Avian Plasmodium infection in field-collected mosquitoes during 2012-2013 in Tarlac, Philippines.

Global warming threatens to increase the spread and prevalence of mosquito-transmitted diseases. Certain pathogens may be carried by migratory birds and transmitted to local mosquito populations. Mosquitoes were collected in the northern Philippines during bird migration seasons to detect avian malaria parasites as well as for the identification of potential vector species and the estimation of infections among local mosquito populations. We used the nested PCR to detect the avian malaria species. Culex vishnui (47.6%) was the most abundant species collected and Cx. tritaeniorhynchus (13.8%) was the second most abundant. Avian Plasmodium parasites were found in eight mosquito species, for which the infection rates were between 0.5% and 6.2%. The six Plasmodium genetic lineages found in this study included P. juxtanucleare -GALLUS02, Tacy7 (Donana04), CXBIT01, Plasmodium species LIN2 New Zealand, and two unclassified lineages. The potential mosquito vectors for avian Plasmodium parasites in the Philippines were Cq. crassipes, Cx. fuscocephala, Cx. quinquefasciatus, Cx. sitiens, Cx. vishnui, and Ma. Uniformis; two major genetic lineages, P. juxtanucleare and Tacy7, were identified.

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.

A dengue vector surveillance by human population-stratified ovitrap survey for Aedes (Diptera: Culicidae) adult and egg collections in high dengue-risk areas of Taiwan.

Aedes aegypti L. is the primary dengue vector in southern Taiwan. This article is the first report on a large-scale surveillance program to study the spatial-temporal distribution of the local Ae. aegytpi population using ovitraps stratified according to the human population in high dengue-risk areas. The sampling program was conducted for 1 yr and was based on weekly collections of eggs and adults in Kaohsiung City. In total, 10,380 ovitraps were placed in 5,190 households. Paired ovitraps, one indoors and one outdoors were used per 400 people. Three treatments in these ovitraps (paddle-shaped wooden sticks, sticky plastic, or both) were assigned by stratified random sampling to two areas (i.e., metropolitan or rural, respectively). We found that the sticky plastic alone had a higher sensitivity for detecting the occurrence of indigenous dengue cases than other treatments with time lags of up to 14 wk. The wooden paddle alone detected the oviposition of Ae. aegypti throughout the year in this study area. Furthermore, significantly more Ae. aegypti females were collected indoors than outdoors. Therefore, our survey identified the whole year oviposition activity, spatial-temporal distribution of the local Ae. aegypti population and a 14 wk lag correlation with dengue incidence to plan an effectively proactive control.

Comparison of the efficacy of CO2-baited and unbaited light traps, gravid traps, backpack aspirators, and sweep net collections for sampling mosquitoes infected with Japanese encephalitis virus.

Two field studies were conducted to determine the efficacy of mosquito collection methods for species composition, species abundance, and Japanese encephalitis virus infection rates in Taiwan. Traps evaluated included John W. Hock (JH) model UD black light traps, JH model 1012 new standard miniature CDC light traps, JH model 1712 CDC gravid traps, and Taiwan-made Pest-O-Lite light traps. Backpack aspirators and sweep nets were also used to collect the resting population. Culex tritaeniorhynchus in all studies and Mansonia uniformis in the Taipei areas were the two most abundance species collected. Dry ice-baited UD black light traps were effective in regard to species diversity, species abundance, and Japanese encephalitis virus infection rates. The unbaited Pest-O-Lite light traps collected significantly more female mosquitoes than the UD black light traps but performed similarly with regard to species diversity and male mosquito collection. Most mosquitoes collected by Pest-O-Lite light traps were dried and not suitable for virus detection. Dry ice-baited CDC light traps collected significantly fewer mosquitoes than other light traps. Although CO(2) -baited UD black light traps with octenol attracted more mosquitoes, no statistical significance was found compared to CO(2) -baited UD black light traps without octenol. Japanese encephalitis viruses were isolated from half of the positive pools in UD black light traps and CDC light traps.

Screening of mosquitoes using SYBR Green I-based real-time RT-PCR with group-specific primers for detection of Flaviviruses and Alphaviruses in Taiwan.

Surveillance for infectious agents carried by mosquitoes is important for predicting the risk of vector-borne infectious diseases. In this study, a method was established to mass-screen mosquitoes for viral infections. The assay detected the viral load of 4 dengue virus (DENV) serotypes (DENV-1, DENV-2, DENV-3, and DENV-4), the Japanese encephalitis virus (JEV), the Sindbis virus and the Chikungunya virus at 1PFU/mL (determined by real-time RT-PCR) in 36.64-43.45 cycles. This method was applied to 75,364 field-captured mosquitoes that were grouped into 10,343 pools. Japanese encephalitis viruses were detected in 25 pools of 906 Culex tritaeniorhynchus females and a single pool of 44 Cx. fuscocephala females. These viruses were isolated from half of the positive pools. Dengue viruses were detected in 2 pools of 43 Aedes aegypti females. Additionally, mosquitoes that were infected orally with dengue viruses in the laboratory were also used to verify the test. The best detection times for individual mosquitoes after being fed virally-contaminated blood were at day 0 and day 10. The number of mosquitoes detected per pool was up to one infected mosquito plus 59 non-infected mosquitoes; the appropriate storage substances for holding samples within 24h included ice cubes and dry ice. This method, combined with a robust and automated RNA-extraction method and a 96 well real-time RT-PCR machine, allows the processing of a large number of samples at once, making it a powerful tool for monitoring simultaneously local and emerging vector-borne infectious diseases of Flaviviruses and Alphaviruses. This study is the first to quantify the viral load in individual mosquitoes over the course of a 16-day extrinsic incubation period.

Evaluation of various control agents against mosquito larvae in rice paddies in Taiwan.

A field test was conducted in rice paddies adjacent to Wufeng, Taichung County in Central Taiwan to evaluate the efficacy of control agents against mosquito larvae. The agents included Bacillus thuringienesis israelensis (Bti), two Lagenidium giganteum products (Lg product A and T), and temephos. The major mosquito species found in the rice paddies were Culex tritaeniorhynchus/vishnui and Anopheles sinensis. Compared to controls, a 7-day treatment with Bti or Lg products A and T caused overall reductions in the number of immatures (larvae and pupae) of Cx. tritaeniorhynchus/vishnui of 77.5%, 49.7%, and 21.9%, respectively, whereas temephos caused an increase of 66.9%. The overall reductions in An. sinensis were 85.4%, 8.6%, 44.6%, and 92.1%, respectively. There was no significant reduction in the number of mosquito larvae following 42 days of treatment with these agents. In summary, 1-week treatments with both biological control agents produced moderate overall reductions in mosquito larvae in rice paddies. The insecticide temephos, on the other hand, was very effective at suppressing the larvae of An. sinensis but significantly increased the number of Cx. tritaeniorhynchus/vishnui larvae in temephos-treated plots.

Mosquito surveys carried out on Green Island, Orchid Island, and Penghu Island, Taiwan, in 2003.

Field surveys of mosquitoes were carried out on Green, Orchid, and Penghu Islands in 2003 to ascertain the status of mosquito vectors. Eighteen species of mosquitoes were collected, including three species of Anopheles, four species of Aedes, eight species of Culex, two species of Armigeres, and one species of Malaya. Seventeen previously recorded species were not collected in this study but 11 species collected had not previously been recorded. Ten newly recorded species, An. maculatus, An. takasagoensis, Ae. alcasidi, Ae. lineatopennis, Ae. vexans vexans, Ar. omissus, Cx. vishnui, Cx. halifaxii, Cx. hayashii, and Cx. neomimulus, were collected on Green Island and one previously unrecorded species, Ar. subalbatus, was collected on Orchid Island. Potential vectors An. maculatus and An. sinensis, malaria vectors in Korea and Mainland China, Ae. albopictus, a vector of dengue in Taiwan and West Nile virus in the USA, Cx. vishnui and Cx. tritaeniorhynchus, Japanese encephalitis vectors in Taiwan, Ae. vexans vexans, an eastern equine encephalitis vector in the USA, and Cx. quinquefasciatus, a vector of filariasis in Taiwan and West Nile virus in the USA, were among the mosquito species collected.