Laboratory Updates

Overview

Laboratory Updates

The District laboratory staff maintains this section monthly with updates on disease surveillance, research, and other laboratory projects.

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Mosquito Larval Samples from January 2021

The heavy rains this month have filled seasonal water sources with rain water, making surveillance for mosquito larvae a top priority. This January, field staff collected 145 larval samples that were submitted to the laboratory for identification.  The most frequently occurring species in the larval samples was Culiseta incidens, the cool weather mosquito. Culiseta incidens larvae are found year-round in a variety of freshwater sources.

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January 2021 CO2 Trap Collections

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of January compared to the five-year average for the six most common mosquito species in San Mateo County. Counts for all species are averaging below five per trap night, which is consistent with the five-year average. The abundance of adult mosquitoes is expected to remain low until spring.

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Improving Laboratory Techniques – Extraction methods

 Due to the increased rain this month, scientific staff spent the time in the lab to optimize DNA extraction techniques. The current laboratory tick extraction protocol allows staff to extract 24 tick pools (five ticks per pool) at a time. A different extraction kit has the ability to double that number to 48, but it utilizes different chemical reagents. Considering the lab processes thousands of ticks each year, this shift should significantly reduce extraction time.

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Ticks and Fire in Pescadero

In August 2020, several small fires in the Santa Cruz Mountains merged into the SZU Lightning Complex, which ultimately burned 86,509 acres. In San Mateo County, the fire burned 22,755 acres, and is now known as the largest fire in San Mateo history. Laboratory staff are conducting research at Butano State Park, a beautiful old-growth Redwood Forest near Pescadero that was significantly affected. Fire damage, strong winds, and heavy rains have rendered the trees unstable. The park is currently closed to the public due to the inherent safety risks.

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Tick Surveillance for Water Year 2020-2021

Laboratory staff continued surveillance for adult Ixodes pacificus (Western black-legged ticks) in January. However, field collection opportunities were limited by weather. Ticks were collected along residential homes in Hillsborough (ticks collected = 225), Costanoa near Pescadero (131), Montara Mountain near Montara (310) and Skyline Ridge Open Space Preserve near Portola Valley (581). In addition, tick surveillance and environmental surveys were conducted at Butano State Park near Pescadero (25).

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Mosquito Larval Samples from December 2020

Surveillance for mosquito larvae typically increases during the month of December as seasonal rains begin and water sources begin to accumulate. Through December 2020 there has not been a lot of late autumn/early winter rain, so many impounds remain dry.  This December, 26 larval samples were submitted to the laboratory. The most frequently occurring species in larval samples was Culiseta incidens, the cool weather mosquito, present in 9 of the 26 samples.

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West Nile Virus Update for December 2020

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of December compared to the five-year average for the six most common mosquito species in San Mateo County. Counts for all species are averaging below five per trap night, which is consistent with the five-year average. The abundance of adult mosquitoes is expected to remain low until spring.

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West Nile Virus – End of Year Review

San Mateo County

In the 2020 calendar year, the District closed out the second year in a row of very low levels of West Nile virus (WNV). The virus was only detected in the county once this year in any of the standard WNV surveillance indicators. The positive detection was a dead American crow from South San Francisco in September. The District followed-up on the detection by trapping and testing mosquitoes near the location of the bird, but all mosquitoes tested negative for the virus.

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Welcome Arielle Crews

On December 16, 2020, the District welcomed a new Vector Ecologist, Arielle Crews. Arielle previously worked as a Vector Biologist for the California Department of Public Health in the Vector-Borne Disease Section. There, she conducted state-wide laboratory disease surveillance for an array of pathogens including West Nile, St. Louis encephalitis, Western Equine Encephalitis, Lyme disease, and plague. Additionally, Arielle has worked on a wide breadth of zoonotic disease research projects from across the country.

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West Nile virus update for October 2020

San Mateo County

As of October 31, 2020, there have been 204 dead birds reported in San Mateo County. Of those, 62 have been suitable for testing and one has tested positive for West Nile virus (WNV). The WNV positive bird was an American crow collected from South San Francisco in September. This has been the only detection of WNV in San Mateo County in 2020. No mosquito samples or sentinel chickens have been confirmed positive for WNV in San Mateo County this year.  

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September 2020 CO2 trap collections

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of September compared to the five-year average for the six most common mosquito species in San Mateo County. Culex erythrothorax was the most frequently collected mosquito in September, seen in higher numbers this year compared to the five-year average. Much of this increase is due to significantly elevated numbers of these mosquitoes in marsh areas on the coast, coupled with improvements to targeted surveillance of this species this season.

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West Nile virus update for September 2020

San Mateo County

As of October 2, 2020, there have been 172 dead birds reported in San Mateo County. Of those, 50 have been suitable for testing and one has tested positive for West Nile virus (WNV). The WNV positive bird was an American crow collected from South San Francisco on September 22, 2020. This has been the only detection of WNV in San Mateo County in 2020. No mosquito samples or sentinel chickens have been confirmed positive for WNV in San Mateo County this year.

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August 2020 CO2 Trap Collections

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of August compared to the five-year average for the six most common mosquito species in San Mateo County. Culex erythrothorax was the most frequently collected mosquito in August, with numbers more than twice the five-year average. These mosquitoes are collected in tule marshes, which will be treated by helicopter. Culex pipiens, typically the most common mosquito trapped in August, is at average levels this year.

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Invasive Aedes surveillance in summer 2020

The District conducts intensive surveillance for invasive Aedes mosquitoes during the summer months. The surveillance program mainly targets two container-breeding species, Aedes aegypti and Aedes albopictus, which have been increasing their range within California over the last several years. This summer, Ae. aegypti and Ae. albopictus were detected for the first time in Shasta County. 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.

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West Nile Virus Update for August 2020

San Mateo County

As of August 31, 2020, there have been 140 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 been confirmed positive for West Nile virus in San Mateo County in 2020.

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West Nile Virus Update for July 2020

San Mateo County

As of August 4, 2020, there have been 120 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). To date, there have been no confirmed West Nile virus detections in mosquitoes or sentinel chickens in San Mateo County in 2020.

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July 2020 CO2 trap collections

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of July compared to the five-year average for the six most common mosquito species in San Mateo County. Culex erythrothorax was collected in above average numbers in July, whereas Culex pipiens, typically the most common mosquito in July, is well below average this year. Cx. erythrothorax, the tule mosquito, is largely treated by helicopter because the sites are often inaccessible by foot.

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June 2020 CO2 Trap Collections

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of June compared to the five-year average for the six most common mosquito species in San Mateo County. Culex erythrothorax was the most frequently collected mosquito in June, but numbers were only slightly above average. These mosquitoes are collected in tule marshes, which will be treated by helicopter. Culex pipiens, typically the most common mosquito in June, is well below average this year.

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West Nile Virus Updates – June 2020

San Mateo County

As of June 30, 2020, there have been 95 dead birds reported in San Mateo County. Of those, 29 have been suitable for testing and all 29 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 2020.

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Local Digger Bee

Beaches are popular among San Mateo County residents this summer, including our local bees. District staff responded to a request in June to identify bees nesting on a beach in Pacifica that were flying in and out of small holes in the sand.