Entomological investigations in a focus of dengue transmission in Cairns, Queensland, Australia, by using the sticky ovitraps

Sticky ovitraps (patent pending) were used to sample female Aedes aegypti (L.) weekly in a focus of dengue activity in Cairns, Queensland, Australia. In February 2003, transmission of dengue virus serotype 2 began in the suburb of Parramatta Park, peaking in mid-March 2003. This suburb features many older, unscreened houses with high populations of Ae. aegypti. Highest densities (2-3.5 females per trap per week) were obtained during peak dengue transmission (January and February) before mosquito control was initiated. Beginning in late March, female Ae. aegypti collected in sticky ovitraps were tested for dengue viral RNA by using a TaqMan reverse transcription-polymerase chain reaction assay. Dengue viral RNA was detected in six pools of Ae. aegypti collected in late March. The highest minimum infection rate was 116/1000 mosquitoes. After the initiation of larval control (containers treated with S-methoprene or lambda-cyhalothrin) and adult control (interior harborage sites sprayed with lambda-cyhalothrin) in early March, trap collections dropped to <0.5 per trap per week, and no virus was detected in trapped mosquitoes. Human cases subsequently dropped from a high of seven cases per day in mid-March to only sporadic cases in late April, with the final reported onset of 7 May. Sticky ovitraps have potential as a monitoring device for gravid Ae. aegypti and can be used to assess control efficacy and dengue virus activity. A sticky ovitrap index (mean number of female Ae. Aegypti per trap per week) could be useful in gauging the risk of dengue transmission.