ADULT SURVEILLANCE:

MOSQUITO LIGHT TRAPS

Collecting adult mosquitoes can provide several important pieces of informatiotesting mosquito surveillancen. When traps are set at specific locations over a period of time, or in response to service requests, increases in the mosquito population can be detected. Once these mosquitoes are identified, control measures can then be more easily directed. Knowing what species of mosquito is breeding can help Vector Control Technicians find the breeding source and take the appropriate control measures. After identification by District Staff, these mosquitoes can also be tested for the presence of disease. The detection of virus in a mosquito which feeds on humans indicates a true potential for human disease, and immediate control measures can be implemented. Trap collections not only determine where control measures are needed, but also determine the effectiveness of control measures which are in place.

CDC-Type CO2-Baited Trap

CDC-type trap

This trap is used to selectively sample host-seeking females attracted to the trap by the sublimation of dry ice into carbon dioxide (CO2) which simulates the exhaled respiratory gases of birds or mammals. The trap consists of a central 3″ diameter plastic cylinder housing a 6V DC motor and a 4″ fan blade, a collection net attached to the bottom of the cylinder, a 6V battery power source, and an insulated container with 2-5 pounds of dry ice. CDC-type traps utilized by the District also incorporate a mini-light source which help attract mosquitoes as well. Mosquitoes attracted to the trap are drawn in through the top of the trap and forced downward by the fan into the collection net. Live-trapped females can be counted and tested for mosquito-borne arboviruses.

Gravid Trap

gravid trapThis trap selectively samples gravid (ready to deposit eggs) female house mosquitoes (Cx. pipiens) that are seeking suitable oviposition sites. The gravid trap incorporates three components: a base reservoir filled with oviposition attractant (hay or manure infusion), a vertically-directed suction apparatus and a top mounted collection carton. The intake orifice of the suction apparatus is positioned one inch above the surface of the oviposition attractant. Gravid females attracted by the infusion descend into the base reservoir where they are swept into the suction apparatus and directed upward into the collection carton.

MOSQUITO LANDING RATES

Landing rates are used to measure adult mosquito activity in a specific area. This is achieved by counting the number of mosquitoes that land on a person in a given amount of time, usually one minute. The same inspector at each location for consistency performs the counts. This is important because mosquitoes react differently to each individual. Several landing rate stations are located throughout the 525 sq. miles of the West Umatilla Vector Control District. Each station is counted daily by 9 a.m. throughout the entire mosquito season. This count is effective for monitoring floodwater mosquitoes that bite in the early morning and during the day. Occasionally, the district performs night counts for permanent-water mosquitoes. This helps the district to determine the extent of the area that needs to be sprayed, or whether an isolated portion needs to be treated. Landing counts are also very helpful when evaluating the efficacy of an adulticide treatment.

DISEASE SURVEILLANCE:

SENTINEL CHICKENS

Sentinel chicken serology is performed by placing chickens in an area over an extended period of time and testing their blood for the presence of antibodies to SLE and WEE as well as West Nile viruses. The District maintains 4 flocks of chickens located strategically throughout the District.

The chickens are bled once every two weeks during the months of May through October. Blood samples are processed and tested by the Oregon Health Department’s Public Health Lab, in Portland, Oregon. The results obtained from these laboratory tests are used to increase inspections and control measures in areas where viral activity is present.

It is important to note that the chickens are well cared for at all times. Only a very small amount of blood is taken from each chicken every other week. The chickens represent a critical element of the District’s surveillance program and help to prevent any transmission of SLE, WEE and WNV to the human population.

Once a small amount of blood is collected, the blood is transferred to a numbered filter paper strip. This filter paper strip is later used for laboratory testing.

The Sentinel Chicken Surveillance program has been in place since 1998. To date no samples have tested positive for any mosquito borne viruses.

MOSQUITO POOLS

What is a mosquito pool?

During the mosquito season we collect adult mosquito pools to test for mosquito borne diseases. A mosquito pool is a collection of mosquitoes (usually about 50) of any given species or group (i.e. Culex mosquitoes) that are likely to carry/transmit a virus. Since stagnant water Culex mosquitoes are the primary mosquitoes implicated in transmission of West Nile Virus (WNV), and Saint Louis Encephalitis (SLE) , and Western Equine Encephalitis (WEE) they are this species is targeted for testing.

What is the VecTest?

The VecTest is a WNV/SLE/WEE antigen panel assay designed by Medical Analysis Systems, Inc. Basically, it’s a rapid detection dipstick test for West Nile Virus (WNV) , Saint Louis Encephalitis (SLE), and Western Equine Encephalitis (WEE). Mosquitoes are ground up in a special solution and then wicked up on to a test strip. The antigen for WNV/SLE, if present, binds to specific antibody on the test strip producing a reddish color change indicating the presence of viral antigen in the sample. The assay doesn’t measure the quantity of viral antigen in a sample only the presence of it.

By keeping track of positive VecTest mosquito pools we will be able to better monitor the distribution of these viruses in the District. A positive mosquito pool means that local mosquitoes are infected with the virus and possibly capable of transmitting it to other hosts. By combining this information with bird surveillance records, horse and human viral infection data, we can better, and more quickly, adapt/enhance our control practices and further reduce the potential for people acquiring mosquito transmitted diseases.

As of today, all mosquitoes have tested NEGATIVE!

WILD BIRD TESTING

The West Umatilla Vector Control District has stepped up its surveillance of mosquito-borne encephalitis to include testing dead birds. Local residents are in a unique position to assist in this effort. We want to encourage your participation. We are seeking appropriate specimens of dead birds for mosquito-borne virus testing.

The West Umatilla Vector Control District began to collect dead crows and related birds for West Nile Virus (WNV) in 2002. The samples were collected and packaged, the exact location information noted, and sent to the Oregon Public Health Laboratory in Portland, Oregon where they are tested for the presence of WNV. This program is partly funded by a grant to the Oregon Health Division by the Centers for Disease Control (CDC).

The District has tested a total of 32 birds. All were negative. Although the virus has not yet been reported in Oregon, monitoring dead crows and other corvids will help identify the virus if it enters the State. State agencies, private organizations, and individuals participate in the surveillance program by reporting dead bird sightings.

WHAT TO DO IF YOU FIND A DEAD BIRD

Call the West Umatilla Vector Control District at 541-567-5201 OR The Umatilla County Public Health Department at 541-278-5432

  • Avoid direct contact with the bird.
  • Wear disposable latex gloves while handling the bird or wear gloves that can immediately be put through a hot soapy wash. A dead bird can also be picked up by inverting a plastic bag on your hand and grasping the bird through the plastic.
  • Double bag the bird in plastic and place in the garbage, unless otherwise instructed by the health district. Wash your hands.
  • Do not bring the bird into your home.
  • Do not eat, drink, smoke or touch your face with the gloves while handling the bird.
  • Wash your hands with soap and water for at least 20 seconds after handling the bird.

Only certain birds will be collected.

Many species of birds can be infected with WNV and have no symptoms or illness. Birds that are more susceptible are the corvids (crows, ravens and magpies) and raptors.

All birds accepted for testing must be:

  • Freshly dead (within 24 hours)
  • Intact (with no physical trauma)
  • Dead by natural causes