As of October 2, 2019, there have been 191 dead birds reported in
San Mateo County. Of those, 44 have been suitable for testing and
all 44 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.
This summer, the District participated in a
collaborative study to evaluate a new formulation of methoprene,
a biorational mosquito larvicide, in catch basins. While
District mosquito control operations has used methoprene products
for many years as part of its Integrated Pest Management program
(IPM), this collaborative effort introduced our staff to new
sampling and testing methods specific to catch basin/storm drain
applications. Instead of using traditional cup-shaped
dippers to collect water samples, District staff used fish nets
attached to long poles to sampl
Eastern equine encephalitis virus, often termed EEEV or Triple-E,
has been making headlines lately in the United States. This
mosquito-borne virus can cause a sometimes-fatal brain infection.
With 31 cases and 9 deaths this year to date, this is the worst
outbreak of EEEV disease since the US began monitoring the
disease 15 years ago. While those numbers sound scary, EEEV
disease is relatively rare. An average of 7 human cases of
EEEV disease are diagnosed in the United States annually.
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.
As of September 3, 2019, there have been 179 dead birds reported
in San Mateo County. Of those, 38 have been suitable for testing
and all 38 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.
In response to parental concerns about the possibility of
children picking up ticks on athletic fields, the District
recently conducted tick surveys at seven elementary and middle
schools in the Pacifica School District (PSD). Many schools in
Pacifica border open spaces that host wildlife and large areas of
tick habitat, and are near parks and other outdoor recreation
areas where tick exposures are common. All athletic fields
and grassy areas were sampled at each school, as well as any
bordering natural habitat that could present a hospitable
environment for ticks.
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.
