First time detection of Japanese encephalitis virus antigen in dry and unpreserved mosquito Culex tritaeniorhynchus Giles, 1901, from Karnal district of Haryana state of India

Japanese encephalitis virus (JEV) antigen has been detected by antigen capture enzyme linked immunosorbentassay (ELISA) in dry specimens of the mosquito Culex tritaeniorhynchus Giles, 1901, collected from Karnal district of Haryana state in northern India. These mosquitoes were stored in dry condition for 20 months, at room temperature, before processing. The procedure of detecting JEV infection in long time stored, dry vector mosquitoes, has important application in the surveillance of Japanese encephalitis.

Epidemiological situation of Japanese encephalitis in Nepal

A human Japanese encephalitis (JE) case is considered to have elevated temperature (over 380 C) along with altered consciousness or unconsciousness and is generally confirmed serologically by finding of specific anti-JE IgM in the cerebro spinal fluid. No specific treatment for JE is available. Only supportive treatment like meticulous nursing care, introduction of Ryle's tube if the patient is unconscious, dextrose solution if dehydration is present, manitol injection in case of raised cranial temperature and diazepam in case of convulsion. Intra venous fluids, indwelling catheter in conscious patient and corticosteroids unless indicated should be avoided. Pigs, wading birds and ducks have been incriminated as important vertebrate amplifying hosts for JE virus due to viremia in them. Man along with bovines, ovines and caprines is involved in transmission cycle as accidental hosts and plays no role in perpetuating the virus due to the lack of viremia in them. The species Cx tritaeniorhyncus is suspected to be the principal vector of JE in Nepal as the species is abundantly found in the rice-field ecosystem of the endemic areas during the transmission season and JE virus isolates have been obtained from a pool of Cx tritaeniorhyncus females. Mosquito vector become infective 14 days after acquiring the JR virus from the viremic host. The disease was first recorded in Nepal in 1978 as an epidemic in Rupandehi district of the Western Development Region (WDR) and Morang of the Eastern Region (EDR). At present the disease is endemic in 24 districts. Although JE as found endemic mainly in tropical climate areas, existence and proliferation of encephalitis causing viruses in temperate and cold climates of hills and valleys are possible. Total of 26,667 cases and 5,381 deaths have been reported with average case fatality rate of 20.2% in an aggregate since 1978. More than 50% of morbidity and 60% mortality occur in the age group below 15 years. Upsurge of cases take place after the rainy season (monsoon). Cases start to appear in the month of April - May and reach its peak during late August to early September and start to decline from October. There are four designated referral laboratories, namely National Public Health Laboratory (Teku), Vector Borne Diseases Research and Training Center (Hetauda), B.P. Koirala Institute of Medical Sciences (Dharan) and JE Laboratory (Nepalgunj), for confirmatory diagnosis of JE. For prevention of JE infection; chemical and biological control of vectors including environmental management at breeding sites are necessary. Segregate pigs from humans habitation. Wear long sleeved clothes and trousers and use repellent and bed net to avoid exposure to mosquitos. For the prevention of the disease in humans, safe and efficacious vaccines are available. Therefore immunize population at risk against JE. Immunize pigs at the surroundings against JE. 225,000 doses of live attenuated SA-14-14.2 JE vaccine were received in donation from Boran Pharmaceuticals, South Korea for the first time in Nepal. Altogether 224,000 children aged between 1 to 15 years were vaccinated in Banke, Bardiya and Kailali districts during 1999. From China also, 2,000,000 doses of inactivated vaccine were received in 2000 and a total of 481,421 children aged between 6m to 10 yrs were protected from JE during 2001/2002. Ministry of Agriculture, Department of Livestock Services has vaccinated around 200,000 pigs against JE in terai zone during February 2001.

New mosquito records of an area known for Japanese encephalitis hyperendemicity, Gorakhpur District, Uttar Pradesh, India

During long-term ecological studies carried out between 1990 and 2000, a total of 67 mosquito species were collected from Gorakhpur District, Uttar Pradesh, India, of which 43 were documented for the 1st time. The genus Aedes was represented by 15 species, Anopheles by 15, Culex by 24, Mansonia by 3, and Mimomyia, Ochlerotatus, and Verrallina by 2 each. The genera Aedeomyia, Armigeres, Coquillettidia, and Uranotaenia were represented by single species. The impact of ecological changes on mosquito fauna in Gorakhpur District is discussed. The role of culicine mosquitoes in disease transmission in the area is highlighted.

Emerging flaviviruses: the spread and resurgence of Japanese encephalitis, West Nile and dengue viruses

Mosquito-borne flaviviruses provide some of the most important examples of emerging and resurging diseases of global significance. Here, we describe three of them: the resurgence of dengue in tropical and subtropical areas of the world, and the spread and establishment of Japanese encephalitis and West Nile viruses in new habitats and environments. These three examples also illustrate the complexity of the various factors that contribute to their emergence, resurgence and spread. Whereas some of these factors are natural, such as bird migration, most are due to human activities, such as changes in land use, water impoundments and transportation, which result in changed epidemiological patterns. The three examples also show the ease with which mosquito-borne viruses can spread to and colonize new areas, and the need for continued international surveillance and improved public health infrastructure to meet future emerging disease threats.

Short report: observations on the multiple feeding behavior of Culex tritaeniorhynchus (Diptera: culicidae), the vector of Japanese encephalitis in Kerala in southern India

A study was undertaken in villages endemic for Japanese encephalitis (JE) in Kerala in southern India during the period 1998-2001 to determine the host-feeding pattern of Culex tritaeniorhynchus, the major vector of JE in southeast Asia. A total of 3,067 blood-engorged Cx. tritaeniorhynchus were tested and 2,553 (82.2%) of the samples could be identified. Culex tritaeniorhynchus had fed mainly (56.6%) on cattle. Pig feeding accounted 6.3% of the total samples. Some samples (n = 980, 38.3%) were of serologic mixed origin. Of 980 mixed blood-fed mosquitoes, 975 (99.5%) had imbibed blood from two distinct hosts and 5 (0.5%) imbibed blood from three distinct hosts. Mixed blood meals were mostly (96.7%) from cattle and goats. The epidemiologic implications of multiple feeding of Cx. tritaeniorhynchus on dampening (dead-end) hosts such as cattle and goats in the transmission of JE virus is discussed.

Illustrated keys to the mosquitoes of Thailand. II. Genera Culex and Lutzia

Illustrated keys for the identification of the fourth-instar larvae and adult females of the mosquito genera Culex and Lutzia is presented, along with information on the geographic distribution of each species, and bionomics. Eighty-two species belonging to subgenera Culex, Culiciomyia, Eumelanomyia, Lophoceraomyia, and Oculeomyia of genus Culex, and three species belonging to subgenus Metalutzia of genus Lutzia are recognized in Thailand. Subgenus Oculeomyia includes a probable new species near Cx. infula and Lt. vorax is recognized as a new country record.

Role of some factors on the breeding of JE vector Culex vishnui group

Vector of JE, Culex vishnui group, prefer to breed in rice field. During the present study, roles of some factors like irrigation, manuring, pesticide application, rainfall, temperature and pH of the breeding water, depth of breeding water and height of paddy plants on breeding of Culex vishnui group larvae have been studied. It is evident from the study that besides striking role of the factors like manuring and pesticide application, other factors have also some role on the breeding of JE vectors at their breeding sites.

Seroepidemiology of neutralizing antibodies to Japanese encephalitis virus in Singapore: continued transmission despite abolishment of pig farming?

Japanese encephalitis virus (JEV) transmission in Singapore appeared to have ceased after pig farming in Singapore was phased out from the early 1980s. However, the recent detection of neutralizing antibodies to JEV in a population of wild boars in an offshore island, as well as the notification of two human cases of JE in Singapore in 2001, prompted us to reconsider the presence and hence the public health threat of JEV in Singapore. We report here a serological study of animals, birds and humans for neutralizing antibodies to JEV. The results indicate that JEV may still be actively transmitted in the peripheral part of the Singapore island and that regular serological surveys of farm animals and birds, such as chickens, may be useful to further elucidate the activity of JEV in Singapore.

Transmission cycles, host range, evolution and emergence of arboviral disease

Many recent viral pandemics have been attributed to the ability of some RNA viruses, for example HIV, dengue virus and possibly the severe acute respiratory syndrome (SARS) coronavirus, to change their host range to include humans. The authors discuss the mechanisms of host-range alteration used by a selection of viruses, including Venezuelan equine and Japanese encephalitis viruses (VEEV and JEV, respectively), dengue virus and West Nile virus (WNV).

Venezuelan equine encephalitis (VEE) was first recognized as a disease of horses, donkeys and mules in northern South America during the mid 1930s, but there has been renewed interest in this virus because of its potential as a biological weapon. Molecular analysis of epidemic strains — which exploit horses for amplification — and comparison with strains that do not cause epidemic disease, have shown that a few amino-acid mutations can affect host-range alteration. Changes on the surface of the VEE virion seem to be important for these host range changes.

JEV causes epidemics of encephalitis in India, Korea, China, South-East Asia and Indonesia. The disease affects children, and is associated with a mortality rate of greater than 20%. However, unlike VEEV, there is no evidence that JEV undergoes mutation and selection to replicate in different hosts. Pigs amplify transmission in peridomestic settings, and migratory birds have a role in dispersion of JEV. Although different genotypes have been isolated, their relevance to pathology and host range is unclear.

WNV is now endemic in the United States after first emerging in New York in 1999. WNV has a very broad host range. Forty-nine species of mosquitoes and ticks, and 225 species of birds are susceptible to infection. Other hosts include horses, cattle, llamas, alligators, cats, dogs, wolves and sheep. Transmission of WNV among these species has not been reported. Although humans are probably dead-end hosts, infection with WNV can cause severe disease.

Dengue viruses are very important human arboviral pathogens and use humans as reservoir hosts. Aedes aegypti and Aedes albopictus mosquitoes are the most common vectors in urban settings. It is thought that the human epidemic form of dengue virus evolved in the last 2000 years, and genetic analysis indicates that mutations have resulted in adaptation to the urban mosquito host. However, links between mutations and human pathogenicity have not been established.

Finally, the authors discuss how host-range changes can be studied experimentally. Cell-culture model systems can be used to find mutations that correlate with virus fitness and adaptation in different host strains. Viruses that replicate in useful laboratory animal models can also be studied in whole animal hosts.

Many pandemics have been attributed to the ability of some RNA viruses to change their host range to include humans. Here, we review the mechanisms of disease emergence that are related to the host-range specificity of selected mosquito-borne alphaviruses and flaviviruses. We discuss viruses of medical importance, including Venezuelan equine and Japanese encephalitis viruses, dengue viruses and West Nile viruses.

Flavivirus isolations from mosquitoes collected from Saibai Island in the Torres Strait, Australia, during an incursion of Japanese encephalitis virus

Adult mosquitoes (Diptera: Culicidae) were collected in January and February 2000 from Saibai Island in the Torres Strait of northern Australia, and processed for arbovirus isolation during a period of Japanese encephalitis (JE) virus activity on nearby Badu Island. A total of 84 210 mosquitoes were processed for virus isolation, yielding six flavivirus isolates. Viruses obtained were single isolates of JE and Kokobera (KOK) and four of Kunjin (KUN). All virus isolates were from members of the Culex sitiens Weidemann subgroup, which comprised 53.1% of mosquitoes processed. Nucleotide sequencing and phylogenetic analysis of the pre-membrane region of the genome of JE isolate TS5313 indicated that it was closely related to other isolates from a sentinel pig and a pool of Cx. gelidus Theobald from Badu Island during the same period. Also molecular analyses of part of the envelope gene of KUN virus isolates showed that they were closely related to other KUN virus strains from Cape York Peninsula. The results indicate that flaviviruses are dynamic in the area, and suggest patterns of movement south from New Guinea and north from the Australian mainland.

First report on high-degree endophilism in Culex tritaeniorhynchus (Diptera: Culicidae) in an area endemic for Japanese encephalitis

An unusually high occurrence of Culex tritaeniorhynchus Giles resting indoors during daytime was observed in a Japanese encephalitis (JE) endemic area, Bellary district, Karnataka, India. Cx. tritaeniorhynchus, the primary vector of JE in this area, was the dominant species collected, and its abundance showed two peaks corresponding to rice crops in the district. More specimens (n = 20,966) were found resting in indoor habitats than in outdoor vegetation (n = 383), despite the availability of outdoor resting sites. This resting behavior is opposite to the Cx. tritaeniorhynchus behavior reported in the majority of JE-affected areas, where this species was captured in small numbers from indoor resting sites. Increased endophilic resting behavior indicates that indoor residual insecticides may provide an effective control method in this area.

Epidemiological processes involved in the emergence of vector-borne diseases : West Nile fever, Rift Valley fever, Japanese encephalitis and Crimean-Congo haemorrhagic fever

Over the past few decades, the geographical distribution of arthropod-borne zoonoses has dramatically expanded. The influence of human-induced or ecological changes on the risk of disease outbreaks is undeniable. However, few hypotheses have been proposed which address the re-emergence of these diseases, the spread of these viruses to previously uninfected areas and their establishment therein. Host and vector movements play an important role in the dissemination of pathogens, and the ability of these diseases to colonise previously uninfected areas may be explained by the diversity of hosts and vectors, the presence of favourable ecological conditions, and the successful adaptations of vectors or pathogens to new ecosystems. The objective of this paper is to describe the epidemiological processes of the vector-borne diseases Rift Valley fever, West Nile fever, Japanese encephalitis and Crimean-Congo haemorrhagic fever.

Japanese encephalitis in India: an overview

Japanese encephalitis (JE)-epidemics have been reported in many parts of the country. The incidence has been reported to be high among pediatric group with high mortality. The incidence of JE in recent times is showing an increasing trend. It appears that JE may become one of the major public health problems in India, considering the quantum of the vulnerable pediatric population, the proportion of JEV infections among the encephalitic children and wide scattering of JE-prone areas. JE burden can be estimated satisfactorily to some extend by strengthening diagnostic facilities for JE confirmation in hospitals and by maintenance of contact with the nearby referral hospitals to collect the particulars on JE cases. Vaccination proves to be the best to protect the individual against any disease. In the case of JE, it is essential to immunize the pigs (amplifying host) also to interrupt the transmission of the disease.

Japanese encephalitis in Kerala, south India: can Mansonia (Diptera: Culicidae) play a supplemental role in transmission?

A 2-yr entomological study was carried out in Kerala, south India, to identify the mosquito vectors of Japanese encephalitis (JE) virus and to determine their seasonal abundance and infection. In total, 150,454 mosquitoes belonging to five genera and 18 species were collected from vegetation surrounding cattle sheds and pigsties in villages at dusk. Culex tritaeniorhynchus Giles (66.7%) was the most abundant species, with increases in numbers associated with rice cultivation. JE virus isolations were made from Cx. tritaeniorhynchus and Mansonia indiana Edwards. Based on high abundance and frequent JE virus infection, Cx. tritaeniorhynchus seems to be the most important vector, whereas Ma. indiana is probably a secondary vector.

Neurovirulence and host factors in flavivirus encephalitis--evidence from clinical epidemiology

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.

An amino acid substitution attributable to insecticide-insensitivity of acetylcholinesterase in a Japanese encephalitis vector mosquito, Culex tritaeniorhynchus

A cDNA sequence encoding a Drosophila Ace-paralogous acetylcholinesterase (AChE) precursor of 701 amino acid residues was identified as the second AChE gene (Ace2) transcript from Culex tritaeniorhynchus. The Ace2 gene is tightly linked to organophosphorus insecticide (OP)-insensitivity of AChE on chromosome 2. The cDNA sequences were compared between an insecticide-susceptible strain and the resistant strain, TYM, that exhibits a 870-fold decrease in fenitroxon-sensitivity of AChE. Two amino acid substitutions were present in TYM mosquitoes. One is F455W whose homologous position in Torped AChE (Phe331) is located in the vicinity of the catalytic His in the acyl pocket of the active site gorge. The other substitution is located to a C-terminal Ile697 position that apparently seems to be excluded from the mature protein and is irrelevant to catalytic activity. The F455W replacement in the Ace2 gene is solely responsible for the insecticide-insensitivity of AChE in TYM mosquitoes.

Climate variability and transmission of Japanese encephalitis in eastern China

A time-series analysis was conducted to study the impact of climate variability on the transmission of Japanese encephalitis in eastern China. Correlation and regression analyses were used to examine the relationship between monthly climatic variables and monthly incidence of Japanese encephalitis in Jieshou County, China over the period 1980-96. Spearman's correlation analysis showed that maximum and minimum temperatures and rainfall were all associated with the transmission of Japanese encephalitis in the county. Regression analysis suggested that monthly mean minimum temperature and monthly precipitation had a significant relationship with the transmission of Japanese encephalitis, with a 1-month lag effect. The results indicated that these climatic variables might be treated as possible predictors for regions with similar geographic, climatic, and socio-economic conditions to Jieshou County.

Mosquito host-feeding patterns and implications for Japanese encephalitis virus transmission in northern Australia and Papua New Guinea

Japanese encephalitis (JE) virus spread to northern Australia during the 1990s, transmitted by Culex annulirostris Skuse and other mosquitoes (Diptera: Culicidae). To determine the relative importance of various hosts for potential vectors of JE virus, we investigated the host-feeding patterns of mosquitoes in northern Australia and Western Province of Papua New Guinea, with particular attention to pigs, Sus scrofa L. - the main amplifying host of JE virus in South-east Asia. Mosquitoes were collected by CDC light traps baited with dry ice and 1-octen-3-ol, run 16.00-08.00 hours, mostly set away from human habitations, if possible in places frequented by feral pigs. Bloodmeals of 2569 mosquitoes, representing 15 species, were identified by gel diffusion assay. All species had fed mostly on mammals: only <10% of bloodmeals were from birds. The predominant species was Cx. annulirostris (88%), with relatively few (4.4%) bloodmeals obtained from humans. From all 12 locations sampled, the mean proportion of Cx. annulirostris fed on pigs (9.1%) was considerably lower than fed on other animals (90.9%). Highest rates of pig-fed mosquitoes (>30%) were trapped where domestic pigs were kept close to human habitation. From seven of eight locations on the Australian mainland, the majority of Cx. annulirostris had obtained their bloodmeals from marsupials, probably the Agile wallaby Macropus agilis (Gould). Overall proportions of mosquito bloodmeals identified as marsupial were 60% from the Gulf Plains region of Australia, 78% from the Cape York Peninsula and 64% from the Daru area of Papua New Guinea. Thus, despite the abundance of feral pigs in northern Australia, our findings suggest that marsupials divert host-seeking Cx. annulirostris away from pigs. As marsupials are poor JE virus hosts, the prevalence of marsupials may impede the establishment of JE virus in Australia.

Variation in morphological characters of Culex tritaeniorhynchus (Diptera: Culicidae), a Japanese encephalitis vector at Mysore, India

Studies on Culex tritaeniorhynchus Giles, were undertaken to find deviation if any, on the mean of siphonal index, comb scales, pecten teeth, denticles on apical pecten tooth, anal gills index and length of basal hair tufts on siphon in the fourth instar larvae from ground pools of Mysore city and paddy fields outside Mysore. A total of 344 larvae including 172 samples from Mysore and 172 samples from a 26 km radius outside Mysore were collected. Analysis of variance demonstrated significant differences between the two populations on 7 parameters based on morphological characteristics such as comb scales, length of siphon, width of siphon at the middle, length of anal gills, siphonal index, anal gills index and the length of basal hair tufts. So Cx. tritaeniorhynchus from different breeding places in and around Mysore city in south India can be different varieties. One variety comparatively has shorter siphon index ratio, less comb scales, less anal gills index ratio and longer basal hair tufts on siphon than the other one. Mating behavior of these varieties show that, variety from the city pools was moderate eurygamous and the one from mainly paddy fields, moderate stenogamous.

Isolation of Japanese encephalitis and Getah viruses from mosquitoes (Diptera: Culicidae) collected near Camp Greaves, Gyonggi Province, Republic of Korea, 2000

As part of an evaluation of the ecology of arthropod-borne diseases in the Republic of Korea (ROK), we examined 8,765 mosquitoes captured in Paju County, Gyonggi Province, ROK, for the presence of viruses. Mosquitoes were captured in propane lantern/human-baited Shannon traps, Mosquito Magnet traps, or American Biophysics Corporation (East Greenwich, RI) miniature light traps with or without supplemental octenol bait and/or dry ice. Mosquitoes were identified to species, placed in pools of up to 40 mosquitoes each, and tested on Vero cells for the presence of virus. A total of 15 virus isolations were made from 293 pools of mosquitoes. Viruses were identified by reverse transcriptase-polymerase chain reaction and sequencing and consisted of 14 isolations of Japanese encephalitis (JE) virus and one isolation of Getah (GET) virus. All JE isolates were from Culex tritaeniorhynchus Giles, and the isolate of GET was from Aedes vexans (Meigen). The minimum field infection rate for JE in Cx. tritaeniorhynchus was 3.3 per 1,000, whereas the GET virus infection rate for Ae. vexans was 0.2 per 1,000. Isolation of JE and GET indicated that both viruses were actively circulating in northern Gyonggi Province, ROK. The lack of human cases of JE among the Korean population probably is because of an effective government-mandated vaccination program. The reason for no cases among >10,000 United States military and others that reside or train nearby is unknown, but may be related to personnel protection measures (permethrin-impregnated uniforms and use of deet repellent), adult mosquito control, mosquito selection of nonhuman hosts (unpublished data), and the low symptomatic to asymptomatic ratio of disease in adults.