Washington County Arbovirus Management Program 2008 Year End Report Page 1 of 12 

WASHINGTON COUNTY

OREGON

Department of Health and Human Services 

Environmental Health Division 

ARBOVIRUS MANAGEMENT PROGRAM

2008 Year End Report 

BACKGROUND 

The Washington County Arbovirus Management Program was initiated in 2003 in anticipation 

of the arrival of West Nile Virus (WNV) in Oregon. The current program is a cooperative effort 

between Washington County and Clean Water Services (CWS), Tualatin Hills Park and 

Recreation District (THPRD), Beaverton School District, and local cities. Efforts are formalized 

through Intergovernmental Agreements (IGA). Participating cities include Beaverton, Cornelius, 

Forest Grove, Hillsboro, Tigard, Tualatin, and Sherwood. The Washington County program 

focuses on education, surveillance, and controlling mosquito larvae capable of vectoring disease 

to humans. Washington County will only consider managing adult mosquito populations 

through adulticide applications in the event of a public health emergency. 

SURVEILLANCE IN 2008 

The Washington County Arbovirus Management Program conducted active larval and adult 

mosquito surveillance in 2008. Washington County field workers and IGA field staff inspects 

over 1300 potential mosquito habitats (see map 1). Field workers collected mosquito samples 

for identification and encephalitis testing, documented potential habitat breeding locations, 

presence of mosquitoes at sites and evaluated habitat risk for mosquito production. 

Larval and adult mosquitoes were collected on a weekly basis from selected sites in Washington 

County using aquatic dippers and Gravid or Encephalitis Virus Surveillance (EVS) CO2 traps. 

Washington County program staff identified and tested mosquitoes for WNV. Species known to 

be capable of transmitting WNV were pooled into all female, single species, single site samples 

and tested for WNV by the County utilizing the Rapid Analyte Measurement Platform (RAMP) 

(see table 1). Washington County tested 31 mosquito pools (5,999 individual female adults); all 

mosquito pools tested were negative. 93% of the adult and 79% of the larval samples collected 

were species considered either “most” capable or “moderately” capable of transmitting WNV. 
AVIAN SURVEILLANCE IN 2008 

Washington County also conducted passive avian surveillance. Avian specimens collected for 

testing were first tested for WNV by the County utilizing RAMP testing equipment. 

Confirmation testing was done through Polymerase Chain Reaction (PCR) testing conducted by 

the Oregon State University (OSU) Veterinary Diagnostic Laboratory (VDL). 

Washington County collected 25 dead birds in 2008 (see map 2). Ten of these birds were 

subsequently submitted to Oregon State University Veterinary Diagnostic Laboratory for 

confirmation testing. No bird tested positive for WNV by PCR confirmation testing by OSU 

VDL. 56% of the birds collected were crows (see table 2). 

PUBLIC REQUESTS FOR INFORMATION IN 2008 

Washington County answers public inquiries as part of their community outreach program. In 

2008, the County received more than 50 calls from the public concerned about mosquitoes 

and/or WNV (see map 3): 

3⁄4 11 complaint calls related to the sighting of sick/dead birds 

3⁄4 37 calls related to larval and adult mosquito nuisances or the presence of standing water 

3⁄4 In addition calls related to sick/dead birds and other vector inquiries were also received 

LARVAL MOSQUITO CONTROL IN 2008 

Mosquito control efforts in Washington County focused on larval breeding in catch basins 

located within the 118 square mile urban growth boundary. Larval mosquito surveillance over 

the past three years has shown that catch basins are a significant source of mosquitoes in urban 

areas of Washington County. Washington County and IGA field staff coordinated efforts to 

control mosquito populations by treating public catch basins once during the mosquito season. 

In 2008, Washington and IGA field staff treated 21,975 sumped catch basins with Altosid XR 

Briquets (see table 3 and map 4). 

In 2008, Washington County’s program continued to identify and treat high-risk natural habitats 

for mosquito larvae. Surveillance was conducted at these sites and treated, as needed, by 

Washington County staff (see map 5). Surveillance and treatment efforts in high-risk natural 

areas have been increased. 

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EDUCATION EFFORTS IN 2008 

The following educational program activities took place in Washington County’s WNV 

Prevention program in 2008: 

3⁄4 Health Fairs - plant nurseries, city events, employers, public and private Schools, public 

libraries, organizations (Kiwanis, Elks, Boy Scouts, Familias Hispanas, Churches 

Americans with Disabilities Group) 

3⁄4 Speaking engagements: organizations (Boy Scouts, Kiwanis, Adelante Mujeres, Centro 

Cultural, Citizen Participation Groups), long term care facilities 

3⁄4 OMSI 

3⁄4 Washington County Fair 

3⁄4 Migrant camps 

3⁄4 Children’s Clean Water Festival 

3⁄4 Farmer’s markets 

3⁄4 Parks and Recreation facilities 

Materials, which included bookmarks, brochures and promotional items, were distributed at the 

above and below listed events/locations. 

3⁄4 Public Libraries 

3⁄4 Pharmacies and Homeowner Associations 

3⁄4 County Public Services Building Foyer 

3⁄4 Beaverton Resource Center 

3⁄4 Beaverton Health Clinic 

3⁄4 Hillsboro Health Clinic 

GAMBUSIA AFFINIS DISTRIBUTED TO PUBLIC IN 2008

In 2008, Washington County distributed Gambusia affinis (Mosquito fish) to county residents to 

help mitigate mosquito production in aquaria sites. 537 mosquito fish were distributed to 31 

County residents (see map 6). 

ADDITIONAL PROGRAM ACTIVITIES IN 2008 

Improvements in 2008, to Washington County’s Mosquito program include: 

3⁄4 Creation of a more robust and complete mosquito surveillance program by expanding 

adult trap locations 

3⁄4 Washington County also took steps to begin treating private catch basins by identification 

and treatment of public common areas such as strip malls, business parks, colleges, etc. 

This activity will continue for the 2009 treatment season. 

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TABLE 1: Mosquito Species Collected in Washington County 2008 

Species breakdown of mosquito larvae and adults collected 

Larval Mosquito Totals Adult Mosquito Totals 

Species Total Species Total

Ae vexans 42 Ae vexans 924

An freeborni 1 An punctipennis 55

An punctipennis 25 An freeborni 12

Cs impatiens 1 Cq perturbans 8

Cs incidens 500 Cs incidens 68

Cs inornata 9 Cx erythrothorax 13

Cs minnesotae 40 Cs particeps 9

Cs particeps 12 Cs inornata 20

Cx boharti 118 Cs minnesotae 367

Cx erythrothorax 21 Cs impatiens 2

Cx pipiens 3155 Oc washinoi 1

Cx stigmatosoma 35 Cx pipiens 6029

Cx tarsalis 250 Cx tarsalis 406

Cx territans 127 7914

Unknown 61

4397

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TABLE 2: Birds Tested in Washington County 2008 

Type of birds collected, confirmed test results, and specimen location in Washington County by zip code. 

Bird 

Type 

Test 

Result 

Zip Code of 

Tested Specimen 

Crow Negative 97224

Crow Negative 97008

Crow Negative 97124

Other Negative 97123

Robin Negative 97062

Crow Negative 97223

Crow Negative 97223

Jay Negative 97007

Jay Negative 97229

Unknown Negative 97007

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TABLE 3: Sumped Catch Basins Treated in Washington County 2008

Number of catch basins treated by Washington County and IGA field partners in Washington 

County. 

Sumped Catch Basin Treatment in 

Washington County for 2008 

Agency that treated sumped catch basins in 2008 Number of Sumped 

catch basins treated 

City of Beaverton 2,716 

City of Forest Grove 541 

City of Sherwood 1,673 

City of Tigard 2,230 

City of Tualatin 1,300 

Clean Water Services 6,871 

Cornelius Public Works 998 

Beaverton School District 501 

Hillsboro Public Works 4,311 

Hillsboro Parks 550 

Tualatin Hills Parks and Recreation District 80 

Washington County WNV Program+ WC Facilities 1506 

TOTAL SUMPED CATCH BASINS TREATED 23,277 

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