ABSTRACT
Objective: To evaluate the potential of local mosquitoes to act as vectors for dengue transmission in Japan. Methods: Serotype 2 ThNH28/93 was used to test the dengue susceptibility profiles of Aedes flavopictus miyarai (Ae. f. miyarai), Aedes galloisi (Ae. galloisi) and Aedes albopictus (Ae. albopictus), which were collected in Japan. We used Aedes aegypti from Thailand as a positive control. The mosquitoes were infected with the virus intrathoracically or orally. At 10 or 14 days post infection, the mosquitoes were dissected and total RNA was extracted from their abdomens, thoraxes, heads and legs. Mosquito susceptibility to dengue virus was evaluated using RT-PCR with dengue virus-specific primers. Differences in the infection and mortality rates of the different mosquito species were tested using Fisher's exact probability test. Results: The infection rates for dengue virus administered intrathoracically to Ae. f. miyarai, Ae. galloisi and Aedes aegypti mosquitoes were identical by RT-PCR on Day 10 post infection. All of the body parts we tested were RT-PCR-positive for dengue virus. For the orally administered virus, the infection rates in the different body parts of the Ae. f. miyarai mosquitoes were slightly higher than those of Ae. albopictus mosquitoes, but were similar to the control mosquitoes (P > 0.05). The mortality rates for Ae. f. miyarai and Ae. albopictus mosquitoes were similar (P = 0.19). Our data indicated that dengue virus was able to replicate and disseminate to secondary infection sites in all of the four mosquito species (Japanese and Thai). Conclusions: Ae. albopictus is a well-known candidate for dengue transmission in Japan. However, our data suggest that Ae. f. miyarai from Ishigaki Island (near Okinawa Island) and Ae. galloisi from Hokkaido (Northern Japan) should also be regarded as potential vectors for dengue transmission in these regions. Further studies on these mosquitoes should be conducted.
ABSTRACT
The emergence of insecticide resistance in mosquito vectors was an important issue to be considered as one of factors influencing the success of vector control. The early detection of resistance could help the health personnel to plan and select appropriate alternative control measures or insecticide for effective control. Therefore biochemical assay of enzymes in mosquito was conducted to detect the emergence of insecticide resistance and to define the machanisms involved in pyrethroid resistance. Adults of Aedes aegypti from two localtities in Ratchaburi province were subjected to permethrin and deltamethrin selection in laboratory. After three generations of selection, permethrin-selected and deltamethrin-selected strains were established. Their LT 50 increased to 7.46 and 1.18 folds in the F3 strains that were selected with permethrin and deltamethrin respectively. The enzymes of these mosquitoes were assayed biochemically to study the mechanisms of resistance. The results revealed significant increase of esterase activity and monooxygenase levels in both strains when compared with labolatory susceptible strain. Glutathione-S-transferase activity was found to increase in permethrin-selected strain but not in deltamethrin-selected strain. This suggested that not only esterase and monooxygenase but also glutathione-S-transferase were associated with permethrin resistance in Ae. aegypti. The exposing of permethrin-selected and deltamethrin-selected mosquitoes to diagnostic concentration of permethrin (0.75%) and deltamethrin (0.05%) indicated no cross resistance for permethrin to deltamethrin while slight cross resistance from deltamethrin to permethrin was evident. It seemed that glutathione S-tranferase was not associated with cross resistance since its activity in deltamethrin-selected strain remained unchanged as compared with that of laboratory susceptible strain.