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Interim CDC Recommendations for Zika Vector Control in the Continental United States

Accompanying guidance to CDC Guidelines for Development of State and Local Risk-based Zika Action Plans *Does not include guidance specific to US territories

Early season mosquito control efforts can decrease the risk of eventual Zika transmission. In addition, effective control of Zika will depend on prompt and aggressive intervention when human cases are first identified. All at-risk communities should prepare for Zika virus activity, and should evaluate and prepare control plans for mosquito populations in their state as part of Zika Action Plan preparedness efforts.  A comprehensive review of health code, enforcement practices and property access will aid the implementation of a vector control plan. 

Many states already have vector control programs. With the exception of states who have responded to past outbreaks of dengue and chikungunya, most state plans focus on control of mosquitoes for the prevention of West Nile virus (WNV). The biology and behavior of Aedes aegypti and Aedes albopictus are different from the mosquitoes that transmit WNV. Therefore, the tools used for surveillance of these species as well as strategies for control will be different from WNV mosquitoes.

Before mosquito season

  • State, tribes, and local governments should consider using an Integrated Vector Management (IVM) strategy as they develop their mosquito control plans (See Appendix).
  • Public health officials and vector control officials should develop a communications network to ensure timely exchange of information, and collaboratively share information to guide optimum vector control efforts. This network should be part of the state’s Incident Management structure, and should report efforts and plans to the state Incident Manager (IM).
  • To prepare for the possible introduction of Zika virus, states, tribes, and local governments should review historical data and maps regarding the presence of Aedes aegypti and Aedes albopictus. If maps are outdated and resources permit, plan new surveys and assessments to be conducted during mosquito season.
  • Responding officials should review existing staffing capacity, resource allocation, and technical expertise at the local level for vector control and consider use of intergovernmental agreements for vector control to help adjacent counties outside their jurisdiction, as well as pre-positioning contracts with vendors to supply additional capacity.
  • Responding officials should link vector control efforts with communication efforts. This includes ensuring public education campaigns include information not just on personal protection measures, but also how citizens may reduce or eliminate breeding sites for Ae. aegypti and Ae. albopictus, and to motivate the community to remove and dispose of any water holding containers.

Mosquito Season

  • Using the plan previously developed, survey and map presence of Aedes aegypti and Aedes albopictus within the state.
  • Actively engage community to encourage removal of larval habitat and Aedes breeding sites, including community cleanup campaigns (tire removal, trash pickup, removal and cleaning of small and large containers). Leverage partnerships with local governments and non-profits for support.
  • If resources and technical expertise permits, conduct rapid insecticide resistance testing for local mosquito populations, in order to know the pesticides most likely to be effective in the event of Zika transmission.
  • Use larvicides in containers and bodies of water that cannot be removed or dumped.

Confirmed transmission (first case, or several cases in a single household or building)

  • Implement Targeted Control efforts around the case-patient’s home or building. Conduct intensified larval and adult mosquito control in a 150 yard radius (or other boundary as deemed appropriate) around the case patient home.  Targeted control activities involving home visits should be closely coordinated with concurrent educational efforts and messaging.
  • Consider adding community-based adult mosquito control consisting of outdoor residual spraying, and space spraying if necessary.
  • Intensify larviciding and source reduction efforts.
  • Consider targeted indoor residual spraying in areas where A/C and screens aren’t widely available.

Widespread transmission within a county or jurisdiction

  • Vector control efforts should align with state, tribal, and local government decisions regarding boundaries for declaring an area as a site of “active Zika transmission”. This may model county lines, or be a zipcode designation. At this phase, officials should plan to intensify and expand vector control efforts within the areas of active transmission.   
  • In addition to continuing to target case-patient homes and the surrounding vicinity, area-wide treatments with larvicides and adulticides using application methods appropriate for the scale of the treatment area should be considered. Control plans should be tailored to the local needs, and might require truck or aerial spraying (aerial for areas > 2,000 acres) or a combination of both.
  • Monitor for effectiveness of treatments through trapping and retreat if mosquito numbers begin to increase again.
  • For areas where A/C and screens aren’t widely available, consider adding targeted indoor residual spraying to vulnerable homes.

Widespread transmission within multiple counties or the state

  • Expand vector control efforts for regional or state coverage.

Appendix

Effective mosquito management programs based on Integrated Vector Management (IVM) principles may help prevent the introduction of Zika to an area. IVM principles include approaching mosquito control through careful planning, and using a variety of interventions targeting both larval and adult mosquito control, and including both chemical and non-chemical methods. Properly planned and executed, IVM ensures a more effective level of control than can be achieved by one single approach. States, tribes, and local governments should develop plans tailored to their individual needs, and should consider basing those plans on the principles of IVM.

IVM is ideally anchored by a mosquito monitoring program providing data that describe local conditions and habitats that produce Aedes mosquitoes, as well as the abundance of those mosquitoes over the course of a season. These data can help inform decisions about implementing mosquito control activities appropriate to the situation. The implementation of an effective IVM program for Aedes requires trained staff with a knowledge of the mosquito life cycle and expertise in monitoring methods. Details for how to conduct assessment and control activities for both larval and adult Aedes mosquitoes may be found on CDC’s Chikungunya website.

Immature Mosquito Monitoring

Larval monitoring can help state, tribal, and local governments monitor Aedes activity and make early decisions for control, even in advance of suspected Zika cases in humans. This involves sampling a wide range of aquatic habitats, and requires trained inspectors to identify larval production sites, collect larval specimens on a regular basis from known larval habitats, and to regularly look for new sources. This information can be used to determine where and when source reduction or larval control efforts should be implemented. Common methods for collecting information on the number and locations of larval Ae. aegypti and Ae. albopictus are ovitraps and larval/pupal surveys.

Adult Mosquito Monitoring

Adult mosquito monitoring is used to determine the abundance adult vector mosquitoes, and identify areas where control measures are needed. It is also useful to assess the effectiveness of intervention methods. Currently, testing mosquitoes for Zika virus is not currently recommended, as this virus does not have a known animal reservoir outside of humans in the United States and there is no expected advantage to be obtained over good human surveillance programs.

Various methods are available for monitoring adult mosquitoes. Traps targeting adult Culex species are not affective at capturing Ae aegypti and Ae. albopictus.  The most frequently used trap for adult Aedes surveillance is the BG Sentinel trap, but other trap types are available. Adult mosquito surveillance should consist of a series of collecting sites at which mosquitoes are sampled on a regular schedule. Fixed trap sites allow monitoring of trends in mosquito abundance over time and are essential for obtaining information to guide control efforts. Additional trap sites can be utilized on an ad hoc basis to provide additional information about mosquito activity and effectiveness of control efforts.

Mosquito Control Activities

Mosquito control should ideally be conducted during mosquito season, even before cases of Zika are recognized, and be based on the results of larval and adult mosquito monitoring programs that have identified areas in need of control. Additionally, at the point of the first human case of Zika, more routine mosquito control efforts must be quickly and aggressively amplified to prevent risk levels from increasing to the point of a widespread human disease outbreak.

Larval Mosquito Control

The objective of the larval mosquito control is to manage mosquito populations before they emerge as adults. This can be an efficient method of managing mosquito populations if the mosquito breeding sites are accessible. However larval control alone may not attain the levels of mosquito population reduction needed to maintain Zika risk at low levels, and must be accompanied by measures to control the adult mosquito populations as well. In outbreak situations, larval control complements adult mosquito control measures by preventing new vector mosquitoes from being produced. However, larval control alone is unlikely to be able to stop Zika outbreaks once virus amplification has reached levels causing human infections.

Numerous methods are available for controlling larval mosquitoes.

  • Source reduction: Source reduction is the elimination or removal of habitats that produce mosquitoes. This can range from draining and scrubbing water holding containers on a weekly basis to properly disposing of discarded tires, rain barrels, and trash containers that may harbor rain water. This can be difficult to accomplish with the Zika virus vector Ae. aegypti that readily utilizes very small water containers. Active community engagement, as well as ensuring community access to trash services for removal of debris, are critical to the success of a source reduction campaign. Source reduction may be improved through home visits to examine possible mosquito breeding sites and educating homeowners.
  • Larvicide Application: For situations not conducive to source reduction, pesticides registered by EPA for larval mosquito control may be applied when larvae are detected or added to containers that could potentially serve as breeding sites. Several larval mosquito control pesticides are available. (See Table 1.) Methods for delivering larvicides include the use of hand-held application devices, from truck-mounted sprayers, from aircraft, or from a combination of methods. More details are provided below.
  • Combined Approach: A combination approach utilizing source reduction and larviciding that is tailored to local contexts and the provision of adequate field staff with proper training is required to properly identify larval production sites and implement the appropriate management tools for that site.

Adult Mosquito Control

Source reduction and larvicide treatments alone are unlikely to be adequate to maintain adult mosquito populations at levels sufficiently low enough to limit virus amplification. The objective of the adult mosquito control component of an IVM program is to complement the larval management program by reducing the abundance of adult, actively biting mosquitoes in an area, thereby reducing the number of eggs laid in breeding sites. In addition, during an outbreak, adult mosquito control is crucial to immediately reduce the abundance of biting, infected adult mosquitoes. A list of EPA registered chemicals available for controlling adult mosquitoes is in Table 2. Numerous methods are available for controlling adult Aedes mosquitoes.

  • Targeted Outdoor Residual Spraying: In situations where long-lasting control is desired (at the case-patient household or building level, for example) an approach aimed at outdoor spraying of surfaces likely to serve as adult mosquito resting sites may be achieved with hand-held application devices (Trout et al. 2010) at the target and in a 150 yard radius around the target. Ideally, pesticide decisions should be preceded by an assessment of possible resistance to the chemicals. Targeted adulticide treatments should be accompanied by larval reduction methods as described above. In these situations (i.e. providing a barrier around a pregnant woman’s or case-patient’s home), in order to arrest viral spread, this method requires aggressive attention and rapid action. (Vasquez-Prokopec 2010)  
  • Indoor Residual Spraying: Indoor residual spraying should be considered for homes that do not have adequate screening or air conditioning. Two chemicals with EPA registration allowing indoor use for mosquitoes are deltamethrin and bifenthrin.  Spraying should target sites within the home where mosquitoes rest.  They include the back of closets, under furniture and other dark undisturbed sites behind furniture and in corners. (Vazques-Prokopec 2010)
  • Widespread Outdoor Application: In situations where adult Aedes mosquito populations are very high or more widespread local transmission of Zika is recognized, in addition to the household or building targeted approach, more widespread adulticide applications using pesticides registered by EPA can be used. Pesticides for adult mosquito control can be applied to wider areas using hand-held application devices, from truck-mounted sprayers, from aircraft, or from a combination of methods. This type of spraying is known as space spraying, as opposed to residual spraying described above, and its effect is transient when used without concurrent larval control (i.e., the insecticide must come into contact with a mosquito at the time of being sprayed in order to have an impact).
    • Hand-held devices are useful to manage relatively small areas, but are limited in their capacity to treat large areas quickly during an outbreak.
    • Truck-based applications may reach larger areas, but may have gaps in coverage due to limitations of the road infrastructure.
    • Aerial application of mosquito control adulticides is required when large areas must be treated quickly.  Applications using trucks and aircraft should be timed around dusk and/or dawn.
    • Both truck and aerially-applied pesticides for adult mosquito control are applied using ultra-low-volume (ULV) technology in which a very small volume of pesticide is applied per acre in an aerosol of minute droplets designed to contain sufficient pesticide to kill mosquitoes that are contacted by the droplets. Information describing ULV spray technology and the factors affecting effectiveness of ground and aerially-applied ULV pesticides is reviewed in Mount et al. 1996, Mount 1998, and Bonds 2012.

Risk and Safety of Vector Control Pesticides and Practices

Insecticides to control larval and adult mosquitoes are registered specifically for that use by the U.S. Environmental Protection Agency (EPA). Instructions provided on the product labels prescribe the required application and use parameters, and must be strictly followed. Pesticide use should be restricted to trained and licensed technicians, according to state, tribal, or local legal requirements. Research has demonstrated that ULV application of mosquito control adulticides did not produce detectable exposure or increases in asthma events in persons living in treated areas (Karpati et al. 2004, Currier et al. 2005, Duprey et al. 2008).

Legal Action to Achieve Access or Control

Individually-owned private properties may be major sources of mosquito production. Examples include accumulations of discarded tires or other trash, neglected water features that become stagnant and produce mosquitoes. Local public health statutes or public nuisance regulations may be employed to gain access for surveillance and control, or to require the property owner to mitigate the problem. Proactive communication with residents and public education programs may alleviate the need to use legal actions. However, legal efforts may be required to eliminate persistent mosquito production sites.

Insecticide Resistance Management

In order to delay or prevent the development of insecticide resistance in vector populations, integrated vector management programs should include a resistance management component (Florida Coordinating Council on Mosquito Control 1998). Ideally, this should include annual monitoring of the status of resistance in the target populations, or resistance assessments in local areas ahead of decisions for chemical applications.  

CDC has developed an assay to determine if a particular active ingredient is able to kill mosquito vectors. The technique, referred to as the CDC bottle bioassay, is simple, rapid, and economical compared with alternatives. The results can help guide the choice of insecticide used for spraying. A practical laboratory manual that describes how to perform and interpret the CDC bottle bioassay is available online [PDF - 28 pages]. For additional information about obtaining and performing the bottle bioassay, contact CDC at bottleassay@cdc.gov.

Table 1 Insecticides targeting larval mosquitoes

Active Ingredient Chemical Type
Bacillus thruengensis isralensis Microbial
Bacillus sphaericus Microbial
Spinosyn Microbial
Oils Surface film
Novaluron Insect growth regulator
Methoprene Insect growth regulator
Temephos Organophosphate

Table 2 Insecticides targeting adult mosquitoes

Active Ingredient Use Chemical Type
Deltamethrin Space spray/residual spray Pyrethroid
Etofenprox Space spray Pyrethroid
Permethrin Space spray Pyrethroid
d-Phenothrin (Sumethrin) Space spray Pyrethroid
Pyrethrins/Pyrethrum Space spray Pyrethroid
Chlorpyrifos Space spray Organophosphate
Malathion Space spray Organophosphate
Naled Space spray Organophosphate
Alpha-cypermethrin Residual spray Pyrethroid
Bifenthrin Residual spray Pyrethroid
Lambda-cyhalothrin Residual spray Pyrethroid
Tau-fluvalinate Residual spray Pyrethroid
Imidacloprid/beta-cyfluthrin Residual spray Neonicotinoid/Pyrethroid mix

References

Bonds JA. 2012. Ultra-low-volume space sprays in mosquito control: a critical review. Med Vet Entomol. 26(2):121-30.

Currier M, McNeill, M, Campbell D, Newton N, Marr JS Perry E, Berg SW, Barr DB, Luber GE, Kieszak MA, Rogers HS, Backer LC Belson MG Bubin C Azziz-Baumgartner E, Duprey ZH. 2005. Human exposure to mosquito-control pesticides- Mississippi, North Carolina, and Virginia, 2002 and 2003. MMWR. 54:529-532.

Duprey Z, Rivers S, Luber G, Becker A, Blackmore C, Barr D, Weerasekera G, Kieszak S, Flanders WD, Rubin C. 2008. Community aerial mosquito control and naled exposure. J Am Mosq Control Assoc. 24:42-46. Doi:10.2987/5559.1

Florida Coordinating Committee Mosquito Control. 1998. Florida mosquito control: the state mission as defined by mosquito controllers, regulators, and environmental managers [PDF - 259 pages]. Gainesville, FL: University of Florida. Accessed 5/7/2013

Karpati AM, Perrin MC, Matte T, Leighton J, Schwartz J, Barr RG. 2004. Pesticide spraying for West Nile virus control and emergency department asthma visits in New York City, 2000. Environ Health Perspect. 112(11):1183-7.

Mount GA. 1998. A critical review of ultralow-volume aerosols of insecticide applied with vehicle-mounted generators for adult mosquito control. J Am Mosq Control Assoc. 14(3):305-34.

Mount GA, Biery TL, Haile DG. 1996. A review of ultralow-volume aerial sprays of insecticide for mosquito control. J Am Mosq Control Assoc. 12(4):601-18.

Trout RT, Brown GC, Potter MR, Hubbard JL. 2007. Efficacy of two Pyrethroid insecticides applied as barrier treatments for managing mosquito (Dipters: Culicidae) populaitons in suburban residential properties.  J. Med. Entomo. 44:470-477

Vazques-Prokopec GM, Kitron U, Montgomery B, Horne P, Ritchie SA. 2010.  Quantifying the spatial dimension of dengue virus epidemic spread within a tropical urban environment. PLoS Negl. Trop. Dis. 4:  e920. doi:10.1371/journal.pntd.0000920

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