Mosquitoes Surveillance and Control

IDPH developed a robust vector surveillance program involving LHDs and Mosquito Abatement Districts (MAD) due to heavy West Nile virus activity in Illinois beginning in 2002. The vector surveillance program affords IDPH the ability to disseminate Zika virus educational materials quickly, along with recommendations for mosquito collection and disease surveillance as appropriate. IDPH provides annual Vector Control Grants and resources for mosquito and dead bird surveillance to LHDs throughout the state. Currently, 93 LHDs are receiving Vector Control Grants. MADs, which are governmental entities with knowledge and expertise on mosquito collection and surveillance, identification, and abatement procedures, also conduct mosquito abatement activities in several areas in Illinois. Additionally, at least one private company conducts mosquito abatement and collects and sends mosquito surveillance data to IDPH. Currently, IDPH has an electronic data submission mechanism for collection of all state-wide vector surveillance data. IDPH meets periodically with these surveillance and abatement cooperators, and assesses their capacity for emergency disease surveillance and abatement. IDPH sends the mosquito data to CDC’s ArboNET system, and beginning in 2017, will also submit Aedes identification data to CDC's MosquitoNET system along with four surveillance partners.  These partners include: the North Shore MAD, the Macon MAD, the Champaign-Urbana Public Health District, and the Chicago Department of Public Health.

Not all species of mosquitoes can transmit pathogens and the pathogens are limited to a specific species of mosquito. For example, the Culex group transmits West Nile virus, whereas the Aedes group of mosquitoes is not an important vector of West Nile virus, but may transmit Zika virus.

Aedes aegypti (yellow fever mosquito) is the primary vector of Zika virus, while the extent of transmission possible via Aedes albopictus (Asian tiger mosquito) is less understood. Aedes are aggressive daytime biters, with dawn and dusk being peak feeding times. Aedes aegypti cannot survive freezing weather, so they are virtually absent in Illinois except when they may be seasonally introduced, e.g., via transport of used tires. Aedes albopictus are present in several counties in the southern two-thirds of the state and in a few other areas of Illinois. IDPH continues to work with the Illinois Natural History Survey to conduct focused surveillance for Aedes aegypti and Aedes albopictus. These surveillance activities will provide more accurate mosquito data and help determine the presence or absence of these mosquitoes in Illinois, as data for these species are limited.

Estimated range of Aedes aegypti in the United States, 2016

Estimated range of Aedes albopictus in the United States, 2016

Although the extent of transmission via Aedes albopictus is still being studied, it would be the most likely Zika virus vector mosquito in Illinois. While mosquito abundance data are most meaningful when collected over several seasons, identifying the presence/absence, rather than abundance of Aedes albopictus in Illinois is the primary goal of Zika virus vector surveillance for purposes of establishing transmission risk and the need for increased vector control.

Vector control efforts would target both Aedes aegypti and Aedes albopictus as control procedures are generally similar for both species. The flight range of both species is short – one-half mile or less – making local populations somewhat easier to manage. IDPH will coordinate with CDC to identify a Zika Virus Transmission Area, a geographic area in which multi-person local transmission has occurred and may be ongoing, to determine response activities and communicate this information to the public and partners.

During a Zika virus outbreak, aggressive vector management and personal protection activities that effectively reduce mosquito density and prevent mosquitoes from feeding on infected people are required to interrupt transmission by mosquito. Unlike West Nile virus, non-human vertebrate animals such as birds do not act as a reservoir for Zika virus: humans and mosquitoes are the only hosts (other than certain forest primates in Africa).

According to the CDC, the efficacy of vector control in reducing mosquito-borne infection risks may be limited, as has been the case with similar mosquito-borne viruses, such as dengue and chikungunya.

Confirmed identification of a vector species in a jurisdiction is needed before any adult mosquito insecticide applications are performed. Initial identification of adult Aedes albopictus is relatively easily, but specialized traps like oviposition traps that draw egg-laying female mosquitoes are needed to collect specimens. Oviposition traps must be checked weekly. If left unattended for longer periods, they can act as breeding sites. About one oviposition trap per city block is sufficient to establish presence or absence of the Aedes albopictus. However, the most reliable way to identify mosquito species is to hatch the eggs and identify larvae. Consequently, there must be suitable laboratory capability for this process. Adult mosquitoes can be sampled using the BG-Sentinel Trap baited with CO2 and/or the manufacturer’s attractant (BG-Lure; Biogents, Regensburg, Germany). As is the case with oviposition traps, the agency must have the proper equipment and facility to work with live adult mosquitoes. The gravid traps currently used to trap West Nile virus vectors, occasionally capture adult Aedes albopictus and are operated by trained individuals so that these data can be compiled with data from other traps.

IDPH is recommending the use of BGS2 traps to conduct surveillance for adult Aedes aegypti or Aedes albopictus. IDPH has procured several of these traps that may be used to assist LHDs with surveillance activities if there is evidence of a locally-transmitted case of Zika virus. For LHDs who need assistance, IDPH can provide staff, traps, and training to assist with building the capacity to conduct field testing for Aedes aegypti or Aedes albopictus. 

More information regarding these traps can be found at http://www.bg-sentinel.com/.

Trap placement may be the most important part of success for mosquito collections. Aedes albopictus, and especially Aedes aegypti, are “urbanized” mosquitoes: they are most likely found in close association with human activities. Consequently, a likely location to detect either of these species would be an older residential area near a scrap yard or where other industrial activities are nearby. Staff should set traps in low, shaded areas, out of sight, and near containers collecting water and vegetation where there is higher humidity. Lower areas will also protect the trap from too much wind and mosquitoes will not have to fly against a stiff breeze. Staff should make sure there is at least 20 inches clear above the trap so airflow is not restricted. The trap should also be about three feet away from any walls or solid structures. After placing the trap with the battery attached, the lures should be checked and if dry ice is being used, assure the mist/vapor is moving toward the trap. Staff should place the traps in the morning and pick them up as early as practical the next morning. Staff running the traps another day can just remove the collection bag with the mosquitoes, tie the top securely, label it with the location and date, and put in a cooler with “blue ice.” Staff can then put a new bag on the trap, attach the charged battery, and take the used battery for recharging.

Determining mosquito abundance requires a larger investment in traps and workforce, and depends on the type and number of traps used per unit area, as well as the availability of alternate oviposition sites in the area. Other species, such as the Aedes triseriatus (Eastern treehole mosquito), also lay eggs in oviposition traps. Identification of the resultant larvae, pupae, or reared adults from these traps must be performed to accurately estimate Aedes albopictus abundance.

LHDs can submit adult mosquitoes for identification of suspected Aedes aegypti or Aedes albopictus. Place tissue in the bottom of the container, then mosquitoes, then loosely put more tissue and cover. If the mosquitoes are not dry, do NOT seal the container tightly as they may become moldy and make identification difficult. Send samples with a filled-out Mosquito Specimen Identification Form to:

Illinois Department of Public Health
Peoria Regional Office
Attn: Insect Identification
5415 North University
Peoria, IL. 61614

Images of Aedes albopictus, Aedes aegypti, and other adult mosquitoes may be found in a manual maintained by the University of Florida http://fmel.ifas.ufl.edu/key/. If field staff observes suspected Aedes aegypti or Aedes albopictus attempting to bite, staff can collect the mosquitoes with a small hand net, remove them using a power aspirator, and freeze the samples to kill the mosquitoes so they can then be sent for identification. Aedes aegypti and Aedes albopictus are relatively small, dark-colored daytime-biting mosquitoes that often land on the lower legs while attempting to feed. A summary Aedes albopictus’ biology may be found at http://www.dph.illinois.gov/topics-services/environmental-health-protection/structural-pest-control/asian-tiger-mosquito.

Source reduction is the removal of mosquito breeding habitats and is a local government activity. LHDs should provide mosquito prevention information to local government authorities and assist in responding to identified breeding grounds, such as unkempt swimming pools. These activities can be partially funded through the Vector Control grants to LHDs.

Removing larval habitats will reduce mosquito densities. Remove discarded, unused, and unmaintained containers through community involvement programs or by vector control personnel. Containers are ideal larval habitats, particularly discarded used tires. But these mosquitoes can develop in a vast variety of water-holding containers such as plant drip pans, clogged gutters, garden pools, etc. However, the primary focus should be on larger containers that can produce more mosquitoes.

IDPH continues to work with the Illinois Environmental Protection Agency (IEPA) on an initiative to remove used tires from locations across Illinois. The two agencies have divided the state into three priority zones for used tire removal. The zones are based on where Illinois would potentially experience Zika virus, such as southern counties that typically have hotter weather. Zone 1 is the highest priority area and is defined by a straight east-west line going through Effingham and areas south of that line. Zone 2 is the next highest priority area and is defined by a straight east-west line through Peoria south to the Effingham line. Zone 3 is the third highest priority area and is defined by the straight east-west line through Peoria north to the Wisconsin border.
 
Illinois EPA is identifying and initiating used tire removal actions for units of local government beginning in Zone 1. Illinois EPA will collect, transport, and properly dispose of used tires from public and abandoned properties. Additional activities planned by the Illinois EPA include close monitoring of regulated used tire sites located in Zone 1 and using larvicide to actively treat and mitigate known sources of improperly managed used tires.
 
In addition, the Illinois EPA and IDPH entered into an Intergovernmental Agreement to allocate $750,000 from the Used Tire Management Fund. This funding has enabled IDPH to enhance statewide mosquito control activities related to Zika virus, and other mosquito-borne diseases through activities associated with the improper storage, handling, and disposal of tires.

In the instance of local transmission, larval surveillance can help identify containers where Aedes and other container-breeding mosquitoes are breeding. This will require ground inspection. Inspection by helicopter can locate unkempt or “green” swimming pools and accumulations of discarded tires. Inspections for larval production sites, such as old tires, should be conducted on residences or properties within 450 feet (150 yards) og the home of a resident with locally acquired Zika virus.

Larviciding is primarily a local government responsibility supported by LHDs in some jurisdictions. When source reduction is not feasible, biological or chemical larvicides should be applied to potential larval habitats. Source reduction and larval control of Aedes albopictus in containers has the added benefit of reducing other container-breeding mosquitoes.

NOTE: Larval control can be expensive and time consuming, and personnel who do mosquito control applications on the property of others must be licensed and/or certified by the Illinois Department of Agriculture. Contact the Illinois Environmental Protection Agency about accumulations of discarded tires or those outside tire and auto repair shops.

Application of mosquito adulticides is generally warranted only in potential outbreak situations in possible or confirmed Zika Transmission Area(s). These control activities are primarily the responsibility of local government entities and IDPH does not have the ability to apply or manage the application of adulticides. As mentioned, the Illinois Department of Agriculture regulates mosquito control companies, which can be found by searching https://www.agr.state.il.us/Environment/Pesticide/aplicatorsearch.php.

Aedes albopictus are most active during the day and are not effectively controlled by standard truck-mounted ultra-low volume (ULV) applications that are typically performed at night. Early morning or late evening ULV applications can be done against this species. Because Aedes albopictus hide in dense vegetation, treatment of individual properties using backpack spray units is likely to give the most effective adult mosquito control. A minimum response would be applying adulticides at the affected residence and adjacent backyards, particularly areas of dense vegetation. . A more robust response would be applying adulticides at the affected residence and other properties within 150 yards (450 feet) of the home of a resident with locally acquired Zika virus. ULV or barrier applications to homes (around windows, doors, etc.) of residents with locally acquired Zika virus, or Zika Virus Transmission Areas, can be done to further reduce the likelihood of vectors feeding on people infected with Zika virus.

LHDs, with IDPH assistance, conducted mitigation activities to reduce the likelihood of Zika virus transmission. Information regarding mosquito breeding sites and habitat were provided to all LHDs prior to the mosquito season, and this information has been disseminated to the public through media, social media, and other alerts. Additional mosquito surveillance activities included conducting targeted Aedes surveillance or reporting the identification of the Aedes species collected during West Nile Virus mosquito surveillance. Should Zika virus cases and local transmission occur, IDPH will assess capabilities for emergency disease surveillance and mosquito management in all areas of the state to help ensure adequate emergency response.

All insecticides used in the U.S. for public health use have been approved and registered by the Environmental Protection Agency (EPA). The EPA has assessed these chemicals and found that, when used according to label directions, they do not pose unreasonable risk to public health and the environment. 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. Additional information about mosquito control may be found on the EPA website at https://www.epa.gov/mosquitocontrol.

Individually owned private properties may be major sources of mosquito production. Examples include accumulations of discarded tires or trash, or neglected swimming pools or bird baths 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.

The Vector Control Act (410 ILCS 95/) gives IDPH, or designated local health departments, the authority to take necessary steps to eliminate vector hazards. The Vector Control Act can be found at: http://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=1537&ChapterID=35.