贵州白纹伊蚊对登革病毒易感性的研究

目的 用细胞、分子生物学技术进行贵州省白纹伊蚊不同地理株对登革病毒(DEN)易感性的研究。方法 采集贵州省9个地(州)市共计15个县(区)白纹伊蚊幼虫标本，饲养为成蚊；取羽化后3～5日龄期的贵州不同地理株白纹伊蚊，用不同型别的DEN分别经口连续感染3d，于首次感染后的4、7、10、14d收集感染成蚊标本；制备蚊悬液，碘化钠法提取RNA，用DENNS1基因区通用引物经逆转录．聚合酶链反应(RT-PCR)检测DEN核酸；蚊悬液接种C6／36细胞进行病毒分离，制作细胞抗原片，经间接免疫荧光法检测DEN抗原；同时感染白纹伊蚊海南株作为对照。结果 DEN1-4型国际参考株感染白纹伊蚊贵州省不同地方株，其感染比率分别为12／15、12／15、8／15和13／15。结论 白纹伊蚊贵州省不同地方株对DEN1-4型国际参考株普遍易感，表明贵州省具备引起登革热流行的条件。     

Outlook of dengue in Malaysia: a century later

Dengue continues to be a major health threat to Malaysia a century after its first reported outbreak in 1902. Examination of the available outbreak data suggested that a major DF/DHF outbreak occurred in Malaysia in a cyclical pattern of approximately every 8 years. All four dengue virus serotypes are found co-circulating in Malaysia, but after the first and only major outbreak involving DEN-4 in 1960's, only DEN-1, DEN-2 and DEN-3 were associated with DF/DHF outbreaks. It is argued that perhaps the spread of the later dengue virus serotypes followed the pattern of spread of the mosquito vector Aedes aegypti, whereas the former was associated with Aedes albopictus, the outdoor and rural area dwelling mosquito. Estimating from the trend and pattern of dengue and the associated dengue virus serotypes, unless there is a major breakthrough in dengue vaccine development, it is likely that dengue outbreaks will continue to occur in Malaysia throughout the 21st century.     

Laboratory evaluation of the response of Aedes aegypti and Aedes albopictus uninfected and infected with dengue virus to deet

Laboratory studies were conducted to compare the response of Aedes aegypti (L.) and Aedes albopictus (Skuse) adults, uninfected and infected with four serotypes of dengue virus to a repellent containing 5% N, N-diethyl-3-methylbenzamide (deet). The results showed that mosquitoes infected with the four serotypes of dengue responded similarly to uninfected mosquitoes.     

Enhanced vector competence of Aedes aegypti (Diptera: Culicidae) from the Torres Strait compared with mainland Australia for dengue 2 and 4 viruses

Australian Aedes aegypti (L.) mosquitoes colonized from the Torres Strait and three mainland localities (Charters Towers, Townsville, and Cairns) were fed on blood suspensions containing dengue virus type 2 (DEN-2) or dengue virus type 4 (DEN-4). Variation was found in oral susceptibility to DEN-2 (59 -99% infection) and DEN-4 (28-79% infection) among Ae. aegypti assayed for virus at 8, 12, 16, or 20 d after ingestion of infected blood. Torres Strait Ae. aegypti were the most susceptible to DEN-2 and were significantly more efficient in transmission to capillary tube at 16 d (76% transmission) than mainland Ae. aegypti populations (20-28% transmission). Torres Strait Ae. aegypti were also the most susceptible to DEN-4, although transmission did not vary significantly from mainland populations at 16 d (12% compared with 0-4%) or 20 d (16% compared with 4-16%). Disseminated infection (i.e., leg infection) with either DEN-2 or DEN-4 was not an accurate predictor of transmission potential. This study demonstrates differences among Australian Ae. aegypti populations in vector competence for DEN-2 and DEN-4. Torres Strait Ae. aegypti were more frequently infected and able to transmit DEN-2 at higher rates than mainland populations. These data indicate that the Torres Strait region is potentially more receptive to dengue transmission than mainland localities, a finding discussed with respect to past outbreaks.     

Susceptibility of urban and rural populations of Aedes albopictus from São Paulo State, Brazil, to infection by dengue-1 and -2 viruses

In Brazil, dengue viruses (DENV) are transmitted by Aedes aegypti (L.). However, the recent introduction of Aedes albopictus (Skuse) has caused concern, because some populations of this species also are capable of DENV transmission. Ae. albopictus from rural and urban localities of S?o Paulo State, Brazil, were artificially exposed to infection with DENV-1 and -2 to evaluate their susceptibility. The rates of infection (6.2 and 5.7% for DENV-1; 5.3 and 12% for DENV-2) and dissemination (22.2 and 40% for DENV-1; 0 and 20% for DENV-2) were low in both urban and rural populations, with no significant differences detected between these mosquito populations.     

Insecticide susceptibility of Aedes aegypti and Aedes albopictus across Thailand

Aedes aegypti (L.) and Aedes albopictus (Skuse), two important vectors of dengue fever and dengue hemorrhagic fever, were collected from Mae Sot, Nakhon Sawan, Nakhon Ratchasima, Surat Thani, and Phatthalung, Thailand, from July 2003 to April 2004. The patterns of insecticide susceptibility to temephos, malathion, and permethrin of both Ae. aegypti and Ae. albopictus larvae were determined. Ae. aegypti from all study sites were resistant to permethrin, they but were susceptible to malathion. Resistance to temephos was detected in all strains of Ae. aegypti, except those from Nakhon Ratchasima. Ae. albopictus larvae had low levels of resistance to all three insecticides, except Mae Sot and Phatthalung strains, which were resistant to permethrin.     

Selection of D2S3, an Aedes aegypti (Diptera: Culicidae) strain with high oral susceptibility to Dengue 2 virus and D2MEB, a strain with a midgut barrier to Dengue 2 escape

Family-based phenotypic selection was used to breed two genetic strains of Aedes aegypti L. that differ in susceptibility to infection with dengue serotype 2 virus (DEN-2) strain JAM1409. A Dengue 2 Susceptible on 3 chromosomes (D2S3) strain was bred from Ae. aegypti aegypti and Ae. aegyptiformosus P1 parents to have a high midgut infection rate (MIR) and a high disseminated infection rate (DIR). A Dengue 2 Midgut Escape Barrier (D2MEB) strain was bred from D2S3 and Houston P1 parents to have a high MIR and a low DIR. After selection in the F2 generation, single strand conformation polymorphism genotypes were determined at cDNA marker loci throughout the genome to test for Mendelian ratios and thereby identify regions containing deleterious or lethal alleles. Both strains were orally challenged with two other DEN-2 genotypes, two DEN-1 genotypes, one DEN-3 genotype, and two DEN-4 genotypes. There were significant differences in MIR and DIR for the different virus strains in both the D2S3 and the D2MEB mosquito lines.     

Flaviviruses can mediate fusion from without in Aedes albopictus mosquito cell cultures

Flavivirus-induced polykaryocytes were detected in monolayers of Aedes albopictus (clone C6/36) mosquito cells as early as 20 min after adsorbing virus to these cells. A high multiplicity of infection with dengue (DEN)-1, 2, 3, 4, Japanese encephalitis, and yellow fever viruses was required to demonstrate fusion from without (FFWO) with these flaviviruses. Optimal conditions for FFWO included exposure of adsorbed virus to pH 6.0 and an incubation temperature of 39 degrees C. DEN-2 monoclonal antibodies to the envelope E glycoprotein inhibited cell fusion, whereas monoclonal antibodies to the prM and NS1 proteins did not inhibit cell fusion. These results indicate that flaviviruses cause FFWO soon after adsorption to C6/36 mosquito cells and the process is most likely mediated by the virion envelope E glycoprotein.     

Vector competence of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) for dengue virus in the Florida Keys

In 2009-2011, Monroe County in southern Florida experienced locally acquired and traveler-imported focal dengue outbreaks. Aedes aegypti (L.) is the primary vector of dengue virus (DENV) worldwide, is prevalent in Monroe County, and is the suspected vector in Florida. Ae. albopictus (Skuse) is also known to be an important vector of DENV and this species is ubiquitous in Florida; however, it is not yet established in Monroe County. Florida Ae. aegypti (Key West and Stock Island geographic colonies) and Ae. albopictus (Vero Beach geographic colony) were fed blood containing 3.7 Log10 plaque-forming unit equivalents of DENV serotype 1 isolated from a patient involved in the Key West, FL, outbreak in 2010. Mosquitoes were maintained at extrinsic incubation temperatures of 28 or 30 degrees C for an incubation period of 14 d. Vector competence was assessed using rates of infection (percent with virus-positive bodies), dissemination (percent infected with virus-positive legs), and transmission (percent infected with virus-positive saliva). No significant differences were observed in rates of infection or dissemination between Ae. aegypti or Ae. albopictus at either extrinsic incubation temperature. Transmission was observed only at 28 degrees C in both Ae. aegypti (Key West) and Ae. albopictus. The assessment of local mosquito populations for their DENV vector competence is essential and will aid mosquito control operators interested in pinpointing specific vector populations for control. The extent to which vector competence is affected by seasonal changes in temperature is discussed and provides baseline risk assessment data to mosquito control agencies.     

Phylogenetic analysis of dengue-3 viruses prevalent in Guatemala during 1996-1998

Summary.  Dengue is an acute viral disease transmitted by the Aedesaegypti mosquito which is present in most tropical urban areas of the world. There are four antigenically distinct serotypes, designated dengue-1 (DEN-1), dengue-2 (DEN-2), dengue-3 (DEN-3) and dengue-4 virus (DEN-4). In this study, we determined the serotypes of dengue viruses isolated in Guatemala in 1995–1998, and found that DEN-3 viruses appeared in 1995 and became predominant in the following three years. We then sequenced cDNAs from fifteen DEN-3 isolates recovered during 1996–1998. From the nucleic acid sequences and previously determined DEN-3 sequences, a phylogenetic tree was constructed using the neighbor joining method. The tree indicated that all fifteen isolates and other DEN-3 viruses isolated in Sri Lanka, India, Samoa and Mozambique formed subtype III. More than two decades ago, DEN-3 virus was prevalent in the Caribbean, but the isolates obtained at that time belonged to subtype IV. Therefore, we concluded that the 1996–1998 dengue epidemic in Guatemala was caused by DEN-3 strains, imported from a tropical area of Asia or Africa or from a Pacific island. Received December 22, 2000 Accepted February 28, 2001     

Comparative potential of Aedes triseriatus, Aedes albopictus, and Aedes aegypti (Diptera: Culicidae) to transovarially transmit La Crosse virus

Aedes triseriatus (Say) (Diptera: Culicidae), the major vector of La Crosse (LAC) virus, efficiently transmits LAC virus both horizontally and transovarially. We compared the vector competence and transovarial transmission ability of Ae. triseriatus, Aedes albopictus Skuse, and Aedes aegypti (L.) for LAC virus. Ae. triseriatus and Ae. albopictus were significantly more susceptible to oral infection with LAC virus than Ae. aegypti. The three species also differed in oral and disseminated infection rates (DIRs). Transovarial transmission (TOT) rates and filial infection rates (FIRs) were greater for Ae. triseriatus than either Ae. albopictus or Ae. aegypti. These measures were integrated into a single numerical score, the transmission amplification potential (TAP) for each species. Differences in TAP scores were due mainly to the differences in DIRs and FIRs among these mosquitoes. Although the TAP score for Ae. albopictus was lower than that of Ae. triseriatus, it was 10-fold greater than that for Ae. aegypti.     

Oviposition responses of Aedes aegypti and Aedes albopictus to certain fatty acid esters

Laboratory studies were carried out to observe the oviposition responses of Aedes aegypti (L.) and Aedes albopictus (Skuse) to several C(21) fatty acid esters. The oviposition activity of these dengue and chikungunya vectors to the long-chain fatty acid esters of C(21) length have not been reported earlier. From the multiple choice experiments on oviposition activity in standard mosquito cages, it was observed that compounds hexadecyl pentanoate, tetradecyl heptanoate and tridecyl octanoate presented significant oviposition repellent activity against the two mosquito species, while one compound propyl octadecanoate was found to attract A. aegypti to the treated oviposition substrate at 1- and 10-ppm concentrations. The possible utilization of these esters in integrated vector management is discussed.     

Molecular and morphological characterization of Aedes albopictus in northwestern Greece and differentiation from Aedes cretinus and Aedes aegypti

The presence of Aedes albopictus (Skuse) was recently confirmed for the first time in northwestern Greece. This location is within the distribution range of a morphologically similar species, Aedes cretinus Edwards, and is a potentially favorable region for the reintroduction of Aedes aegypti (L.). It was thus compelling to use methods in addition to morphology-based keys to correctly identify specimens badly damaged, rubbed, or otherwise altered in their external characteristics. It was decided to use molecular techniques as a novel and reliable method for differentiating the three Stegomyia species. The nuclear internal transcribed spacer 2 (ITS2) fragments from morphologically identified Ae. albopictus and Ae. cretinus specimens were amplified, and their sequences were compared with those in GenBank for Ae. albopictus, Ae. cretinus, and Ae. aegypti. Also, mitochondrial cytochrome oxidase I (COI) fragments were amplified for Ae. albopictus and Ae. cretinus (so far not available in GenBank) and compared with Ae. aegypti fragments. ITS2 and COI sequences generated in our study were deposited in GenBank and could be useful in future studies of mosquitoes by other research workers.     

Complete genome sequence analysis of dengue virus type 2 isolated in Brunei

In a previous study, we have reported the detection and isolation of dengue virus in Brunei (Osman, O., Fong, M.Y., Devi, S., 2007. A preliminary study of dengue infection in Brunei. JJID 60 (4), 205-208). DEN-2 was the predominant serotype followed by DEN-1. The full genomic sequences of 3 DEN-2 viruses isolated during the 2005-2006 dengue incident in Brunei were determined. Twenty-five primer sets were designed to amplify contiguous overlapping fragments of approximately 500-600 base pairs spanning the entire sequence of the viral genome. The amplified PCR products were sent for sequencing and their nucleotides and the deduced amino acids were determined. All three DEN-2 virus isolated were clustered in the Cosmopolitan genotype of the DEN-2 classification by Twiddy et al. This work constitutes the first complete genetic characterization of three Brunei DEN-2 virus strains.     

Comparative laboratory study on the reaction of Aedes aegypti and Aedes albopictus to different attractive cues in a mosquito trap

The behavioral responses of Aedes aegypti (L.) and Aedes albopictus (Skuse) adults to several attractive cues, as reactions to mosquito traps, are compared in the laboratory, and differences in the primary attractive factors for both species are discussed. Target-attacking frequency of unfed Ae. aegypti females was >30 times that of unfed Ae. albopictus females under simulated conditions. Changes in the percentage of trapped mosquitoes under several attractive conditions using commercial mosquito traps showed that Ae. aegypti mosquitoes were trapped 2-3 times faster than Ae. albopictus. For Ae. aegypti, the combination of a visual cue + CO, alone enhanced attractiveness, whereas both a visual cue + CO, as well as a visual cue + octenol enhanced Ae. albopictus. The combination of at least three factors, such as a visual cue, CO2, and a chemical cue is thought to be valuable for trapping and estimating the relative adult population sizes of Ae. aegypti and Ae. albopictus