INTRODUCTION

In New York State, surveillance for arthropod-borne viruses (arboviruses) is coordinated by the Arthropod-borne Disease Program of the New York State Department of Health. Specimens are assayed by the Highly Infectious Unit (HIU) of the Wadsworth Centers for Laboratories and Research located in Albany. Potential human arthropod-borne viruses known to occur in New York State include Eastern Equine Encephalitis (EEE) virus, members of the California encephalitis (CAL) group including LaCrosse and Jamestown Canyon strains, Cache Valley virus and the tick-borne Powassan virus (Srihongse et al. 1980). Although all counties in New York State can conduct vector surveillance activities, in recent years relatively few have maintained active surveillance programs. In 1996, there were ten participating counties in three areas of the state: Cattaraugus, Chautauqua, Erie and Niagara counties in the Buffa1o Region: Madison, Onondaga, Oneida and Oswego in the Syracuse Region and Nassau and Suffolk counties on Long Island .

County personnel are responsible for the collection, speciation and preparation of specimens for laboratory testing.

METHODS AND MATERIALS

The CDC miniature light trap supplemented with dry ice (Newhouse et al. 1966), is the standard tool used for arbovirus surveillance in New York State. In the Syracuse Region, diurnal resting boxes (Morris, 1981) are also used for surveillance for the Culiseta vectors of EEE virus. Weekly collections are pooled by species and site in groups up to 100 specimens per pool. Pools are shipped weekly on dry ice to the HIU for virus assay. Up to 200 pools can be processed in a week. Vero cells are the primary assay method employed. Viral isolates are confirmed by indirect immunofluorescent antibody test (Howard et al. 1996).

RESULTS

During the 1996 field season. 266,685 mosquito specimens, represented in 4,659 pools, were assayed for arboviruses in New York State. This represents a 2-fold increase over the number of specimens assayed in 1995, a drought year, but less than the 275,000 specimens processed in 1994 (Table 1). Representatives of 23 mosquito species in 6 genera were assayed in 1996. There were 37 virus isolations: 30 alphaviruses, 29 EEE and 1 Highlands J (HJ), and 7 bunyaviruses (California group). There were no human cases of arboviral disease. The assaying of tissue samples from 22 equines with central nervous system symptoms, submitted for and determined to be rabies negative, were negative for alphaviruses. Other vertebrate specimens tested were sera and clots from 3 sentinel pheasants flocks of 7 birds each. Virus assays and serologies on 93 sera and clots collected from pheasants between July I to mid-September were also negative for alphaviruses.

REGIONAL SUMMARIES

The Buffalo Region (Cattaraugus, Chautauqua, Erie and Niagara counties) submitted 136,136 specimens of which 97% were Aedes spp. (Table 2). The 6 California group virus isolations from the Region were from Ae. trivittatus (n=4) collected in Cattaraugus County and one each from Ae. canadensis and Ae. stimulans collected in Erie County. The Syracuse Region (Madison, Oneida, Onondaga and Oswego counties) submitted 89,105 specimens of which 94% were the primary (Culiseta melanura and Cs. morsitans) or secondary (Ae. canadensis and Coquillettidia perturbans) vectors of EEE virus (Table 2) . There were 3 isolations of EEE virus from specimens collected at 3 separate resting box sites in Oswego County the week of August 4. Two of the isolations were from blooded Cs. melanura and one isolation was from blooded Cs. morsitans. The Long Island Region (Nassau and Suffolk counties) submitted 41,444 specimens of which 93% were from Suffolk County (Table 2). The 28 virus isolations from the Region were from specimens submitted by Suffolk County. There were 26 isolations of EEE virus and one isolation each of HJ virus and a California group virus. Twenty-three of the EEE virus isolations were from Cs. melanura collected at 5 surveillance sites: Southaven Park (n=9), Manorville (n=11), and one each from Bayview, Shelter Island and Montauk. Table 3 lists the numbers assayed, virus isolations and minimum field infection rates (MFIR) per 1,000 for Cs. melanura collected at 7 permanent CDC surveillance sites in Suffolk County during 1996. The initial EEE virus isolations (n=3) were from Cs. melanura collected at Southaven Park on July 30 and the last from Cs. melanura from Manorville collected on September 26. The other 3 EEE virus isolations were from Culex pipiens-restuans gr. collected at Southaven Park on July 30, August 27 and September 4, respectively. The isolation of Highlands J virus and a California group virus were from Cs. melanura and Ae. cantator, respectively, collected at Montauk. This is the third year out of the past four that Suffolk County has experienced EEE virus activity (Howard et al. 1995).

CONTROL ACTIVITIES

In the Syracuse Region, the Onondaga County Health Department aerially applied Dibrom 14 (naled) to 12,000 acres of Cicero Swamp and surrounding uplands on July 23 to reduce populations of vector mosquitoes. In response to the EEE virus isolations, the Suffolk County Department of Health Services in cooperation with the Suffolk County Department of Public Works initiated helicopter applications of the mosquito adulticide Scourge (resmetherin) and between August 14 and September 11 a total of 17,120 acres were treated. In response to continuing virus activity, four applications to Southaven Park occurred on August 14, 17 and 29 and September 11 accounting for 40% of the total area treated. Bayview (1,600 acres) and Manorville (1,440 acres) were treated once each on August 22 and 27, respectively. The remaining acres treated were areas in proximity to Southaven Park on the south shore of Suffolk County. Oswego County did not initiate control activities in response to the EEE virus isolations.

ACKNOWLEDGMENTS

Our thanks to the personnel of the county health and public works departments for providing the surveillance data cited herein. Our appreciation to the staff of the HIU for their excellence in performing the laboratory testing of these specimens.

LITERATURE CITED

Howard, J. J., M. A. Grayson, D. J. White & J. Oliver. 1996. Evidence of multiple foci of eastern equine encephalitis virus (Togaviridae: alphavirus) in central New York State. J. Med. Entomol. 33: 421-432.

Howard, J. J., J. Oliver, S. Guirgis & J. P. Woodall. 1995. Eastern equine encephalitis virus in Suffolk County, Long Island, New York, 1994. Proceedings 82nd Annual Meeting, N.J. Mosq. Control Assoc. 12-16.

Morris, C. D. 1981. A structural and operational analysis of diurnal resting shelters for mosquitoes (Diptera: Culicidae). J. Med. Entomol. 18: 419-424.

Newhouse, V. F. , R. W. Chamberlain, J. G. Johnston, Jr. & W. D. Sudia. 1966. Use of dry ice to increase mosquito catches of the CDC miniature light trap. Mosq. News 26: 30-35.

Srihongse, S., J.P. Woodal I , M. A. Grayson, R. Deibel, T.F. Bast C. D. Morris, E. M. Bosler, J. L. Benach. J. J. Howard & J. Berlin. 1980. Arboviruses in New York State: surveillance in arthropods and nonhuman vertebrates, 1972 - 1977. Mosq. News 40: 269-276.

Table 1. Summary of arbovirus surveillance activities by region in 1994 and 1996 and total number of specimens processed in New York State, 1995.

Table 2. Number assayed by species and virus isolations in New York State, 1996.

Buffalo Syracuse Long Island

Species1 Assay Isol. Assay Isol. Assay Isol.

Ae. atropalpus 73 0 0 - 0 -

Ae. canadensis 15,277 1 CAL2 41,197 0 11,212 0

Ae. cantator 0 - 0 - 984 1 CAL

Ae. cinereus 13 0 1,401 0 139 0

Ae. communis gr. 2,097 0 1,230 0 333 0

Ae. sollicitans 0 0 0 - 2,698 0

Ae. stimulans gr. 61,098 1 CAL 957 0 160 0

Ae. triseriatus 3,300 0 36 0 30 0

Ae. trivittatus 22,571 4 CAL 186 0 151 0

Ae. vexans 27,386 0 1,125 0 1,458 0

An. punctipennis 1,668 0 0 - 96 0

An. quadrimaculatus 23 0 94 0 0 -

An. earlei 30 0 0 - 0 -

Cs. melanura 15 0 12,134 2 EEE3 10,632 23 EEE

1 HJ4

Cs. morsitans 728 0 6,968 1 EEE 12 0

Cq. perturbans 1,040 0 23,640 0 1,804 0

Cx. pipiens-restuans gr. 611 0 80 0 11,735 3 EEE

Table 3. Numbers assayed, numbers of EEE virus isolations and minimal field infection rates for Cs.

melanura collected at 7 permanent CDC surveillance sites, Suffolk County, Long Island 1996.

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