In Rhode Island, an EEE Advisory Committee, based on arbovirus surveillance results, makes recommendations to the State Health Department concerning the appropriate actions to take. The EEE Committee is composed of representatives from the Department of Health, Department of Environmental Management and the University of Rhode Island. The committee's response to viral isolations may include any combination of the following: setting of additional traps, press releases urging the public to take personal precautions in order to reduce mosquito biting, curtailing evening activities and closing parks, larviciding, and adulticiding.

The first isolation of Eastern Equine Encephalitis (EEE) virus for 1996, was obtained from a pool of 41 Culex spp. in a trap set on the night of 14 August in southern Westerly. In an effort to determine the extent of the zoonosis in Westerly, 8 additional traps were set within a 1 mile radius around the initial EEE positive site. Press releases were also issued. From that night (21 August) of trapping there were 4 more EEE isolations: A pool of 26 Culiseta spp. and 3 pools from a trap near Chapman Swamp: 32 Aedes canadensis, 100 Cx. spp., and 38 Cs. spp. Additionally 3 isolations of Highlands J (HJ) virus were found in the same area.

The 3 isolations on the southern edge of Chapman Swamp prompted an investigation of larval production in an artificially impounded 500 acre portion of the swamp. The impoundment of Chapman Swamp was caused by clogged culverts in a road that crosses the northern part of the swamp.

Based on the results of the 21 August trap night, surveillance was expanded to include the entire town, making sure to encircle Chapman Swamp. The trap nights of 27 and 30 August yielded 20 EEE isolates from 22 traps. EEE was isolated from at least 6 species: Ae. canadensis, Ae. vexans, Anopheles spp., Cx. spp., Cs. spp. and Coquillettidia perturbans. Multiple HJ isolations were also reported from Westerly.

Based upon the high percentage of EEE infected mosquitoes collected and the extensive larval production in the impounded portion of Chapman Swamp, the State on 3 September made the decision to apply larvicide to the 500 acre impounded area. As more of the results became known, the decision was made on 5 September to aerially apply adulticide to the town of Westerly. The following day Governor Almond declared a state of emergency in Westerly. This action greatly heightened the public's awareness to the severity of the situation and stressed the importance of taking personal precautions. Concurrently, evening activities at schools and parks had been severely curtailed, and the town of Westerly had taken action to help drain the artificially flooded portion of Chapman Swamp.

The larvicide application took place on 6 September. Granular Bacillus sphaericus (Vectolex) was applied to the artificially impounded 500 acre portion of Chapman Swamp via helicopter (North Fork Helicopters, Ltd.). To assess the impact of the larvicide application, ten dips were taken at each of ten stations on 8 September. The average number of larvae pre-treatment was 4.3 per dip. Post-treatment, no larvae were collected at the same locations. In addition, three 5-gallon buckets containing 100-200 mosquito larvae were placed in the swamp prior to treatment. On 8 September we observed larvicide granules in the buckets, indicating that it had penetrated the tree canopy. All larvae in the buckets were dead.

During the first week of September, before the adulticide, 11 additional isolations of EEE were found in Westerly. The first EEE isolations outside the town of Westerly were also detected. The adulticide application (Duflo Spray-Chemical Inc.) began in Westerly on 10 September and took place over several days. The entire town (23,000 acres) was aerially sprayed with resmethrin (SCOURGE). To assess the efficacy of the adulticide treatment, adult mosquito numbers in Westerly were compared to the neighboring town of Charlestown, which was not sprayed. Immediately after the spray there was

approximately a 90% reduction in adult numbers. The mosquito numbers began to rebound such that within a week and a half they were comparable to numbers observed in Charlestown. To further assess the impact of the adulticide, we looked at minimum infection rates (MIR) calculated from Westerly. In the two weeks prior to the treatment, MIR values were 0.016 for both weeks in Cs. spp. and 0.006 (25-31 August) and 0.005 (1-7 September) in possible bridge vectors (Ae. canadensis, Ae. vexans, Cx. spp., and An. spp.). In contrast, during the 2 weeks post-treatment no virus was detected. The only post-treatment EEE isolations (September 24) in Westerly, were from a pool of 7 Cx. spp. and 10 Cs. spp. from one trap near Chapman Swamp.

The costs accrued in responses to EEE isolations statewide were as follows: aerial larvicide (Westerly) $26,242; aerial adulticide (Westerly) $75,670; distribution of Bactimos briquettes $15,227; truck and back pack spraying $18,488; overtime and miscellaneous costs $3,411, totaling $139,039.

It is important to note that throughout the season Westerly had an aggressive program to control salt marsh mosquitoes. This helped to lessen the severity of the situation.

ACKNOWLEDGMENTS

Al Gettman, Daniel Markowski, and Mary Jane James-Pirri participated in all aspects of the surveillance. The personnel of the Division of Agriculture were instrumental in the state's response.

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