Fight the Bite!

The Vector Control Program (VCP) operates within the County of San Diego Department of Environmental Health (DEH). The VCP is responsible for mosquito and vector-borne disease surveillance and control services in all 18 cities, as well as the unincorporated areas of the county. The VPC first detected West Nile Virus (WNV) in San Diego County in 2003. The VPC works collaboratively with the Community Epidemiology Branch (CEB) of public health to investigate human cases. No known human cases of WNV were locally acquired in San Diego until 2006. All previous cases investigated by CEB were acquired outside the county - the first case investigated in San Diego County was 2003. In 2007, there were fifteen locally acquired human infections with the majority of those infected above 50 years of age.

In order to minimize the exposure to citizens of San Diego County from WNV, the VCP developed a WNV Strategic Response Plan: an integrated, risk-based approach that has three response levels identified as normal season, emergency planning, and epidemics. The VCP operates under the normal season response level. Between August and September 2007, the VCP elevated their response level to emergency planning due to the increased number of reported human WNV cases.

The VCP utilizes a wide range of vector surveillance techniques to detect the presence of WNV in the environment. Some of the more common methods of surveillance include:

• sentinel chickens
• dead bird pick-up
• mosquito trapping and pooling
• 'green swimming pool' flyovers
• investigating and inspecting the over 1900 known mosquito breeding areas within the county

Sentinel chicken serology is performed for the presence of antibodies to WNV. The VCP maintains four flocks of chickens located strategically throughout the county. Dead birds are one of the earliest warning signs that WNV is present in the area. The Corvid family, including crows, ravens, and jays, are especially susceptible to the virus. Raptors such as falcons and hawks can be susceptible to the virus as well. Mosquitoes are trapped using either a Gravid or CDC trap and then are pooled for laboratory testing. The VCP uses the sheriff's helicopter for flying over neighborhoods and looking for neglected or "green" swimming pools, which are prime habitats for breeding mosquitoes. VCP staff routinely investigate and inspect the known mosquito breeding areas within the county to determine the mosquito population levels for appropriate treatment.

Control of mosquito sources and populations by VCP has been traditionally through the use of chemicals such as "Golden Bear," a petroleum-based insecticide and mechanical habitat removal. Over the past few years, the VCP has shifted away from these environmentally sensitive control measures to more environmentally friendly control measures, such as mosquito fish, larvacides, and habitat management. Mosquito fish - Gambusia affinis - are small, freshwater fish that eat mosquito larvae and are ideal for controlling mosquito larvae in backyard ponds, birdbaths, fountains, animal troughs, unused swimming pools, and other standing water sources. The larvicides used by the VCP are a Bacillus bacteria that acts specifically on mosquito larvae and will not harm other wildlife. They kill the larvae before they can develop into biting adults. They are applied by a helicopter to the vegetation in the larger bodies of water that cannot be applied by hand. The VCP is developing a Vector Control Habitat Management Plan that will be used as a model plan for eliminating mosquito breeding sources.

Mosquitoes can breed wherever they can find standing water to lay their eggs - all they need is a quarter of a cup of water. Backyard breeding sources of mosquitos are common in San Diego County and require homeowners to assist in the fight against WNV. Outreach through presentations, media events, press releases, website postings, and written materials is consistently provided by the VCP to residents, businesses, and agencies throughout the year. This year, the VCP is focusing their outreach efforts on senior organizations and 'baby boomers.' For more information about the VCP, call (858) 694-2888 or visit the DEH website at www.sdcounty.ca.gov/deh/pests/wnv.html.

Human West Nile Virus Cases by Year of Report

San Diego County, 2003-2007

2003 Total Cases: 1

• Locally Acquired?
  
  • Yes: 0
  • No: 1
  • Unknown: 0

2004 Total Cases: 2

• Locally Acquired?
  
  • Yes: 0
  • No: 1
  • Unknown: 1

2005 Total Cases: 1

• Locally Acquired?
  
  • Yes: 0
  • No: 1
  • Unknown: 0

2006 Total Cases: 2

• Locally Acquired?
  
  • Yes: 1
  • No: 1
  • Unknown: 0

2007 Total Cases: 16

• Locally Acquired?
  
  • Yes: 15
  • No: 1
  • Unknown: 0

Resource: County of San Diego, Health & Human Services Agency, Community Epidemiology Branch.