Thực trạng véc tơ sốt xuất huyết dengue, mối tương quan giữa khí hậu với chỉ số véc tơ và số mắc sốt xuất huyết dengue tại 4 tỉnh miền bắc việt nam (2016 2017) tt tiếng anh

1 INTRODUCTION Dengue hemorrhagic fever (DHF) is an extremely dangerous acute infection caused by Aedes mosquitoes, which can be massively lethal if a major pandemic occurs An estimate of 500,000 people with severe dengue infection require hospitalization each year, and about 2.5% of the cases die of the disease There hasn’t been specific treatment for dengue fever, and vaccines are in the clinical trial stage so vector control is very important for disease prevention In Vietnam, although there have been many efforts in active prevention and control, dengue epidemics tend to increase and expand its scope The annual average number of cases is still very high, about 70,000 - 100,000 with hundreds of deaths In the world, there have been many studies on the dengue transmission role of dengue virus, as well as determination of the affinity of dengue virus against Aedes aegypti and Aedes albopictus In Vietnam, few studies on this matter have been raised; moreover Ae.aegypti and Ae.albopictus have different biological, ecological and behavioral characteristics What is the correlation between climatic factors and the transmission of dengue fever? Because of the above reasons, we conducted the study: “Current situation of dengue vectors, the correlation between climate, vector indices and dengue cases in northern provinces of Vietnam (2016 - 2017)” with the following objectives: Describe the distribution, resting habits, dengue transmission role and insecticide susceptibility of Ae.aegypti and Ae.albopictus in Hanoi, Hai Phong, Thanh Hoa and Ha Tinh, 2016 - 2017 Analyze the correlation between climatic factors, vector indices, and dengue cases in Hanoi, 2016 - 2017 NOVELTY, SCIENTIFIC AND PRACTICAL SIGNIFICANCE OF THE THESIS The study has identified Ae aegypti as a dengue transmission agentive, specifically discovered Ae.albopictus at the dengue outbreak in Vietnam 2 The study has identified the correlation between climatic factors, vector indices, and dengue prevalence in Hanoi, especially the close relation between average monthly temperature, entomology indices and the number of cases This is useful information for forecasting the development direction of dengue THESIS STRUCTURE The thesis consists of 124 pages divided into the following sections: Introduction (02 pages), literature review (32 pages), study subjects and methods (20 pages), study results (36 pages), discussions (32 pages), conclusions (02 pages), and recommendations (1 page) There are 41 tables, 11 figures, and 117 references CHAPTER LITERATURE REVIEW 1.1 Situation of dengue fever 1.1.1 Situation of dengue fever in the world The first outbreak of dengue fever was recorded with a clear causative agent in Australia in 1897, followed by Greece in 1928 and Taiwan in 1931 Today, dengue outbreaks occur in more than 100 countries in different territories from Africa, America, the Middle East, Southeast Asia to the Western Pacific, in which America, Southeast Asia and the Western Pacific are the most infected 1.1.2 Situation of dengue fever in Vietnam First dengue outbreaks were recorded in Northern Vietnam in 1958 and in the Mekong Delta in Southern Vietnam in early 1960s The situation of dengue fever in the last years (2015 - 2017) has increased sharply both in the number and expansion Especially, dengue no longer occurs in cities and plains but has spread to highland and mountainous areas In 2017, dengue outbreaks bloomed in many provinces and cities nationwide, with a focus on Hanoi and Ho Chi Minh City 3 1.1.3 Situation of dengue fever at study sites 1.1.3.1 Situation of dengue fever in Hanoi In the past 20 years, Hanoi has witnessed many big dengue outbreaks such as in 1998 with the main cause is dengue virus In 2009, the number of cases across the North was 18,485 cases, in which there were 16,090 cases and deaths recorded in Hanoi, accounting for 87% In 2015, Hanoi had 15,412 cases In 2017, dengue occurred throughout the city with 37,651 cases and deaths 1.1.3.2 Situation of dengue fever in Hai Phong Through surveillance, Hai Phong had 113 cases in 2015, cases in 2016, and a sharp increase of 431 cases in 2017 1.1.3.3 Situation of dengue fever in Thanh Hoa The situation of dengue fever in Thanh Hoa increased sharply with 171 cases recorded in 2016 and 3,374 cases in 2017 1.1.3.4 Situation of dengue fever in Ha Tinh The total number of dengue fever cases in 2016 was 39 with deaths, which decreased by 33.8% compared to the same period in 2015 In 2017, there were 194 cases and deaths 1.2 Causative agent of dengue fever Dengue fever is an acute infectious disease caused by Dengue virus The disease can progress to cause death Dengue virus includes types: Dengue (D1), Dengue (D2), Dengue (D3) and Dengue (D4) 1.3 Life cycle and morphology of Aedes mosquitoes 1.3.1 Life cycle of Aedes The life cycle of Aedes includes stages: Eggs - Larvae Pupae - Adult mosquitoes, in which the first stages live in water, only adult mosquitoes live on land 1.3.2 Morphological characteristics of Aedes 1.3.2.1 Aedes eggs The eggs of Aedes mosquitoes are under 1mm, oval in shape, white at birth and then turning dark black 1.3.2.2 Aedes larvae The eighth abdominal segment of Aedes larvae is devoid of any chitinous plates The comb scales of the eighth abdominal segment form a line, with middle and lateral spines for Ae aegypti and without lateral spines for Ae albopictus 4 1.3.2.3 Aedes pupae Aedes pupae are shaped like a large question mark similar to other mosquito larvae 1.3.2.4 Aedes adults Aedes adults are easy to identify with distinct black and white compartments in legs and abdomens, and silvery scales on bodies concentrated in clusters or lines 1.4 Distribution and habits of Aedes 1.4.1 Distribution of Aedes 1.4.1.1 Distribution of Ae aegypti and Ae albopictus in the world In the first half of the 20th century, Ae aegypti was mostly found in tropical and subtropical regions between latitude 450 North and latitude 340 South across Asia, America and Africa Ae aegypti is widely distributed in South and Central America Ae albopictus is currently classified as the most invasive mosquito species and they are distributed on many continents: Asia, America, Europe and Africa This species is widely distributed in the tropics and subtropics of continents mainly located from 350 north latitude to 350 south latitude and to 450 north latitude limited by the 100C isotherm 1.4.1.2 Distribution of Aedes aegypti and Aedes albopictus in Vietnam Ae aegypti is found in most cities, towns, rural areas and even in mountainous and highland areas Ae albopictus is commonly found in the Northern region In recent years, it is also found in the South, Central region and Central Highlands 1.4.2 Habits of Aedes 1.4.2.1 Resting habits Ae aegypti has indoor resting habits Meanwhile, Ae albopictus mainly lives outdoors, hiding under shrubs near or away from houses 1.4.2.2 Biting habits Ae aegypti is usually collected in daytime 5 1.4.2.3 Oviposition habits Domestic studies have shown that Ae aegypti larvae were found in artificial water containers in and around houses Ae albopictus often lays eggs in clean natural water 1.5 Disease transmission role of Ae aegypti and Ae albopictus 1.5.1 Disease transmission role of Aedes in the world Studies have shown that the percentage of Ae Aegypti caught at study sites and location of dengue outbreaks that was positive for Dengue virus ranged from 1.33% to 12.7% For Ae albopictus, this rate was from 2.9% to 11.76% 1.5.2 Disease transmission role of Aedes in Vietnam The study on dengue outbreaks by Vu Sinh Nam (1995) showed that all active dengue outbreaks contained Ae Aegypti; few outbreaks had both species, including a very small percentage of Ae albopictus Tran Van Tien (2003) showed that Ae albopictus was widely present in many localities and different populated areas, especially in suburban areas covered with many green trees Meanwhile, Ae aegypti is often found in urbanized areas and inner cities with dense populations Vu Trong Duoc (2012) identified the role of Ae aegypti and Ae albopictus in some outbreaks in Hanoi in 2011 Results showed that 10.4% of Ae aegypti at active outbreaks were infected with dengue virus, however, dengue virus was not found in any Ae.albopictus at outbreaks 1.5.3 Correlation between vector density and dengue fever situation According to Vu Trong Duoc (2015), a study on the relationship between Ae.aegypti and Ae.albopictus density with dengue fever situation in Hanoi, 2011 - 2013, both Ae.aegypti and Ae Albopictus were present in an outbreak In an active outbreak, Ae.aegypti density was higher than that of Ae albopictus In contrast, in areas without outbreaks, Ae.aegypti density was much lower than that of Ae.albopictus 1.6 Insecticide resistance of dengue vectors 1.6.1 Insecticide resistance of dengue vectors in the world According to the announcement of the World Health Organization, of the 200 arthropod species of medical importance, up to 50% are dengue, malaria, filariasis transmission mosquitoes Therefore, the determination of insecticide resistance and resistance mechanisms for dengue vectors is necessary to improve the effectiveness of the national program for dengue prevention and control 1.6.2 Insecticide resistance of dengue vectors in Vietnam Ae.aegypti is resistant to DDT and most of the pyrethroid insecticides in many places, but sensitive to malathion Ae albopictus is still susceptible to insecticides 1.7 Correlation between climatic factors and dengue fever 1.7.1 Studies on the correlation between climatic factors and dengue fever in the world Patz (1998) studied climatic factors and found that temperature was associated with the spread of dengue fever Hales (1999) found that there was a link between the prevalence of dengue fever and temperature, usually the incubation period was shorter as temperatures rised Poveda (2000) showed that most of the peaks of the dengue epidemics in Colombia corresponded to the El Nino + phenomenon 1.7.2 Studies on the correlation between climatic factors and dengue fever in Vietnam Tsuzuki (2009) with the study on transmission risks of dengue fever during summer in Nha Trang city found that less water containers resulted in a reduction in mosquito breeding sites, leading to a lower risk of dengue transmission Hoang Thuy Nguyen (1994) with the study on the dengue situation showed that mosquito density increased during the rainy season CHAPTER STUDY SUBJECTS AND METHODS 2.1 Study subjects - Ae aegypti and Ae Albopictus larvae and mosquitoes - Dengue virus - Climatic factors: Climatic data were taken from the National Centre for Hydro-Meteorological Forecasting - Dengue cases: Data of dengue cases were taken from Hanoi Preventive Medical Center 2.2 Study duration - From January 2016 to December 2017 7 2.3 Study sites 2.3.1 In the field 2.3.1.1 Cross-sectional survey With the above selection criteria, provinces/cities with districts and 16 communes/wards were chosen 2.3.1.2 Longitudinal survey Longitudinal survey was conducted in Lang Thuong, Lang Ha wards, Dong Da district and Tan Trieu, Tu Hiep communes, Thanh Tri district, Hanoi 2.3.1.3 Outbreak investigation When a dengue outbreak was notified by the local authorities, an entomological survey would be carried out at the outbreak location of the four studied provinces/cities 2.3.1.4 Determination of susceptibility of mosquitoes Larvae collected from cross-sectional surveys and outbreaks were preserved and brought to the laboratory for rearing into adult mosquitoes If the number of adult mosquitoes was sufficient, susceptibility testing was conducted 2.3.2 In the laboratory Testing was conducted in laboratories of Department of Entomology, Department of Molecular Biology in the National Institute of Malariology, Parasitology, and Entomology 2.4 Study contents - Survey of larval and mosquito indices of Ae.aegypti and Ae.albopictus in studied provinces - Assessment of the distribution characteristics of Aedes mosquitoes by habitat and season - Description of resting habits of Aedes mosquitoes - Identification of the disease transmission role of Ae aegypti and Ae albopictus at study sites - Evaluation of insecticide susceptibility of Aedes at study sites - Analysis of the correlation between climatic factors and vector indices of Ae aegypti - Analysis of the correlation between climatic factors, vector indices, and dengue cases 8 2.5 Study methods - Cross-sectional descriptive study: Cross-sectional survey was onducted two times per year in studied provinces/ cities - Laboratory research: Molecular biology tests were conducted to determine the rate of dengue virus infection in mosquitoes Biological testing was carried out to assess the insecticide susceptibility of mosquitoes - Longitudinal study: The survey to collect mosquitoes and larvae was carried out monthly in the year in communes/wards in Hanoi Data of dengue cases and climate in Hanoi were also collected by month to analyze and determine the correlation between climatic factors, vector indices, and dengue cases 2.5.1 Sample size - All mosquitoes and larvae collected from households - The number of households to be surveyed in accordance with Decision No 3711/QD-BYT - Sensitivity evaluation: According to the World Health Organization - Household outbreak: 30 households in an outbreak - Investigated outbreaks: 117 outbreaks - Climatic factors of Hanoi, 2016 - 2017 - Dengue cases in Hanoi, 2016 - 2017 2.5.2 Sampling 2.5.2.1 For description of Aedes distribution Households were selected randomly from the list 2.5.2.2 For study of disease transmission role of Aedes All adult mosquitoes collected indoors and outdoors by Mosback 2.5.2.3 For susceptibility testing - Chemical impregnated papers according to the World Health Organization standards included types: Alphacypermethrin 30mg/m2, deltamethrin 0,05%, permethrin 0,75%, lambdacyhalothrin 0,05% malathion 5% 2.5.2.4 For study of the correlation between climatic factors, vector índices, and dengue cases - Climatic factors in Hanoi, 2016 - 2017 - Mosquito density index, BI - Dengue cases in Hanoi, 2016 - 2017 9 2.6 Techniques used in the study 2.6.1 Techniques for entomological survey 2.6.1.1 Mosquito collection and preservation 2.6.1.2 Larva collection and preservation 2.6.2 Techniques for identification of disease transmission role of Aedes 2.6.2.1 Dengue virus RNA purification by ARN adsorption column using gene Jet RNA Purification (SOP NIMPE.HD03.PP/18) 2.6.2.2 Identification of dengue virus in Ae aegypti and Ae albopictus Multiplex reverse Transcriptase PCR (SOP NIMPE.HD03.PP/19) 2.6.3 Techniques for evaluation of insecticide susceptibility of mosquitoes by biological testing method 2.7 Research indices - Mosquito density index - House index (HI) - Breteau index (BI) - Container index (CI) - Breteau index (HI) 2.8 Errors in research and how to fix it 2.9 Data input and analysis 2.9.1 Data input Data input by Microsoft Excel software and all data converted into SPSS format 2.9.2 Data analysis - Identify the percentage (%) of dengue virus in Ae aegypti and Ae Albopictus larvae and mosquitoes - Use the correlation coefficient (r) to analyze the correlation between climatic factors, vector indices and dengue cases 2.10 Data processing Analyze, process and present data of research results by Exel and SPSS 16; compare the average value with the statistical functions 2, t-test to determine the degree of difference 10 2.11 Ethical issues The study strictly follows the regulations set forth for biomedical research in the National Institute of Malariology, Parasitology and Entomology CHAPTER STUDY RESULTS 3.1 Dengue vectors at study sites 3.1.1 Distribution of Aedes at study sites Study results showed that Ae aegypti and Ae albopictus were mostly present at study sites in Hanoi, Hai Phong, Thanh Hoa and Ha Tinh During the cross-sectional survey, Ae aegity and Ae albopictus larvae and adults were collected, but Ae aegypty larvae and adults were not surveyed in Hai Phong and Thanh Hoa 3.1.2 Resting habits of Aedes at study sites 3.1.2.1 Percentage of Ae aegypti resting indoors and outdoors Ae aegypti was mainly active and resting indoors (94.5%) Only 5.5% of the surveyed Ae aegypti populations rested outdoors 3.1.2.2 Resting locations of Ae aegypti were mainly household living spaces Table 3.18 Number and percentage of Ae aegypti in household living spaces Living Bedroom Kitchen Restroom room No Location No Perce No Perce No Perc No Perc (mos ntage (mos ntage (mos enta (mos entag ge e q.) (%) q.) (%) q.) q.) (%) (%) Hanoi 98 6.6 117 79.6 60 4.06 144 9.7 Hai Phong 30 9.7 236 76.4 2.3 36 11.7 Thanh Hoa 32 7.7 312 74.8 21 5.0 52 12.5 Ha Tinh 28 8.2 267 78.5 2.7 36 10.6 Total (%) 188 7.4 1991 78.3 97 3.8 268 10.5 11 3.1.2.3 Resting heights of Ae aegypti Table 3.19 Percentage of Ae aegypti resting at different heights Number of mosquitoes collected at different heights < 0.5 m 0.5 – 1.0 -2.0 m >2m No Location Perc No Perce No Perce No Perce No entag (mos ntage (mos ntage (mosq ntage (mos e q.) (%) q.) (%) ) (%) q.) (%) Hanoi 145 9.4 208 13.5 1163 75.7 21 1.4 Hai Phong 67 20.4 54 16.5 198 60.4 2.7 Thanh Hoa 98 22.5 92 21.1 234 53.8 11 2.5 Ha Tinh 45 11.5 43 10.9 297 75.6 2.0 Total (%) 355 13.2 397 14.7 1892 70.3 49 1.8 3.1.2.4 Resting locations of Ae aegypti Most of Ae aegypti (75.9%) were collected on clothes 3.1.2.5 Percentage of Ae albopictus resting indoors and outdoors Table 3.21 Number of Ae albopictus resting indoors and outdoors at study sites Trong nhà Ngoài nhà No Location Total No Percent No Percent (mo age (%) (mo age (%) sq.) sq.) Hanoi Hai Phong Thanh Hoa Ha Tinh Total (%) 602 731 506 634 2473 20 23 30 22 95 3.3 3.1 5.9 3.5 3.8 582 708 476 612 2378 96.7 96.9 94.1 96.5 96.2 3.1.2.6 Resting locations of Ae albopictus Results showed that Ae albopictus mostly rested around larval sources outdoors (95.73%), followed by bedrooms 12 (3.15%), living rooms (0.45%), restrooms (0.36%), and kitchen (0.31%) 3.1.2.7 Resting heights of Ae albopictus Table 3.23 Percentage of Ae albopictus resting at different heights < 0.5 m 0.5-1 m 1.0-2.0 m >2m Per No Perce No Perce No Perce No cen No Location (mo ntage (mo ntage (mos ntage (mo tag sq.) (%) sq.) (%) q.) (%) sq.) e (%) Hanoi 98 16.3 189 31.4 298 49.5 17 2.8 Hai 102 14.0 179 24.5 435 59.5 15 2.1 Phong Thanh 87 17.2 145 28.7 267 52.8 1.4 Hoa Ha Tinh 84 13.2 188 29.7 346 54.6 16 2.5 Total (%) 371 15.0 701 28.3 1346 54.4 55 2.2 3.1.2.8 Resting locations of Ae albopictus Ae albopictus were mostly collected around larval sources outdoors (86.00%), followed by clothes (7.5%), woods (2.3%), bednets (2.3%), and walls (0.5%) 3.1.3 Dengue transmission role of Aedes 3.1.3.1 Number of Ae aegypti and Ae albopictus at outbreak locations Among 117 outbreaks investigated, 107 outbreaks contained Ae Aegypti, accounting for 91.5%; 71 outbreaks contained Ae albopictus accounting for 60.7% and 61 outbreaks had both the species accounting for 52.1% Hanoi had the biggest number of outbreaks (71.8%), followed by Thanh Hoa (12%), Hai Phong (8.5%), and Ha Tinh (7.7%) 3.1.3.2 Results of identifying Dengue virus on Ae aegypti at outbreak locations Table 3.27 Results of identifying Dengue virus on Ae aegypti at outbreak locations, 2016 - 2017 13 N Province/ o city Hanoi District Perce Type No ntage of of Positiv (%) dengue outb e (+) virus reaks Ba Dinh Cau Giay Dong Da Ha Dong Hai Ba Trung 2 13 18 12 Thanh Xuan Thanh Tri Nam Tu Liem Hai Phong Cat Hai 16 8 10 Thanh Hoa Tinh Gia Ha Tinh city 11 Ha Tinh Thach Ha 12 Total 12 8 0 2 1 0 11 0.00 0.00 23.00 11.10 16.6 12.5 12.5 0.00 12.50 0.00 0.00 0,00 (-) (-) D1, D4 D1, D2 D1 D1, D3 D1 (-) D1 (-) (-) (-) 107 10.28% D1, D2, D3, D4 3.2.3.3 Percentage of Dengue virus on Ae aegypti larvae at outbreaks None of 540 samples of Ae aegypti larvae were found positive for dengue virus 3.1.3.4 Percentage of Dengue virus on Ae albopictus at outbreaks Ae albopictus found at outbreaks was positive for dengue virus; 2/71 outbreaks were infected with Dengue virus type D1, accounting for 2.82% 3.1.3.5 Percentage of Dengue virus on Ae albopictus larvae at outbreaks A total of 88 samples of Ae albopictus larvae were detected at study sites No samples were positive for dengue virus 14 3.1.3.6 Percentage of Dengue virus on Ae aegypti through cross-sectional survey At the sites of cross-sectional survey, no positive samples were found 3.1.3.7 Percentage of Dengue virus on Ae albopictus larvae and mosquitoes through cross-sectional survey No positive samples were found 3.1.4 Susceptibility of Aedes mosquitoes at study sites 3.1.4.1 Insecticide susceptibility of Ae aegypti Ae aegypti was sensitive to alphacypermethrin at 3/13 points, possibly resistant at 1/13 points and resistant at 9/13 points; susceptable to deltamethrin at 4/13 points and resistant at 9/13 points; susceptable to lambdacyhalothrin at 3/13 points, possibly resistant at 2/13 points, resistant at 8/13 points; sensitive to permethrin at 1/13 points, possibly resistant at 3/13 points, resistant at 9/13 points; sensitive to malathion at 8/13 points, possibly resistant to 1/13 points, and resistant at 4/13 points 3.1.4.2 Insecticide susceptibility of Ae albopictus Ae albopictus was sensitive to alphacypermethrin at 12/23 points, possibly resistant at 5/23 points, and resistant at 6/23 points; sensitive to deltamethrin at 17/23 points, possibly resistant at 1/23 points and resistant at 7/23 points; susceptable to lambdacyhalothrin at 10/23 points, possibly resistant at 8/23 points and resistant at 5/23 points; susceptible to permethrin at 16/23 points, possibly resistant at 4/23 points and resistant at 3/23 sites; sensitive to malathion at 21/23 points, possibly resistant at 1/23 points and resistant at 1/23 points 3.2 Correlation between climatic factors, vectors and dengue situation in Hanoi 3.2.1 Average temperature, humidity, rainfall in Hanoi In 2016 and 2017, the average temperature of the corresponding months was of no significant difference The average monthly rainfall in Hanoi was much different between the rainy and dry season The humidity did not have much difference between months in year 3.2.2 Correlation between climatic factors and vector indices Table 3.35 Correlation between climatic factors and Ae aegypti indices in Hanoi 15 Factors Average monthly temperature Average monthly humidity Average monthly rainfall Density r p 24 0.29 0.24 n BI r 0.55 p 0.006 24 -0.31 0.14 -0.22 0.31 24 0.30 0.16 0.37 0.07 P < 0.05 3.2.3 Correlation between climate, vectors and dengue cases in Hanoi Table 3.36 Correlation between climate, vectors and dengue cases in Hanoi Cases Factors n r p Average monthly 24 0.24 0.27 temperature Average monthly humidity 24 -0.03 0.89 Average monthly rainfall 24 0.19 0.38 Monthly mosquito density 24 0.39 0.06 Monthly BI 24 0.66 0.00 P < 0.05 3.2.4 Correlation between climate, vector indices, dengue cases of the previous month and dengue cases of the following month in Hanoi Table 3.37 Correlation between climate, vector indices, dengue cases of the previous month and dengue cases of the following month in Hanoi Cases Factors n r p Average last month temperature 23 0.49 0.02 Average last month humidity 23 0.01 0.95 Average last month rainfall 23 0.39 0.06 Last month mosquito density 23 0.48 0.02 Last month BI 23 0.74 0.00 Last month cases 23 0.83 0.00 P < 0.05 16 CHAPTER DISCUSSIONS 4.1 Situation of dengue vectors at study sites 4.1.1 Distribution of dengue vectors at study sites Study results showed that Ae aegypti and Ae albopictus were mostly present at study sites in Hanoi, Hai Phong, Thanh Hoa and Ha Tinh During cross-sectional investigation, Ae aegypti and Ae albopictus larvae and mosquitoes were found at the study sites, but no Ae aegypty larvae and mosquitoes found in Hai Phong and Thanh Hoa (tables 3.3 and 3.5) However, their distribution was different at the study sites The study on the distribution of Ae.aegypti and Ae albopictus at the study sites in 2016 - 2017 showed that 94.5% of Ae.aegypti were active and rested indoors; 96.2% of Ae.albopictus were active and rested outdoors This finding is similar to some studies of determination of distribution of Aedes mosquitoes in some Northern provinces in the past, typically Vu Sinh Nam (1995) Common resting places of Ae.aegypti were dark, windless such as hanging clothes, blankets, bednets, accounting for over 90% A small percentage of Ae.aegypti was seen on the wall Studies show that Ae.aegypti prefers to rest indoors, their larvae live in artificial water containers, they live close to people, so they are often present in densely populated urban areas In contrast, Ae.albopictus often rests outdoors with larvae living in natural and artificial water containers 4.1.2 Ecological characteristics of Aedes mosquitoes Study results in Hanoi, Hai Phong, Thanh Hoa and Ha Tinh showed that Ae.aegypti adults rested on clothes (77%), mosquito nets (7.6%), clothesline (4.4%), wood furniture (4.5%), and walls (1.6%) Only a small number of Ae.aegypti (1.6%) rested on the wall, which is the reason why no residual spraying on the wall is applied When investigating households, we found that, because of economic and social conditions or habits of the people, clothes were directly on the wall in poorly-ventilated rooms, which is a favorable condition for Ae.aegypti Ae.aegypti lives in house close to people, but not every location they are present Their life span depends on natural conditions such as temperature, humidity so they often rest in cool 17 places with high humidity, weak light density, and lots of substrates for shelter By daytime indoor light trap catching we found that Ae.aegypti mainly rested in the bedroom (78.3%), followed by toilets (10.5%), living room (7.4%), and kitchen (3.8%), which is consistent with the habit of this species Ae.albopictus mainly lives and rests outdoors Survey of the households at the research sites showed that Ae.albopictus was mostly present around outdoor larvae sources (95.73%), followed by bedrooms (3.15%), and living rooms, toilets and kitchens (0.45%, 0.36% and 0.31% respectively) Resting locations of Ae.albopictus included objects around outdoor larva sources (86.0%), clothes (7.5%), wood (2.3%), nets (2.3%), and walls (0.5%) 4.1.3 Disease transmission role of Aedes In order to prove that Aedes mosquitoes are responsible for transmitting dengue fever, we have to determine their presence in active outbreaks The results in Table 3.25 indicate that Ae.aegypti or Ae.albopictus or both was found in all the outbreaks Ae.aegypti found in the active outbreak accounted for the highest percentage of 91.5%, followed by Ae albopictus (60.7%), and both (52.1%) From the data above, we can see that all dengue outbreaks saw the presence of Aedes mosquitoes, indicating that Aedes mosquitoes play a role in transmitting dengue virus Our study results are similar to those of Vu Trong Duoc (2015) with the study of the dengue transmission role of Aedes in Hanoi His study showed that the rate of Ae.aegypti at outbreaks was 94% of the total species, but this rate was only 28.5% by cross sectional survey About half of the active outbreaks reported the presence of only Ae.aegypti but Ae albopictus Among the remaining outbreaks containing both the species, Ae.aegypti overwhelmed Ae.albopictus [13] Our findings are somewhat different from those of Vu Sinh Nam (1995), which said that most of the dengue outbreaks had the presence of Ae.aegypti and only a few outbreaks had both Ae.aegypti and Ae.albopictus [28] In this study we found 10.28% of Ae.aegypti positive for dengue fever, 2.82% of Ae.albopictus positive for dengue fever at the outbreaks Although testing was not carried out on mosquito individual, this result is quite consistent with some studies in Vietnam and around the world Typically, Vu Trong Duoc 18 (2012) has identified the role of Ae.aegypti and Ae.albopictus in some dengue outbreaks in Hanoi in 2011 Results showed that 10.4% of Ae.aegypti at active outbreak were infected with dengue virus, however, dengue virus was not found in Ae.albopictus[11] 4.1.4 Insecticide susceptibility of Aedes Test results showed that Ae.aegypti in Hanoi was resistant to alphacypermethrin, deltamethrin, permethrin, lambdacyhalothrin at all study sites with mortality of - 72%; resistant to malathion at 4/5 study sites at a mortality rate of 59-73%; sensitive to this chemical in Phuong Liet ward, Dong Da district (mortality 100%) Testing in Hai Phong showed that Ae.aegypti in Cat Hai was resistant to alphacypermethrin, deltamethrin, permethrin, lambdacyhalothrin (mortality from 67 - 88%); sensitive to alphacypermethrin, deltamethrin, lambdacyhalothrin in Phu Long commune, Cat Hai district (mortality rate from 98 to 100%), increased endurance with permethrin with mortality rate of 90% Ae.aegypti was susceptable to malathion at 3/3 study sites (100% mortality) At the study sites in Thanh Hoa, Ae aegypti was also sensitive to alphacypermethrin at 4/6 study sites (98% - 100% mortality); resistant to this chemical in Hai Ha commune, Tinh Gia district (mortality rate 72%); susceptable to lambdacyhalothrin at 1/7 sites (mortality 98%); increased tolerance to this chemical at 4/6 sites (mortality 90% - 94%); resistant to this chemical at 1/6 research point (mortality 88%); sensitive to permethrin 3/6 research points (98% - 100% mortality rate); increased endurance with this chemical in Dong Hai ward, Thanh Hoa city and Hai Ha commune, Tinh Gia district (92% and 94% respectively); resistant to this chemical in Dong Tho ward, Thanh Hoa city (mortality 88%); susceptable to malathion at 6/6 research sites (100% mortality) Ae aegypti was sensitive to alphacypermethrin at 1/3 sites (100% mortality); resistant to this chemical at 1/3 sites (92% mortality); resistant to this chemical at 1/3 sites (87% mortality); sensitive to deltamethrin 2/3 sites (mortality from 99% - 100%); resistant to this chemical in Thach Dong Commune, Ha Tinh City (mortality 83%); sensitive to lambdacyhalothrin at 1/3 sites (100% mortality); possibly resistant to this chemical at 1/3 sites (90% mortality); resistant to this chemical at 1/3 sites (mortality 19 82%); possibly resistant to permethrin at 1/3 sites (mortality 95%); resistant to this chemical at 2/3 sites (mortality rate from 78% to 84%); sensitive to malathion at 2/3 sites (100% mortality); resistant to this chemical in Thach Trung commune, Ha Tinh city (mortality rate of 93%) Susceptibility testing of Ae.albopictus at research sites in Hanoi, Hai Phong, Thanh Hoa and Ha Tinh found that Ae.albopictus was sensitive to alphacyhalothrin at 12/23 research sites; resistant to this chemical at 5/23 research sites; and resistant to this chemical at 6/23 research sites; sensitive to deltamethrin at 17/23 research sites; resistant to this chemical at 1/23 research sites; resistant to this chemical at 5/23 research sites; sensitive to lambdacyhalothrin at 10/23 research sites, resistant to this chemical at 8/23 research sites, and resistant to this chemical at 5/23 research sites; sensitive to permethrin at 16/23 research sites, resistant to permethrin at 4/23 research sites and resistant to this chemical at 3/23 research sites; Susceptible to malathion at 21/23 research sites, resistant to this chemical at 1/23 research sites, resistant to malathion at 1/23 research sites Different from Nguyen Van Dung (2011), the study on mosquito, larva indices and insecticide susceptibility of dengue vectors in some northern provinces of Vietnam such as Thai Binh, Nam Dinh, Nghe An and Ha Tinh showed that Ae.albopictus at most study sites was also sensitive to deltamethrin, permethrin, malathion and resistant to DDT It was possibly resistant to alphacypermethrin, lambdacyhalothrin Thus, our results showed that Ae.albopictus was still sensitive to most of the tested insecticides: Alphacypermethrin, deltamethrin, lambdacyhalothrin, permethrin, and malathion 4.2 Correlation between climatic factors and dengue situation in Hanoi When analyzing the correlation between climatic factors and Ae aegypti index in Hanoi (2016 – 2017) we found that only average monthly temperature was positively correlated with BI, with r = 0.55 and statistically significant (p = 0.006) Rainfall, average monthly humidity were correlated with BI but not statistically significant Meanwhile, average monthly temperature, average monthly humidity and average monthly rainfall were correlated with surface temperature but not statistically 20 significant Our results showed a difference with the research of Amarakoon (2007); Glenn L Sia Su (2009); Hay (2002) In addition to assessing the correlation between climatic factors and vector indices, we also analyzed the correlation between climate factors and vector indices and dengue cases in Hanoi Ambient temperature, average monthly rainfall and mosquito density index with dengue cases in Hanoi had a positive correlation r = 0.24, r = 0.19 and r = , 39, but not statistically significant with p = 0.27, p = 0.38 and p = 0.06; The average monthly humidity and dengue cases were inversely correlated with r = - 0.03, not statistically significant with p = 0.89; Only BI and dengue cases had a positively, closely correlated r = 0.66, which is statistically significant with p = 0.00 Thus, only the BI index was correlated with the number of dengue cases by months in Hanoi, somewhat similar to that of Pham Van Hau (2011), with the study on ecological factors In the Central Highlands, Vietnam we found that after seasonal adjustments, the risk of dengue fever was significantly associated with the house index and BI When studying the correlation between climate factors, vector 01 month ago and the dengue case of next month in Hanoi, 2016 - 2017 found that: Temperature, average rainfall, DM, BI, Case The disease of the previous month is correlated with the case of dengue fever in the following month (p 0.05 RECOMMENDATIONS The study on biological and ecological characteristics of Ae aegypti and Ae albopictus should be continued to determine any change in the future The efficacy of insecticides against Ae.aegypti and Ae.albopictus should be continuously studied by biological methods to select the appropriate chemicals for dengue prevention and control To prevent and control dengue fever, attention should be paid to the following factors: Average temperature, BI and Ae.aegypti density and the number of cases to predict the direction of dengue fever for the following month  ... 189 31 .4 298 49 .5 17 2.8 Hai 102 14. 0 179 24. 5 43 5 59.5 15 2.1 Phong Thanh 87 17.2 145 28.7 267 52.8 1 .4 Hoa Ha Tinh 84 13.2 188 29.7 346 54. 6 16 2.5 Total (%) 371 15.0 701 28.3 1 346 54. 4 55 2.2... 145 9 .4 208 13.5 1163 75.7 21 1 .4 Hai Phong 67 20 .4 54 16.5 198 60 .4 2.7 Thanh Hoa 98 22.5 92 21.1 2 34 53.8 11 2.5 Ha Tinh 45 11.5 43 10.9 297 75.6 2.0 Total (%) 355 13.2 397 14. 7 1892 70.3 49 ... Hanoi 98 6.6 117 79.6 60 4. 06 144 9.7 Hai Phong 30 9.7 236 76 .4 2.3 36 11.7 Thanh Hoa 32 7.7 312 74. 8 21 5.0 52 12.5 Ha Tinh 28 8.2 267 78.5 2.7 36 10.6 Total (%) 188 7 .4 1991 78.3 97 3.8 268 10.5