The seasonal invasive Aedes surveillance primarily targets the detection of two mosquito species that have been expanding their range in California, Aedes aegypti, and Aedes albopictus. The presence of these mosquitoes is highly undesirable because they are aggressive human biters and also transmit diseases including dengue, chikungunya, yellow fever and Zika. From 2013-2015, the District supressed Ae. aegypti in a small area of Menlo Park, but no invasive Aedes have been detected since August 2015.
The District conducts surveillance for invasive Aedes mainly with two traps – ovicups and BG-Sentinel traps. Ovicups are small black cups with water and seed germination paper in them. The wet paper provides an attractive substrate for female Aedes mosquitoes to deposit eggs. The papers are checked once a week for the presence or absence of eggs. BG-Sentinel traps collect adult mosquitoes using a scented lure that is attractive to host-seeking females. The District previously used a third type of trap, Autocidal Gravid Oviposition (AGO) traps that were placed around Menlo Park. This effort was discontinued this year because of the amount of time that has passed without invasive Aedes detection in that neighborhood.
Seasonal invasive Aedes surveillance consists of ovicups, placed throughout San Mateo County in areas where introductions are of higher likelihood. This includes plant nurseries and cemeteries, because of the presence of small containers of water and plants that have been imported from tropical locations around the world. These traps were taken back to the District for the year at the end of October and will be re-deployed next May. Two surveillance sites are maintained year-round, because of the continual threat of introduction. These are the USDA office in South San Francisco, which inspects imported plants, and the Verily office, also in South San Francisco, which has a colony of Ae. aegypti which it uses for research purposes.
The District also responds year-round to travel-related human cases of mosquito-borne disease, although the majority of these occur during the warmer months. In 2018 to date, the District has conducted enhanced mosquito surveillance in response to thirteen confirmed or probable cases of imported mosquito-borne disease. These included cases of dengue, malaria, Zika virus and chikungunya. When notified that a traveler has returned with an infection, laboratory staff place BG-Sentinel traps and ovicups near the residence. These traps are used to determine whether there are any mosquitoes in the surrounding area that could serve as vectors of the imported disease and transmit it to other local residents.