Studies on dengue in rural areas of Kurnool District, Andhra Pradesh, India

A dengue case was reported for the 1st time in a rural area of Kurnool District, Andhra Pradesh, India. Entomological and serological investigations were carried out to determine the prevalence of dengue vectors and dengue virus. Aedes aegypti was recorded for the 1st time in rural areas of Andhra Pradesh. Breeding of Ae. aegypti was observed only in containers with nonpotable water. Cement cisterns and tanks, stone tubs, and clay pots were the major breeding habitats of Ae. aegypti. Larval indices for Ae. aegypti ranged as follows: house index 28-40%, container index 13-37%, and Breteau index 32-60. A serological survey indicated that humans in Kurnool District have been exposed to dengue virus infections. The potential threat of an outbreak of dengue fever in rural areas because of the prevalence of the vector (Ae. aegypti) and dengue virus is discussed.     

中缅边境地区孟连和澜沧县登革热媒介蚊虫调查

目的了解中缅边境地区孟连和澜沧县登革热媒介种类、生态习性和登革热病毒自然感染状况,为登革热预防控制提供科学依据。方法在孟连和澜沧县选择3个自然村作为监测点,采用人工诱捕法白天诱捕成蚊,并在房屋内外积水容器捕捞幼虫,采用RTPCR方法对现场捕获的成蚊进行登革热病毒检测。结果 2010年6-10月在孟连和澜沧县监测点共捕获蚊虫6属8亚属22种3436只,其中白纹伊蚊为优势蚊种,占捕蚊总数的33.82%;未捕到埃及伊蚊。3个观察点白纹伊蚊平均房屋指数19.3,容器指数5.84,布雷图指数30.3,千人指数68.5;白纹伊蚊孳生环境类型以竹筒、土罐类和旧轮胎等临时积水容器为主,分别占阳性积水容器数的34.1%、27.5%和17.6%;白纹伊蚊成蚊平均密度为8.98只/人工小时;成蚊密度高峰出现在7-8月;对捕获的29批白纹伊蚊(1162只)进行RTPCR检测,未发现登革热病毒感染。结论白纹伊蚊密度较高且分布广泛,应加强当地登革热监测工作。     

埃及伊蚊监测

埃及伊蚊清除后，从１９９３年开始在旧发生区分别采用诱卵器诱测、面上定期检查及定期检查从疫区来的到港船只等３种方法进行系统监测。已查诱卵器２８２０个次，查出白纹伊蚊阳性容器８６８个次，容器指数为２６．３１；库蚊类阳性容器１１８个次，容器指数为４．１８。面上调查５１７４户次，检查积水容器１０５５６个次，查出白纹伊蚊７４０个次，容器指数为７．０１；库蚊类阳性容器５９６个次，容器指数为５．６５。检查到港船只７０４艘次，船上积水容器１８７５个次，未查出携带蚊子。３种监测方法均未查到埃及伊蚊。用诱卵器法查到的白纹伊蚊容器指数，比面上的调查高２．７５倍，两者在统计学上存在显著差异（Ｐ＝５．４５９．Ｐ０．５＝２．７７６，Ｐ０．０１＝８．６１）。目前对到港船只进行全面检查尚存在一定困难，故坚持在旧发生区布放诱卵器诱测及定期作好面上调查，就有可能及时发现新传入的埃及伊蚊，可作为目前埃及伊蚊监测的重要手段。     

Different spatial distribution of Aedes aegypti and Aedes albopictus along an urban-rural gradient and the relating environmental factors examined in three villages in northern Thailand

A larval survey of dengue vectors was conducted from July to November 1966 and from May to November 1997 in Chiangmai Province, Thailand. Three villages in urban, transition, and rural areas were selected for the survey to clarify the spatial distribution of Ae. aegypti and Ae. albopictus along an urban-rural ecological gradient. The average number of Ae. aegypti larvae in larvitraps was higher in the urban area than in the rural area, as we expected, whereas the opposite was found for Ae. albopictus, rural area > urban area. A house survey of larvae-inhabiting containers showed significant differences in the number and composition of these containers among the study areas. Significant differences were also found in the average distance between houses, average tree height, and average percentage of vegetation cover for each house. The seasonal pattern of rainfall recorded in each study area did not show great differences among the study areas. The response of Ae. aegypti and Ae. albopictus to the urban-rural gradient is discussed in relation to the possibility of applying geographic information system techniques to plan the control strategy and surveillance of dengue vectors.     

Subsoil drain sumps are a key container for Aedes aegypti in Cairns, Australia

The contribution of subterranean drain sumps to pupal and adult populations of Aedes aegypti is reported for the 1st time in Cairns, Australia. Pupal surveys were used to quantify the relative contribution of drain sumps to the total population of Ae. aegypti by concurrent survey of sump and water-bearing containers in yards of inner-city premises. A total of 854 mosquito pupae were collected, predominantly Ae. aegypti and Culex quinquefasciatus (26.3 and 69.8%, respectively). Drain sumps provided a relatively uncommon (n = 4) but productive source for pupal Ae. aegypti, producing 14.7% of the combined yard and drain sump population. Drain sumps in inner-city Cairns most commonly occurred in parking lots (52.6%). Subsequently, a sticky emergent adult trap (SEAT) was developed to provide a pragmatic method to assess production of Ae. aegypti by drain sumps. A total of 866 adult mosquitoes were trapped from 162 drain sumps over a 48-h exposure period, comprising Ae. aegypti and Cx. quinquefasciatus (21 and 79%, respectively). Advantages of the SEAT are an ability to rapidly count, identify, and sex mosquitoes and to provide specimens for molecular analysis where necessary. The treatment of water-bearing drain sumps is a critical element of control campaigns against Ae. aegypti.     

An inexpensive intervention for the control of larval Aedes aegypti assessed by an improved method of surveillance and analysis

A sampling method coupled with statistical calibration factors was developed to accurately assess the numbers of larvae and pupae of Aedes aegypti in large water-storage containers of variable capacities and water levels. Aedes aegypti productivity in different types of breeding sites found in an urban study area in central Colombia was assessed and compared. In this study, water-storage tanks and drums were found to comprise 79% of the containers positive for larval Ae. aegypti, which contributed to 93 and 92% of the total production of populations of 4th-stage larvae and pupae, respectively. These main breeding sites of Ae. aegypti were found at an indoor to outdoor ratio of 2.4:1 and no correlation was found between temporal fluctuation of populations of larval Ae. aegypti and monthly rainfall. Netted lids that used inexpensive local materials were designed to prevent oviposition by Ae. aegypti. During a 6-month trial period, 56% of inspected containers had netted lids correctly in place. Of these, 78% had no mosquito larvae. Because only 37% of uncovered containers were free of mosquito larvae, a significant difference was demonstrated when these inexpensive mechanical barriers were used (chi2 = 138.7; P < 0.001). These netted lids and the improved methods described to assess the productivity of larval and pupal Ae. aegypti in this study are now being used in combination with other strategies to assess and control these populations of dengue virus vectors in the main port city on the Atlantic Coast of Colombia.     

Use of a funnel trap for collecting immature Aedes aegypti and copepods from deep wells in Yogyakarta, Indonesia

During the course of a "dry" season dengue vector survey, indoor and outdoor household wells were sampled for the possible presence of immature mosquitoes and copepods. With a simple floating funnel trap, Aedes aegypti immature stages were captured in over 33% of the sampled wells (n = 93) during a 24-h trapping period per well. Average number of larvae (all instars) per positive well was 8.8 (range 1-63). Positive wells varied in depth from 2.7 to 14.7 m (8.8-48.2 ft), with a mean of 7.9 +/-SE 0.5 m in well rim to water surface. Only 4 wells (4.3%) contained Culex quinquefasciatus larvae. Only 1 of 31 infested wells contained both species. Aedes albopictus was not detected in any of the wells. Cyclopoid copepods were captured in 15% of the wells. No significant difference was found between positive and negative wells with regard to the physical characteristics (inside diameter, distance to water level) or the depth and volume of water held at the time of sampling. A significant association was found between wells positive for larvae and numbers of other positive containers in the vicinity of the wells. In general, wells containing copepods had fewer larvae present in the trap, possibly indicating some level of natural population regulation of Ae. aegypti occurring in the well; however, this association was not significant. Preliminary results indicate that wells in Yogyakarta serve as important permanent habitats for Ae. aegypti, especially during the dry season.     

长江流域白纹伊蚊刺叮活动节律及孳生情况调查

目的了解甘肃省长江流域地区登革热媒介白纹伊蚊刺叮活动节律及孳生情况。方法人诱法、电动吸蚊器、容器法、捕虫网捕捉成蚊。结果长江流域白纹伊蚊刺叮活动主要是在白天,以午后高峰为主,上午9时和午后13时各出现一个小高峰,下午18时达最高峰。密度为78只/人工小时。在不同生境调查各类积水容器431个,阳性容器80个,容器指数为18.56%。经观察甘肃省长江流域白纹伊蚊的交配没发现群舞现象。结论该地区白纹伊蚊密度较高,依据其活动节律及孳生情况,需采取综合防治措施,做好灭蚊防病工作。     

Integrated control of the dengue vector Aedes aegypti in Liu-Chiu village, Ping-Tung County, Taiwan

Because of an inadequate supply of potable water, villagers of Small Liu-Chiu Isle, Ping-Tung County, Taiwan, store water in containers supporting a large population of Aedes aegypti. In 1989-96, integrated control measures against Ae. aegypti were implemented on the basis of community participation. These measures included release of mosquito larvivorous fish in the drinking water storage facilities, application of larvicides to the water storage facilities in vegetable gardens, removal of discarded and unused containers and tires, improvement of household water storage facilities, and increase of potable water supply. Before implementation of the integrated control measures in 1988, 74% of the water-containing vessels were water storage facilities, and 24% of those were infested by Ae. aegypti. In 1989, the Breteau index for the entire island, indicating the average distribution density for larval Ae. aegypti, was 53.9, as compared to an index of 1.2 in 1996. In 4 villages located at the southwest and middle of the island, Ae. aegypti nearly became extinct because of the enthusiastic participation of the community. Before the implementation of integrated control, Ae. aegypti was the dominant species in containers both inside and outside the household, but after the integrated control, Aedes albopictus became predominant outside.     

Dengue emergence and adaptation to peridomestic mosquitoes

Phylogenetic evidence suggests that endemic and epidemic dengue viruses (DENV), transmitted among humans by the anthropophilic mosquitoes Aedes aegypti and Ae. albopictus, emerged when ancestral, sylvatic DENV transmitted among nonhuman primates by sylvatic Aedes mosquitoes adapted to these peridomestic vectors. We tested this hypothesis by retrospectively examining evidence for adaptation of epidemic and endemic versus sylvatic strains of DENV-2 to Ae. albopictus and Ae. aegypti. First and second-generation offspring of mosquitoes from different geographic regions in the Americas and Southeast Asia were tested for their susceptibility to epidemic/endemic and sylvatic DENV-2 isolates from West Africa, Southeast Asia, and Oceania. Both Aedes species were highly susceptible (up to 100% infected) to endemic/epidemic DENV-2 strains after ingesting artificial blood meals but significantly less susceptible (as low as 0%) to sylvatic DENV-2 strains. Our findings support the hypothesis that adaptation to peridomestic mosquito vectors mediated dengue emergence from sylvatic progenitor viruses.     

An evaluation of some Trinidadian plant extracts against larvae of Aedes aegypti mosquitoes

In recent times, bioprospecting for plants that show bioactive properties has yielded many chemicals that can be used in controlling mosquitoes. Crude extracts of 4 terrestrial and 3 mangrove plants were assayed against 2-3 larval instars of Aedes aegypti. Among the plants tested, Cordia curassavica showed the highest levels of activity for all the extracts tested. Azadirachta indica showed the least activity, whereas the 2 cultivars of Mangifera indica showed substantial activity for the aqueous extracts. The mangrove species proved to be relatively nontoxic to Ae. aegypti larvae when compared to the terrestrial plants. The results of this study suggest that some common plants in Trinidad may be highly effective in controlling the urban vector of yellow fever and dengue fever, Ae. aegypti.     

Surveillance and behavioral investigations of Aedes aegypti and Aedes polynesiensis in Moorea, French Polynesia, using a sticky ovitrap

The effectiveness of the sticky ovitrap was assessed for the container-breeding Aedes aegypti and Aedes polynesiensis in Moorea, French Polynesia. These mosquitoes are the primary vectors of dengue viruses and Bancroftian filariasis, respectively, in the area. Both Ae. aegypti and Ae. polynesiensis were collected in greatest numbers in sticky ovitraps baited with water or grass infusions rather than leaf infusions. Sticky ovitrap collections were significantly higher for both species in the 12 h post-midday than pre-midday and in traps set in shaded compared with open locations. More females of Ae. aegypti were collected in ovitraps at west-facing walls, although Ae. polynesiensis collected at east- or west-facing traps did not differ in number. Female Ae. aegypti (bloodfed, marked, and released for oviposition) were readily recaptured (19-26%) by sticky ovitraps, exhibiting movement of up to 30 m, and between outdoor and indoor situations. Overall, the sticky ovitrap proved an effective tool for investigating the oviposition behavior and dispersal of these container-breeding species.     

海口市登革热媒介分布与控制的研究

目的掌握登革热媒介的地理分布、孳生习性和季节消长情况，科学合理、有的放矢地投入卫生资源，在存在埃及伊蚊的主要地区开展媒介控制工作，预防和控制登革热的发生或流行。方法采用整群随机抽样方法，对全市24个乡镇、5个街道办事处和4个农场的1522个村（居委会）运用蚊幼虫调查法开展登革热媒介——埃及伊蚊和白纹伊蚊孳生地调查，掌握其地理分布、季节消长及密度，并与以往监测资料相比较，明确登革热媒介的地理分布、变迁和季节消长规律；在埃及伊蚊密度较高的6个乡镇采用“社区参与、健康教育、环境制约”的“儋州模式”开展以消灭媒介孳生地为主要措施的媒介控制工作。结果（1）调查的各乡镇、街道办事处和农场均有白纹伊蚊分布，阳性率为100％，自然村（居委会）阳性率为87．84％；埃及伊蚊分布在16个乡镇和2个农场，阳性率为54．54％，自然村（居委会）阳性率为32．46％；（2）埃及伊蚊幼虫全年均存在，密度高峰在5—11月，12月开始下降，12月至次年3月处于较低水平，4月开始上升；（3）埃及伊蚊布雷图指数从52．5降至34．4，控制效果明显，前后比较差异有统计学意义（χ^2=832．18，P〈0．005）。结论海口市仍广泛存在登革热流行的自然环境，通过媒介控制能有效降低蚊虫密度，从而阻断登革热的传播，而且媒介分布调查对科学合理、有的放矢投入或使用卫生资源，防控登革热具有十分重要的意义。     

云南省瑞丽市2013年登革热暴发的流行病学分析

目的分析云南省瑞丽市2013年登革热暴发疫情的流行病学特征,为登革热控制提供依据。方法对所有登革热病例进行流行病学个案调查,采用登革热病毒NS1抗原法检测病例血清标本,采用布雷图指数法进行蚊媒密度监测。结果本次疫情流行历时104 d,共确诊病例232例,其中本地感染145例,缅甸输入87例。流行季节为8-11月,病例主要集中在瑞丽市城区（124/232,53.45%）;男女性别比为1.23∶1,发病年龄最小1岁,最大80岁,以20~49岁年龄组为主;职业分布以商业服务、农民和家务及待业者居多。结论此次疫情为瑞丽市首次发生登革热本地流行;采取伊蚊综合控制措施,布雷图指数≤5.0,疫情可得到有效控制。     

Pupal surveys for Aedes aegypti surveillance and potential targeted control in residential areas of Mérida, México

A mosquito larval-pupal survey was conducted in 1,160 households of the Mexican city of Mérida during the rainy season of 2003 to determine their differential productivity for Aedes aegypti. Larvae and pupae were detected in 15 broad categories of container types. All breeding sites were found in the patios (backyards) and were potentially rain filled. Ae. aegypti pupae were produced from all categories of breeding site, and no single container type was predominately responsible for pupal production. The most productive buckets comprised 42% of the pupae-positive containers and provided 34% of the total pupae collected. Pupal production in buckets, together with plastic rubbish, pet dishes and basins, utensils for cooking and washing, tires, and flowerpots, accounted for almost 87% of pupal production. However, the most important pupal producers had low infestation indices for immature forms, illustrating that the use of positive-container indices can underestimate the importance of certain breeding sites. Overall, 40% of containers that were observed harboring Ae. aegypti pupae were classified as disposable. The remaining containers were considered useful, although some were seldom used. The discussion focuses on the potential utility of the pupal survey for targeting control, and its resulting pupae-per-person entomological indicator, both for comparison with a theoretical threshold for dengue transmission and for targeting vector control in this Mexican city.     

Investigation of relationships between Aedes aegypti egg, larvae, pupae, and adult density indices where their main breeding sites were located indoors

Aedes aegypti (L.) density indices obtained in a dengue fever (DF) endemic area were compared. One hundred and twenty premises, in an urban area of Colombia where dengue type-1 and type-2 virus cocirculated, were randomly selected and sampled for 7 months. The geometric mean monthly numbers (density index, DI) of Ae. aegypti eggs (ODI), 4th instar larvae (LDI), pupae (PDI), and adults (ADI) were calculated based on the use of ovitraps, nets, and manual aspirators, respectively. A negative temporal correlation was observed between the LDI and the ODI (r = -0.83, df = 5, and P < 0.01). Positive temporal correlations were only observed between the LDI and the PDI (r = 0.90, df = 5, and P < 00.5) and the Breteau and House indices (r = 0.86, df = 5, and P < 0.01). No other correlations were found between these indices and any of the other density indices or the incidence of suspected DF cases in residents, the temperature, the rainfall, or seasonal fluctuations. Our results were, therefore, probably due to the most productive Ae. aegypti breeding sites (large water containers) being located indoors within this study area. The number of adult female Ae. aegypti/person (n = 0.5) and pupae/person (n = 11) in our study area were lower and dramatically higher than the transmission thresholds previously reported for adult and pupae, respectively. Because there were confirmed DF cases during the study period, the transmission threshold based on the Ae. aegypti pupae was clearly more reliable. We found that the mean ovitrap premise index (OPI) was 98.2% during this study and that the mean larval (L-4th instars) premise index (LPI) was 59.2%, and therefore we suggest that the OPI and LPI would be more sensitive methods to gauge the effectiveness of A. aegypti control programs.     

Aedes albopictus may not be vector of dengue virus in human epidemics in Brazil

Over 60,500 dengue cases were reported in the state of Espírito Santo (ES), Brazil, between 1995 and 1998. The study's purpose was to identify whether Aedes albopictus was transmitting the dengue virus during an epidemic in the locality of Vila Beth nia (Viana County),Vitória, ES. From April 3 to 9, 1998, blood and serum samples were collected daily for virus isolation and serological testing. Four autochthonous cases were confirmed through DEN 1 virus isolation and two autochthonous cases through MAC ELISA testing. Of 37 Ae. aegypti and 200 Ae. albopictus adult mosquitoes collected and inoculated, DEN1 virus was isolated only from a pool of two Ae. aegypti female mosquitoes. The study results suggest that Ae. albopictus still cannot be considered an inter-human vector in dengue epidemics in Brazil.     

Evaluation of surveillance devices for monitoring Aedes aegypti in an urban area of northeastern Peru

In this study, we assessed the efficacy of the American Biophysics Corporation Standard Professional (ABC-PRO) light trap, the Omni-Directional Fay-Prince trap (with and without CO2), and the Centers for Disease Control and Prevention Wilton trap as a means of evaluating populations of adult Aedes aegypti in an urban area of northeastern Peru. Efficacies of collections from each of the trap types were compared to backpack-aspirator collections and human-landing collections. Collections were conducted twice daily, 3 days per week, for 27 wk from July 2001 to July 2002. Backpack-aspirator collections yielded significantly more mosquitoes (1,764) than any of the other collecting methods with a mean of 21.80 mosquitoes collected per sampling period. This method was less specific for Ae. aegypti than were human-landing collections because only 28.3% of mosquitoes collected with backpack aspirators were Ae. aegypti. Human-landing collections yielded only 23% (554/2,411) of the total mosquitoes collected. However, more than 80% (445/554) of the mosquitoes collected by this method were Ae. aegypti. None of the trapping devices evaluated collected mosquitoes, specifically Ae. aegypti, as effectively as backpack-aspirator or human-landing collections. The ABC-PRO trap, which was the most effective device in collecting mosquitoes, particularly Ae. aegypti, collected less than 2% of the total mosquitoes (mean of 0.12 mosquitoes/sampling period), and less than 3% of total Ae. aegypti (mean of 0.11 Ae. aegypti/sampling period). We conclude that none of the trap devices evaluated in this study is an acceptable alternative to backpack-aspirator or human-landing collections for monitoring populations of adult Ae. aegypti in Peru.     

A biodegradable lethal ovitrap for control of container-breeding Aedes

Lethal ovitraps (LO) have been successfully deployed in dengue control operations in north Queensland, Australia since 2004. However, the current plastic-bucket LO must be retrieved before the pesticide-treated strip degrades and the trap begins producing mosquitoes. The logistics involved with trap retrieval are considerable and include recording trap location and retrieval date onto a database, locating and retrieving each trap, and examining lethal ovitraps for eggs. Collectively, these necessary activities greatly reduce the efficiency of dengue control. In response, we have developed a biodegradable lethal ovitrap (BLO) that does not need to be retrieved for the control of container-breeding Aedes, particularly Aedes aegypti. The BLOs were made by injection molding with the use of 2 proprietary blends of thermoplastic starch (TPS) polymer based on plasticised amylose maize polymers. In field trials, Ae. aegypti readily oviposited in BLOs, with those dyed black with the use of carbon black preferred. Water loss was higher in BLOs than in standard plastic LO because of weeping from the walls, although none of the BLOs failed in the 5 wk of the trial. The occurrence and rate of Ae. aegypti oviposition in both BLOs and the LO was comparable. In an accelerated standard composting trial (ISO16929:2002E), both BLOs fragmented within 4 wk, and no BLO particles were visible after 12 wk. Large numbers of BLOs could be deployed in a "set it and forget it" strategy to control Ae. aegypti and to stop dengue transmission, and could be used in a community participation program to maximize coverage.