Bedbugs are found in many countries around the world, and in some regions they are resistant to numerous insecticides. This study surveyed bedbugs in Thailand and determined their resistance to insecticides. The surveys were carried out in six provinces that attract large numbers of foreign tourists: Bangkok, Chonburi, Chiang Mai, Ubon Ratchathani, Phuket, and Krabi. Bedbugs were collected from hotels and colonized in the laboratory to evaluate their resistance to insecticides. Cimex hemipterus (F.) was found in some hotels in Bangkok, Chonburi, Phuket, and Krabi, whereas Cimex lectularius L. was found only in hotels in Chiang Mai. No bedbugs were found in Ubon Ratchathani. The colonized bedbugs showed resistance to groups of insecticides, including organochlorines (dichlorodiphenyl trichloroethane, dieldrin), carbamates (bendiocarb, propoxur), organophosphates (malathion, fenitrothion), and pyrethroids (cyfluthrin, deltamethrin, permethrin, lambda-cyhalothrin, etofenprox) in tests using World Health Organization insecticide-impregnated papers. The new insecticides imidacloprid (neonicotinoid group), chlorfenapyr (pyrrole group), and fipronil (phenylpyrazole group) were effective against the bedbugs; however, organophosphate (diazinon), carbamates (fenobucarb, propoxur), and pyrethroids (bifenthrin, cypermethrin, esfenvalerate, etofenprox) were ineffective. Aerosols containing various pyrethroid insecticides with two to four different active ingredients were effective against the bedbugs. The results obtained from this study suggested that both species of bedbugs in Thailand have developed marked resistance to various groups of insecticides, especially those in the pyrethroid group, which are the most common insecticides used for pest control. Therefore, an integrated pest management should be implemented for managing bedbugs in Thailand.
BackgroundThe re-emergence of chikungunya (CHIK) fever in Thailand has been caused by a novel lineage of chikungunya virus (CHIKV) termed the Indian Ocean Lineage (IOL). The Aedes albopictus mosquito is thought to be a primary vector of CHIK fever in Thailand, whereas Ae. aegypti acts as a secondary vector of the virus. The vertical transmission is believed to be a primary means to maintain CHIKV in nature and may be associated with an increased risk of outbreak. Therefore, the goal of this study was to analyze the potential of these two Thai mosquito species to transmit the virus vertically and to determine the number of successive mosquito generations for the virus transmission.MethodsTwo-hundred-and-fifty female Ae. aegypti and Ae. albopictus mosquitoes were artificially fed a mixture of human blood and CHIKV IOL. Mosquito larvae and adults were sampled and screened for CHIKV by one-step qRT-PCR. LLC-MK2 cell line was used to isolate CHIKV in the mosquitoes each generation. The virus isolate was identified by immunocytochemical staining and was confirmed by sequencing. Both mosquito species fed on human blood without CHIKV and uninfected LLC-MK2 cells were used as controls.ResultsAedes aegypti and Ae. albopictus mosquitoes were able to transmit CHIKV vertically to F5 and F6 progenies, respectively. The virus isolated from the two mosquito species caused cytopathic effect in LLC-MK2 cells by 2 days post-infection and immunocytochemical staining showed the reaction between CHIKV IOL antigen and specific monoclonal antibody in the infected cells. DNA sequence confirmed the virus transmitted vertically as CHIKV IOL with E1-A226V mutation. No CHIKV infection was observed in both mosquito species and LLC-MK2 cells from control groups.ConclusionsThe study demonstrated that Ae. aegypti and Ae. albopictus mosquitoes from Thailand are capable of transmitting CHIKV IOL vertically in the laboratory. Our results showed that Ae. albopictus is more susceptible and has a greater ability to transmit the virus vertically than Ae. aegypti. This knowledge would be useful for risk assessments of the maintenance of CHIKV in nature, which is crucial for disease surveillance, vector control and the prevention of potential CHIKV epidemics.
BackgroundIn the past few decades, several researchers have proposed highly accurate prediction models that have typically relied on climate parameters. However, climate factors can be unreliable and can lower the effectiveness of prediction when they are applied in locations where climate factors do not differ significantly. The purpose of this study was to improve a dengue surveillance system in areas with similar climate by exploiting the infection rate in the Aedes aegypti mosquito and using the support vector machine (SVM) technique for forecasting the dengue morbidity rate.Methods and FindingsAreas with high incidence of dengue outbreaks in central Thailand were studied. The proposed framework consisted of the following three major parts: 1) data integration, 2) model construction, and 3) model evaluation. We discovered that the Ae. aegypti female and larvae mosquito infection rates were significantly positively associated with the morbidity rate. Thus, the increasing infection rate of female mosquitoes and larvae led to a higher number of dengue cases, and the prediction performance increased when those predictors were integrated into a predictive model. In this research, we applied the SVM with the radial basis function (RBF) kernel to forecast the high morbidity rate and take precautions to prevent the development of pervasive dengue epidemics. The experimental results showed that the introduced parameters significantly increased the prediction accuracy to 88.37% when used on the test set data, and these parameters led to the highest performance compared to state-of-the-art forecasting models.ConclusionsThe infection rates of the Ae. aegypti female mosquitoes and larvae improved the morbidity rate forecasting efficiency better than the climate parameters used in classical frameworks. We demonstrated that the SVM-R-based model has high generalization performance and obtained the highest prediction performance compared to classical models as measured by the accuracy, sensitivity, specificity, and mean absolute error (MAE).
Several mosquito species have been described as vectors for the Zika virus (ZIKV), such as those in the Aedes , Anopheles , Mansonia and Culex genera. Our previous survey studies were found the ZIKV RNA positive in both male, female and larvae of Culex quinquefasciatus Say and Aedes aegypti (L.) mosquitoes collected from active ZIKV infected patients’ homes in Thailand. Therefore, the aims of this study were to investigate whether ZIKV could be vertically transmitted in Cx . quinquefasciatus , Ae . aegypti and Ae . albopictus . Laboratory and field colonies of these mosquito species were maintained and artificially fed with ZIKV in human blood. Fully engorged mosquitoes (F 0 ) were selected and reared for the vertical transmission study. The subsequent mosquito generations were fed with human blood without the virus. ZIKV in the mosquitoes was detected by hemi-nested RT-PCR and sequencing. C6/36 cells were used to isolate ZIKV from samples that tested positive by hemi-nested RT-PCR. Moreover, ZIKV was identified by immunocytochemical staining 7 days after infection in several organs of infected F 0 females, including the salivary glands, midguts, yoke granules and facet cells of the eye. The localization of the ZIKV antigen was identified by the presence of the specific antibody in the salivary glands, midguts, yoke granules and facet cells. ZIKV was detected in female and male Cx . quinquefasciatus until the F 6 and F 2 generations, respectively. The isolated virus showed cytopathic effects in C6/36 cells by 5 days postinfection. The results suggested that the vertical transmission of ZIKV occurs in Cx . quinquefasciatus in the laboratory. However, we were able to detect the presence of ZIKV in Ae . aegypti in only the F 1 generation in both male and female mosquitoes, and Ae . albopictus mosquitoes were not able to vertically transmit the virus at all. Data obtained from this study could be valuable for developing a better understanding of the role of Cx . quinquefasciatus as a potential vector for ZIKV transmission in Thailand and may be useful in creating more effective mosquito vector control strategies in the future.
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