Laboratory staff continued collecting Ixodes pacificus ticks in the nymph life stage and adult Dermacentor ticks during the month of May. Collections in May occurred at Thornewood Open Space Preserve near Woodside, Wunderlich County Park in Woodside, Water Dog Lake Park in Belmont, Big Canyon Park and Eaton Park in San Carlos, Edgewood Park in Redwood City, Costanoa campground near Año Nuevo, and Laurelwood Park in San Mateo.
As of June 3, 2019, there have been 86 dead birds reported in San Mateo County. Of those, sixteen have been suitable for testing and all sixteen have tested negative for West Nile virus (WNV). No mosquito pools or sentinel chickens have tested positive for West Nile virus in San Mateo County in 2019.
During April, laboratory staff shifted focus from collecting adult stage to nymphal stage Ixodes pacificus (western black-legged) ticks. Tick nymphs are more difficult to collect than adults because they don’t quest on vegetation along trails. Instead, they are found on tree stumps, downed longs, rocks, and in leaf litter.
Surveillance for West Nile virus began in California in mid-April. The District protects residents from this mosquito-borne disease with control methods that target mosquitoes in the larval stage, as well as mosquito population monitoring, disease surveillance and public education. The laboratory staff conducts disease surveillance in three main ways:
During March, laboratory staff continued surveillance for adult Ixodes pacificus (Western black-legged ticks). The continuous on-and-off rainfall continued into March and greatly limited the number of tick-flagging opportunities this winter. The weather reduces the questing activity of the ticks and moisture saturates the tick flag, making it less effective as a collecting tool.
During February, laboratory staff continued surveillance for adult Ixodes pacificus (Western black-legged ticks). The continuous on-and-off rainfall greatly limited the number of tick flagging opportunities in February, which is typically a peak month for collecting adult Ixodes pacificus. The weather reduces the questing activity of the ticks and moisture saturates the tick flag, making it less effective as a collecting tool. Parks that were surveyed in February were Ano Nuevo State Park, south of Pescadero and Sweeney Ridge in San Bruno.
During January, laboratory staff began winter surveillance for adult Ixodes pacificus (Western black-legged ticks). Ticks are collected by dragging a 1 meter square piece of white flannel over the vegetation alongside trails. Ixodes pacificus ticks will be tested for the presence of bacteria Borrelia burgdorferi, Borrelia miyamotoi and Anaplasma phagocytophilum.
The lab wraps up another busy year providing scientific support for our vector control programs.
We analyzed 479 field-collected larval and 1,206 adult mosquito collections, enabling quick and appropriate integrated vector management responses by our operations staff. We improved our primary adult mosquito trap (CO2 trap) with simple modifications based on scientific trials we conducted the previous year that compared the performance of different designs.
At the District, the majority of our tick surveillance focuses on three tick species, Ixodes pacificus, (western black-legged tick), Dermacentor varabilis, (American dog tick) and Dermacentor occidentalis, (Pacific coast tick). These ticks quest for hosts in the vegetation along trails, and are easily picked up by hikers and dogs. While these three species present the greatest risk of disease transmission to humans and pets, there are many more species of ticks that live in San Mateo County that we do not collect as part of our usual surveillance.
This year, in addition to testing for Lyme disease and hard-tick relapsing fever, the District conducted testing for Anaplasma phagocytophilum which causes the disease human granulocytic anaplasmosis (HGA). HGA is a tick-borne disease that causes reoccurring bouts of mild to moderate fever, aches, nausea and vomiting. It is carried by adults and nymphs of the western black-legged tick (Ixodes pacificus). The District conducted real-time PCR testing of adult ticks collected from parks in San Mateo County for the 2017-2018 water year (October through September).
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.
This summer, the laboratory has been assisted by Alexander Flores, who conducted most of the surveillance for invasive Aedes mosquitoes this season. For the past five years, Alex has worked for the District as a seasonal technician in the Operations department. This year he took a position in the Laboratory department for a new experience. Alex started the summer as the invasive Aedes technician, funded by a grant from Public Health Foundations Enterprises, Inc. on behalf of the California Department of Public Health.
As of September 28, 2018, there have been 330 dead birds reported in San Mateo County. Of those, 103 have been suitable for testing and five have tested positive (5%) for West Nile virus (WNV). Two mosquito pools have tested positive for WNV, both from East Palo Alto during the month of August. Positive birds and pools for 2018 are summarized in the tables below. No sentinel chickens have tested positive for West Nile Virus in San Mateo County in 2018.
Every year the District collects ticks from recreational areas in the county to assess the risk of tick-borne disease. One way to measure this is by determining the minimum infection prevalence (MIP), which estimates what percentage of these ticks are expected to be carrying a given disease agent in a population. The laboratory has completed testing for two vector-borne diseases from ticks collected from November 2017 to May 2018.
Autumn is the time of year for termite swarms as adult winged termites (called alates), leave their colonies, mate, and establish new colony sites. Residents often see the swarms around their neighborhood or find discarded wings and dead termites scattered on the ground or caught in spider webs. Only a very small proportion of termites are successful in establishing a new colony.
As of August 31, 2018, there have been 291 dead birds reported in San Mateo County. Of those, 91 have been suitable for testing and five have tested positive (5%) for West Nile virus (WNV). Additionally, two mosquito pools have tested positive for WNV, both from East Palo Alto. Positive birds and pools for 2018 are summarized in the tables below. No sentinel chickens have tested positive for West Nile Virus in San Mateo County in 2018, although a sentinel chicken in Santa Clara County, near the border with San Mateo County, tested positive in August.
The vast majority of mosquito control work at the District targets mosquitoes when they’re in the aquatic larval stage. However, occasionally the mosquitoes need to be controlled in their adult stage, such as when there is a human health risk from West Nile Virus. At this District, adult mosquitoes are treated with a backpack in small, isolated areas or by truck for larger sections of a neighborhood.
As of August 1, 2018, there have been 247 dead birds reported in San Mateo County. Of those, 66 have been suitable for testing and two have tested positive (3%) for West Nile virus (WNV). No mosquito pools or sentinel chickens have tested positive for West Nile Virus in San Mateo County in 2018.