Entomological investigation of Japanese encephalitis outbreak in Malkangiri district of Odisha state, India

BACKGROUND A severe outbreak of Japanese encephalitis (JE) and acute encephalitis syndrome (AES) with high case fatality was reported from Malkangiri district of Odisha state, India during September to November 2016 affecting 336 children with 103 deaths. OBJECTIVES The purpose of this study was to investigate the outbreak in the light of entomological determinants. METHODS Entomological investigation was carried out in 48 villages from four mostly affected Community Health Centres (CHCs) of Malkangiri district. Dusk collections of resting adults was done in villages from indoor and outdoor sites to record the density of mosquito species, including the known JE vectors, feeding behaviour, parity, dusk index and infection status with JE virus (JEV). FINDINGS The per man hour density and dusk index of JE vector species varied from 2.5 to 24.0 and 0.81 to 7.62, respectively in study villages. A total of 1136 mosquitoes belonging to six vector species were subjected to PCR and one pool of Culex vishnui was found to be positive for JEV. CONCLUSION The JE transmission in Malkangiri district was confirmed. Thorough screening of human blood samples of JE/AES suspected cases and JE vector mosquitoes for the presence of JEV during rainy season every year is recommended.

Toxicity of saponin isolated from Gymnema sylvestre R. Br. (Asclepiadaceae) against Culex tritaeniorhynchus Giles (Diptera: Culicidae) Japanese encephalitis vector mosquito in India / Toxicidade da saponina isolada de Gymnema sylvestre R. Br. (Asclepiadaceae) contra Culex tritaeniorhynchus Giles (Diptera: Culicidae) mosquito vetor da encefalite japonesa na Índia

To determine the larvicidal activity of various extracts of Gymnema sylvestre against the Japanese Encephalitis vector, Culex tritaeniorynchus in Tamilnadu, India. To identify the active principle present in the promising fraction obtained in Chlorofom:Methanol extract of Fraction 2. The G. sylvestre leaf extracts were tested, employing WHO procedure against fourth instar larvae of C. tritaeniorhynchus and the larval mortalities were recorded at various concentrations (6.25, 12.5, 25.0, 50 and 100 µg/mL); the 24h LC50 values of the G. Sylvestre leaf extracts were determined following Probit analysis. It was noteworthy that treatment level 100 µg/mL exhibited highest mortality rates for the three different crude extracts and was significantly different from the mean mortalities recorded for the other concentrations. The LC50 values of 34.756 µg/mL (24.475-51.41), 31.351 µg/mL (20.634-47.043) and 28.577 µg/mL (25.159-32.308) were calculated for acetone, chloroform and methanol extract with the chi-square values of 10.301, 31.351 and 4.093 respectively. The present investigation proved that G. Sylvestre could be possibly utilized as an important component in the Vector Control Program.

O presente trabalho é para identificar a atividade larvicida de vários extratos da Gymnema sylvestre contra o vetor da encefalite japonesa, Culex tritaeniorhynchus em Tamilnadu, Índia. Com este propósito o princípio ativo presente na fração mais promissora foi obtida através de um extrato clorofórmio:metanol da fração 2. Os extratos das folhas do G. sylvestre foram testados empregando o procedimento da WHO contra estágios quaternários da larva do C. tritaeniorhynchus e as mortalidades larvais foram registradas após várias concentrações (6,25, 12,5, 25,0 e 100; 34,756 µg/mL (24,475-51,41), 31,351 µg/mL (20,634-47,043) e 28,577 µg/mL (25,159-32,308) g/mL); os valores de LC50 de 24 horas dos extratos das folhas de G. sylvestre foram determinados seguindo a análise Probit. Foi notado que o nível de tratamento de 100 µg/mL exibiu a mortalidade mais alta para os três diferentes extratos crus e foi significantemente diferente das mortalidades médias registradas para as outras concentrações. Os valores de LC50 de 34,756 µg/mL (24,475-51,41), 31,351 µg/mL (20,634-47,043) e 28,577 µg/mL (25,159-32,308) foram calculados para os extratos de acetona, clorofórmio e metanol com os valores de qui-quadrado de 10,301, 31,351 e 4,093 respectivamente. A presente investigação mostra que o G. sylvestre pode ser usado como componente importante no programa de controle do vetor.

Japanese encephalitis: a review of the Indian perspective

Japanese encephalitis virus (JEV) causes Japanese encephalitis, which is a leading form of viral encephalitis in Asia, with around 50,000 cases and 10,000 deaths per year in children below 15 years of age. The JEV has shown a tendency to extend to other geographic regions. Case fatality averages 30% and a high percentage of the survivors are left with permanent neuropsychiatric sequelae. Currently, there is no cure for JEV, and treatment is mainly supportive. Patients are not infectious, but should avoid further mosquito bites. A number of antiviral agents have been investigated; however, none of these have convincingly been shown to improve the outcome of JEV. In this review, the current knowledge of the epidemiology and the pathogenesis of this deadly disease have been summarized.

Ecological study on mosquito vectors of Japanese encephalitis virus in Bellary district, Karnataka.

BACKGROUND & OBJECTIVE: Japanese encephalitis virus (JEV) has been a serious public health problem in Bellary district since 1981. Though JE is a vector borne disease, no published record was available regarding prevalence of mosquito species in this region. A two years ecological study was therefore conducted to determine species composition, seasonal prevalence and relative abundance of culicid taxa, particularly JE vectors endemic to this area. METHODS: Three villages with recent JE out breaks, were selected for regular mosquito collections. During daytime, adult mosquitoes resting inside human and domestic animal habitations were collected using aspirators and flashlights at weekly intervals. Similarly, adult mosquitoes were collected from cattle sheds and pig enclosures at dusk hours. RESULTS: A total of 120113 mosquitoes collected at dusk belonged to 5 genera and 24 species, including 13 species those have already yielded JE virus in India with Cx. tritaeniorhynchus contributing to 70.3 per cent. General mosquito population showed bimodal pattern of peak occurrence during February and October in both the peaks, Cx. tritaeniorhynchus contributed maximum JE. Substantial densities of An. subpictus and An. peditaeniatus during JE season suggest the supportive role of these species. Other vector species viz., Cx. quinquefasciatus, Cx. pseudovishnui, Cx. vishnui, Cx. gelidus, Cx. fuscocephala, Cx. bitaeniorhynchus, Ma. annulifera, Ma. uniformis and An. barbirostris perhaps have a limited role in the transmission of JE virus due to their extremely poor density. INTERPRETATION & CONCLUSION: Cx. tritaenorhynchus appears to have a major role in the transmission of JE virus in Bellary district. Risk of transmission of JEV to humans can be reduced by house spraying with residual insecticides and intermittent paddy irrigation.

Illustrated keys to the mosquitoes of Thailand. IV. Anopheles.

Illustrated keys for the identification of the larvae and adult female Anopheles mosquitoes of Thailand are presented along with distribution maps, tabulated bionomics information, and a checklist. A total of 73 species are treated, including 71 previously and newly described species (An. cracens = dirus B, An. scanloni = dirus C, An. baimaii = dirus D, An. latens = leucosphyrus A, and An. epiroticus = sundaicus A). Also, two undescribed species are included, i.e., An. minimus C and a new species near An. gigas. Thirty-four chromosomal forms of 14 species are discussed, with suggestions provided for resolving their taxonomic status.

Differential tolerance of two morphological variants of Culex tritaeniorhynchus (Diptera: Culicidae), a Japanese encephalitis vector, to pyrethroid insecticides in Mysore, India.

Five synthetic pyrethroids, deltamethrin, cypermethrin, permethrin, alpha-cypermethrin, and lambdacyhalothrin, were tested on the larvae of 2 morphological variants of Cx. tritaeniorhynchus collected from Mysore City (ground pools) and outside Mysore (paddy fields), in Karnataka State, India. The morphological characters, ie, length and width of siphon, siphonal index, comb scale numbers, pecten teeth numbers, length of anal gills and anal gill index of larvae of two Cx. tritaeniorhynchus populations were found to be significantly different (p<0.05). To elicit further detail of these two variants, pyrethroid bioassays were undertaken. In general, the toxicity ranking of these pyrethroids tested on the Cx. tritaeniorhynchus variants from Mysore City was deltamethrin > lambdacyhalothrin > cypermethrin > permethrin > alpha-cypermethrin. However, for the rural variety it was deltamethrin > lambdacyhalothrin > alpha-cypermethrin > permethrin > cypermethrin. Of the 5 pyrethroids tested, deltamethrin was the most effective on both variants. Alpha-cypermethrin and lambdacyhalothrin were respectively 2.17 and 2.09 times more effective on the city variety (p<0.05), based on LC50 values. The results suggest that, in addition to morphological differences, the 2 tested varieties of Cx. tritaeniorhynchus also differ in susceptibility status.

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.

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.

Venereal transmission of Japanese encephalitis virus in Culex bitaeniorhynchus mosquitoes.

Experiments were conducted in the laboratory on C. bitaeniorhynchus to determine the possible role of males in maintaining or sustaining the Japanese encephalitis virus activity in nature. It was found that infected males are capable of passing on the virus to female mosquitoes while mating. The occurrence of phenomenon of venereal transmission of this virus may have epidemiological importance.

Cross-sectional serosurvey for Japanese encephalitis specific antibody from animal sera in Malaysia 1993.

Serum specimens were collected from 6 species of animals living in 9 states of Malaysia including Sabah, North Borneo in 1993. Antibodies against Japanese encephalitis (JE) virus in these sera were detected by means of hemagglutination-inhibition (HI) and neutralization (NT) tests. By HI test, 702 of 2,152 (32.6%) sera showed positive results. Higher positive rates were obtained by the NT test, in which 1,787 of 1,927 (92.7%) sera had antibodies against JE virus. All serum specimens with positive HI were confirmed as positive by the NT. Swine sera showed especially higher rates of antibody positive and higher antibody titers compared with other animals. These results suggest that JE infections are widely distributed among many animals of Malaysia, and pig is the most susceptible amplifier host for JE virus.

Role of some environmental factors in modulating seasonal abundance of potential Japanese encephalitis vectors in Assam, India.

Temporal changes in the abundance of host-seeking, potential Japanese encephalitis (JE) vector mosquitos and the role of some ecological factors that are modulating the abundance of vector mosquitos were studied. Vector surveillance was conducted for one year in 4 JE prone villages of Dibrugarh, Assam. Among potential JE vectors, the most abundant mosquito was Culex vishnui s.s. comprising about 22.32%. Maximum density of the mosquito was found during the month of April and another peak was observed in the month of September. The influence of meteorological factors on the abundance of JE vectors was found to vary from species to species. The final multiple regression equations (after variables were selected using STEPWISE procedure) consisted of a combination of linear, quadratic, cubic and interactive ecological variables and accounted for 25-98% of the variations in the abundance of JE vector mosquitos. Complex interactions among environmental factors, such as minimum and maximum temperature, rainfall and flood level are involved in modulating the seasonal abundance of mosquitos. A time lag is involved before a cause and effect relationship is established between environmental parameters (independent variables) and entomological variables (dependent variables). Inundation caused by flooding is favorable for mansonioid mosquito species whereas it has an adverse effect on non-mansonioid mosquito species.

Susceptibility status of two species of Japanese encephalitis vectors to insecticides in the Thar desert, district Bikaner (Rajasthan).

Susceptibility tests were conducted on the adults of two species of Japanese encephalitis vectors viz., Culex pseudovishnui and C. tritaeniorhynchus against diagnostic doses of DDT, dieldrin, malathion, fenitrothion, propoxur and permethrin at different exposure duration. C. pseudovishnui was found susceptible to permethrin and resistant to dieldrin and propoxur while C. tritaeniorhynchus was found susceptible to permethrin and resistant to DDT, dieldrin, fenitrothion and propoxur. A verification, however, was required with other insecticides for both the species.

Host feeding patterns of Culex vishnui sub group of mosquitoes in Dibrugarh district of Assam.

The host feeding patterns of three species of mosquitoes belonging to vishnui sub group, Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui, the most prevalent species in Dibrugarh district were determined by analysing their blood meals. All 3 species were found be essentially zoophilic. High percentage of pig feeding was observed in Culex tritaeniorhynchus (40 per cent) and Culex vishnui (35.3 per cent) in comparison to other prevalent species in this area. In contrast Culex pseudovishnui another member of this group was not attracted to pigs (0.4 per cent). Few human feeds were recorded for Culex tritaeniorhynchus (0.4 per cent), Culex vishnui (0.4 per cent) and Culex pseudovishnui (0.8 per cent), indicating their occasional contact with human hosts. Considering the importance of this group as proven vectors of Japanese encephalitis the relevance of these results to JE transmission in this area are discussed.

Comparative susceptibility of two Japanese encephalitis vectors from Mysore to six insecticides.

Larval populations of Culex tritaeniorhynchus and C. fuscocephala from Mysore city were tested for their susceptibility against two pyrethroids viz., cypermethrin and deltamethrin and four organophosphorus (OP) compounds viz., fenthion, fenitrothion, temephos and malathion. The investigations revealed that, among the pesticides tested, efficacy of pyrethroids was very high as compared to OP compounds. C. tritaeniorhynchus was found to be highly tolerant to all the insecticides used. It registered 4.0, 6.5, 17.0, 6.5, 14.0 and 1.5 times more tolerance than C. fuscocephala to cypermethrin, deltamethrin, fenthion, fenitrothion, temephos and malathion respectively in terms of the LC50 value. Further studies are needed to determine the development of resistance if any, by C. tritaeniorhynchus, an important JE vector in Karnataka.

Ecology of mosquitos (Diptera: Culicidae) at a site endemic with Japanese encephalitis on Luzon, Republic of the Philippines.

A 2-year study of the ecology of mosquitos was conducted in a rice-growing area in the Philippines. Forty-four species in 8 genera were collected using 6 techniques, with Culex vishnui being most abundant. Of all the Anopheles collected, most species were exophagic, while most of the Culex species collected were endophagic. Anthropophilic or zoophilic feeding patterns were estimated using man-to-animal biting ratios. Peak periods of mosquito abundance occurred several months after the onset of both the rainy season and the rice irrigation period. Seasonal populations of the more abundant species revealed 3 distinct patterns: 1) populations are high during the rainy season and low during the irrigation period; 2) populations are equally strong during both periods; and 3) populations are highest during the irrigation period. Species' biting activity was grouped into 2 patterns: 1) those that feed primarily from 1800-0000; and 2) those that feed evenly throughout the night. Mosquito abundance and Japanese encephalitis virus activity were related to rainfall and rice-growing practices.