Dengue fever vectors in the southern of Vietnam

The dengue (DF)/dengue hemorrhagic fever (DHF) are mosquito-borne diseases known to occur in the whole country.

The disease was reported in the northern provinces of Ha Noi and Hai Phong since 1959, then the disease has become widely spread throughout Vietnam. And in recent years the disease has had a great impact on South Vietnam, where the geographical distributions of Ae. aegypti and Ae. albopictus overlap, where simultaneously DF/DHF, as well as malaria is presenting.

Dengue is transmitted by the primary vector, Aedes aegypti is distributed in all provinces, and by the secondary vector, Aedes albopictus, this vector is mainly distributed in South Vietnam.

There are 59 species of subgenera were found in Vietnam, include Ae. aegypti and Ae. albopictus. In which there are 22 Aedes species in South Vietnam: Aedes aegypti, Ae. albopictus, Ae. amesii, Ae. andamanensis,; Ae. annandalei, Ae. caecus, Ae. cancricomes, Ae. desmotes, Ae. dux, Ae. eldriger, Ae. helenac, Ae. imprimens, Ae. laniger, Ae. lineotopennis, Ae. maclalanei, Ae. mediolineatus , Ae. niveus, Ae. poicilius, Ae. pulcheiventer, Ae. vexans, Ae. vigilax, Ae. vittatus.

Fig 1. Activities collected Aedes mosquitoes in the field

Mosquito susceptibility to insecticides

Similarly, like malaria, the monitoring of Aedes mosquito susceptibility to insecticides is regularly maintained to detect insecticide resistance to make comments for the national dengue control program. The result on sensitivity of dengue mosquito to insecticides from 2000 – 2018 as follows:

Fig 2. Activities of Aedes mosquito susceptibility tests in the field

From 2000 - 2002 (Table 1):

  • Deltamethrin 0,05%: Ae. aegypti collected in Ben Tre Town, Binh Dai District and District 2 which were possible resistance (mosquitoes mortality 90 – 97%); Ae. aegypti collected in Can Gio District, Binh Long District and Dong Xoai Town which were resistance (mosquitoes mortality 19.33 – 84%).
  • Permethrin 0,75%: Ae. aegypti collected in Binh Dai District and District 2 which were possible resistance (mosquitoes mortality 94 – 96%); Ae. aegypti collected in Ben Tre Town, Can Gio District, Binh Long District and Dong Xoai Town which were resistance (mosquitoes mortality 8 – 79%).
  • Alpha-Cypermethrin 30mg/m2: Ae. aegypti collected in Binh Dai District, District 2 and Binh Long District which were possible resistance (mosquitoes mortality 92 – 96%); Ae. aegypti collected in Ben Tre Town, Can Gio District and Dong Xoai Town which were resistance (mosquitoes mortality 25 – 82%).
  • Lamda-Cyhalothrin 0.05%: Ae. aegypti collected in Binh Dai District and District 2 which were possible resistance (mosquitoes mortality 92 – 96%); Ae. aegypti collected in Ben Tre Town, Can Gio District, Binh Long District and Dong Xoai Town which were resistance (mosquitoes mortality 24 – 67%).
  • Malathion 5%: Ae. aegypti collected in Binh Dai District, Can Gio District and Dong Xoai Town which were susceptibility (mosquitoes mortality 99 – 100%); Ae. aegypti collected in District 2, Binh Long District which were possible resistance (mosquitoes mortality 90 – 95%); Ae. aegypti collected in Ben Tren Town which were resistance (mosquitoes mortality 81%).
  • Etofenprox 0.05%: Ae. aegypti collected in all sites (Ben Tre Town, Binh Dai District, Can Gio District, District 2, Binh Long District and Dong Xoai Town) which were resistance (mosquitoes mortality 1 – 53%).
  • DDT 4%: Ae. aegypti collected in all sites (Ben Tre Town, Binh Dai District, Can Gio District, District 2, Binh Long District and Dong Xoai Town) which were resistance (mosquitoes mortality 0 – 20%).

From 2010 – 2014 (Table 2):

The result on sensitivity of dengue mosquito to insecticides from 2010 - 2014 in Table 2 show that:

  • Deltamethrin 0,05%: 98,5% (64/65 samples) Aedes aegypti (F1) was resistance and possible resistance.
  • Permethrin 0,75%: 96,1% (49/51 samples) Aedes aegypti (F1) was resistance and possible resistance.
  • Alpha-Cypermethrin 30mg/m2: 54,3% (19/35 samples) Aedes aegypti (F1) was resistance and possible resistance.
  • Malathion 5%: 100% (38/38 samples) Aedes aegypti (F1) was susceptibility.

In 2018 (Table 3):

  • Deltamethrin 0.05%: Ae. aegypti collected in Tra Vinh, Soc Trang and Ben Tre that was resistance (mosquitoes mortality 73-87%). Ae. aegypti collected in Ca Mau province, Bac Lieu province, Kien Giang, Ba Ria - Vung Tau which were possible resistance (mosquitoes mortality 91 - 94.29%).
  • Permethrin 0.75%: Ae. aegypti collected in all provinces (Ca Mau, Bac Lieu, Tra Vinh, Soc Trang, Binh Phuoc and Lam Dong) which were possible resistance (mosquitoes mortality 91 - 96.05%).
  • Malathion 5%: Ae. Aegypti collected in three provinces (Ca Mau, Bac Lieu, Soc Trang) that was sensitive (mosquitoes mortality from 99% - 100%)
  • Cyfluthrin 0.05%: Ae. Aegypti collected in Soc Trang that were sensitive (mosquitoes mortality 100%).

Fig 3. Insecticides used for space treatment for Aedes mosquitoes control

Table 1. Results of susceptibility tests on Ae. aegypti (F1) to insecticides (from 2000 - 2002).

N0

Province

Deltamethrin 0,05%

Permethrin 0,75%

Alpha-Cypermethrin 30mg/m2

Lamda-Cyhalothrin 0.05%

Malathion 5%

Etofenprox 0.05%

DDT 4%

The mosquito mortality (%) after a holding period of 24 hours (60 minutes exposure)

1

Ben Tre

Ben Tre Town

90

62

82

67

81

4

2

Binh Dai District

97

94

92

90

100

53

20

2

Ho Chi Minh

Can Gio District

84

18

75

24

99

1

0

District 2

97

96

96

93

95

20

11

3

Binh Phuoc

Binh Long District

84

79

96

56

90

1

0.8

Dong Xoai Town

19.33

8

25

28

99

7

2

Vu Duc Huong and et al, (2002). Susceptibility of Aedes aegypti to Insecticides in Viet Nam.

Table 2. Results of susceptibility tests on Ae. aegypti (F1) to insecticides (from 2010 - 2014).

Provinces

Times

Deltamethrin 0,05%

Permethrin 0,75%

Alphacypermethrin 30mg/m2

Malathion 5%

Total

Test

Result

Total

Test

Result

Total

Test

Result

Total

Test

Result

S

PR

R

S

PR

R

S

PR

R

S

PR

R

HCM

2010

2

0

1

1

1

0

0

1

-

-

-

-

-

-

-

-

2011

4

0

2

2

3

0

1

2

-

-

-

-

-

-

-

2012

6

0

0

6

6

0

1

5

5

5

0

0

5

5

0

0

2013

7

0

5

2

6

0

5

1

2

0

1

1

8

8

0

0

2014

8

0

5

3

5

0

4

1

8

0

2

6

2

2

0

0

Binh Phuoc

2010

2

0

0

2

1

0

0

1

-

-

-

-

-

-

-

-

2011

2

0

0

2

1

0

0

1

-

-

-

-

-

-

-

-

2012

4

0

0

4

4

0

0

4

4

4

3

3

0

0

2013

3

0

1

2

3

0

3

0

1

0

0

1

1

1

0

0

2014

1

0

1

0

-

-

-

-

1

0

1

0

0

-

-

-

Tay Ninh

2010

1

0

0

1

1

0

0

1

-

-

-

-

-

-

-

-

2011

1

0

0

1

1

0

0

1

-

-

-

-

-

-

-

-

2013

4

0

1

3

5

0

1

4

2

0

2

0

2

2

0

0

An Giang

2012

4

0

0

4

4

1

2

1

4

4

4

4

0

0

2013

1

0

1

0

0

2

0

0

2

2

2

0

0

2014

-

-

-

-

1

0

0

1

1

0

0

1

-

-

-

-

Ba Ria - Vung Tau

2010

-

-

-

-

-

-

-

-

-

-

-

-

1

1

0

0

2011

1

0

0

1

1

0

0

1

-

-

-

-

1

1

0

0

2012

3

1

2

3

1

2

3

3

0

0

3

3

0

0

2013

2

0

0

2

2

0

2

0

1

0

1

0

1

1

0

0

2014

1

0

1

0

1

0

1

0

-

-

-

-

-

-

-

-

Ca Mau

2010

1

0

0

1

-

-

-

-

-

-

-

-

1

1

0

0

2011

1

0

0

1

-

-

-

-

-

-

-

-

1

1

0

0

Ben Tre

2010

1

0

0

1

-

-

-

-

-

-

-

-

1

1

0

0

2011

1

0

0

1

-

-

-

-

-

-

-

-

1

1

0

0

Dong Nai

2012

2

0

2

0

1

0

1

0

-

-

-

-

-

-

-

-

2013

2

0

2

0

1

0

1

0

1

0

0

1

1

1

0

0

Total

65

1

22

42

51

2

24

25

35

16

7

12

38

38

0

0

Note: The current recommendations are: Mortality ≥ 98 - 100% (Susceptibility); Mortality between 90% - 97% (Possible resistance); Mortality ˂90% (Resistance). S: Susceptibility; PR: Possible resistance; R: Resistance.

Table 3. Results of susceptibility tests on Ae. Aegypti (F1) to insecticides.

N0

Province

Deltamethrin 0,05%

Permethrin 0,75%

Malathion 5%

Cyfluthrin 0,05%

The mosquito mortality (%) after a holding period of 24 hours (60 minutes exposure)

1

Ca Mau

91

93

99

-

2

Bac Lieu

94.29

92

100

-

3

Tra Vinh

73

93

-

-

4

Soc Trang

87

92

100

99

5

Ben Tre

77

-

-

-

6

Binh Phuoc

-

96.05

-

-

7

Lam Dong

-

93.22

-

-

8

Kien Giang

91

-

-

-

9

Ba Ria – Vung Tau

94

-

-

-

Note: The current recommendations are: Mortality ≥ 98 – 100% (Susceptibility); Mortality between 90% - 97% (Possible resistance); Mortality ˂90% (Resistance).