Tóm tắt Luận án Current situation of dengue vectors, the correlation between climate, vector indices and dengue cases in 4 northern provinces of Vietnam (2016 - 2017)

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 6 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 + 1 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 2 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, 4 provinces/cities with 8 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 4 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 4 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 4 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 5 types: Alphacypermethrin 30mg/m2, deltamethrin 0,05%, permethrin 0,75%, lambdacyhalothrin 0,05% và 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 3 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 No. Location Living room Bedroom Kitchen Restroom No. (mos q.) Perce ntage (%) No. (mos q.) Perce ntage (%) No. (mos q.) Perc enta ge (%) No. (mos q.) Perc entag e (%) 1 Hanoi 98 6.6 117 6 79.6 60 4.06 144 9.7 2 Hai Phong 30 9.7 236 76.4 7 2.3 36 11.7 3 Thanh Hoa 32 7.7 312 74.8 21 5.0 52 12.5 4 Ha Tinh 28 8.2 267 78.5 9 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 No . Location Number of mosquitoes collected at different heights 2 m No. (mos q.) Perce ntage (%) No. (mos q.) Perce ntage (%) No. (mosq. ) Perce ntage (%) No. (mos q.) Perc entag e (%) 1 Hanoi 145 9.4 208 13.5 1163 75.7 21 1.4 2 Hai Phong 67 20.4 54 16.5 198 60.4 9 2.7 3 Thanh Hoa 98 22.5 92 21.1 234 53.8 11 2.5 4 Ha Tinh 45 11.5 43 10.9 297 75.6 8 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 No. Location Total Trong nhà Ngoài nhà No. (mo sq.) Percent age (%) No. (mo sq.) Percent age (%) 1 Hanoi 602 20 3.3 582 96.7 2 Hai Phong 731 23 3.1 708 96.9 3 Thanh Hoa 506 30 5.9 476 94.1 4 Ha Tinh 634 22 3.5 612 96.5 Total (%) 2473 95 3.8 2378 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 No. Location 2 m No. (mo sq.) Perce ntage (%) No. (mo sq.) Perce ntage (%) No. (mos q.) Perce ntage (%) No. (mo sq.) Per cen tag e (%) 1 Hanoi 98 16.3 189 31.4 298 49.5 17 2.8 2 Hai Phong 102 14.0 179 24.5 435 59.5 15 2.1 3 Thanh Hoa 87 17.2 145 28.7 267 52.8 7 1.4 4 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 o. Province/ city District No. of outb reaks Positiv e (+) Perce ntage (%) Type of dengue virus 1 Hanoi Ba Dinh 2 0 0.00 (-) 2 Cau Giay 2 0 0.00 (-) 3 Dong Da 13 3 23.00 D1, D4 4 Ha Dong 18 2 11.10 D1, D2 5 Hai Ba Trung 12 2 16.6 D1 6 Thanh Xuan 16 2 12.5 D1, D3 7 Thanh Tri 8 1 12.5 D1 8 Nam Tu Liem 7 0 0.00 (-) 9 Hai Phong Cat Hai 8 1 12.50 D1 10 Thanh Hoa Tinh Gia 12 0 0.00 (-) 11 Ha Tinh Ha Tinh city 1 0 0.00 (-) 12 Thach Ha 8 0 0,00 (-) Total 107 11 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 n Density BI r p r p Average monthly temperature 24 0.29 0.24 0.55 0.006 Average monthly humidity 24 -0.31 0.14 -0.22 0.31 Average monthly rainfall 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 Factors Cases n r p Average monthly temperature 24 0.24 0.27 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 Factors Cases 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 4 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 hung 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 2 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 3 - 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