serology was helpful in confirming the diagnosis. Magnetic resonance imaging showed distinctive changes of multiple, discrete, and small high signal lesions, best seen with fluid-attenuated inversion recovery (FLAIR) sequences. Mortality was high at 40% and death was probably due to severe brainstem involvement. The main necropsy finding in acute encephalitis was that of disseminated microinfarction associated with vasculitis and direct neuronal involvement. Ribavirin was able to reduce the mortality by 36%. Relapse encephalitis was seen in 7.5% of those who recovered from acute encephalitis, and late-onset encephalitis in 3.4% of those with initial non-encephalitic or asymptomatic diseases. The mean interval between initial illness and the onset of the complication was 8.4 months. The relapse and late-onset encephalitis which manifested as focal encephalitis arose from recurrent infection. Conclusion: Nipah virus, a recently discovered paramyxovirus, causes a unique encephalitis with high mortality as well as relapse and late-onset encephalitis. The infection is mainly spread from pigs to man.

Nipah virus—a potential agent of bioterrorism?

Nipah virus, a newly emerging deadly paramyxovirus isolated during a large outbreak of viral encephalitis in Malaysia, has many of the physical attributes to serve as a potential agent of bioterrorism. The outbreak caused widespread panic and fear because of its high mortality and the inability to control the disease initially. There were considerable social disruptions and tremendous economic loss to an important pig-rearing industry. This highly virulent virus, believed to be introduced into pig farms by fruit bats, spread easily among pigs and was transmitted to humans who came into close contact with infected animals. From pigs, the virus was also transmitted to other animals such as dogs, cats, and horses. The Nipah virus has the potential to be considered an agent of bioterrorism.