Epidemiology Of Japanese Encephalitis Virus Research Articles

Sero-molecular epidemiology of Japanese encephalitis virus in swine population of western Uttar Pradesh, India: Unraveling the geographical expansion of the virus.

Swine is a good sentinel for forecast of Japanese encephalitis virus (JEV) outbreaks in humans. The present study was envisaged with objectives to know the sero-conversion period of JEV and to assess the prevalence of JEV in swine population of western Uttar Pradesh state of India. A total of 252 swine serum samples were screened using IgM ELISA over the period of one year to determine the sero-conversion rate and compared seasonally to check the transmission peak of virus. Further, 321 swine blood and serum samples were collected from all seven divisions of western Uttar Pradesh to determine prevalence of JEV using real time RT-PCR and ELISA. Seasonal sero-conversion rate was high during monsoon and post-monsoon (32%) followed by winter (22.91%) and summer (10.71%) seasons. The sero-conversion was observed in all months indicating viral activity throughout the year in the region. The low degree of correlation was found between meteorological variables (day temperature, rainfall) and sero-conversion rate. A total of 52 samples (16.19%) were found positive by real time RT-PCR while sero-positivity of 29.91% was observed using IgG and IgM ELISA(s). The overall prevalence of JEV was 39.25%. The presence of JEV was recorded throughout the year with peak occurrence during monsoon and post-monsoon season indicating that virus has spread its realm to western region of the state. The information generated in the present study will aid in initiating timely vector control measures and human vaccination program to mitigate risk of JEV infection in the region.

The Ecology and Evolution of Japanese Encephalitis Virus.

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus mainly spread by Culex mosquitoes that currently has a geographic distribution across most of Southeast Asia and the Western Pacific. Infection with JEV can cause Japanese encephalitis (JE), a severe disease with a high mortality rate, which also results in ongoing sequalae in many survivors. The natural reservoir of JEV is ardeid wading birds, such as egrets and herons, but pigs commonly play an important role as an amplifying host during outbreaks in human populations. Other domestic animals and wildlife have been detected as hosts for JEV, but their role in the ecology and epidemiology of JEV is uncertain. Safe and effective JEV vaccines are available, but unfortunately, their use remains low in most endemic countries where they are most needed. Increased surveillance and diagnosis of JE is required as climate change and social disruption are likely to facilitate further geographical expansion of Culex vectors and JE risk areas.

Spatial epidemiology of Japanese encephalitis virus and other infections of the central nervous system infections in Lao PDR (2003-2011): A retrospective analysis.

BackgroundCentral nervous system (CNS) infections are important contributors to morbidity and mortality and the causative agents for ~50% patients are never identified. The causative agents of some CNS infections have distinct spatial and temporal patterns.Methodology/Principal findingsHere we present the results of a spatial epidemiological and ecological analysis of CNS infections in Lao PDR (2003–2011). The data came from hospitalizations for suspected CNS infection at Mahosot Hospital in Vientiane. Out of 1,065 patients, 450 were assigned a confirmed diagnosis. While many communities in Lao PDR are in rural and remote locations, most patients in these data came from villages along major roads. Japanese encephalitis virus ((JEV); n = 94) and Cryptococcus spp. (n = 70) were the most common infections. JEV infections peaked in the rainy season and JEV patients came from villages with higher surface flooding during the same month as admission. JEV infections were spatially dispersed throughout rural areas and were most common in children. Cryptococcus spp. infections clustered near Vientiane (an urban area) and among adults.Conclusions/SignificanceThe spatial and temporal patterns identified in this analysis are related to complex environmental, social, and geographic factors. For example, JEV infected patients came from locations with environmental conditions (surface water) that are suitable to support larger mosquito vector populations. Most patients in these data came from villages that are near major roads; likely the result of geographic and financial access to healthcare and also indicating that CNS diseases are underestimated in the region (especially from more remote areas). As Lao PDR is undergoing major developmental and environmental changes, the space-time distributions of the causative agents of CNS infection will also likely change. There is a major need for increased diagnostic abilities; increased access to healthcare, especially for rural populations; and for increased surveillance throughout the nation.

Molecular epidemiology of Japanese encephalitis virus in pig population of Odisha, Assam and Manipur states of India

Japanese encephalitis virus (JEV) comes under the family Flaviviridae and genus flavivirus. Pigs act as reservoir and amplifying intermediate host for JEV. The current investigation was conducted to understand the prevalence of JEV infection in pigs in three different geographical sites in India (Odisha, Assam and Manipur). Total 857 serum samples were tested by ELISA and RT-PCR, while only RT-PCR was performed in case of 275 tonsils tissues for detection of JEV. It was observed that JEV prevalence was highest in Manipur (positive 39, 25.5% in serum and 10% in tonsil) but lower in Assam (positive 15, 3.8% in serum and 0% in tonsils) and Odisha (positive 7, 1.5% in serum and 3.7% in tonsils). Genotype III (GIII) of JEV was the dominant genotype. Further, analysis of E gene revealed sporadic mutations of S83G, H76P, E78Q, C55S, and S64W along with two consistent mutations V46S and V51I in GIII. Whereas, a single mutation S118N was observed in the GI strain. In conclusion, the high JE virus infection rate of pig in the current locations suggests the need for continuous surveillance of this virus in pigs which will ultimately help to adopt an effective control strategy to prevent the spread of JE infection to human.

Review of Emerging Japanese Encephalitis Virus: New Aspects and Concepts about Entry into the Brain and Inter-Cellular Spreading.

Japanese encephalitis virus (JEV) is an emerging flavivirus of the Asia-Pacific region. More than two billion people live in endemic or epidemic areas and are at risk of infection. Recently, the first autochthonous human case was recorded in Africa, and infected birds have been found in Europe. JEV may spread even further to other continents. The first section of this review covers established and new information about the epidemiology of JEV. The subsequent sections focus on the impact of JEV on humans, including the natural course and immunity. Furthermore, new concepts are discussed about JEV’s entry into the brain. Finally, interactions of JEV and host cells are covered, as well as how JEV may spread in the body through latently infected immune cells and cell-to-cell transmission of virions or via other infectious material, including JEV genomic RNA.

Molecular Epidemiology of Japanese Encephalitis Virus in India

The global reach of Japanese Encephalitis Virus (JEV) with an estimated 3 billion people at risk makes this virus a severe threat to the public health. Since its first detection in 1955, this virus has managed to spread throughout the country. Understanding the molecular epidemiology of Japanese Encephalitis Virus in India will help in designing vaccine strategies for preventive initiatives necessary to control the Acute Encephalitis Syndrome (AES) the main implication of the infection caused by the Japanese Encephalitis Virus (JEV).

Differential Infectivities among Different Japanese Encephalitis Virus Genotypes in Culex quinquefasciatus Mosquitoes.

During the last 20 years, the epidemiology of Japanese encephalitis virus (JEV) has changed significantly in its endemic regions due to the gradual displacement of the previously dominant genotype III (GIII) with clade b of GI (GI-b). Whilst there is only limited genetic difference distinguishing the two GI clades (GI-a and GI-b), GI-b has shown a significantly wider and more rapid dispersal pattern in several regions in Asia than the GI-a clade, which remains restricted in its geographic distribution since its emergence. Although previously published molecular epidemiological evidence has shown distinct phylodynamic patterns, characterization of the two GI clades has only been limited to in vitro studies. In this study, Culex quinquefasciatus, a known competent JEV mosquito vector species, was orally challenged with three JEV strains each representing GI-a, GI-b, and GIII, respectively. Infection and dissemination were determined based on the detection of infectious viruses in homogenized mosquitoes. Detection of JEV RNA in mosquito saliva at 14 days post infection indicated that Cx. quinquefasciatus can be a competent vector species for both GI and GIII strains. Significantly higher infection rates in mosquitoes exposed to the GI-b and GIII strains than the GI-a strain suggest infectivity in arthropod vectors may lead to the selective advantage of previously and currently dominant genotypes. It could thus play a role in enzootic transmission cycles for the maintenance of JEV if this virus were ever to be introduced into North America.

Molecular and serological epidemiology of Japanese encephalitis virus (JEV) in a remote island of western Japan: an implication of JEV migration over the East China Sea.

BackgroundJapanese encephalitis (JE) is a mosquito-borne infectious disease caused by Japanese encephalitis virus (JEV). About 1–10 cases with severe central nervous system symptoms have been constantly reported every year in Japan. To clarify the mechanism of maintenance of JEV, the present study surveyed pigs for serological evidence of JEV infection and isolated JEV strains from pigs and mosquitoes in Isahaya City (Isahaya) and Goto City (Goto) in the islets of Goto in Nagasaki Prefecture from 2008 to 2014.ResultsThe serological survey of pigs showed the increase of IgM sero-positivity against JEV in July or August, and it was maintained until October or November in both Isahaya and Goto every year. There were 47 JEV strains isolated in Nagasaki from 2001 to 2014 including the isolates in this study, and they belonged to genotype 1. Thirty four of the isolated strains were from pigs in Isahaya and were classified under six subclusters (1-A-1, 1-A-2, 1-A-3, 1-A-4, 1-A-5, and 1-A-9). Thirteen strains were isolated from pigs and mosquitoes in Goto and were classified into three subclusters (1-A-5 (2008); 1-A-1 (2009); and 1-A-2). In the subcluster 1-A-2, three different monophyletic subgroups, 1-A-2-2 (2010), 1-A-2-3 (2011), and 1-A-2-1 (2013, 2014), appeared in Goto.ConclusionsThese data strongly suggested that JEV appearance in Goto seems to depend on the frequent introduction of JEV from outside of the island and this pattern is different from what has been observed in subtropical islands in the East China Sea such as Okinawa and Taiwan, where the same populations of JEV (1-A-7 (1998–2008) in Okinawa; genotype 3 (until 2012) in Taiwan) have been maintained for a long period.

Molecular Epidemiology of Japanese Encephalitis Virus in Mosquitoes during 2013- 2014

Japanese encephalitis (JE) is a mosquito-borne zoonotic disease caused by the Japanese encephalitis virus (JEV). Japanese encephalitis is widespread in Asia and endemic in Taiwan. Virological surveillance in mosquitoes showed that the genotype III (GIII) strains of JEV were the predominant epidemic strains circulating in Asia before 1990; however, the genotype I (GI) strains have been introduced into China, Japan, Vietnam, South Korea, and Thailand, and cocirculated with or replaced the GIII strains in Asia. Previous studies showed that in Taiwan, all of the JEV strains obtained during 2005- 2007 belonged to GIII of JEV, but the predominant genotype has shifted from GIII to GI during 2008-2012. This study continued to report the genotype distribution, genetic variation, and mosquito species potentially involved in the transmission of JEV during 2013-2014. Overall, 37,637 mosquitoes were collected; 96 pools were tested JEV positive by RT-PCR, including Culex tritaeniorhynchus (94 pools) and Cx. annulus (2 pools). Phylogenetic analysis of envelope gene sequences of JEV isolated from mosquitoes demostrated that GI was the predominant genotype of JEV between 2013 and 2014, whilst only a few GIII strains of JEV were found in Eastern Taiwan. We will continue the monitoring of endemic and newly introduced JEV in Taiwan.

Molecular epidemiology of Japanese encephalitis virus in mosquitoes in Taiwan during 2005-2012.

Japanese encephalitis (JE) is a mosquito-borne zoonotic disease caused by the Japanese encephalitis virus (JEV). Pigs and water birds are the main amplifying and maintenance hosts of the virus. In this study, we conducted a JEV survey in mosquitoes captured in pig farms and water bird wetland habitats in Taiwan during 2005 to 2012. A total of 102,633 mosquitoes were collected. Culex tritaeniorhynchus was the most common mosquito species found in the pig farms and wetlands. Among the 26 mosquito species collected, 11 tested positive for JEV by RT-PCR, including Cx. tritaeniorhynchus, Cx. annulus, Anopheles sinensis, Armigeres subalbatus, and Cx. fuscocephala. Among those testing positive, Cx. tritaeniorhynchus was the predominant vector species for the transmission of JEV genotypes I and III in Taiwan. The JEV infection rate was significantly higher in the mosquitoes from the pig farms than those from the wetlands. A phylogenetic analysis of the JEV envelope gene sequences isolated from the captured mosquitoes demonstrated that the predominant JEV genotype has shifted from genotype III to genotype I (GI), providing evidence for transmission cycle maintenance and multiple introductions of the GI strains in Taiwan during 2008 to 2012. This study demonstrates the intense JEV transmission activity in Taiwan, highlights the importance of JE vaccination for controlling the epidemic, and provides valuable information for the assessment of the vaccine's efficacy.

Molecular epidemiology of Japanese encephalitis virus in mosquitoes during an outbreak in China, 2013.

Japanese encephalitis virus (JEV) can cause serious encephalitis and Culex mosquitoes are the primary vector. In 2013, a JE outbreak occurred in Shandong Province, China with 407 confirmed cases, including 11 deaths. An investigation on JEV in mosquitoes during the outbreak was conducted. A total of 14,719 mosquitoes were collected at 3 sites. For the 12,695 Culex tritaeniorhynchus mosquitoes, 88/201 pooled samples were positive by RT-PCR for the presence of the pre-membrane or envelope protein coding genes. The maximum likelihood estimates of JEV positive individuals per 1,000 vectors were 12.0, 7.2, and 6.0 in the 3 sites respectively with an overall estimate of 9.1. Phylogenetic analysis on these pre-membrane (n = 72) and envelope (n = 26) sequences with those of reference strains revealed they belonged to genotype I. This study describes the molecular epidemiology of JEV and suggests the high infection rate in mosquitoes is an important factor for the outbreak.

Molecular epidemiology of Japanese encephalitis virus circulating in South Korea, 1983-2005

We sequenced the envelope (E) gene of 17 strains of the Japanese encephalitis virus (JEV) isolated in South Korea in 1983-2005 and compared the sequences with those from previously reported strains. Our results show the remarkable genetic stability of the E gene sequence in Korean JEV strains. Five pairs of E gene sequences from 10 Korean strains were identical, despite geographical differences and a maximum five-year time span. Sequence comparisons with other Asian strains revealed that the Korean strains are closely related to those from China, Japan, and Vietnam. Genotype 3 strains were predominant in Korea before 1993, when genotype 1 strain K93A07 was first isolated. The two genotypes were detected simultaneously in 1994 but since then, only genotype 1 has been isolated in South Korea. Thus, the genotype change occurred according to the year of isolation rather than the geographical origin.

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Study of Japanese encephalitis virus in Chiangmia Valley, Thailand. V. Animal infections.

Johnsen, D. O., R. Edelman, R. A. Grossman, D. Muangman, J. Pomsdhit and D. J. Gould (SEATO Medical Research Laboratory. Bangkok, Thailand). Study of Japanese encephalitis virus in Chiangmai Valley, Thailand. V. Animal infections. Am J Epidemiol 100: 57–68, 1974.—In this study, we examined the temporal nature of animal infections and sought to determine which animal species play an important role in the transmission of Japanese encephalitis virus (JEV) in the Chiangmai Valley. Sera were collected from a sample of domestic mammals and fowl residing in four study villages before the start of the 1970 Japanese encephalitis epidemic and three times during the epidemic year. Antibody-free pigs, placed in each village as sentinels, were bled every month from April 1970 until June 1971. Tree sparrows and bats were also trapped and bled in the villages. Attempts to isolate JEV from domestic and wild animal specimens were unsuccessful. Census data revealed that the turnover rate in one year for pigs was much higher than for other domestic mammals. JEV transmission to sentinel pigs was detected in each of the 14 consecutive months, except for two months of the cool-dry season; transmission rapidly increased with the start of the seasonal rains. The prevalence of JEV antibody (HAI) was high in dogs, bovines and indigenous pigs, but, except for a small group of horses, the geometric mean titer was much higher in pigs than in other mammals. Antibody to Tembusu virus, rather than to JEV, was prevalent in high titer in domestic fowl. Paired serum samples collected from indigenous pigs, bovines and dogs confirmed that primary JEV infections occurred during the human epidemic in these species; animals with prior JEV antibodies were not infected. Only a small percentage of tree sparrow and bat sera neutralized JEV. One pig infected with JEV under laboratory conditions developed a viremia of high titer and long duration. Buffalo and cattle, on the other hand, failed to develop detectable viremia and had a poor HAI antibody response following exposure to JEV-infected Culex tritaeniorhynchus and repeated inoculations of JEV. One of three dogs developed low level viremia after being bitten by JEV-infected mosquitoes. The serologic responses of these experimentally infected animals mimic the serologic patterns observed in domestic animals in the field. All of these results together suggest that pigs are important in the epidemiology of JEV in the Chiangmai Valley; the role of other domestic mammals is less certain. A pig-mosquito-man transmission sequence may be sufficient to account for human infections that occur throughout the year.

Study of Japanese encephalitis virus in Chiangmai Valley, Thailand. I. Introduction and study design.

Following the large epidemic of Japanese encephalitis which occurred in northern Thailand in 1969, a one year epidemiologic study of Japanese encephalitis virus (JEV) transmission was instituted in the centrally located Chiangmai Valley. The Valley has a subtropical climate and is situated geographically between the two major zones of JEV transmission: epidemic transmission in countries with temperate climates and endemic transmission in countries with tropical climates. The presence of concurrent human dengue virus transmission in the Chiangmai Valley, a unique situation in an epidemic JE area, provided further impetus to study this region. In order to investigate human and nonhuman variables of JEV transmission and, at the same time, determine what effect the presence or absence of historical dengue transmission has on JEV transmission, four scattered rural villages in the Valley and one urban school were selected for study. Samples of humans, domestic and wild animals, and mosquitoes were studied, with appropriate methods, from November 1969 to November 1970. Encephalitis case ascertainment was established at the major Valley hospitals. Data from the randomly selected village human samples suggest that they are representative of the Valley's population. It is therefore believed that inferences may be drawn about the epidemiology of JEV which are valid for the entire Chiangmai Valley.

The Epidemiology of Japanese Encephalitis Virus on Taiwan in 1961 *

Summary A study of the most severe epidemic of Japanese encephalitis in recent years occurring on the island of Taiwan has been presented. The entire north and central portions of the Island, plus an administrative district at the southern end, were areas of high incidence of the disease. The over-all attack rate in 1961 was 7.15 per 100,000 population as compared with 2.91 for 1960 and 6.0 for the entire 5-year period of 1955–1959. The overall case fatality rate, however, was lower than during previous years. More than one-half of the total cases were reported between 11 July and 10 August 1961. Serological confirmation of the disease was first obtained in June and, during the course of the epidemic, was obtained from almost all administrative areas. The last serologically confirmed case occurred in early October, although sporadic cases were reported through early November. A higher percentage of clinically diagnosed cases of encephalitis were confirmed as JE by a four-fold rise in the hemagglutination-inhibition (HI) test (43%) than by the complement-fixation (CF) test (18%) in this study due to the earlier time of collection of convalescent sera. Single serum specimens with HI titers of 1:160 or greater or with CF titers of 1:16 or greater were considered presumptively positive for JE based on evidence presented in the text above.