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

Therefore, we conducted the study “Species composition, distribution, ecological characteristics of Anopheles and susceptibility of malaria vectors to insecticides used for malaria contr

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:

1 To determine the species composition of Anopheles, distribution, biology, ecology and disease transmission role of malaria vectors in the Central-Highlands, 2014-

2017

2 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 1 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 3 genera) and Culicinae (including 3 genera) [75] Particularly, the subfamily Anophelinae Grassi, 1900 now has

547 species of 3 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 do 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 4 cases [15]

CHAPTER 2 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 4 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 4 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

+ 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 3 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 Highlands region, including 16 species from the Central and 14

Central-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

Study sites No of

species

Percentage (%)

No of vectors Primary Secondary Quang

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

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

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

Daytime indoor resting shelter catch: DIRSC

Daytime outdoor resting shelter catch: DORSC

An

minimu

s

0 0 0.66 1.33 0.66 2.0 1.33 0

Table 3.12 Density of malaria vectors in Phuoc Thanh

commune - Ninh Thuan

3.1.2.2 Biting habit of malaria vectors in the forest area

+ Biting habit of malaria vectors in in Khanh Vinh district, Khanh Hoa province

Table 3.11 Landing density of malaria vectors in field huts in

Khanh Vinh district

Table 3.21 Biting density of malaria vectors inside and outside

field huts in Khanh Vinh district

+ Biting habit of malaria vectors in Gia Lai province

Table 3.28 Landing density of malaria vectors in field huts in

Krong Pa

Table 3.31 Biting density of malaria vectors inside

and outside field huts in Krong Pa

Table 3.41 Average lifespan of malaria vector populations in

Khanh Vinh, Khanh Hoa

Locatio

No

Percentag

e of mosquito breeding (%)

Probabilit

y of daily survival (P)

Average lifespan (day)

No

Percentag

e of mosquito breeding (%)

Probabilit

y of daily survival (P)

Average lifespan (day)

Table 3.42 Average lifespan of malaria vector populations in

Krong Pa, Gia Lai

Location Species No

Percentage

of mosquito breeding (%)

Probability

of daily survival (P)

Average lifespan (day)

Table 3.43 Number of mosquitoes infected with malaria

parasites in Khanh Hoa and Gia Lai

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)

- 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 Pa-Gia Lai)

- An aconitus was sensitive to alpha – cypermethrin (Khanh

Vinh-Khanh Hoa, Krong Pa-Gia Lai, Krong Na-Dak Lak)