Samrerng Prummongkol

Prospective Field Study of Transovarial Dengue-Virus Transmission by Two Different Forms of Aedes aegypti in an Urban Area of Bangkok, Thailand

ABSTRACT: n A prospective field study was conducted to determine transovarial dengue-virus transmission in two forms of Aedes aegypti mosquitoes in an urban district of Bangkok, Thailand. Immature Aedes mosquitoes were collected monthly for one year and reared continuously until adulthood in the laboratory. Mosquitoes assayed for dengue virus were processed in pools and their dengue virus infection status was determined by one-step RT-PCR and nested-PCR methods. Of a total 15,457 newly emerged adult Ae. aegypti, 98.2% were dark and 1.8% of the pale form. The results showed that the minimum infection rate (MIR) by transovarial transmission (TOT) of dengue virus during the one-year study ranged between 0 to 24.4/1,000 mosquitoes. Dengue virus TOT increased gradually during the hot summer months, reaching a peak in AprilJune, while dengue cases peaked in September, a rainy month near the end of the rainy season. Therefore, mosquito infections due to TOT were prevalent four months before a high incidence of human infections. TOT dengue virus infections occurred in both forms of Ae. aegypti. All four dengue serotypes were detected, with DEN-4 predominant, followed by DEN-3, DEN1, and DEN-2, respectively.

Biology of Culex sitiens, a Predominant Mosquito in Phang Nga, Thailand after a Tsunami

Abstract A tsunami affected area in Phang Nga province, Thailand was explored randomly as some freshwater sites had changed into brackish-water sites. A survey of four areas found Culex sitiens to be the most dominant mosquito species.This mosquito prefers to breed in putrefied water with garbage and it was found in almost every stagnant, brackish-water site in full sunlight. The larval density was more than 300 larvae/dip/250 ml water. Its biting cycle, determined by human landing catch, was nocturnal, with a single peak at 19.00–20.00 hr. The maximum rate was 108 mosquitoes per person/hour. The biology of the mosquito was studied by colonization in natural water under laboratory conditions. The mean number of eggs per raft was 158.1 ± 31.7, hatchability 96.6 ± 4.1%, development from 1st instar larvae to adult was 8.8–11.7 days, and longevity of adult males was 7.3–41.3 days and females 11.0–52.7 days. The ratio of adult males to adult females was 1:1.1 ± 0.2.