Thành phần loài,phân bố,đặc điểm sinh thái và sự nhạy cảm của véc tơ sốt rét với các hóa chất đang sử dụng trong phòng chống sốt rét ở khu vực miền trung–tây nguyên tt tiếng anh

1 INTRODUCTION Malaria is a serious infectious disease for humans, caused by Plasmodium (P.) parasites There are hundreds of millions of infected people and hundreds of thousands of deaths from malaria every year worldwide To date, there have been 420 Anopheles species identified, of which about 70 species are human malaria vectors in natural conditions [21] In Vietnam, about 64 Anopheles species have been identified, including 15 malaria vectors with three main vectors An dirus, An minimus and An epiroticus [21] In Vietnam, malaria is highly endemic with two thirds of the area of malaria, and about 50% of the populations live in malaria areas Central Highlands is the most complicated malaria area in Vietnam with more than 70% of the populations at risk and high population mobility Every year, the number of malaria patients accounts for nearly 50%, malaria parasites 75%, severe malaria and malaria deaths > 80% of the whole country Therefore, we conducted the study “Species composition, distribution, ecological characteristics of Anopheles and susceptibility of malaria vectors to insecticides used for malaria control in Central-Highlands of Vietnam, 2014 – 2017” to provide database for developing a vector control plan, reducing the morbidity and mortality and controlling malaria in these provinces in particular and in the country in general The objectives of the study are: To determine the species composition of Anopheles, distribution, biology, ecology and disease transmission role of malaria vectors in the Central-Highlands, 20142017 To evaluate the susceptibility of malaria vectors to lambda -cyhalothrin and alpha-cypermethrin at study sites THESIS STRUCTURE The thesis consists of pages divided into the following sections: Introduction (2 pages); literature review (24 pages); study subjects and methods (15 pages); study results (47 pages); discussions (22 pages); conclusions (2 pages); and recommendations (1 page) There are 63 tables, 13 figures, and 119 references CHAPTER LITERATURE REVIEW 1.1 Species composition and distribution of Anopheles According to Ralph Harbach (2008), the family Culicidae Meigen 1818 belonging to the subdivision Nematocera of Diptera is divided into two subfamilies: Anophelinae (including genera) and Culicinae (including genera) [75] Particularly, the subfamily Anophelinae Grassi, 1900 now has 547 species of genera worldwide 1.2 Ecology, behavior, and disease transmission role of Anopheles Each habitat has specific mosquito species Each season also has specific active mosquito populations such as rainy season Anopheles and dry season Anopheles The behavior and the distribution of mosquitoes is related to the landscape and impact of the landscape on people They are distributed everywhere by species Mosquitoes need human blood so they bite peole Mosquito bites vary by locality and depend on the presence of other animals such as cattle 1.3 Malaria vector control In 1939, Muller discovered the insecticidal activity of DDT, then he found organic phosphorus, organic Chlorine and Carbamate, and Pyrethroids had the same activity In 1989, WHO recommended using Permethrine-impregnated bed nets for malaria prevention because they were safe for humans, low odor, colorlessness, and able to limit vector exposure and malaria spread 1.4 Resistance of malaria vectors to insecticides Insecticide resistance is a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a insecticide product to achieve the expected level of control when used according to the label recommendation for that pest species According to the WHO’s definition, "Insecticide resistance is the ability of certain individuals to tolerate doses of toxicants which would prove lethal to the majority of individuals in a normal population of the same species” (Martinez, 1998) 1.5 Situation of insecticidal resistance of malaria vectors Pyrethroid resistance of malaria vectors widely spreads in many African countries as well as Central Asia and Southeast Asia In 2015, more than three-quarters of the countries reported the resistance of malaria vectors to pyrethroid groups Currently, Pyrethroid insecticides are widely used in malaria control programs in many countries around the world including Vietnam Therefore, the development of resistance of malaria vectors to these chemicals may hinder the success of malaria control activities 1.6 Malaria situation in the Central Highlands Central Highlands is a focal point of malaria in Vietnam, including 15 provinces with a population of about 20 million people, over 40 ethnic groups, of which nearly 50% of the populations live in malaria endemic areas After many years of malaria control, malaria in the Central Highlands has significantly decreased, but the risk of malaria coming back is still of great concern The malaria control program is facing with obstacles and challenges such as poverty, low-education, shifting cultivation, field hut sleeping, people mobility, etc The movement of people from the plain to the mountain, from the North to the Central Highlands is still too high In addition, they not have effective measures for malaria control [2], [7] In highly malaria-endemic and remote areas, the communal health system is weak and not well equipped According to the Ministry of Health's 2010 report, there were 4,481 malaria cases and one death in Vietnam Malaria in the Central Highlands increased by 30.5% and in the South increased by 24.83% According to the report of Quy Nhon Institute of Malariology, Parasitology, and Entomology, the number of malaria patients in the Central Highlands in 11 months of 2013 decreased by 10.52% compared to the same period in 2012; malaria parasites decreased by 6.10%; severe cases decreased by 46.91%; and deaths of malaria reduced cases [15] CHAPTER STUDY SUBJECTS AND METHODS 2.1 Subjects, time, location of the study 2.1.1 Study subjects Subjects of the study include Anopheles Meigen, 1818 (Diptera: Culicidae) adult mosquitoes and larvae in the Central Highlands of Vietnam 2.1.2 Time of study: 08/2014 – 10/2017 2.1.3 Study locations 2.1.3.1 Field study Study sites: Forest fringe: The following sites were selected: Ngan Thuy commune, Le Thuy district, Quang Binh province; Canh Hoa commune, Van Canh district, Binh Dinh province; Phuoc Thanh commune, Bac Ai district, Ninh Thuan province; Easo conservation area, Eaka district, Dak Lak province Forest: The following sites were selected: Son Thai and Khanh Phu communes, Khanh Vinh district, Khanh Hoa province, Ia Mlah and Chu RCam communes, Krong Pa district, Gia Lai province 2.1.3.2 Laboratory study Entomology tests and ELISA techniques were conducted in laboratories of Quy Nhon Institute of Malariology, Parasitology and Entomology 2.2 Study materials - Instruments for insect collection: Light traps, flashlights, mosquito traps, handheld magnifying glasses, waterprof cottons, larval traps, surgical needles, notebooks, etc - Instruments for mosquito analysis: (mosquito surgery) ether, surgical needles, physiological saline 90/00, forceps, scissors, microscopic slides, lamen, magnifying glasses, microscope, slide racks, identification keys - Mosquito cages and rearing equipment - ELISA machine and ELISA testing tools and chemicals used to determine malaria parasite-infected mosquitoes - WHO susceptibility test kits and 02 types of impregnated papers (alpha-cypermethrin and lambda-cyhalothrin) 2.3 Scope of the study - The study is to determine the species composition and distribution of Anopheles, biology, ecology and disease transmission role of malaria vectors at study sites in Quang Binh, Binh Dinh, Khanh Hoa, Ninh Thuan, Gia Lai, Dak Lak Further research would be conducted at two focal points in Gia Lai and Khanh Hoa - The study is also to evaluate the susceptibility of malaria vectors to insecticides in Quang Binh, Binh Dinh, Khanh Hoa, Ninh Thuan, Gia Lai, Dak Lak 2.4 Study methods 2.4.1 Study design 2.4.1.1 Descriptive cross-sectional study - Entomology surveys: WHO survey methods were used At malaria focal points of Gia Lai and Khanh Hoa, surveys were conducted in May and July (dry season), and September and November (rainy season) in forest habitats Each survey last nights Adult mosquitoes were collected with the following methods: Indoor light trap (ILT), outdoor light trap (OLT), indoor night human bait (INHB), outdoor night human bait (ONHB), cattle landing catch (CLC), daytime indoor resting shelter catch (DIRSC), and daytime outdoor resting shelter catch (DORSC) Larvae were collected in water bodies - In Quang Binh, Binh Dinh, Ninh Thuan and Dak Lak, two surveys were conducted in the rainy season (August and November) in forest fringe habitats Each survey last nights Adult mosquitoes were collected with the following methods: Indoor light trap (ILT), outdoor light trap (OLT), indoor night human bait (INHB), outdoor night human bait (ONHB), cattle landing catch (CLC), daytime indoor resting shelter catch (DIRSC), and daytime outdoor resting shelter catch (DORSC) Larvae were collected in water bodies The aim of the surveys was to assess the species composition, behavior, disease transmission role of Anopheles and susceptibility to insecticides in the study area 2.4.1.2 Laboratory study Enzyme-linked immunosorbent assay (ELISA) was used to identify vectors infected with malaria parasites 2.4.2 Techniques used in the study 2.4.2.1 Survey techniques 2.4.2.2 Identification techniques 2.4.2.3 Techniques for mosquito surgery and observation of ovaries 2.4.2.4 ELISA techniques for determination of mosquitoes infected with malaria parasites 2.4.2.5 Susceptibility testing techniques 2.4.3 Evaluation indicators + Species composition and species ratio (%) + Density of each species by each method + ELISA positive rate + Birth rate, daily survival rate, average lifespan of the populations + Malaria transmission indices + Susceptibility of malaria vectors to insecticides being used for malaria control 2.4.4 Data processing and analysis - Survey data were entered and processed by Excel 2007 software: + Calculate the percentage of variables + Calculate the mosquito density by collection methods - Data were analyzed by SPSS 20., including the followings: + Calculate the value of variables: Average value, standard deviation + Compare variables using one-way ANOVA, Independent sample test CHAPTER STUDY RESULTS 3.1 Anopheles species composition, distribution, ecological characteristics and disease transmission role of malaria vectors in Central-Highlands of Vietnam 3.1.1 Species composition of Anopheles and vector distribution in the Central-Highlands A total of 18 Anopheles species were found in the CentralHighlands region, including 16 species from the Central and 14 species from the Highlands Two primary malaria vectors An dirus and An minimus and three secondary vectors An aconitus, An jeyporiensis and An Maculatus were collected Table 3.2 Number of species and percentage of Anopheles at study sites No of vectors Study sites No of species Percentage (%) Primary Secondary Quang Binh 12 75 Binh Dinh 15 93.8 Khanh Hoa 11 68.75 Ninh Thuan 14 87.5 Gia Lai 12 75 Dak Lac 10 62.5 Total 18 100 Table 3.4 Malaria vector distribution by habitat Habitat Forest fringe No Percentage (%) 189 42.1 254 Khanh Hoa 45 Gia Lai An minimus Percentage (%) An jeyporiensis An maculatus No 131 12 Forest Ninh Thuan An Dirus Dak Lak An aconitus Binh Dinh Quang Binh Malaria vector 260 57,9 100 1950 97 26 81.3 54 61 3.03 946 18.7 201 16 282 25.7 522 295 817 74.3 12 21 62 74.7 25.3 26 62 The distribution of malaria vectors by habitat is shown in Table 3.4 Two main vectors An dirus and An minimus were found more in the forest (An dirus: 97%; An minimus: 74.7%) compared to in the forest fringe (An dirus: 3.03%; An minimus: 25.3%) The percentage of secondary vectors An.aconitus, An jeyporiensis, An maculatus in the forest habitat was also higher than that in the forest fringe 10 3.1.2 Biological, ecological characteristics and disease transmission role of malaria vectors in the Central Highlands 3.1.2.1 Biting habit of malaria vectors in the forest fringe area Table 3.6 Density of malaria vectors in Ngan Thuy commune, Le Thuy district, Quang Binh province Collection methods and density of malaria vectors An aconitus An maculatus An minimus Larvae (larvae/container) CLC (mosq/cattle) ONHB (mosq/pers/night) INHB (mosq/pers/night) OLT (mosq/night/trap) ILT (mosq/night/trap) DORSC (mosq/pers/night) DIRSC (mosq/pers/night) Species 0 0 0 0.33 0 0.33 0.33 0 9.33 0.3 0 0 1.0 1.33 Table 3.9 Density of malaria vectors in Canh Hoa commune, Van Canh district, Binh Dinh province Notes: Indoor light trap: ILT Outdoor light trap: OLT Indoor night human bait: INHB Outdoor night human bait: ONHB Cattle landing catch: CLC 15 DORSC (mosq/pers/night) 2.5 12.5 0 0.5 0 0.5 DIRSC (mosq/pers/night) DORSC (mosq/pers/night) DIRSC (mosq/pers/night) DORSC (mosq/pers/night) 4.5 DORSC (mosq/pers/night) ONHB (mosq/pers/night) INHB (mosq/pers/night) ONHB (mosq/pers/night) INHB (mosq/pers/night) ONHB (mosq/pers/night) INHB (mosq/pers/night) ONHB (mosq/pers/night) INHB (mosq/pers/night) 15 12.5 0 0 4.5 19 4.5 12 11 27 9.5 23 An dirus An DIRSC (mosq/pers/night) Species 3.5 An DIRSC (mosq/pers/night) dirus An s macula tus Table 3.31 Biting density of malaria vectors inside and outside field huts in Krong Pa May July September November aconitus 16 An 0.5 0 0 0.5 10.5 18.5 3.5 5.5 0.5 3.5 1 1.5 0 0 jeyporiensi s An maculatus An minimus 3.1.3 Disease transmission role of malaria vectors at two highly endemic sites of the Central Highlands 3.1.3.1 Average lifespan of malaria vector populations in Gia Lai and Khanh Hoa Table 3.41 Average lifespan of malaria vector populations in Khanh Vinh, Khanh Hoa Locatio n Khanh Phu Species No Percentag e of mosquito breeding (%) An dirus 21 67.9 0.88 8.0 An maculatu s 44 54.5 0.82 5.1 Σ: Average: Average: Average Probabilit y of daily survival (P) Average lifespan (day) 17 Locatio n Species No 25 Son Thai Total Percentag e of mosquito breeding (%) 61.2 Probabilit y of daily survival (P) Average lifespan (day) 0,85 : 6.55 An dirus 39 74.7 0.91 10.6 An maculatu s 43 46.5 0.78 4.0 Σ: 43 Average: 60.6 Average: 0.85 Average : 7.3 An dirus 61 71.3 0.90 9.3 An maculatu s 87 50.5 0.80 4.5 Σ: 69 Average: 60.9 Average: 0.85 Average : 6.9 Table 3.42 Average lifespan of malaria vector populations in Krong Pa, Gia Lai 18 Location Ia Mlah Chu R Cam Species An dirus 333 70.3 0.89 8.8 An maculatus 78 47.4 0.79 4.2 Σ: 411 Average: 58.9 Average: 0.84 Average: 6.5 An dirus 206 71.4 0.90 9.2 An maculatus 94 45.7 0.78 4.0 An minimus 35 51.4 0.81 4.7 Σ: 335 Average: 56.2 Average: 0.83 Average: 6.0 539 70.9 0.89 9.0 An 172 maculatus 46.6 0.78 4.1 35 51.4 0.81 4.7 Σ: 849 Average: 56.3 Average: 0.83 Average: 5.9 An dirus Total Percentage Probability of Average of daily No mosquito lifespan survival breeding (day) (P) (%) An minimus Table 3.43 Number of mosquitoes infected with malaria parasites in Khanh Hoa and Gia Lai Species No Malaria parasite Total 19 (+) P vivax 210 (+) P vivax 247 (+) (-) (+) P falcipar um An aconitus 260 260 0 0 An dirus 1.131 1.120 2 13 An jeyporiensis 22 22 0 0 An maculatus 683 683 0 0 An minimus 62 55 0 Total 2.158 2.140 9 20 Results in Table 3.43 show 20 individuals infected with malaria parasites Secondary vectors An aconitus, An jeyporiensis and An maculatus were found uninfected with parasites, while the two main vectors An dirus and An minimus were ELISA positive with both Plasmodium falciparum and Plasmodium vivax 3.2 Susceptibility of malaria vectors to insecticides being used for malaria control in the Central Highlands - An minimus was sensitive to lambda - cyhalothrin (Van Canh, Binh Dinh) - An dirus was sensitive to alpha - cypermethrin, lambda cyhalothrin (Bac Ai-Ninh Thuan, Khanh Vinh-Khanh Hoa) 20 - An aconitus was susceptible to alpha - cypermethrin and lambda - cyhalothrin (Binh Dinh) - An maculatus was resistant to alpha - cypermethrin and lambda - cyhalothrin (Le Thuy-Quang Binh,Van Canh-Binh Dinh, Bac Ai-Ninh Thuan, Khanh Vinh-Khanh Hoa, Krong PaGia Lai) - An aconitus was sensitive to alpha – cypermethrin (Khanh Vinh-Khanh Hoa, Krong Pa-Gia Lai, Krong Na-Dak Lak) 21 CHAPTER DISCUSSIONS 4.1 Anopheles species composition, distribution, ecological characteristics and disease transmission role of malaria vectors in Central-Highlands of Vietnam 4.1.1 Species composition of Anopheles in the CentralHighlands There were 16 Anopheles species found in the Central region and 14 Anopheles species collected in the Highlands Both the main malaria vectors An dirus and An Minimus were present in the two regions However, An dirus outnumbered An minimus in the Central region, while they were equal in same in the Highlands In addition, secondary vectors An aconitus, An jeyporiensis and An maculatus were also detected in the study sites This result is similar to the result of a species composition survey in hydropower and irrigation areas in Gia Lai province from 2014 to 2016, including 18 species of Anopheles (Se San hydropower plant: 17 species; Krong Pa hydropower plant: 13 species) Five main and secondary vectors and members of Minimus (An harisoni) were found In Ia Khai commune (belonging to Se San 3A and hydropower plants), there were 14 species collected in the forest, 16 species collected in the forest fringe, 11 species found in the residential area (village) In Ia Kreng commune (belonging to Se San and Yaly hydropower plants), there were 10 species found in the forest, 11 species in the forest fringe, and 10 species in villages In Chu Gu commune (belonging to Krong Pa hydropower and irrigation plant), species were collected in the forest, 10 species in the forest fringe, and species in the village Ia Mlah commune (belonging to Krong Pa hydropower and irrigation plant) had species in the forest, species in the forest fringe, and species in the village [40] 22 4.1.2 Distribution of malaria vectors in the CentralHighlands 4.1.2.1 Distribution by area Different areas had different vector distribution densities In this study, the density of An minimus in the Central was lower than that in the Highlands (25.3% vs 74.7%) However, there are also areas where this species is not present as in research by Chen (2002), Foley (2008) In China, An minimus is almost absent in the north [88], and is only present in the south from 32 o5 going down, including Yunnan, Guangdong, Guangxi, Taiwan and Hainan Islands [65], [71] Some studies state that An minimus ss is absent or rare in Indonesia and the Philippines, while An flavirostris with the similar morphology to An minimus is present in these islands [97] In addition, An flavirostris has also been identified as a malaria transmission vector in some West Asian countries such as Nepan, Pakistan [71] It is likely that there is an overlap in the distribution of An minimus and An flavirostris in some countries According to the research results in Vietnam by Nguyen Huu Duc (1973), An minimus was popular at elevations from to 800 m In this study, we did not assess the elevation but selected survey sites based on malaria epidemic areas, because the area of endemic malaria exists transmission vectors 4.1.2.2 Distribution by habitat Vegetation is the decisive factor for the development of malaria vectors In this study, survey sites included forests and forest fringes The rate of main vector An minimus in the forest was higher than that in the forest edge (74.7% vs 25.3%) In the world, the main vector An minimus is mainly found in the mountainous forest, and this study result is completely consistent with this finding In Thailand, An minimus is one of the main malaria vectors Many studies showed that they were present in most of the mountainous areas nationwide, and overlapped the distribution of An harrisoni in some places [80] 23 In Vietnam, although the environment is changing and insecticides are continuously used in health and agriculture sectors for a long time on a large scale, An minimus is still present in almost survey sites in midlands and mountainous areas nationwide, especially in the North Our finding is also consistent with the study on the distribution of malaria vectors in the period of 2003-2012 by Vu Duc Chinh, in which An minimus was found at 119 points all over the country, all of which were mountains and forests [5] 4.1.3 Biological, ecological characteristics and disease transmission role of malaria vectors in the Central Highlands 4.1.3.1 Host preference in malaria vectors An minimus preferred biting cattle to people, except for Van Canh, Binh Dinh where An minimus bit people outdoor more than cattle In contrast, An dirus mainly bites people other than cattle, which can be due to the fact that An dirus mainly lives in forests and fields where other hosts such as cattle are less common The secondary vectors An aconitus, An maculatus, and An Jeyporiensis mainly bite humans This study is also consistent with the results of other studies on host selection in malaria vectors In the central province of Quang Nam, human biting index of An dirus was about 92% and no An dirus bit cattle at night [43] In other central provinces, human biting rate of An dirus was times higher than cattle biting rate [35] The ratio of human bites/animal bites of An dirus was 6:1 [36] in Khanh Phu (Khanh Hoa), and 11:1 in the Highlands [26] The main vector An minimus is catergorized into the group of near human mosquitoes [75] In Assam (India) human biting index of An minimus was 93% [67] This index in central Vietnam was 90% [35] However, the presence of different hosts also affects the host selection of An minimus In short, An minimus populations in the Central Highlands, Southeast and North bite both humans and animals However, the majority of An minimus were collected by lighttrap catch in cattle sheds A few were caught by using human bait method According to the research by Nguyen Tuyen 24 Quang (1996), human biting index of An minimus in Van Canh, Binh Dinh was 90% [35] 4.1.3.2 Indoor and outdoor biting activities of malaria vectors In this study, the biting activity of mossquitoes was higher outdoor than indoor in both the village and in the field This finding is also consistent with other domestic and international studies However, indoor or outdoor biting activities vary depending on the time and place Some other studies show that the indoor biting activity is higher than outdoor activity According to Krajana (2014) in Thailand, An dirus had the ratio of indoor biting/outdoor biting was 9:8 [83] In Northern Thailand, the indoor biting habit of An dirus was not much more than outdoor [113], while in Cambodia [70] and in Central Vietnam, An dirus was caught indoor 2-5 times more than outdoor [43] A survey conducted in Van Canh district as well as in central Vietnam showed that An dirus was more active outdoor from 18h to 22h and more active indoor from 22h to 5h, so the indoor and outdoor biting density was equal for the whole night [35] 4.1.3.3 Nighttime biting of malaria vectors In our study, human biting activity of An dirus, An minimus, An aconitus, An jeyporiensis and An maculatus mainly occurred before midnight in both residential and forest areas, then decreased to morning It is obvious that early human biting increases the chance of exposure of vectors to people and limites the effectiveness of bedbets (including insecticide impregnated bed nets) because mosquito bites occur before the bed time Therefore, in order to prevent vectors in places with early biting activities of vectors, in addition to residual spraying (residential areas) and bed net impregnation (residential areas; for people sleeping in forests and fields), other personal protection measures (such as mosquito repellent cream) may be effective in restricting contact between people and vectors during the pre-bedtime period, especially for those who work and stay overnight in the forest and field The biting activity of An minimus usually last all night However, the biting peak varies by space and time Our finding is also consistent with other studies In Vietnam, our study 25 found a earlier biting peak compared to the previous study by Nguyen Tho Vien suggesting that the biting peak of An minimus was from 22h to 3h [49] 4.1.3.4 Disease transmission role of malaria vectors at two highly endemic sites of the Central Highlands The malaria transmission role of vector species may increase or decrease depending on many factors, including impact of environmental changes The presence of two or several vector species in the same region increases the risk of malaria spread in that area, especially when the main vectors are simultaneously present This can be obvious in some mountainous areas in Southeast Asia, including the CentralHighlands-Southeast region of Vietnam where exists both the main vectors An minimus and An dirus and several secondary vectors, causing many difficulties for malaria control Through ELISA analysis, the two main malaria vectors An dirus and An minimus were ELISA positive with both parasite species P falciparum P vivax The secondary vectors An aconitus, An jeyporiensis and An maculatus had not been infected with malaria parasites Parasite infection rate of An dirus ranged from 0.8 to 2.05%, while this rate of An minimus was higher at 11.3% This result is also consistent with some domestic and foreign studies 4.2 Susceptibility of malaria vectors to insecticides being used for malaria control in the Central Highlands 4.2.1 Susceptibility of An minimus to insecticides In this study, we have not found any resistance of An minimus to pyrethroid groups Compared with some other studies in the world, WHO sensitive tests showed that An minimus was increasingly resistant to deltamethrin with the mortality of 92% [106] In Tripura, research revealed that both An minimus s.s and An baimaii were also sensitive to DDT [105] In spite of no resistance of An minimus to pyrethroid found in this study, the susceptibility test results in the period of 2003-2012 indicated a few study sites with pyrethroid resistance, only in northern Vietnam [5] 26 4.2.2 Susceptibility of An dirus to insecticides The main vector An dirus at test sites was still sensitive to alpha-cypermethrin 30 mg/m2 and lambda-cyhalothrin 0.05% in northern Thailand An dirus s.l was still susceptible to deltamethrin 0.05% (mortality of 100%) [56] In Thailand, An dirus was sensitive to bifenthrin 0.09% and deltamethrin 0.05% with the mortality of 100% [101] In Laos, WHO susceptibility test showed the two main vectors An dirus, An minimus had not been resistant to pyrethroid [98] So far, in Vietnam as well as other countries with the presence of An Dirus, no resistance of this species to insecticides used in malaria control has been reported However, some studies have recorded the insecticidal avoidance of these mosquitoes [35], [51], [113] In fact, insecticidal avoidance is also a kind of behavioral resistance caused by the presence of insecticides Behavioral resistance also makes it difficult for vector control because the efficacy of chemicals is limited due to a decreased chemical exposure of vectors [51] An dirus is a species living in the forest habitat It only comes to a host when needing blood, so its exposure to insecticides is limited, resulting in its weak insecticidal resistance compared to An epiroticus and An Minimus which live near humans Thus it can be said that no insecticidal resistance of An dirus populations has been found, and available insecticides can be used to contain this species CONCLUSIONS Anopheles species composition, distribution, ecological characteristics and disease transmission role of malaria vectors in Central Highlands of Vietnam - A total of 18 Anopheles species were collected in the Central Highlands, including 16 species in the Central and 14 species in the Highlands Two main malaria vectors An dirus and An Minimus and three secondary vectors An aconitus, An 27 jeyporiensis and An maculatus were present in the two regions - Biological and ecological characteristics of malaria vectors at study sites Main vectors An minimus and An dirus preferred biting humans They carried malaria parasites and were active all night The rate of An Dirus and An.minimus in the forest was high The human biting activity of An.dirus and An minimus occurred from 18h to 6h, with the peak from 20h to 24h indoor and outdoor - Disease transmission role of malaria vectors at the focal points: In Khanh Vinh district, the vectors infected with malaria parasites accounted for 0.98%, An dirus infected with P falciparum 0.51% and P vivax 1.04 - 1.54% In Krong Pa district, the overal infection rate was 0.89%, in which P falciparum infection in An minimus was 11.3%; An dirus infected with P vivax was 0.8% In Khanh Vinh, the transmission index of An dirus ranged from 0.094 to 0.138 In Krong Pa, the transmission index of malaria vectors varied from 0.096 to 0.135; An dirus and An minimus had the main role of malaria transmission Susceptibility of malaria vectors to insecticides being used for malaria control in the Central Highlands, 2014 2017 - An minimus was susceptible to Lambda - cyhalothrin 0.05% (Van Canh, Binh Dinh) - An dirus was susceptible to Alpha - cypermethrin 30 mg/m2, Lambda - cyhalothrin 0.05% (Bac Ai-Ninh Thuan, Khanh Vinh-Khanh Hoa) - An aconitus was sensitive to Alpha - cypermethrin 30 mg/m2 and Lambda - cyhalothrin 0.05% (Binh Dinh) - An maculatus was resistant to Alpha - cypermethrin 30 mg/m2 and lambda - cyhalothrin 0.05% (Le Thuy-Quang 28 Binh,Van Canh-Binh Dinh, Bac Ai-Ninh Thuan, Khanh VinhKhanh Hoa, Krong Pa-Gia Lai) - An aconitus was sensitive to Alpha - cypermethrin 30 mg/m2 (Khanh Vinh-Khanh Hoa, Krong Pa-Gia Lai, Krong Na-Dak Lak) RECOMMENDATIONS There should be further studies on ecology, behavior, disease transmission role of malaria vectors and vector control measures in at-high-risk areas, especially in the areas where people still have habits of field sleeping without personal protection measures against mosquito bites Vector control measures should be studied and implemented for field sleepers who are at high risk of malaria infection, helping them protect themselves and their families when working and sleeping in the field, and at the same time protect their communities from getting transmitted Alpha-cypermethrin and Lambda-cyhalothrin belonging to the pyrethroid group are still effective against An aconitus, An dirus and An minimus; however An maculatus in all test sites could be resistant to these insecticides, so its insecticidal susceptibility should be closely monitored during use LIST OF PUBLICATIONS RELATED TO THE THESIS Kim Khue Ngo, Xuan Quang Nguyen, Van Chuong Nguyen (2018), “Species composition, distribution and ecological features of Anopheles populations in some provinces of the Central Highlands, 2016 – 2017”, Proceedings of the 3rd National Scientific Conference (20/5/2018), Publishing House of Natural Science and Technology, Vietnam, pp 643 – 649 Kim Khue Ngo, Thi Kim Thoa Ngo, Xuan Quang Nguyen, Van Chuong Nguyen (2018), “Evaluating the susceptibility of malaria vectors to insecticides in some provinces of the Central Highlands, 2015 – 2017”, Proceedings of the 3rd National Scientific Conference (20/5/2018), Publishing House of Natural Science and Technology, pp 863869 Kim Khue Ngo, Xuan Quang Nguyen, Van Chuong Nguyen, Thi Mong Diep Nguyen, “Vector abundance and species composition of Anopheles mosquitoes in Central Region and Central West Highlands, Viet Nam”, International Journal of Health and Clinical Research, 2018, 1(1):22-29 ... cyhalothrin (Le Thuy-Quang Binh,Van Canh-Binh Dinh, Bac Ai-Ninh Thuan, Khanh Vinh-Khanh Hoa, Krong PaGia Lai) - An aconitus was sensitive to alpha – cypermethrin (Khanh Vinh-Khanh Hoa, Krong Pa-Gia Lai,... Thuy-Quang 28 Binh,Van Canh-Binh Dinh, Bac Ai-Ninh Thuan, Khanh VinhKhanh Hoa, Krong Pa-Gia Lai) - An aconitus was sensitive to Alpha - cypermethrin 30 mg/m2 (Khanh Vinh-Khanh Hoa, Krong Pa-Gia... preferred biting cattle to people, except for Van Canh, Binh Dinh where An minimus bit people outdoor more than cattle In contrast, An dirus mainly bites people other than cattle, which can be