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 albop
Trang 1INTRODUCTION
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 4 northern provinces of Vietnam (2016 - 2017)” with the following 2 objectives:
1 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
2 Analyze the correlation between climatic factors, vector indices, and dengue cases in Hanoi, 2016 - 2017
NOVELTY, SCIENTIFIC AND PRACTICAL
SIGNIFICANCE OF THE THESIS
1 The study has identified Ae aegypti as a dengue
transmission agentive, specifically discovered Ae.albopictus
at the dengue outbreak in Vietnam
Trang 22 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 1 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 3 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
Trang 31.1.3 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 3 In 2009, the number of cases across the North was 18,485 cases, in which there were 16,090 cases and 4 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 7 deaths
1.1.3.2 Situation of dengue fever in Hai Phong
Through surveillance, Hai Phong had 113 cases in 2015,
8 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 0 deaths, which decreased by 33.8% compared to the same period in 2015 In 2017, there were 194 cases and 0 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 4 types: Dengue 1 (D1), Dengue 2 (D2), Dengue
3 (D3) and Dengue 4 (D4)
1.3 Life cycle and morphology of Aedes mosquitoes
1.3.1 Life cycle of Aedes
The life cycle of Aedes includes 4 stages: Eggs - Larvae - Pupae - Adult mosquitoes, in which the first 3 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
Trang 4on 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 450north 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
Trang 51.4.2.3 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
Trang 6transmission 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
Trang 72.3 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
- 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
Trang 82.5 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
Trang 92.6 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
2.10 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
Trang 102.11 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 (%)
Trang 113.1.2.3 Resting heights of Ae aegypti
Table 3.19 Percentage of Ae aegypti resting at different
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 (%)
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