Risk Level 5

RISK LEVEL 5 - PUBLIC HEALTH ALERT

Condition:     Human outbreak is confirmed

Trigger:         Multiple human cases. 

Nivel de riesgo 5 - Alerta de Salud Pública

Recommended Response:
Surveillance:
Continue to conduct routine surveillance of mosquito populations. If resources allow, increase surveillance in areas were arthropod-borne virus/disease positive samples were collected. Use geographic information systems to plot the location of WNV positive mosquito samples, and provide this information to the public.   

Public Information/Education:

• Implement all steps for public information established by the Public Communication Office for this Risk Level, which includes public notification, press releases, and City of Denton web page updates with a map of the WNV positive trap location(s).
• Update web page map for all subsequent WNV positive trap locations    
• Notify medical professionals, veterinarians, public health officials, and all those registered with the City of Denton’s various public notification options of the presence of the disease.
• Increase public education, emphasizing source reduction, personal protection, and disease symptoms.

Control Measures:
Use public information to promote source reduction and personal protection. Intensify larviciding efforts using Bti in targeted areas. Additional larvicides containing IGRs or pesticides such as Spinosad may be applied at this time. If appropriate, intensely treat standing water in City Parks. If the threat to human health is considered imminent, consider targeted adulticide applications using ground-based Ultra-Low Volume (ULV) equipment. The decision to spray will be made by a Resolution of the City Council of Denton prior to the first application, for each mosquito season. Based on information available at the time of the Council decision, the Resolution may include specific requirements in addition those outlined in this plan. ULV applications should be implemented in the vicinity (approximately 1 mile) of areas where positive human cases were detected. When ULV applications are initiated, notification will be provided to the public as outlined in Section 7.1.

The City of Denton utilized Duet, a synthetic pyrethroid product with an additional chemical designed to induce “benign agitation” of mosquitoes. The purpose of benign agitation is to increase the likelihood of mosquitoes flying during the application, which increases application effectiveness. The Duet product is also mineral oil based, versus water based, which likely increases the compound’s effectiveness in the higher air temperatures typical during summer applications. Mineral oil based compounds may also be less likely to affect non-target organisms in aquatic environments because of the lack of solubility of the oil based compound in water.

Control measures will be implemented based on the following IPM criteria: time of year, the extent of previous mosquito control activities, the current level of mosquito activity, weather conditions, the species of mosquitoes that test positive for disease, the number of local mosquito pools which test positively for disease, the likely time until a killing frost, the density of roads or other access to mosquito breeding grounds, and the density of human populations. 

Epidemiological data associated with reported human cases of WNV will also be considered. In general, if an area has been sprayed, that area will not be sprayed again in response to an additional human case unless the date of onset of the new case indicates exposure occurred after the previous spraying event. Areas will also not be sprayed in response to a reported human case if epidemiological information clearly indicates that exposure did not occur in the City of Denton. If public health emergencies are declared at the county or state level, the recommended responses associated with the declaration will take precedence over the control plan of the City of Denton.

Rationale:
Larviciding and source reduction/elimination are considered to be the most effective long-term solutions for mosquito control. Increasing these measures in areas where positive mosquito pools are detected offers an additional degree of risk reduction. However, at this Risk Level, applications of adulticides may be needed to rapidly reduce mosquito populations and halt disease transmission. The objective is to kill a high enough proportion of older adult mosquitoes to break the disease transmission cycle. If adult mosquito controls are implemented, the approaches for adulticiding outlined in this plan are effective and are designed to minimize adverse effects to the environment and non-target organisms.

For More Information: 

For more information concerning mosquito control and the West Nile virus, please use the following resources:
• Texas Department of Health website at http://www.dshs.state.tx.us/idcu/disease/arboviral/westNile/
• Denton County Health Department website at http://dentoncounty.com/wnv/
• Center for Disease Control and Prevention website at http://www.cdc.gov
• Brochure - Fight the Bite: Learn how to control mosquitoes and help prevent West Nile virus
• Fact sheet on mosquito repellent: DEET 
• Questions and answers about mosquito repellent: Picaridin http://www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm
• FAQs about West Nile virus
• City of Denton Mosquito Response Plan