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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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. 

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Mosquito Spotlight: Orthopodomyia signifera

The District works to control mosquitoes in our county because they are disease vectors and aggressive biting pests. However, there are several mosquito species that are not known to bite people. One of these infrequently-encountered mosquitoes is called Orthopodomyia signifera. It breeds in the holes of trees that hold water year-round and feeds exclusively on birds.

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May 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 May 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 below average for Culex pipiens at this time of year, but consistent with the five-year average for other species. Adult mosquito abundance will likely continue to rise as the daily temperatures increase in the summer months.

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West Nile Virus Update – May 2020

San Mateo County

As of May 31, 2020, there have been 68 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 2020.

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April 2020 CO2 Trap Results

The following table and graphs show the average number of mosquitoes collected per CO2 trap per night during the month of April 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. April was the first month in 2020 the Aedes sierrensis, the western treehole mosquito was collected. This mosquito is a vector of dog heartworm and adults are usually present from spring to fall.

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March 2020 CO2 Trap Results

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of March 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 numbers are expected to remain low until after spring rains.

Species

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Tick Surveillance Update for Water Year 2019-2020
April 2020 Update

During early March, laboratory staff continued surveillance for adult Ixodes pacificus (Western black-legged ticks). Ticks are collected by dragging a 1 meter square sheet of white flannel over the vegetation alongside trails. Ixodes pacificus ticks will be tested for the presence of bacteria Borrelia burgdorferi, the causative agent of Lyme disease, as well as Borrelia miyamotoi and Anaplasma phagocytophilum.

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February 2020 CO2 Trap Results

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of February 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 numbers are expected to remain low until spring.

Species

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Tick Surveillance Update for Water Year 2019-2020
March 2020 Update

During February, laboratory staff continued surveillance for adult Ixodes pacificus (Western black-legged ticks). Ticks are collected by dragging a 1 meter square sheet of white flannel over the vegetation alongside trails. Ixodes pacificus ticks will be tested for the presence of bacteria Borrelia burgdorferi, the causative agent of Lyme disease, as well as Borrelia miyamotoi and Anaplasma phagocytophilum.

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Studying Mosquito Parasites

District staff are assisting in a collaborative study on a mosquito parasite that is spearheaded by researchers from Stanford University and the University of Innsbruck in Austria. The parasite is a ciliate type of protozoa, Lambornella clarki, which is a single-celled animal that lives in water. Lambornella clarki is found in water that collects in tree holes, and can enter the body of the mosquito larvae of Aedes sierrensis, the western tree-hole mosquito. Inside the mosquito larvae, it multiplies and kills the hosts.

Commands