From February 13 – 17, Laboratory Director Nayer Zahiri, Operations Supervisor Casey Stevenson and Trustee Peter DeJarnatt attended the annual conference of the American Mosquito Control Association in San Diego. Dr. Zahiri gave two presentations at the conference: “Monitoring Susceptibility of Culex pipiens to Larvicide Products Currently in use in San Mateo County” and “Aedes aegypti Surveillance in San Mateo County from 2013-2016.” Both presentations were well-received by attending mosquito control professionals.
Tick collection continued through the month of February during periods of dry weather. Parks visited in February include Quarry Park in El Granada, Montara Mountain in San Pedro Valley Park near Montara, Eaton Park in San Carlos, Edgewood Park in Redwood City and Purisima Creek Redwoods Preserve near Woodside.
Winter 2017 Tick Collections through February 2017
It is unusual to detect West Nile Virus in dead birds during the winter months. West Nile Virus season begins mid-April, with most activity in the summer. However, residents can report some species of dead birds (crows, ravens, scrub-jays, finches, sparrows, hawks and owls) year-round online at westnile.ca.gov and the District laboratory will test fresh specimens without signs of trauma (roadkill or partially decomposed specimens cannot be tested).The first West Nile Virus positive bird of 2017 in San Mateo County was detected in Redwood City.
Tularemia, rabbit or deerfly fever, is a relatively rare bacterial disease transmitted to humans and animals by the bite of ticks. It is much less common that Lyme disease in California and is primarily transmitted by the American dog tick (Dermacentor variablis) and possibly by the Pacific Coast tick (Dermacentor occidentalis).
The District laboratory is taking advantage of breaks in rainy weather to collect ticks from parks and open space areas in San Mateo County. Ticks are collected by dragging a tick flag – a large white piece of flannel attached to a wooden rod – over the vegetation alongside trails. The main target species of tick is Ixodes pacificus, the western black-legged tick, which vectors Lyme disease, Borrelia miyamotoi infection, and anaplasmosis. The ticks collected will be tested for the presence of bacteria that cause these diseases. The Ixodes pacificus ticks are in
In addition to testing for Borrelia burgdorferi and Borrelia miyamotoi, the District tested ticks collected this year from four parks for another bacteria that causes the disease Anaplasmosis. This disease is less common than Lyme disease in California but is transmitted by the same tick, the western black-legged tick (Ixodes pacificus). The ticks from these four parks were all close to an area where Anaplasmosis has been detected in the past.
The laboratory has filled two open positions. The part-time Laboratory Technician position has been filled by Theresa Shelton, formerly a Vector Ecologist at the District. The open Vector Ecologist position has been accepted by Tara Roth. Tara recently completed a Ph.D. in Integrative Pathobiology from University of California, Davis, where she studied the disease Tularemia, an infection of a bacteria that can be transmitted by ticks. Tara will be joining the District on January 9, 2017.
The District laboratory will be deploying two additional New Jersey light traps for mosquito monitoring in the upcoming year. The new traps will be located at a residence in Half Moon Bay and the Daly City Fire Station. Currently, four traps are already deployed in Woodside, Menlo Park, San Bruno and Belmont . The addition of these two traps will allow for greater county-wide coverage of monitoring by New Jersey Light traps. The map shows the distribution of New Jersey light traps for 2017.
Thus far in 2016, the District has received reports of 26 human cases of mosquito-borne diseases in San Mateo County, acquired during travel. Thirteen of the cases were dengue fever, twelve were Zika virus and one was an unspecified flavivirus (any of most mosquito-borne diseases other than malaria). Cases of Zika virus have been contracted only in the Western Hemisphere (the Carribean, Central and South America, Mexico), whereas dengue fever cases have been contracted in Asia also. The total number is similar to imported cases during 2015 (27), but the types of diseases a
The District laboratory received several insect identification requests this October for subterranean termites. These termites are common in the San Francisco bay area, but typically noticed after the first fall rains, when they swarm from their nests to find mates and establish new nesting sites. After they land, their wings drop off, which can be seen in abundance after the swarms have dissipated. They are one of three groups of termites in San Mateo County (subterranean, drywood, and dampwood).
On September 15, the District hosted the Vector-Borne Disease Group Meeting for the coastal region of California. This meeting is held three times a year at various districts near the bay area. Primarily laboratory staff meet to report ongoing disease surveillance, current projects and notable findings within each county. It informs participants on regional trends, and fosters collaboration among staff of neighboring districts. The meeting also encourages communication among staff at surrounding districts, so that each laboratory can take advantage of particula
Lizards are a primary host for Ixodes pacificus ticks during the nymphal stage of their life. Engorged tick nymphs can often be seen attached to the neck area of lizards caught in the wild. Ticks and lizards are so associated with each other that removing lizards from an area can lead to a drastic drop in tick population as well, according to a 2011 study by Swei et al.1 However, some lizards such as the Western Fence lizard and the Southern Alligator lizard can also combat Lyme Disease because a protein within the lizard blood will kill the infectious
Tick testing is completed for the 2015-2016 season. Staff flagged for ticks at fifteen parks this season, although only 10 parks had sufficient numbers for estimating infection prevalence. Ticks were tested for the presence of two disease-causing bacteria, Borrelia burgdorferi which causes Lyme Disease and Borrelia miyamotoi which causes a relapsing fever type illness. As seen in the table below, infection prevalence of either of the two Borrelia ranged from 2.6% to 0%, and was highest at Thornewood Open Space Preserve near Woodside.
The District conducted two wild rodent disease surveys on San Bruno Mountain this year, and all test results have been received. Each survey consisted of 100 Sherman traps placed along trails, targeting wild mice. The first survey resulted in fifteen captured Peromyscus maniculatus mice and the second survey resulted in eleven captured P. maniculatus mice.
In August, laboratory staff responded to a service request regarding a home infestation of bugs. Specimens brought to the office were millipedes, a common outdoor arthropod in the bay area, but not usually seen indoors in high numbers. Possible means of introducing these creatures in the home include potting soil for indoor plants and cracks in the home or open doorways, especially near leaf litter or old wood. Millipedes do no harm to property and pose no risk to public health, and typically die quickly in a house because moisture levels are too low.
When the District treats a neighborhood to control adult mosquitoes carrying West Nile Virus, caged mosquitoes are placed inside and outside of the fogging zone in the evening prior to the fogging. These cages are filled with 20-25 female Culex pipiens mosquitoes that have been reared from the District mosquito colony.
School is starting and that means a lot of residents will be dealing with a common insect pest – head lice. This summer, Laboratory Director Nayer Zahiri assisted a local campsite that experienced an infestation of lice among campers and staff. Dr. Zahiri demonstrated how to inspect hair for evidence of lice, and advised with treatments. With her help, the camp was able to eliminate the problem.