Mosquito Surveillance and Polymerase Chain Reaction Detection of West Nile Virus, New York State

Materials and Methods

The New York State Department of Health (NYSDOH) developed a system of mosquito pool allocations that would allow rapid detection of virus should WN virus appear anywhere in the area affected by the 1999 outbreak or in peripheral counties in the general metropolitan area or surrounding lower Hudson Valley area. Based on data from the 1999 surveillance, initial priority was placed on mosquito species considered likely first indicators of virus circulation, primarily in the Culex genus. LHDs conducted early season larval surveillance and habitat descriptions, initiated habitat management and larval control in habitats where immature mosquitoes were present (focusing on container breeding, storm drain, or catch basin habitats), and developed a local database of these habitats. Adult mosquito surveillance activities could start at any time in the individual counties, and mosquito pools could be submitted to the NYSDOH Arbovirus Research Laboratory beginning the first week of June. The NYSDOH provided CO₂-baited CDC miniature light traps^[14] and gravid mosquito traps^[15] to LHDs to conduct adult mosquito surveillance. Anticipating a total statewide weekly submission of 400 mosquito pools (up to 50 mosquitoes/pool), we provided LHDs with a weekly pool allocation and scheduled day of submission for all mosquito pools to be tested for arboviruses.

The department also provided other surveillance supplies that LHDs would need to conduct initial mosquito surveillance activities or to enhance existing programs. We divided the surveillance equipment among the counties on the basis of 1) 1999 surveillance data and recognized geographic distribution of WN virus and 2) the anticipated geographic distribution of WN virus in the metropolitan NYC and lower Hudson Valley area during 2000. We also allocated pools for eastern equine encephalitis surveillance conducted annually in Long Island and central New York. Mosquito pool allocations for 2000 were divided among the LHDs in NYC and the rest of the state on the basis of human population density and distance from the 1999 epicenter. Weekly pool allocations ranged from 90 pools for NYC, 45 pools for each county on Long Island, 40 pools for Westchester County, and 10-15 pools for counties further upstate that were conducting adult mosquito surveillance.

Mosquitoes submitted for virus testing arrived at the Arbovirus Research Laboratory on a weekly basis; some counties submitted specimens midweek and others at the end of the week to split the initial 400-pool weekly load. Mosquito pools contained specimens from a single species (or combined species such as Cx. pipiens and Cx. restuans) collected at a single site during the week. In some cases where numbers were below the target of 50 specimens per pool, collections from 2 sequential weeks or from closely adjacent sites were combined. Although the NYSDOH initially requested separation, it is unlikely that all counties effectively removed all blood-fed or gravid females from weekly collections. Therefore, some pools positive by polymerase chain reaction (PCR) may have contained blood-fed or gravid mosquitoes. Mosquito pools submitted to the Arbovirus Research Laboratory were tested for viral RNA by reverse transcription (RT)-PCR techniques following established protocols and reported as described (16). Briefly, mosquitoes were tested by TaqMan RT-PCR with two primer-probe sets. Virus isolation attempts in Vero cell culture followed the detection of PCR-positive pools, as described^[16].

Surveillance data related to adult mosquito populations, adult mosquito pool submissions for virus testing, and laboratory test results (as well as bird, animal, and human data) were entered into the NYSDOH Health Information Network, a secure statewide health agency communication network. These surveillance data were maintained on a daily basis and available to NYSDOH and the contributing LHD. Local agency data were held confidential for 24 hours before all other LHDs were provided summary information.

All LHDs were responsible for the entry of mosquito surveillance data in the Health Information Network, as described. All surveillance mechanisms (mosquito, bird, animal, and human) provided data for this secure database. Program and laboratory review of the surveillance database, as well as laboratory entry of virus detection results, provided a current picture of mosquito populations and a virus infection registry of statewide data. When used fully and properly by the LHDs, mosquito population dynamics, rates, and location of arbovirus activity could be derived from regular review of this comprehensive database. All analyses conducted for this report were developed through the summary of the information extracted from that network.

Emerging Infectious Diseases. 2001;7(4) © 2001 Centers for Disease Control and Prevention (CDC)

Cite this: Mosquito Surveillance and Polymerase Chain Reaction Detection of West Nile Virus, New York State - Medscape - Jul 01, 2001.