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 Specific research studies Entomology
Catching mosquitoes in the forest.
Evaluation of the relationship between risk factors for malaria increase and the impact of climate change and ecological environment around hydroelectric, irrigational buildings in Gia Lai province

 

Name of investigators: Dr. Nguyen Xuan Quang, BA. Le Giap Ngo, BA. Vu Tuan AnhTechnician. Le Hoang Dung, Technician. Le Dinh Vinh, Nurse. Trinh Thi Nhu

Introduction

Malaria situation in the Central - Western Highlands in 2013 and the first nine months of 2014 tended to decrease. However in the last 2 months of 2014 (October, November), malaria was recorded with unexpected occurrence in the Central - Western Highlands areas, the proportion of malaria patients and parasites increased in almost every province. In particular, in October and November 2014, parasite rate of Gia Lai province increased from 71.38 to 168.89% compared to the same period in 2013. Therefore, we conducted surveys, epidemiological surveillance of malaria and the variation, distribution and behaviour of Anopheles mosquitoes in order to attain the objectives:

1. Evaluation of indicators of malaria in the community

2. Determination of the species composition, the number of species, density of malaria vectors in Ia Mla commune.

3. Dissection and conduction of ELISA tests to evaluate the proportion of mosquitos infected with Plasmodium parasite.

IILocation, duration, object andmethodology

2.1. Location: Ia Mla commune, KrongPa district, GiaLai province

2.2. Duration: From 12/16/2014 to 12/28/2014 (13 days).

2.3. Research design: The cross-sectional and retrospective study

2.4. Object of study

- Local people (especially forest goers, field-hut sleepers)

- Malaria transmitting Anopheles mosquitoes

2.5. The techniques and methods of investigation

2.5.1. Epidemiological investigation of malaria

- Epidemiological situation of malaria in the locality

- Examination and determination of clinical malaria cases and conduction of smear tests for 400 people to identify Plasmodium parasite in Ia Mla community.

2.5.2. Survey insect indicators

Implement measures to investigate, monitor, collect adult mosquitoes and larvae due to the method of WHO (1994) and the National Institute of Malariology and Parasitology and Entomology, Ha Noi (2011).

Species composition, Anopheles larval and mosquito densities.

Ecology and behaviour of vectors such as biting and resting behaviour, host preference.

2.5.3 Mosquito dissectionDetermine the rate of mosquitoes infected with malaria parasite

(Alive mosquitoes were dissected for oocyste, sporozoits and lay egg or not yet).

III. Results and discussions

a.The situation of malaria in the Ia Mla commune in 2014 (data district health)

Table 1: Malaria situation in 2014 compared to the same period in 2013

Indicator

Year

Commune Ia Ml ? Themonthsin2014

Total

1

2

3

4

5

6

7

8

9

10

11

12

Patients withmalaria

2014

9

19

5

2

3

0

3

3

19

13

36

29

141

2013

5

15

9

5

2

10

16

16

25

48

28

15

194

%(+,-)

+280

-40

-44,4

-60

+50

-100

-81,3

-81,3

-24

-72,9

+28,6

+93,3

-27,3

Slides, test strips

2014

61

89

40

34

28

52

58

132

75

76

120

100

865

2013

47

58

66

58

36

36

78

79

61

133

115

86

853

Parasites

2014

19

9

5

2

3

0

3

3

19

13

36

29

141

2013

5

14

9

5

2

10

16

16

25

48

28

15

193

%(+,-)

+280

-35,7

-44,4

-60

+50

-100

-81,3

-81,3

-24

-72,9

+28,6

+93,3

-26,9

Malaria situation in Ia Mla commune in 2014:

- The proportion of Plasmodium /slides + test strips in 2014 is 16.3% (141/865).

- In 2014, Plasmodium in January increased by 280% while reduced from 24 to 100% in other months. Especially the last 2 months (November and December) of 2014, Plasmodium parasite surged from 28.6 to 93.3% in comparison with the same period in 2013.

- The overall number of Plasmodium reduced 26.9% in 2014 compared with the same period in 2013.

Graph 1: Performance ratio Plasmodium/slides+test strips in 2014 of Ia Mla commune

3.2. Results of the survey on the prevalence of malaria in the Ia Mla commune

Table 2: Results of cross-sectional survey on the prevalence of malaria in the Ia Mla commune

Group
age

Number

Clinical malaria

Spleen

Parasites

N.

%

N.

%

N.

%

P.f

P.v

PH

GB

< 1

0

0

0

0

0

0

0

0

0

0

0

1 - 2

2

0

0

0

0

0

0

0

0

0

0

3 - 4

10

0

0

0

0

0

0

0

0

0

0

5 - 8

46

0

0

0

0

0

0

0

0

0

0

9 - 16

65

0

0

0

0

1

1,5

1

0

0

1

>16

277

6

2,17

0

0

6

2,17

2

3

1

2

Total

400

6

1,5

0

0

7

1,75

3

3

1

3

Conducting smear examination and blood tests for 400 people in the Ia Mla commune, 6 patients were found with clinical malaria, accounting for 1.5% and 7 blood tests found the malaria parasites, accounting for 1.75% and notfoundspleen.

3.3Results of survey on social insects in Ia Mla commune

Table 3: Anopheles mosquito species composition in the Ia Mla commune

No.

Species

In hamlet

Buffer zone (near forest)

In upland forest

Mosquitoes

Larvae

Mosquitoes

Larvae

Mosquitoes

Larvae

N.

(%)

N.

(%)

N.

(%)

N.

(%)

N.

(%)

N.

(%)

1

An.aconitus

0

0

0

0

20

17,7

0

0

6

12,5

0

0

2

An.barbirostris

8

6,4

4

5,8

5

4,4

0

0

0

0

0

0

3

An.dirus

0

0

0

0

2

1,8

0

0

19

39,6

0

0

4

An.kochi

14

11,2

0

0

8

7,1

0

0

0

0

0

0

5

An.maculatus

8

6,4

0

0

15

13,3

0

0

8

16,7

8

16,7

6

An.peditaeniatus

21

16,8

15

21,7

16

14,2

14

31,8

8

16,7

16

33,3

7

An.philippinensis

6

4,8

0

0

0

0

0

0

0

0

0

0

8

An.sinensis

25

20,0

18

26,1

11

9,7

12

27,3

7

14,5

24

50,0

9

An.splendidus

18

14,4

0

0

14

12,4

0

0

0

0

0

0

10

An.vagus

25

20,0

32

46,4

22

19,4

18

40,9

0

0

0

0

 

Total

125

100

69

100

113

100

44

100

48

100

48

100

- In the hamlet, 8 species of anopheles were found not catching the disease vectors. In the hamlet, An. vagus and An. sinensis predominate.

- In the buffer zone (near the forest), 9 species of Anopheles were found, including the presence of main malaria vector - An. dirus and sub vector - An. aconitus and An. maculatus. In the buffer zone, An. aconitus and An. vagus dominate.

- In the plot-huts, 5 species of Anopheles were found, including the presence of main malaria vector - An. dirus and 2 sub vector - An. aconitus and An. maculatus. In the forests, An. dirus predominate.

Table 4: Results of investigation of Anopheles mosquitoes in residential areas in the Ia Mla commune

No.

Species

Total

Collection Methods

Light trap in door

Light trap out door

Collected by the human bait in door

Collected by the human bait out door

Collection in door-daytime

Catch mosquitoes cattle

N.

Density

N.

density

N.

density

N.

density

N.

density

N.

density

1

An.barbirostris

8

0

0

0

0

0

0

0

0

0

0

8

2,0

2

An.kochi

14

0

0

0

0

0

0

0

0

0

0

14

3,5

3

An.maculatus

8

1

0,17

0

0

0

0

2

1,0

0

0

5

1,25

4

An.peditaeniatus

21

2

0,33

1

0,17

4

2,0

3

1,5

0

0

11

2,75

5

An.philippinensis

6

0

0

0

0

0

0

0

0

0

0

6

1,5

6

An.sinensis

25

4

0,67

1

0,17

8

4,0

3

1,5

0

0

9

2,25

7

An.splendidus

18

2

0,33

2

0,33

3

1,5

4

2,0

0

0

7

1,75

8

An.vagus

25

2

0,33

0

0

0

0

0

0

0

0

23

5,75

 

Total

125

11

1,83

4

0,67

15

7,5

12

6,0

0

0

83

20,75

Investigation of mosquitoes in residential areas showed that the main malaria vectors - An. dirus, An. Minimus were not found; only found the sub vector - An. maculatus.

Table 5: Results of the survey on Anopheles mosquitoes in the buffer zone of the Ia Mla commune

No.

Species

Total

Collection Methods

Light trap in door

Light trap out door

Collected by the bait in door

Collected by the bait out door

Collection in door-nighttime

Catch mosquitoes cattle

N.

density

N.

density

N.

density

N.

density

N.

density

N.

density

1

An.aconitus

20

9

1,5

0

0

2

1,0

3

1,5

0

0

6

1,5

2

An.barbirostris

5

0

0

0

0

0

0

0

0

0

0

5

1,25

3

An.dirus

2

2

0,33

0

0

0

0

0

0

0

0

0

0

4

An.kochi

8

0

0

0

0

0

0

0

0

0

0

8

2,0

5

An.maculatus

15

3

0,5

0

0

1

0,5

4

2,0

0

0

7

1,75

6

An.peditaeniatus

16

2

0,33

2

0,33

0

0

3

1,5

0

0

9

2,25

7

An.sinensis

11

2

0,33

0

0

2

1,0

1

0,5

0

0

6

1,5

8

An.splendidus

14

2

0,33

1

0,17

0

0

1

0,5

0

0

10

2,5

9

An.vagus

22

1

0,17

0

0

0

0

0

0

0

0

21

5,25

 

Total

113

21

3,5

3

0,5

5

2,5

12

6,0

0

0

72

18,0

Investigation of mosquitoes has found that the main malaria vector is An. Dirus in the buffer zone, with a density of 0.33 mosquito/trap/night and also found the sub vectors: An. aconitus and An. maculatus.

Table 6: Results of investigation of Anopheles mosquito in the plot-huts in the Ia Mla commune

No.

Species

Total

Collection Methods

Light trap in door

Light trap out door

Collected by the human bait in door

Collected by the human bait out door

Collection in door-nighttime

N.

density

N.

density

N.

density

N.

Density

N.

density

1

An.aconitus

6

4

0,67

0

0

0

0

2

0,5

0

0

2

An.dirus

19

8

1,33

1

0,17

4

1,0

6

1,5

0

0

3

An.maculatus

8

3

0,5

0

0

2

0,5

3

0,75

0

0

4

An.peditaeniatus

8

3

0,5

2

0,33

1

0,25

2

0,5

0

0

5

An.sinensis

7

2

0,33

0

0

2

0,5

3

0,75

0

0

 

Total

48

20

3,33

3

0,5

9

2,25

16

4,0

0

0

Investigation of mosquitoes in the plot-huts has found that the main malaria vector is An. Dirus, with a density of 1.0-1.5 mosquito/person/night and 0.17 to 1.33 mosquito/trap/night; in addition the sub vectors An. maculatus and An. Aconitu are also found.

3.4 Activity of anopheles mosquito

Table 7: Activities of Anopheles mosquitoes in the upland forest of Ia Mla commune

TT

Species

Total

Operation ofhourlyanopheles

18-19

19-20

20-21

21-22

22-23

23-24

0-1

I

O

I

O

I

O

I

O

I

O

I

O

I

O

1

An.aconitus

2

0

0

0

0

0

0

0

1

0

1

0

0

0

0

2

An.dirus

10

0

0

0

0

1

2

2

2

1

1

0

1

0

0

3

An.maculatus

5

0

0

0

0

0

1

1

1

1

1

0

0

0

0

4

An.peditaeniatus

3

0

0

0

0

0

0

1

1

0

1

0

0

0

0

5

An.sinensis

5

0

0

0

0

1

1

0

1

1

1

0

0

0

0

 

Total

25

0

0

0

0

2

4

4

6

3

5

0

1

0

0

Noted: I: Collected by the human bait indoor; O: Collected by the human bait outdoor

Anopheles mosquitos fly and bite after 8 p.m., after 23 p.m. due to bad weather conditions: cold, windy, Anopheles mosquitos were not caught.


Graph 2: Activities of Anopheles mosquitos in the fields


3.5. Results of dissection

Table 8: Results of dissecting Anopheles mosquito species

No.

Species

Quantity

Sella

Sporozoit

Stomach

Ovaries

N.

Sporozoit

N.

Oocyste

Parous

Nulliparous

1

An.aconitus

20

12I8II

20

0

12

0

13

7

2

An.dirus

18

10I8II

18

0

10

0

11

7

3

An.maculatus

24

14I10II

24

0

14

0

9

15

 

Total

62

36I26II

62

0

36

0

33

29

- Oocyste and sporozoite were not found (salivary gland and stomach).

- Laying mosquito rate is 53.2%.

IV. Conclusions and suggestions:

4.1 Conclusion

4.1.1. Results of retrospective study and epidemiological investigation of malaria in the Ia Mla commune

- The proportion of parasites/slides + test strips in 2014 in Ia Mla commune is 16.3%.

- In 2014, malaria parasites increased by 280% in January and reduced from 24% to 100% in other months. In particular, in the last 2 months (November and December), malaria parasites surged from 28.6% to 93.3% in comparison with the same period in 2013.

- The overall number of malaria parasites reduced 26.9% in comparison with the same period in 2013.

- Conducting smear examination and blood tests on 400 people in the Ia Mla commune, which found 6 patients with clinical malaria, accounting for 1.5%. Seven malaria parasites were found in blood tests, accounting for 1.75% and spleens were not found.

4.1.2. Species composition, density of malaria vector in the commune Ia Mla

Of the Anopheles mosquitoes collected in Ia Mla, there are 268 adult Anopheles mosquito species and 161 larval (of 10 species). In particular the main malaria vector An.dirus was found with a density of 1.0-1.5 mosquito/person/night and 0.17 to 1.33 mosquito/trap/night and sub vectors such as An. aconitus, An. maculatus and An. Vagus were also found.

4.1.3. Results of mosquito dissection

- 62 Anopheles mosquitoes were dissected (of 3 species). They were main and sub malaria vectors, but oocyste and sporozoite were not found (salivary gland and stomach of mosquitoes).

- Laying mosquito rate is 53.2%

4.2. Suggestion

Through the result of retrospective data in CHC in health station and investigation group, we suggest:

- More funds, malaria epidemiology supervision, especially the people who are entering the forests and sleeping in plot-huts and comeback from the long-time trip.

- Provide communication and education regularly about malaria control measures so that everybody knows to protect themselves and their families.

- The forest-goers and plot-huts sleepers should bring bed-nets and hammock nets when they go to work and sleep in the forest and plot-huts.


03/04/2015
By Dr. Nguyen Xuan Quang, Head of Entomology Department
(Modified by Huynh Thi An Khang and Nguyen Thai Hoang)
 

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