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).