Intervention Thresholds  »  Intervention Thresholds

Intervention Thresholds

To better guide UCMAD treatments for adult mosquitoes, thresholds were established according to different criteria. These criteria have been established based on the fact that UCMAD was created to treat either for nuisance and/or for public health protection (potential transmission of diseases by the mosquitoes). The WNV plan includes three levels of responses based on surveillance thresholds.

Level 0 (None)

  • Surveillance
    • No adult mosquito biting activity.
  • Action:
    • Develop and review WNV response plan.
    • Review mosquito control program.
    • Maintain source reduction projects.
    • Secure surveillance and control resources necessary to enable emergency response.
    • Review and update community outreach and public education programs.
    • Establish communication with other public health professionals such as department of agriculture, veterinarians, etc.

Level 1 (Low) Late Spring early Summer

  • Surveillance:
    • Biting adult mosquitoes active.
    • Field sampling of known Culex species habitats, determined from data base, to monitor development of mosquito populations.  (Beginning mid April)
    • Limited CDC traps, will be used to detect adult mosquito vector emergence.  Early trapping will begin in May, dependent on weather conditions, and regular weekly trapping will be conducted June-September. 
      • Selected traps in Goshen Elementary, Genola, Wild Wings, Camelot, Provo Bay, and Inlet Park will serve as early sentinel traps for WNV.  These areas have historically caught mosquitoes infected with WNV. 
    • Conduct a resistance study using CDC bottle Bio Asay or caged field trails to assess the level of resistance found in the mosquito populations for the adulticides we use.
  • Action:
    • Response as in level 0, plus
    • Mosquito pools of Culex species will be tested weekly for WNV, SLE and WEE in our lab by qPCR testing.  Positive tests for WNV raises the health threat and urgency for added control to level 3 response.
    • Vector Control employees will assess mosquito numbers and metamorphic development to determine if chemical larviciding is needed. They will access aquatic life, organic matter, water quantity, temperature, and mosquito species to determine which product will be most effective and environmentally friendly.
      • Target mosquitoes reaching a threshold of >3-5/dip may be treated with a larvicide product.
    • Evening (9-12 PM) adulticiding with ULV foggers will be used as needed to control mosquitoes based on trapping data.
      • A threshold of > 50 adult mosquitoes that are potential vectors of West Nile virus, i.e. Culex tarsalis, Culex pipiens or Culex erythrothorax from selected traps in Goshen Elementary, Genola, Wild Wings, Camelot, Provo Bay and Inlet Park will serve as early sentinel traps for WNV.  These areas have historically produced disease vector mosquitoes. 
    • Evening (9-12 PM) adulticiding with ULV foggers will be used as needed to control mosquitoes based on trapping data.

Level 2 (Moderate) Trap number over 1000

  • Surveillance:
    • Increase in biting adult mosquito activity
    •   Continue regular field work to monitor upcoming mosquito hatches indicating increase in Culex. species.
    •   Continue regular CDC trapping county wide. June through September.
    •   Monitor those traps located near the east side of Utah Lake to monitor potential need for air spraying in areas inaccessible to ULV fogging.
    • Monitor veterinarian clinics, and EDCO website for the presence of WNV in the horse population.  If WNV detected will move to level 3 response.
  • Action:
    • Response as in level 1, plus
    • When trap counts reach a threshold of 1000 Culex species, this indicates a rapid increase in WNV vector mosquitoes.  This is the threshold to begin initial air spray, usually occurring in late June-early July.
    • Mosquito pools of Culex species will be tested weekly for WNV, SLE and WEE in our lab by qPCR testing.  Positive tests for WNV raises the health threat and urgency for added control to level 3 response.
    • Increase evening fogging (4-9 trucks) targeting areas of concern to create buffer zone between source and major county populations.  Weekly spray routes are conducted targeting areas with high trap count numbers.
    • Contact Vector Disease Control Inc. (VDCI) of need and provide shape files of area posing health threat targeted for aerial control.  Initiate 1st spray for control of Cx. speciesto continue weekly up to 8 sprays or until numbers drop below 1000.
    • Post trapping will monitor effectiveness of air spraying.  The goal is the reduction of 50-80% of adult mosquitoes.

Level 3 (High) Positive WNV, SLE, WEE Test

  • Surveillance:  
    • Detection of arborviruses in mosquito, horse, or human population.
    • Continue regular field work to monitor upcoming mosquito hatches indicating increase in Culex. species.
    • Continue regular CDC trapping county wide. June through September.
    • Monitor those traps located near the east side of Utah Lake to monitor potential need for air spraying in areas inaccessible to ULV fogging.
    • Monitor veterinarian clinics, and EDCO website for the presence of WNV in the horse population.  If WNV detected will move to level 3 response.
  • Action:
    • Response as in level 2, plus
    • Alert and coordinate with Dr. Eric Edwards (Health Department Director) and PIO (Ailsynn Tolman-Hill) of impending threat and intended control actions.  PIO will make statement to media.
    • Increase evening fogging (4-9 trucks) targeting where positive test results are found or where horse or human cases have been reported.