Surveillance for the dengue vector Aedes aegypti in Tobago, West Indies

An island-wide house survey was conducted in January 2002 to determine the geographic distribution, container profile, and population density of the Aedes aegypti in Tobago, West Indies. The results showed the Ae. aegypti infestation levels were significantly different (P > 0.01) among the 4 districts, with greater infestation levels (P > 0.01) observed in the Northern and Windward districts than in the Central and Leeward districts. From the 50 towns in Tobago, houses were found positive in Delaford (21), Argyle (18), and Goodwood (14). representing 42.1% of the total number of positive houses in the Windward district (3,971 houses); Parlatuvier (15), Whim (14), Castara (12), and Bloody Bay (12), representing 62.3% of the total number of positive houses in the Northern district (3,087 houses); Calderhall (12), Mason Hall (11), and Government House (10), representing 46.5% of the total number of positive houses in the Central district (4,706 houses); and Lambeau (10), Bucco (6), and Bethel (6), representing 53.7% of the total number of positive houses in the Leeward district (3,175 houses). The majority (66 or 63.5%) of dengue cases occurred in the Central district where the Breteau indices ranged from 7.1 to 44.0 (mean = 16.6). These results suggest that a more systematic and sustained vector control program that uses both biological and chemical control methods should be adopted to reduce Ae. aegypti populations to below dengue transmission thresholds.     

我国登革热重要媒介埃及伊蚊的研究进展

登革热是经蚊虫叮咬人体传播的重要传染病,广泛流行于热带和亚热带地区。埃及伊蚊是登革热病毒的主要媒介,随着全球气候变暖,旅游业及交通业的迅速发展,该蚊在我国的分布发生了区域上的变化;长期的蚊虫控制措施,引起了一些生态习性的改变;通过对埃及伊蚊及登革热病毒传播关系的研究表明,垂直传播和水平传播方式是该蚊保存登革热病毒的重要方式,该蚊对登革热病毒高度易感和带病毒率较高。现就埃及伊蚊在我国的地理分布、生态习性及与登革热传播关系的研究做一综述。     

Genetic structure and phylogeography of Aedes aegypti, the dengue and yellow-fever mosquito vector in Bolivia

Between the 16th and 18th centuries, Aedes aegypti (Diptera: Culicidae), a mosquito native to Africa, invaded the Americas, where it was successively responsible for the emergence of yellow fever (YF) and dengue (DEN). The species was eradicated from numerous American countries in the mid-20th century, but re-invaded them in the 1970s and 1980s. Little is known about the precise identities of Ae. aegypti populations which successively thrived in South America, or their relation with the epidemiological changes in patterns of YF and DEN. We examined these questions in Bolivia, where Ae. aegypti, eradicated in 1943, re-appeared in the 1980s. We assessed the genetic variability and population genetics of Ae. aegypti samples in order to deduce their genetic structure and likely geographic origin. Using a 21-population set covering Bolivia, we analyzed the polymorphism at nine microsatellite loci and in two mitochondrial DNA regions (COI and ND4). Microsatellite markers revealed a significant genetic structure among geographic populations (F(ST)=0.0627, P<0.0001) in relation with the recent re-expansion of Ae. aegypti in Bolivia. Analysis of mtDNA sequences revealed the existence of two genetic lineages, one dominant lineage recovered throughout Bolivia, and the second restricted to rural localities in South Bolivia. Phylogenic analysis indicated that this minority lineage was related to West African Ae. aegypti specimens. In conclusion, our results suggested a temporal succession of Ae. aegypti populations in Bolivia, that potentially impacted the epidemiology of dengue and yellow fever.     

慈溪市登革热媒介白纹伊蚊综合防治措施的研究

目的评价2004—2005年慈溪市登革热媒介综合性防治的效果。方法综合防治清除蚊虫孳生地,灭蚊以白纹伊蚊密度指数考核灭效。结果2004年疫区的白纹伊蚊幼虫房屋指数、容器指数和布雷图指数分别下降了96．6％、92．5％和99．0％,疫情得到了控制。2005年疫区白纹伊蚊幼虫房屋指数、容器指数和布雷图指数分别为4．1、5．2和4．5,全年无新发病例。结论采取清除蚊虫孳生地为主的综合性防治措施,可迅速有效地遏制登革热的发生或流行。     

Experimental infection of Aedes aegypti and Aedes albopictus with dengue viruses

The susceptibility of two Aedes (Stegomyia) species, Ae. aegypti and Ae. albopictus, to infection with dengue virus was assessed using both natural feeding on a viraemic gibbon and a membrane feeding technique. Both species were highly susceptible to dengue virus infection.     

Fructose variation in the dengue vector, Aedes aegypti, during high and low transmission seasons in the Mae Sot region of Thailand

To understand the potential for facultative sugar feeding by Aedes aegypti, an important vector of dengue viruses, we evaluated seasonal and villagewide variation in sugar feeding during high- and low-dengue transmission seasons (rainy and dry seasons, respectively) in the Mae Sot region of Thailand. These seasons in Thailand are represented by different periods of flowering plant phenology. Although overall sugar feeding among female and male mosquitoes was low (ranging from 0.60 to 7.53 microg fructose per mosquito), sugar feeding among females was significantly greater during the dry, low-dengue transmission season. This variation could reflect specific preferences for flowering plants that were abundant in and around village homes during the dry season, such as Bougainvillea, Hibiscus, and Euphorbia.     

Emergency control of Aedes aegypti as a disease vector in urban areas.

Techniques for the emergency control of adult Aedes aegypti populations and their development are reviewed. Larviciding and environmental measures provide only delayed control of adult populations. Large-scale field trials of the ultra-low volume application of insecticide concentrates in Southeast Asia, South America and Africa, using aerial, ground, vehicle-mounted and hand-carried equipment, have, in most cases, resulted in satisfactory levels of control of adult populations. Sequential or indoor ULV applications of fenitrothion have provided immediate control and sustained reduction of the adult populations, often lasting well through normal peak transmission periods of dengue. Many ULV application trials in the Caribbean have not produced satisfactory control, but it is considered that this was due to the type of house construction, to the lower dosage rates of the malathion 96% ULV concentrates used, or to inappropriate droplet sizes. While ULV applications can provide rapid and effective emergency control of vectors at the time of outbreaks of disease in urban and periurban areas, they should not be used as a routine mosquito control measure nor as an alternative to reducing vector populations by environmental measures.     

Simulation modelling of Aedes aegypti prevalence,an environmental hazard surveillance tool for the control of dengue epidemics

We performed a five-year simulation of Aedes aegypti population dynamics in Townsville, Queensland to better understand local Ae. aegypti ecology and thus improve the potential effectiveness of interventions aimed at dengue control. Using the Container Inhabiting Mosquito Simulation Model (CIMSiM), public health interventions can use a wealth of environmental knowledge about Ae. aegypti, a disease vector hazard, towards its surveillance. We conducted larval surveys to initialise the simulation of Ae. aegypti prevalence and parameterise Townsville's artificial container habitats. Our simulations indicate (1) a seasonal, but stable Ae. aegypti prevalence, (2) the importance of bromeliads, striking vases, pot plant bases and car tire containers as breeding sources and (3) the potential effectiveness of breeding container source reduction and pesticide space spraying. Although it is unlikely that simulation modelling will ever be used to forecast impending dengue epidemics, the limitations of modelling do not preclude their role in environmental health programs aimed at improving the effectiveness of available interventions.     

Genetic diversity of the dengue vector Aedes aegypti in Australia and implications for future surveillance and mainland incursion monitoring

In February 2004, the discovery of an incursion of the dengue vector Aedes aegypti into the town of Tennant Creek in the Northern Territory caused concern for the Northern Territory health authorities who proceeded to implement a Commonwealth-funded eradication program. To determine the origin of the incursion, we performed a genetic analysis on Ae. aegypti from several Queensland and overseas localities. A comparison of DNA sequences from the mitochondrial cytochrome oxidase 1 gene indicated that the incursion was probably from Cairns or Camooweal. This genetic marker was also useful in identifying a separate Townsville haplotype population and another population on Thursday Island in the Torres Strait that was genetically divergent to the mainland populations. The possible use of this marker as a surveillance tool for identifying the origins of local and overseas incursions is discussed.     

Infection and dissemination of dengue virus type 2 in Aedes aegypti, Aedes albopictus, and Aedes scutellaris from the Torres Strait, Australia

To determine their relative roles in transmission of dengue virus (DENV) in the Torres Strait region of northern Australia, we examined infection and dissemination of a sympatric strain of dengue virus type 2 (DENV-2) in Aedes scutellaris, Ae. albopictus, and Ae. aegypti. In experiments using membrane feeders for virus exposure, infection rates were 83% and 43% for Ae. scutellaris and Ae. aegypti, respectively. Salivary gland infection rates for both species were 43%. In experiments using pledgets for virus exposure, infection rates for Ae. aegypti, Ae. scutellaris, and Ae. albopictus were 68%, 55%, and 37%, respectively. Aedes albopictus exhibited the greatest barriers to infection with only 7% tested developing a salivary gland infection, compared to 42% and 24% of Ae. aegypti and Ae. scutellaris, respectively. These results suggest that Ae. scutellaris may have been responsible for DENV transmission on Torres Strait islands, where Ae. aegypti does not occur. In contrast, Ae. albopictus may not be an important vector of DENV-2 from the Torres Strait.     

Aedes aegypti infestation and occurrence of dengue in the city of Belo Horizonte, Brazil

OBJECTIVE: To assess the association between the proportion of buildings positive for Aedes aegypti larvae measured by means of building infestation rate and dengue incidence rate. METHODS: Autochthonous dengue cases were selected and building infestation rates assessed in the coverage areas of health districts in the city of Belo Horizonte, Brazil, from October 1997 to May 2001. After grouping building infestation rates according to their distribution in quartiles, mean dengue incidence rates (for the month following the building infestation assessment) were compared using ANOVA. RESULTS: A weak though statistically significant correlation was observed between monthly dengue incidence and building infestation rates for the health districts (r=0.21; p=0.02) and coverage areas (r=0.14; p=0.00) in the study period. After grouping building infestation rates in quartiles, coverage areas of building infestation between 0.46% and 1.32% (second quartile) showed a mean monthly dengue incidence rate twice as high as areas of building infestation lower or equal to 0.45% (first quartile). Areas of building infestation between 1.33% and 2.76% (third quartile) and equal to or higher than 2.77% had a mean monthly dengue incidence rate five and seven times, respectively, higher than those areas showing 0.45% or less. CONCLUSIONS: Despite the well-known limitations of building infestation rates for estimating vector infestation and prediction of dengue epidemics, the study results indicate that higher building infestation rates were associated to a higher risk of disease transmission in the health districts and coverage areas of Belo Horizonte.     

2020年湖南省登革热媒介伊蚊监测结果分析

目的了解湖南省登革热媒介伊蚊种群、季节消长规律及抗药性情况,为本省登革热防控提供依据。方法2020年在全省设立6个监测点,4—10月份每月监测媒介伊蚊幼虫和成蚊种群、密度,采集伊蚊幼虫进行抗药性测定。幼虫密度监测采用布雷图指数法和诱蚊诱卵器法,成蚊采用双层叠帐法,抗药性监测幼虫采用浸渍法,成蚊采用接触筒法。结果布雷图指数法共调查25200户,布雷图指数为10.08,其中城镇居民区为11.06,农村居民区为9.10。7月份到达高峰为19.42,10月份最低为3.22。全年共布放25100个诱蚊诱卵器,诱蚊诱卵指数为6.31,其中城镇居民区为7.98,农村居民区为4.67。7月份到达高峰,诱蚊诱卵指数为15.56,4月份最低为0.16。成蚊监测共布放1008帐次,捕获白纹伊蚊590只,总帐诱指数为1.17只/顶·h。其中公园/竹林帐诱指数最高为1.60只/顶·h,城镇居民区次之为1.49只/顶·h。全年密度高峰在7月份为2.39只/顶·h,最低在4月份0.03只/顶·h。抗药性监测显示,六个监测点的成蚊对所提供的拟除虫菊酯类杀虫剂均产生了不同程度的抗性,对两种氨基甲酸酯类杀虫剂均敏感。各监测点幼虫对所提供的三种杀虫剂的抗药性水平主要为敏感或低抗。结论本省登革热的传播媒介为白纹伊蚊,在全省广泛分布且夏秋季节密度较高。一旦有输入性病例,可造成本地暴发和流行的风险。采取以孳生地治理为主的综合治理措施,科学防蚊灭蚊,是防控登革热的根本措施。     

Malathion resistance in Aedes aegypti and Culex quinquefasciatus after its use in Aedes aegypti control programs

The continued widespread use of malathion in Aedes aegypti control programs in Latin America has generated insecticide resistance to this chemical in Culex quinquefasciatus but not in Ae. aegypti. To determine the extent of this resistance, the susceptibility of Cx. quinquefasciatus and Ae. aegypti from several countries to malathion was evaluated. Bioassay results indicated that all Ae. aegypti strains evaluated from Cuba, Venezuela, Costa Rica, and Jamaica were susceptible to malathion in spite of the historical use of this insecticide in Ae. aegypti control programs in these countries. In contrast, a high level of resistance to this insecticide was found in Cx. quinquefasciatus from Venezuela, Colombia, Brazil, and Cuba. Synergist assays indicated that neither esterases nor mixed-function oxidases (MFOs) were involved as the resistance mechanism to malathion in any of the Ae. aegypti strains tested. In Cx. quinquefasciatus, synergist assays confirmed that esterases played an important role in malathion resistance but MFOs were not involved in causing malathion resistance in this species. Biochemical assays showed that both resistance mechanisms were present in the Ae. aegypti and Cx. quinquefasciatus populations. Acrylamide electrophoresis gels revealed that all Ae. aegypti strains had a strongly staining, clear band, named A4, and had a relative mobility (Rm) value of 0.7. Analysis if the results of this study suggested that malathion could continue to be used for the emergency control of Ae. aegypti, the mosquito vector for dengue and dengue hemorrhagic fever in the Americas, but that malathion is probably not effective for the control of adult Cx. quinquefasciatus in urban areas. Therefore, control operations should integrate nonorganophosphate insecticides such as pyrethroids for control of these 2 species found in the urban environment.     

Space treatments of insecticide for control of dengue virus vector Aedes aegypti in southern Mexico. I. Baseline penetration trials in open field and houses

We studied the efficacy of space ultra-low volume treatments of 3 insecticides for the control of the dengue virus vector Aedes aegypti in southern Mexico. Insecticides tested were permethrin (Aqua-Reslin Super), d-phenothrin (Anvil), and cyfluthrin (Solfac), applied at rates of 10.87, 7.68, and 2 g/ha, respectively, by using London Fog, HP910-PHXL, or Micro-Gen pumps mounted on vehicles. Studies included 1) open field penetration tests and 2) house penetration tests. Open field tests indicated that Anvil and Solfac were more effective than Aqua-Reslin Super. In house tests, Anvil yielded the highest mosquito mortalities (>/=88%) of the three insecticides in the front porch, living room, bedroom, and backyard. Therefore, Anvil proved to be better than other insecticides evaluated to control Ae. aegypti in Chiapas, Mexico.     

浙江省登革热传播媒介白纹伊蚊调查研究

目的对浙江省白纹伊蚊分布区进行调查,掌握登革热传播媒介白纹伊蚊季节性动态变化规律。方法主要采用人工小时法,对不同地理环境中的室内成蚊进行调查研究。结果白纹伊蚊是湖州地区主要优势种,占总量的52.9%,5~6月为活动高峰。嘉兴地区的白纹伊蚊为当地亚优势种,所占比例为24.2%,6~9月为密度高峰。宁波、舟山、温州以及衢州白纹伊蚊活动高峰集中在8月。结论白纹伊蚊在我省广泛分布,应进一步加强白纹伊蚊监测工作,并采取有效综合控制措施,将其种群密度控制在经济阈值范围之内。