Evaluation of the efficacy of Bistar 80SC by residual application in dengue vectors control in the North of Vietnam

Background: Two species, Aedes aegypti and Aedes albopictus are the main intermediate vectors of transmission of the dengue viruses in Vietnam. Insecticide applications by different methods that may help interrupt the spread of dengue outbreaks. Many different groups of insecticides have been used for dengue vector control. Some recent studies revealed that Aedes vectors obscuring their resistance to insecticides at different levels. Therefore, a new insecticide formula is required for effective dengue vectors control. Objective: To evaluate the efficacy of Bistar 80SC by residual application in suppression of Aedes species in a northern province of Vietnam. Subject and methods: Bistar 80 SC with a component of Bifenthrin 80g/L was evaluated by residual application in suppression of 2 Aedes species in vitro and in an intervention commune of Hien Giang, Thuong Tin district and a control commune of Van Mo, Ha Dong town, Ha Tay province from March, 2004 to June, 2004. Results: WHO Bifenthrin paper test kit was effective at the concentration of 37.5mg/m2 and over with Aedes aegypti vectors ranged from 80% to 100% mortality in the North, In other words, Aedes vector remains susceptible to Bifenthrin in the region. The mortality on wood surface after 60 minutes of exposure to Bistar 80SC at concentrations of 25mg/m2 by using residual application was higher than those on brick walls. Up to 100% Aedes aegypti was killed after 60 minutes in exposure and remains in effect until the end of the third months and one month with Aedes albopictus. No side effects, to the sprayer and humans, livestock and environment caused by Bistar 80SC were reported in the intervention area. Conclusion: Bistar 80SC is suggested as a nominated alternative to effectively control the dengue outbreak by residual application.

Evaluation of the effectiveness of Interceptor bed net on controlling disease vectors Aedes aegypti in Vietnam, 2007

Background: Using insecticides is considered as a temporary and rapid method for interrupting the disease transmission through disease vectors such as dengue. The insecticide Fendona, when absorbed into bed nets, is slowly released and rapidly knocks out, kills or repels mosquitoes as they come into contact with the bed net. Objectives: To evaluate the effectiveness of the Interceptor bed net (a unique textile-finishing product developed by BASF, Singapore PTE. LTD, that were coated with the Fendona insecticide) on controlling disease vector Aedes aegypti. Subjects and method: An experimental trial was carried out at the National Institute of Hygiene and Epidemiology and in the field of Hien Giang commune, Thuong Tin district, Ha Tay province. The changes of efficacy of Interceptor bed net were compared by not washing with washing at the different levels. Results: The unwashed bed nets can knock out and kill Aedes aegypti mosquitoes by 50% after 20 minutes of exposure on every trial. About 90-100% of total mosquitoes were killed after the first 30 minutes of exposure. Bed net\u2019s efficacy remains until 24 hours of the trial. The recovery rate of the mosquito is 0%. The same results were also observed after 90 days, 36 days and 18 days of bed nets being laundered. However, after 9 day of washing, the bed nets can only kill the mosquitoes up to about 90-95% of the total after the first 30 minutes of exposure. It also reached 100% of killing after 24 hours. However, its efficacy was conversely reduced with regard to the increase of laundry times. Conclusion: The density of adult mosquitoes and larvae for Aedes aegypti was significantly reduced in the intervention areas, even at zero level in comparison to the control sites. The insecticide had no side-effect or any stimulation to users, community, poultry, cattle and environment in the intervention sites.

Morbidity and mortality of acute respiratory infections in Thai Binh province, Vietnam, 2002-2005

Background: Acute Respiratory Infection (ARI) is a common disease in developing countries. Morbidity and mortality of ARI are high, especially among children under 15 years old. Objectives: To describe socio-graphic factors, seasonal patterns, risky areas and determine the morbidity and mortality rates of acute respiratory infections in Thai Binh province. Subjects and method: This retrospective study reviewed the medical records of 4,585 hospital admitted patients who were diagnosed with ARI including upper and lower respiratory infections such as sore throat, pharyngitis, bronchitis, pneumonia and bronchitis-pneumonia at 8 district hospitals and 1 provincial hospital in Thai Binh province during 2002-2005. The selected medical records were based on the available check list and two standard screening tests. Results:Morbidity and mortality of ARI in Thai Binh province were 61.6 and 0.52, respectively. ARI mainly occurred among children under 5 years old, of which the highest mortality was among those under 12 months of age. Male children were at higher risk of acquiring ARI, but less prone to death than female. Occupation did not significantly associate with the risk of ARI. The morbidity increased sharply during inter-season, e.g. March and October. Thai Binh city, Kien Xuong and Tien Hai district were reported with the highest morbidity in accompany of the high mortality as consequences. Conclusion: The prevention and control methods were recommended to annually focus on the male children aged less than 5 years old during March and October in Thai Binh city, Kien Xuong and Tien Hai district.

Evaluation of the efficacy of cynoff 25 ULV to eradicate aedes species, dengue vectors in Vietnam, 2004

Background: Dengue fever remains a major public health problem in Vietnam. It was transmitted through two main Aedes species, namely Aedes aegypti and Aedes albopictus in which Aedes aegypti played the predominant role in transmitting the dengue viruses (accounted for 94% of the Aedes genus).Different groups of insecticides have been widely used in the community. As a consequence, it increased the resistance level of Aedes vectors to the insecticides. Therefore, a new synthesized insecticide was required for future control and prevention of dengue epidemics. \r\n', u'Objectives: To evaluate the efficacy of Cynoff 25 ULV in suppressing Aedes species in Vietnam. \r\n', u'Subjects and methods: The study was conducted in the entomology laboratory and in the fields of Ha Tay province. ULV spraying was implemented in Hiengiang commune, Thuongtin district, in comparison with a control area, Van Mo commune in Ha Dong town.\r\n', u'Results and conclusions: : Cynoff 25 ULV had a high efficacy that kills over 90% of 2 dengue vector species, namely Aedes aegypti and Aedes albopicctus after 24 hours exposure at the distance of 30 meters from the brass nozzle of a STIHL SR 400 sprayer. In the field trials, Cynoff 25 ULV also had high efficacy in killing Aedes species, e.g. 100% of Aedes species were killed after spraying and the effects lasted for 3 months for Aedes aegypti and one month for Aedes albopictus species. The insecticide had no side-effects or any other adverse effects to humans, livestock and the environment in the intervention areas. \r\n', u'

Key containers of Aedes species, vectors to transmit dengue viruses in Nam Dinh province, 2007

Background: Dengue Fever/Dengue Hemorrhagic Fever (DF/DHF) has emerged as one of the most important public health concerns in Viet Nam in recent years. Key breeding containers plays an important role in driving dengue vector control in the public. Objectives: The research was conducted to discover the dengue situation, its vectors and key containers to make relevant recommendations in reducing effectively the vector population. Subjects and methods: Two hundred households in two communes of Nam Dinh province (100 in each studied commune) were selected randomly. Vectors collected from the field were identified using mosquito key. The number of dengue larvae and mosquitoes were directly counted or adjustment methods were used to estimate the true number in each type of water storage facility. Results: In Minh Thuan commune, Ae. albopictus larvae were mainly concentrated in jars (49%) and discards (59%), most of Ae. aegypti was found in cement tanks with a volume more than 500L (72%). In Trung Dong commune, larvae of Ae. albopictus concentrated in jars (40%) and discards (25%) and aquariums (15%), while most of the Ae. aegypti larvae was discovered in cement tanks with volumes more than 500L (86%). Mosquito density index of Ae. albopictus in Trung Dong and Minh Thuan communes was 0.56 and 0.38, respectively. The Aedes larvae, houses for larvae and Breteau index were nearly at the threshold of dengue epidemic occurrence for Ae. aegypti and over a certain threshold for Ae. albopictus. Some recommendations were provided to help reduce the dengue vectors. Conclusion: Investigation of key mosquito larvae in water containers was useful in driving the effective dengue vector control. Further studies are required to evaluate the impact and methods to manage water containers in the local area.