Molecular Identification of Species Belonging to Culex vishnui Subgroup (Diptera: Culicidae), Vectors of Japanese Encephalitis Virus, in Taiwan

Classification of mosquitoes with overlapping features remains problematic when using traditional morphological identification alone. In this study, we used molecular methods to elucidate the taxonomic status of Culex tritaeniorhynchus, Culex annulus, and Culex pseudovishnui species as vectors of the Japanese encephalitis virus belonging to the Culex vishnui subgroup and gene flow among them. In this study, 76, 59, and 3 samples of Cx. annulus, Cx. tritaeniorhynchus, and Cx. pseudovishnui, respectively, were collected around Taiwan. Phylogenetic analysis and genetic divergence were based on genomic sequence variations in ribosomal DNA and the internal transcribed spacer (rDNA) and cytochrome c oxidase subunit I (COI). Our results revealed that Cx. annulus and Cx. vishnui are genetically similar and share a gene pool among the species from Taiwan and other Asian countries. However, two hidden taxa of Cx. tritaeniorhynchus, which clustered together according to the rDNA sequences, were discovered based on the COI sequences. In addition, Cx. pseudovishnui has different gene pools from those of the strains from other countries, implying that the population from Taiwan is probably either a unique strain or a sibling species. This study provides molecular information on the taxonomic status of the species in the Cx. vishnui subgroup in Taiwan and gene flow between these species, providing valuable information for vector control operations and the delineation of the evolutionary process.

Eighth nerve involvement in meningo-encephalitis

Seventy-two patients suffering from meningo-encephalitis were studied, clinically, biochemically, microbiologically and virologically. Evidence of rising titre in serum and CSF of antibodies to Japanese encephalitis were present in 50% of cases, and recent past infection in 20% of cases. Cranial nerve involvement particularly the "8th" was present in 70% of cases though there was a 2.5% involvement of the 2nd, 3rd and 6th nerves. All the patients belonged to plain Tribal population and all had a history of eating pork 7-10 days prior to development of the infection.

[Surveillance and control of Japanese encephalitis in Henan province, 1950 - 2008]

OBJECTIVE

To analyze the characteristics and trend of Japanese encephalitis (JE) in Henan province.

METHODS

Adopting descriptive epidemiological method to analyze the data on the epidemic situation of JE from 1950 to 2008, and on mosquitoes and host animals at disease surveillance points. The host serum JE IgG antibody was detected by ELISA. Data was analyzed using SPSS 12.0 and Excel 2003 software.

RESULTS

The incidence of JE in Henan province had a fluctuant downward trend. Peak of the incidence fell in July to September, accounting for 88.09% of total cases. The scope of geographical distribution was increasing from northern to southern parts of the province. Cases mainly concentrated in the southern and south-eastern parts of the province. 0 - 14 year-old group had the highest incidence (81.95%). In Luoyang city, there was a significant increase in children at 15-years or older (58.93%). Most patients were farmers (42.33%). The positive-times for half of the antibodies of JE in piglets of the surveillance sentinels were different, which might be the reason for the different levels for the incidence rates. The proportion of different kinds of mosquitoes were also different in surveillance sentinel sites, and the time for the density peak of the mosquitoes was in accordance with the incidence peak of JE.

CONCLUSION

To develop control strategies, evidence should be based on the characteristics of geographical variance, age, occupation differences, data related to monitoring on animal host and media mosquitoes of JE incidence in Henan province.

The effects of climatic factors on the distribution and abundance of Japanese encephalitis vectors in Kurnool district of Andhra Pradesh, India

BACKGROUND & OBJECTIVES

Climatic attributes have been associated with relative mosquito abundance and transmission of mosquito borne infections in many parts of the world, especially in warm and tropical climatic regions. The main objectives of this study were to assess the change in seasonal pattern of Japanese encephalitis (JE) vectors, their density, to elucidate whether the lagged climate variables (precipitation, temperature and humidity) are associated with JE vector density, and to determine if temperature and precipitation are similarly important for the rise in the number of potential mosquito vectors for JE virus in the temperate climate of Andhra Pradesh, India.

METHODS

Mosquito samples were collected from Kurnool district of Andhra Pradesh using hand catch and light-trap methods during 2002 to 2006. The type and abundance of recovered species were compared to ecological correlates. In each geographic area, temperature and precipitation are the two possible proxy variables for mosquito density, in conjunction with other seasonal factors for JE epidemics.

RESULTS

Out of the various mosquito species collected, Culex gelidus and Cx. tritaeniorhynchus were noticed in high numbers. There was considerably high prevalence of Cx. gelidus (68.05%) in urban area than in rural areas whereas, Cx. tritaeniorhynchus (57.51%) was found to be more in rural areas than in the urban area. It is noticed that the factors such as rainfall and temperature were found to be correlated with the per man hour (PMH) density, whereas the humidity was inversely correlated with the PMH.

INTERPRETATION & CONCLUSION

The environmental and eco-climatic factors are assisting in enhancing the breeding of these mosquitoes in Kurnool district of Andhra Pradesh, India. Both Cx. tritaeniorhyncus and Cx. gelidus are quite adaptable to these environmental conditions and this necessitates immediate control measures in both rural and urban areas of Kurnool district.

Japanese Encephalitis Among Three U.S. Travelers Returning from Asia, 2003-2008

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is a leading cause of encephalitis in Asia. The risk for Japanese encephalitis (JE) for most travelers is low, but varies by travel destination, duration, season, and activities. As part of routine surveillance and diagnostic testing, state health officials or clinicians send specimens from patients with unexplained encephalitis to CDC. To characterize the epidemiologic and clinical features of JE cases, CDC reviewed all laboratory-confirmed cases that occurred during 1992 (when a JE vaccine was first licensed in the United States) to 2008. Four cases were identified, including one previously reported. This report describes the three previously unpublished cases. All were Asian immigrants or family members who traveled to Asia to live or to visit friends or relatives and had not been vaccinated for JE. The three patients experienced fever with mental status changes, but JE was recognized early in the clinical course of only one patient. All recovered, but two patients had residual neurologic deficits. Travelers to Asia might be at increased risk for JE because of rural itineraries and lack of perceived risk. To protect against JE, travelers should seek medical advice on protective measures, including possible JE vaccination, well in advance of departure for Asia. While in Asia, travelers should use personal protective measures to reduce the risk for mosquito bites. Health-care providers should assess the risk for JE in travelers to Asia and provide appropriate preventive or supportive treatment measures.

Concepts of control of Japanese encephalitis and dengue

Japanese encephalitis and dengue are mosquito-borne virus diseases of major human disease importance to the Asian region. Our current knowledge of their distribution and transmission cycles is reviewed, the classical approaches to their control are discussed. The development of live attenuated vaccines for both disease offers possible elimination of human epidemics through combined use of vaccine and mosquito control.

[Dengue, arbovirus and migrations in the Indian Ocean]

An arbovirus requires a competent haematophagous arthropod for transmission from one vertebrate to another susceptible host. Air transportations allow quick transfers from place to place and the diffusion of potential vectors or infectious hosts. The merchandise transportation by containers allowed the diffusion of Ae. albopictus from Asia through Africa and America. Emerging arbovirusis may occur in zones where they do not exist. Dengue which originally was located in southeastern Asia, is the most important arbovirusis in the world. The occurrence of dengue haemorrhagic fever (DHF) in Asia and America, mostly in urban areas, increased the global concern about dengue. Likewise, cases of DHF are not reported in Africa and in the Indian Ocean southwestern islands. The principal vector of dengue, Aedes aegypti, was present during the dengue 1 outbreak in Comoros, in 1993. In the other islands, only few specimens of Ae. aegypti are observed, and described mostly as none anthropophilic forms. The role of Ae. albopictus as vector of dengue was suspected and reported during outbreaks in Seychelles and Réunion island in 1977-1978. Yellow fever, present in Africa mostly in restricted areas, is absent in Asia. Japanese encephalitis considered as an emerging disease in India could expand through the islands. Rift valley fever, with periodic epizootics in domestic ungulates in Africa, was described as a new disease in Madagascar in 1990-1991. Crimean-Congo haemorrhagic fever is also present in Madagascar. Humans can be infected by vector bite or by handling infectious animal products. The distribution of other viruses (West Nile, Sindbis, Wesselsbron or Chikungunya) is discussed.

A system for studying vector competence of mosquitoes for Japanese encephalitis virus

A method to infect mosquitoes with Japanese encephalitis virus (JEV) and to demonstrate virus transmission after an extrinsic incubation period is described. Using per oral feeding method infection rate as high as 90% could be achieved. Demonstration of transmission of the virus was achieved by allowing the infected mosquitoes to probe a suitable serum medium and testing the probed serum for virus. Both infection and transmission were demonstrated by using insect-bioassay.

[Japanese encephalitis in Southern Europe]

In 2012, a fragment of the Japanese encephalitis virus (JEV) genome was isolated from a pool of Culex pipiens mosquitoes caught in 2010 and 2011 in Northern Italy. JEV has a broad geographical distribution in South and Southeast Asia and Oceania, and is the most important cause of viral encephalitis in Asia in humans and also causes encephalitis in horses and fertility problems in pigs. However, recently isolated JEV genome fragments in mosquitoes in Italy could be an indication of repeated introduction of JEV, enzootic circulation of JEV or a related virus in Southern Europe. Until more information is available, Japanese encephalitis remains a travel-related infectious disease for travellers to JEV endemic and epidemic areas outside of Europe.