Virologic surveillance for dengue through the detection of the prevalent serotype(s) circulating in the human population during inter-and intra-epidemic periods constitutes a reliable sentinel system for dengue outbreaks. We have applied a rapid and sensitive, semi-nested, reverse transcription-polymerase chain reaction (RT-PCR) assay using nonstructural protein 3 gene primers for the type-specific-detection of dengue viruses in artificially infected and in field-caught adult Aedes mosquitoes. In laboratory experiments, the assay was sensitive enough to detect one virusinfected mosquito head in pools of up to 59 uninfected heads. In a prospective field study conducted from April 1995 to July 1996, female adult Ae. aegypti and Ae. albopictus mosquitoes were caught from selected dengue-sensitive areas in Singapore and assayed by RT-PCR. Approximately 20% of 309 mosquito pools were positive for dengue viruses. Of the 23 RT-PCR-positive Ae. aegypti pools (containing 1-17 mosquitoes each), 18 pools (78.3 %) were positive for dengue 1 virus. There were 40 RT-PCR-positive Ae. albopictus pools (containing 1-33 mosquitoes each) of which 31 (77.5%) were positive for dengue 1 virus. The predominant virus type responsible for the current dengue epidemic since 1995 was also dengue 1. The geographic locations of the virus-infected mosquitoes correlated with the residences or workplaces of patients within dengue outbreak areas. A total of 43.5% of the positive Ae. aegypti pools and 25.0% of the positive Ae. albopictus pools contained only a single mosquito. Both Aedes species showed similar overall minimum infection rates of 57.6 and 50 per 1,000 mosquitoes. Infected Ae. aegypti were detected as early as six weeks before the start of the dengue outbreaks in 1995 and 1996. However, infected Ae. albopictus appeared later, when the number of cases was increasing. Virologic surveillance by RT-PCR for detecting dengue virus-infected Aedes mosquitoes in the field may serve as an early warning monitoring system for dengue outbreaks.

Repeated use of oils and fats for frying of food brings about many changes in their physical and chemical properties. Due to increasing health concerns, the assessment of the quality of reused oils has received much attention, since such assessment is useful in determining the discarding point of the oils. The official analytical methods used in laboratories for this purpose need skill, time, and a large consumption of solvents. To make the oil testing simpler, several rapid test kits have been developed based on either physical parameters (such as viscosity or dielectric changes) or chemical parameters (such as free fatty acids, oxidized fatty acids, or carbonyl compounds). These test kits usually comprise a portable instrument or colorimetric reaction sticks, capable of providing a direct or indirect measurement of a single parameter. The review presented in this paper evaluates the use of such rapid test kits and highlights the need to develop multi-parameter test kits in order to establish the quality of reused oil and the point at which it should be discarded. The review also encompasses pertinent details on the standard analytical methods, and deterioration of frying oils that occur during and after their use and the associated health consequences.

The laboratory diagnosis of dengue has largely relied on serological assays, although many different RT-PCR protocols have been reported. Owing to its limited use, the value of RT-PCR in the clinical laboratory has not been fully evaluated. During the outbreak of severe acute respiratory syndrome (SARS) in Singapore in 2003, RT-PCR to detect dengue viral RNA was used as a rapid diagnostic tool to differentiate dengue from SARS among patients who presented to a hospital designated to manage and quarantine SARS cases. A total of 343 results for RT-PCR and 439 results for serology were analysed and compared with the final discharge diagnosis. Our experience indicates that RT-PCR for dengue can be set up rapidly in a clinical laboratory, with very sensitive and specific results for the diagnosis of dengue, particularly in the first 5 days from onset of symptoms.

SummaryWe developed a single-step reverse transcription-polymerase chain reaction (RT-PCR) followed by a seminested PCR using an upstream consensus primer and four type-specific primers within the nonstructural protein gene (

To improve the operational efficiency of dengue vector control in Singapore, larvicide and adulticide were applied together by thermal fog generator (Agrofog AF40). The mixture consisted of Bacillus thuringiensis var. israelensis (Vectobac 12 AS) as biological larvicide at 1.5 L/ha and pirimiphos-methyl (Actellic 50 EC) as adulticide at 100 g ai/ha, diluted 10-fold with water. Aerosol of this mixture was evaluated against the mosquito Aedes aegypti (L.) (Diptera: Culicidae) in bioassays using cages of 10 adult females exposed at heights of 0.3-2.4 m and distances of 3-12 m from the hand-held generator. Cups containing 200 mL water were treated at ground level by exposure to the aerosol application at the same distances from the generator. Subsequent larval bioassays on days 1, 7, 14, 21 and 28 post-spray involved exposing 20 larvae/cup for 48 h. Droplets had VMD 57 microm and female mosquitoes were killed by 2 s exposure to the aerosol at 3 m. We obtained 92-100% mortality of the adult mosquitoes and 100% control of larvae at 3 m distance, but only 10-13% mortality at 12 m from the fogger. In treated cups, larvae showed high mortality (92%) when exposed for 48 h even 1 month post-treatment. Results demonstrate the practical advantage of using this mixture of Vectobac 12AS and Actellic 50 EC for simultaneous control of Aedes adults and larvae, with prolonged larvicidal efficacy in treated containers.