As of August 1, 2019, there have been 155 dead birds reported in
San Mateo County. Of those, 31 have been suitable for testing and
all 31 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.
Laboratory staff continued collecting Ixodes pacificus
ticks in the nymph life stage and adult Dermacentor
ticks during the month of June. Collections in June occurred at
Año Nuevo and the nearby Costanoa campground. A very high number
of Dermacentor ticks have been collected from this
location because District staff have made multiple collecting
trips as part of a study on Tularemia.
As of June 28, 2019, there have been 120 dead birds reported in
San Mateo County. Of those, 23 have been suitable for testing and
all 23 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.
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.
In January of 2019 an alert went out from the California
Department of Food and Agriculture warning people about an
outbreak of Newcastle disease in domestic poultry in southern
California.
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.
