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Joumnlof theAmerican Control Association, 19(3):179-189,2003 Copyright @ 2003 by the American Association, Inc.

ARBOVIRUS SURVEILLANCE IN RHODE ISLAND: ASSESSING POTENTIAL ECOLOGIC AND CLIMATIC CORRELATES

TSUTOMU TAKEDA,' CHRIS A. WHITEHOUSE,'3 MICHAEL BREWER,I,4 ALAN D. GETTMAN'AND THOMAS N. MATHER'J

ABSTRACT, During 1995-2000, mosquitoes were collected from sites throughout Rhode Island and tested for the presence of . Mosquito trapping was done weekly from June to October with COr-baited light traps. In all, 186,537 mosquitoes belonging to 7 different genera were collected, of which Coquillettidia per- turbans was most abundant. A total of 6,434 pools were processed for isolation, from which 193 arboviral isolations were made. These included 109 Highlands J, 71 eastem equine encephalomyelitis, 1 Cali- fornia encephalitis serogroup, 2 Jamestown Canyon, 3 Cache Valley, and 9 Flanders . Our isolations of Flanders represent the lst reported occurrence of this virus in Rhode Island. After the 1999 sudden occurrence of the (WN) in the New York City area, a dead- surveillance proglam was started to test for this virus. Although no isolations of WN were made from mosquitoes, 87 virus isolations were made from a total of 330 wild tested. All the WN-infected birds were either American crows or blue jays. Isolation of WN from dead birds marked the lst documented appearance of this virus in Rhode Island. Significant interannual variation of arbovirus activity in Rhode Island prompted us to examine if climate-associated factors such as rainfall and temperature correlate with virus activity. Total rainfall amounts from May to June were higher than normal in 1996 and 1998. These years showed significantly higher arbovirus activity. Deviations from normal temperature showed low correlation with arbovirus activity during the 6-year study period. There- fore, precipitation appeared to be more important than temperature in predicting arbovirus activity in Rhode Island.

KEY WORDS Arbovirus activity, climate, mosquitoes, precipitation, Rhode Island

INTRODUCTION 1993, a l4-year-old boy was diagnosed with infec- tion by EEE and died a few weeks later (Bandy and Island Knowledge of arbovirus activity in Rhode Donnelly 1994, Sotomayor and Josephson 1999), results, and the is limited to mosquito surveillance and in 1998 an elderly man also died from EEE with environmental or relation of arboviral activity infection (RIDOH, unpublished data). Two emus ecologic factors are poorly understood. Human dis- died of EEE infection in the southern part of Rhode ease caused by mosquito-borne viruses is relatively Island in 1996. An arbovirus surveillance program rare in the northeastern USA. However, when they began in 1984 as a direct result of the lst human occur, human infections lead to significant morbid- cases in 1983. Eastern equine encephalomyelitis vi- ity and mortality. Of the arboviruses known to rus was isolated for the lst time in Rhode Island cause disease in Rhode Island, eastern equine en- and Aedes mosquito species in 1990 cephalomyelitis virus (EEE) is probably the most from (Cookman, In addition to EEE, important (Gettman 1993, Markowski 1996). Spo- unpublished data). radic epizootics of EEE have occurred in Rhode surveillance identified a number of other arbovirus- Island horse and bird populations since 1938. In es, including Highlands J (HJ), Jamestown Canyon total, more than 100 horse deaths attributed to EEE (JC), Cache Valley (CV), and Flanders viruses from have been reported, and several thousand game several mosquito species in Rhode Island. birds have died as a result of EEE infection. In During late summer and early fall of 1999, an Rhode Island, 4 human cases caused by EEE have episode of West Nile virus (WN) occurred in the been confirmed since 1983. The lst 2 cases oc- New York City area, resulting in fatal neurologic curred in 1983, resulting in I fatality (Centers for disease in humans and a variety of native and ex- Disease Control and Prevention [CDC], 1984). In otic bird species (CDC 1999a, 1999b, 1999c). That occurrence resulted in 62 human cases, including 7 deaths and thousands of bird deaths. In 2000, the I Center for -Borne Disease, University of Rhode epizootic spread throughout the northeastern USA, Island, 9 East Alumni, Suite 7, Kingston, RI 02881. including Rhode Island, but few human infections 'Rhode Island Department of Environmental Manage- (CDC ment, Mosquito Abatement, Stedman Government Center, were identified 2000). Phylogenetic analysis Wakefield, RI 02879. of the New York strain of WN (WN-NY99) has 3 Present address: Division, U.S. Army Med- shown it to be most closely related to a strain of ical Research Institute of Infectious Diseases ruSAM- WN isolated from a goose in Israel in 199E (Lan- RIID), 1425 Porter Street, , Frederick, MD ciotti et al. 1999). Although WN is common in 21702-50tr. parts of Africa, western Asia, and the Middle East, a Present address: National Oceanic and Atmospheric the lst incidence of this Administration, National Weather Service, 1325 East West the New York episode was Highway, Silver Spring, MD 20910. virus reported in the Western Hemisphere. The vi- 5 To whom correspondence should be addressed. rus is now well established in North America, with

179 180 JoURNAL oF THE AMERICANMosQUITo Corvrnol AssocIATIoN Vor,. 19, No. 3 isolations occurring as far north as Canada and as Vector-Borne Disease, University of Rhode Island, far south as Florida. for virus isolation and identification. Increasingly, attention is being focused on the Virus assays: Adult mosquitoes collected from relation between climate variation and vector-borne 1995 to 1997 were screened for viruses at the Ar- diseases (Longstreth and Wiseman 1989). The re- bovirus Research Laboratory at Yale University. In cent El Niflo and La Niffa events and the prospect 1998, mosquito pools were tested by the Massa- of global warming have stimulated interest in de- chusetts Department of . In 1999, veloping predictive models to help forecast the on- mosquito testing was pennanently transferred to the set of vector-borne disease epidemics (Reeves et al. Center for Vector-Borne Disease at the University 1994, Hales et al. 1999, Maelzer et al. 1999). For of Rhode Island. example, several studies in the USA have focused In all 6 years, mosquitoes were tested by the on associations between temperature and rainfall same procedure. Briefly, mosquito pools were ho- amounts and infections with EEE. In 1 of those mogenized in the presence of 199 medium contain- studies, Hayes and Hess (1964) found a relation ing l%o fetal calf serum and 500 IU/ml penicillin between precipitation and human EEE cases only and 500 pglrnl streptomycin. Homogenates were when excessive rainfall and the cases occurred in centrifuged at 3200 X g for 20 min at 4'C to pellet the same summer and in the fall of the year pre- particulate material. Aliquots (0.1-ml) of each su- ceding the epidemic. In Massachusetts, epidemics pematant were inoculated onto a monolayer of Vero caused by EEE occurred in the 2nd of successive cells growing in 6-well plates and incubated at37"C years when rainfall was 20 cm above average (Gra- tnder 5Vo CO, for up to 7 days. Cultures were ex- dy et al. 1987). More recently, I-etson et al. (1993) amined daily for cytopathic effect. reexamined the hypothesis that excessive rainfall is During 1999-2OOO, specimens were also tested predictive of the occurrence of human disease cases by plaque assay in a Vero cell culture growing in caused by EEE. They found an association between 6-well plates. Briefly, specimens were inoculated in the occurrence of human cases and excessive rain- 0.I-ml quantities and adsorbed for t h at 37oC, then fall and that the association was stronger with data the cells were overlaid with 2 ml of a mixture con- from local weather stations than from statewide taining l7o agar and O.lVo DEAE in 199 medium. rainfall averages. Moreover, these models were Cultures were incubated for 48 h, and a secondary predictive most when applied to the northern states. overlay containing lOVo nettral red and lvo agar in heavy rainfall has been implicated as a Unusually 199 medium was added to the wells. Cultures were possible factor contributing to previous occurrences incubated at 37"C and examined for up to 7 days of WN in South Africa (Jupp 20Ol), but dry con- for the presence of plaques. ditions existed during the summers when WN epi- Supernatants from positive cell cultures were sodes occurred in southern Romania. Russia. and harvested and frozen at -80"C, and cells were the northeastern USA (Hayes 2001). scraped from the wells to prepare a cell lysate an- This report summarizes mosquito-borne virus ac- tigen (Ansari et al. 1993). Viruses were identified tivity in Rhode Island during the 6-year period, by indirect immunofluorescent (IFA) by 1995-2000, and examines relations between virus using reference monoclonal antibodies provided by activity and climate factors. the Division of Vector-Borne Infectious Diseases, CDC in Fort Collins, CO. These included EEE, HJ, MATERIALS AND METHODS western equine encephalomyelitis virus, LaCrosse (LAC), Mosquito collections: Weekly mosquito collec- virus WN, and St. Louis encephalitis virus (SLE) tions were made in Rhode Island from June to Oc- antibodies. Dr. Robert Shope, University of tober, 1995-2000, with CDC light traps baited with Medical Branch, Galveston, TX, provided dry ice. Mosquito collections were immediately reference antibodies to JC and Flanders viruses. placed on dry ice for transport to the laboratory, Twelve-well slides (Cel-Line Associates, Inc., where they were stored at -80"C until processed. Newfield, NJ) containing virus-infected cells were All mosquitoes were identified on a chill table, and fixed in acetone, incubated with monoclonal anti- females were sorted into pools according to species, bodies for I h at 37'C. and then washed 3 times site, and collection date. The number of mosquitoes with phosphate buffered saline. Slides were then was <50 per pool. incubated with fluorescein isothiocyanate-labeled Bird collections: After the WN occurrence of goat anti-mouse IgG (1:200 dilution; Kirkegaard 1999 in New York, a dead-bird surveillance pro- and Perry Laboratories, Inc., Gaithersburg, MD) for gram was established to facilitate virus detection in I h at 37"C and examined under a fluorescence mi- Rhode Island. Dead birds were collected statewide croscope for a positive reaction. by the Rhode Island Department of Environmental Positive samples from 2000 were also confirmed Management and transported to the Rhode Island by reverse transcriptase polymerase chain reaction Department of Health Laboratories for brain nec- (RT-PCR) of the cell culture supernatants and di- ropsy. The brains were placed in dry ice and rectly from avian brain tissue by virus-specific shipped to the BSL-3 laboratory at the Center for primers for EEE (Armstrong et al. 1995), HJ SEPTEMBER2003 ARBovrRUs SrinveIIIANcB Ill Rgooe IsL.lNo

Table 1. Summary of mosquitoescollected and arbovirusesdetected in Rhode Island, 1995-2000- Individual viruses No. of No. of Voof mosquitoes Total no. of pools positive pools CEI Year Collected tested pools positive EEE HJ JC WN OthET 199s 20,389 16,461 822 10 1.206 1NT'3 t996 45,OO7 35,957 l5r4 100 6.6 56 43 INTO r997 46,266 27"814 1087 18 1.7 2 16 ONTO 1998 35,240 18,539 776 492 6.3 12 39 000 1999 11 141 19,065 1114 30.300102 15 007 2000 11,949 10,688 1121 13r.2'1r Total t86,537 128,524 6434 193 3.0 109 3012

rNT; not tested. 'Two pools were co-infected with EEE and HJ.

(Whitehouse et al. 2001), and WN (Lanciotti et al. year total). During the 6-year study period, 193 2000). mosquito pools were positive for arboviruses, rep- Climatological data: Precipitation and tempera- resenting 3Vo of the total pools tested. The most ture data were taken from 13 National Weather Ser- prevalent arbovirus isolated was HJ (lO9 isolates, vice (NWS) weather stations in Rhode Island and comprising 56.57o of the total). Eastern equine en- nearby Connecticut and Massachusetts, with sup- cephalomyelitis virus was isolated 71 times (36.87o plemental information added from the Army Corp of total isolations), making it the 2nd most com- of Engineers (ACE) stations in the same general monly detected virus. Other virus isolations includ- area. The NWS stations provide average monthly ed California Encephalitis serogroup (2), JC (l), climate variables and climatic information at time CV (3), and Flanders (9) (Fig l). Isolation of Flan- increments as frequent as hourly. The ACE data ders virus in 1999 represented the lst appearance were included to provide increased spatial resolu- of this virus in Rhode Island. There were no iso- tion but were often available only as a monthly lations of either LAC or SLE during the study pe- summary. Combining these sources provided a riod. Also, there were no isolations of WN from dense climate observation network from which to mosquitoes between 1995 and 2000, although nu- document the dominant weather patterns statewide merous isolations were obtained from wild birds in for any particular month as well as for the mosquito 2000 (see below). Retrospective testing of mosquito season. Temperature data were analyzed based on pools from 1998 and 1999 failed to detect WN- monthly as well as seasonal averages. Average positive samples. monthly temperature and departure from the 30- Mosquitoes collected during 2 of the 6 study year normal monthly temperature were computed years had significantly higher levels of virus activ- for 1990-99. Precipitation was examined for ity (P < 0.05) than the other years. In 1996 and monthly and multi-month accumulations and for 1998, the percentages of mosquito pools positive any duration of insufficient precipitation. Devia- for virus were 6.6 and 6.3Vo, respectively, whereas tions from 30-year monthly nornal precipitation virus-positive rates for mosquito pools tested dur- amounts were computed. ing the other years never exceeded l.1%o. Except Statistical analyses: Simple linear regression for single isolations of EEE in North Smithfield and was used as the primary statistical method to eval- HJ in Lincoln, all viral isolations were from mos- uate relations between climate and mosquito-borne quitoes collected in southern Rhode Island (Wash- virus activity. The annual number of virus-positive ington County), where 53Vo of the trapping effort mosquito pools for each virus was correlated with occurred. The majority of isolations were made in precipitation and temperature during the time peri- the southwestern part of the state, especially in or ods previously identifled. Chi-square and Student's near the town of Westerly. This area has an abun- /-tests were used to analyze annual differences in dance of mixed hardwood swamps and coastal salt virus activity. All statistical tests were performed marshes, which may contribute to larger popula- using SPSS v7.5 for Windows. tions of mosquitoes carrying these viruses. Dead-bird surveillance: After the WN episode in New York City in the late sununer and early fall RESULTS of 1999, Rhode Island and many other eastern Mosquito surveillance: A total of 187,537 mos- states began a dead-bird surveillance program for quitoes were collected and identified in Rhode Is- detecting WN. A total of 330 wild birds were tested land between 1995 and 2OOO(Table l). Of these, for the presence of virus activity during 20OO (Ta- 128524 were tested for virus in a total of 6,434 ble 2). Of those, 95 (27.3Vo) were positive. The pools. Coquillettidia perturbans (Walker) was the majority was infected with WN (26.4Vo); WN was most abundant mosquito collected (277o of the 6- lst isolated in Rhode Island from an infected crow 182 JounNll oF THE AMERTcIN Mosquno CoNrnol AssocrerroN 19,No. 3

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Fig. l. Map of Rhode Island indicating the towns and locations where arboviral isolations were made from collected mosquitoes. EEE, eastern equine encephalomyelitis; HJ, Highlands J; CV Cache Valley; JC, Jamestown Canyon. on August 8, 2000. Figure 2 slrows collection sites was the only virus isolated from sparrows (White- of WN-positive birds. Other viral isolations from house et al. 2001). The WN positivity rate among dead birds included 4EF,E (l.2Ea) and2HJ (O.67o). birds increased through late summer and fall with Additionally, 2 of 15 pigeons tested'were infected 4.6Vo positive in August, 37.9Vo in September, with Rhode Island virus, a newly described rhab- 43.7Vo in October, and 13.87o in November. The dovirus (Tiavassos da Rosa et al. 2OO2). Of the weekly positive rate among crows tested peaked WN-infected birds, American crows (Corvus bra- during the 2nd week of October and began to fall chyrhynchos) were infected most commonly with the onset of colder weather (Fig. 3). A cluster (79.3Vo, n : 69), whereas blue jays (Cyanocitta of 39 WN-infected birds (44.8Vo of total WN-pos- cristata) (2O.7Vo,n : 18) were the only other spe- itive birds) was detected in the town of Westerly, cies infected with WN. The EEE is6lations were RI (Fig. 2). The significance of this clustering is made from a variety of birds including American not yet known but may be related to the finding crow, , house spuurow (Passer domesticus), and reporting of dead birds in Rhode Island com- and a northern raven (Corvus corax). Highlands J munities. SsPrENaspn2003 AnsovRus SunvsueNcn rN RHoDEIsLAND 183

Table 2. Arbovirus isolations from wild birds collected was isolated from a number of other mosquito spe- in Rhode Island durins 2000. cies including Ochlerotatus canadensis (Theobald), (Meigen), No. No. Aedes vexans and Cq. perturbans. Dlur- Virust Bird species tested positive 7o positive ing 1996, a significantly higher level of EEE activ- ity in Rhode Island was identified, which most like- WN American crow t34 69 49.5 ly resulted in a spillover of EEE from its primary blue jay 48 18 37.8 enzootic vector into a number of other, potentially EEE American crow 134 0.9 Indeed, duing 1996,2 fa- bluejay 48 2.2 epizootic vector species. sparTow 30 3.7 tal infections of EEE were reported in emus in HJ northern raven I 100 southern Rhode Island. In southeastern Connecti- sparTow 30 2 7.4 cut, Andreadis et al. (1998) reported 36 isolations Total 330 952 27.3 of EEE from 8 different species of mosquitoes.

'WN, West Nile virus; EEE, eastem equine encephalomyelitis; Eastern equine encephalomyelitis virus is consid- HJ, Highlmds J. ered to be the most important mosquito-borne ar- 'Includes 2 pigeons that were infected with an unknown rhab- bovirus occurring in Rhode Island, causing sporad- dovirus isolate. ic cases of disease among horse and bird populations. Examining isolations of EEE from mosquitoes Climntological factors: Significant interannual during the 6-year study period revealed a pattern of variation of virus activity prompted us to examine interannual variation in which 1996 and 1998 had climate variables (e.g., temperature and rainfall) for signiflcantly higher levels of EEE than the other "high-virus" possible correlation. The May-July total rainfall years. These years corresponded to amounts were higher in 1996 (29.8 cm) and 1998 sporadic cases reported in emus in 1996 and a fatal (50.6 cm), years with significantly higher virus ac- human case in 1998. In 2000, the only year for tivity. For example, rainfall in Rhode Island during which we have data on EEE in native birds, the this period in 1998 was 27.5 cm higher than the virus was isolated from the brains of 4 different 3O-year average for the region (Fig. 4a). The pos- species, including an American crow, blue jay, itive correlation of rainfall with mosquito pool virus spz[Tow, and northern raven. These birds showed positivity was highest with HJ (0.86; Table 3). East- no obvious signs of trauma, and the virus was iso- ern equine encephalomyelitis virus showed the low- lated directly from brain tissue; therefore, we spec- est correlation with rainfall with a maximum of ulated that these native bird species died as a result -0.91 0.38. Correlations were negative but high at of infection with EEE. for mosquito-borne viruses other than HJ and EEE. The enzootic transmission cycle of HJ is similar Comparing the monthly mean temperatures with to EEE, being transmitted by Cs. melanura. among the Rhode Island 30-year average, we observed passerine birds in freshwater swamps. Moreover, warmer-than-normal temperatures during the later like EEE, HJ exhibited peak prevalence in Rhode half of the 1990s. These data were consistent with Island in 1996 and 1998. However. unlike EEE, HJ those from other USA stations (Fig. ab). Deviation has not been shown to be pathogenic in humans or from normal temperature showed the highest cor- horses, with the exception of a single report of the relation of any temperature measurement to virus virus being isolated from a horse that died of en- activity during the 6-year study period. However, cephalitis in Florida (Karabatsos et al. 1988). High- correlation still tended to be low (Table 3). Corre- lands J is emerging as an important bird pathogen, lations ranged between negative and positive values causing disease in a number of domestic avian spe- depending on the virus, reaching a maximum of cies (Ficken et al. 1993, Eleazer and Hill 1994). -0.69 "other for viruses." The ratio of EEE/HJ Apparently, HJ also may be pathogenic for native was positively correlated with temperature but birds. as the virus was recovered from the brains reached a maximum of iust 0.76. of 2 dead sparrows in 2000 (Whitehouse et al. 2OOl). Wild birds such as sparrows usually are con- sidered reservoirs for many mosquito-borne arbo- DISCUSSION viruses and are not normally expected to succumb Mosquito surveillance for arbovirus activity con- to infection with these viruses. The relatively low ducted in Rhode Island during the 6-year period, numbers of wild birds infected with and presum- 1995-2000, was compared with measures of pre- ably killed by EEE and HJ (as compared with WN- cipitation and ambient temperature. Of the viruses infected birds) do indicate that the 2 sparrows may isolated from 193 positive mosquito pools, HJ was have had some undetected preexisting infection or the most prevalent, followed by EEE. The majority had been exposed to an environmental stress that of isolates were from Culiseta melanura (Coquil- weakened their immune systems, thereby making lett), an ornithophilic mosquito incriminated as the them more vulnerable to any pathologic effects of primary enzootic vector of both EEE (Scott and the HJ infection. We cannot rule out the possibility Weaver 1989, Morris 1988) and HJ (Hayes and of increased virulence or neuroinvasiveness of spe- Wallis 1977). In some years (e.g., 1996), EEE also cific EEE or HJ strains. Additional isolations and 184 Joumer oF THE AMERTcIN Moseuno CoNrnor- AssoclATIoN Vor-. 19, No. 3

5 0 5 l0KilofiEfiers =--- h rx.x1,( (__,)

Fig. 2. Map of Rhode Island indicating the towns and sites where West Nile virus-infected birds were collected. WNV, West Nile virus; EEE, eastern equine encephalomyelitis; HJ, Highlands J.

genotyping from bird surveillance programs will be and produces very small plaques in tissue culture, needed to answer such possibilities. thus it may have been overlooked previously in The lst isolation of Flanders virus in Rhode Is- Rhode Island. land was made in 1999 from a pool of Culiseta Isolations of CV in 1995 and JC in 1996 and mosquitoes collected from the southwest part of the 1999 confirm the presence of these California se- state. During 2000, the virus was isolated from 7 rogroup viruses in Rhode Island. Only 2 isolations additional mosquito pools collected from the same of JC were made during the study period, both from area. Flanders virus was lst isolated from a pool of Oc. cantator. Jamestown Canyon also has been Cs. melanura mosquitoes collected in 1961 in Flan- identifled from the neighboring states of Connecti- ders, Long Island, NY (Whitney 1964). Flanders cut and Massachusetts (Sprance et al. 1978, Walker virus is not known to cause disease in et al. 1993). Therefore, it was not surprising that SBpreNrssn2003 Annovnus Sunl.nuaucn rN RHoDEIsLAND 185

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Week of 2000 Fig. 3. Weekly infection rates of West Nile virus-infected American crows and blue jays collected in Rhode Island during 2000. the virus was isolated from Rhode Island mosqui- mosquitoes or human cases were detected. The ef- toes as well. Three isolations of CV from Oc. can- fectiveness of bird surveillance for predicting hu- adensis were identified, and an untyped California man or horse WN infection remains unknown. It serogroup virus was isolated from Cq. perturbans appears that bird surveillance data may well depict in 1995, but no additional isolations of CV have the geographic range of the virus but not accurately been made in Rhode Island. Cache Valley virus has reflect human risk for infection. However, - been shown to cause embryonic death and congen- biting mosquitoes infected with WN must have ital malformations of sheep (Edwards et d. 1989), been present in the state because a 2-year-old horse and retrospective serologic studies in humans sug- from Wakefield, RI, with no history of travel out- gest that CV may be the cause of some cases of side the state became infected with WN and was congenital defects of the central nervous system euthanized. (Calisher and Sever 1995). Recently, the lst human In 2000, our laboratory began using RT-PCR case of severe encephalitis and multiorgan failure analysis in addition to traditional biological assays caused by CV virus was described in a patient from for detecting arboviruses. This molecular-based as- North Carolina (Sexton etal.1997). The geograph- say offers the advantage of being more rapid and ic distribution of this virus includes all of North more specific than classical culturing techniques for America, except the extreme southeastern states detecting viruses. The RT-PCR assay correctly and southern Mexico (Calisher et al. 1986). Prev- identified every EEE, HJ, and WN isolated in the alence of the virus in Rhode Island appears to be 2000 season (data not shown). Results were IOOVo rare. concordant with the biological assay of isolation in The sudden occurrence of WN in the New York Vero cell culture and identification by IFA with ref- City area in 1999 prompted many states in the east- erence monoclonal antibodies. We were not able to em USA to increase their mosquito-borne arbovirus obtain a positive PCR product of Flanders virus but surveillance efforts beginning in 2000. The sensi- were able to identify it by IFA. tivity of birds, especially crows, to WN also The mosquito vectors of various arboviruses prompted many states, including Rhode Island, to likely respond differently to climatic variation. Ac- adopt a dead-bird surveillance program to aid in the cordingly, we examined possible relations between early detection of WN. Of the 330 dead birds tested arbovirus isolations and climate factors in Rhode during 2000, 87 (26Vo) were infected with WN as Island. As in several other studies, we found links determined by direct culture and RT-PCR. The between precipitation and virus activity (Hayes and American crow was by far the most common spe- Hess 1964, Grady et al. 1987, Letson et al. 1993). cies infected, although blue jays also were infected. However, the correlation between EEE activity in Dead-bird surveillance was very effective as an mosquitoes and precipitation was insignificant, re- early warning system for WN; 87 isolations of the gardless of the time period measured. Highlands J virus were made from birds, but no WN-infected activity showed maximum positive correlation 186 JourNel or tuE AtnlBnrcANMoseulTo CoNrnol AssoctertoN Vor-. 19, No. 3 l A. t.rl I Tffipcntuil drp|iuro

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1995 1996 1997 1998 1999 2000 Fig. 4. Departure from a 3O-year average (1961-1990) of the mean monthly (A) temperature and (B) precipitation in Rhode Island during 1995-2000.

Table 3. Results of linear regression correlating climate factors to annual positive mosquito pools.' Correlation values' Time period Climate factor EEE/HJ HJ Others3 Jan-May Precipitation 0.3083 o.6121 o.6032 -o.88414 Temperature -o.3703 o.75735 o.2294 -0.5839 Jun-Aug Precipitation 0.3838 0.8320 o.85'764 -0.78555 Temperature -o.3605 o.6205 o.1761 -o.690tr Jan-Aug Precipitation 0.3506 0.68886 0.71086 -0.91054 Temperature -0.3699 0.71556 o.2126 -o.6257

rEEE, eastem equine encephalomyelitis; HJ, Highlands J. 'Significmt only at levels above q : 0.15, unless otherwise marked. 3 California serogroup, Jamestown Canyon (JC), Cache Valley and Flanders. JC was included in the Califomia serogroup and was detected separately. a Significant at c = 0.05 level. s Significant at c : 0.10 level. 6Sienificant at a = 0.15 level. SsPTEt"Bpn2003 AnsovrRus SunverreNcn rx RHooe ISLANo 187

Table 4. Expected variation around seasonal temperature and precipitation normals in the northeastern USA as a result of the El Nifio/Southern Oscillation cvcle.

Precipitation Temperature

Season El Niffo La Nifra El Niffo La Niffa Winter Above Above Above Above Spring Below Normal Normal NormaVbelow Summer NormaUbelow NormaVabove NormaVbelow Below Autumn Below NormaUabove NormaVabove NormaVbelow

(0.86) with June-August precipitation totals (P < longest running La Nifra recorded; it was still active 0.05), indicating an increase in activity with abun- just before the mosquito season of 2001. In Rhode dant precipitation. This also proved to be the only Island, this La Niffa likely contributed to annual and precipitation period with any significant correlation summer-season precipitation varying from well to virus activity (P < 0.05). Low-level, nonsignifi- above normal in 1998 to near normal in 1999 and cant (ct : 0.05) positive correlations (0.31-O.38) of 2000. Additionally, warmer-than-normal annual EEE with precipitation may indicate a response to temperatures dominated the region during 1998 and how frequently the precipitation falls but not to total 1999, whereas near-normal temperatures were re- amounts of precipitation. No correlation of virus ac- corded during 2000. Summer season temperatures tivity was found with either January-May (presea- also were well above normal in 1998 but were near son) or January-October (through-season) values. normal in L999 and 2000. Although El Niffo and "Others" Viruses labeled in Table 3, including Cal- La Nifla events may not be causative in triggering ifomia serogroup, CV JC, and Flanders, showed changes in mosquito and virus activity in Rhode negative correlation with precipitation, perhaps in- Island during the past 6 years, anomalous weather dicating a preference for drier conditions. The best can contribute to environmental changes affecting correlation for this group of viruses was -0.91 with mosquito populations and virus infection rates. It the January-August precipitation (P < 0.05). This may be possible to use increasingly sophisticated group, not surprisingly, also was correlated with the dynamic and statistical models that predict episodes January-May precipitation (-0.88, P < 0.05). of climate variability, particularly ENSO, in devel- Temperature showed low to moderate correlation oping models predicting increased mosquito virus with arbovirus activity. Eastern equine encephalo- activity. myelitis virus activity tended to be lower during seasons and years with warmer-than-normal tem- ACKNOWLEDGMENTS peratures, whereas the reverse trend was observed for HJ virus activity (Table 3). However, tempera- We thank all the members of the RI Office of ture was only significantly correlated (c : 0.05 lev- Mosquito Abatement Coordination surveillance el) with the ratio of EEE/HJ virus activity. crews from 1995 to 2000 for collecting and iden- The significant El Niflo event beginning in 1997 tifying mosquitoes. We also thank Frank Meglio of and ending early in 1998 has been ranked as one the RI Department of Health for technical assis- of the largest such events of the past century (Wol- tance during the 2000 bird surveillance, Jennifer ter and Timlin 1998) and has brought considerable Douglass for assistance with virus testing, and Carl attention to the potential impact of extreme climate Sawyer for providing climate data. This study was variability on vector-borne diseases (Patz et al. supported in part by the University of Rhode Island 2000). However, the effect of El Niflo on mosquito Public Health Partnership and a gift from the Island populations in the USA has yet to be assessed. In Fund of the New York Community Trusts. It is Rhode Island, El Nifio contributed to lower-than- Contribution Number 3932 of the Rhode Island Ae- normal annual and summer-season precipitation ricultural Experiment Station. and higher-than-normal annual and summer tem- peratures between 1997 and 1998 (Table 4). During REFERENCES the 1997 season, arbovirus activity was rare in Rhode Island. Nearly twice as many virus-positive Andreadis TG, Anderson JE Tinell-Peck SJ. 1998. Mul- mosquito pools were found in 1996 and 1998, years tiple isolationsof Easternequine encephalitis and High- not dominated by extreme weather events. Al- lands J viruses from mosquitoes (Diptera: Culicidae) though more observations are needed, it may be during a 1996 epizootic in SoutheasternConnecticut. J M Entomol 35:296-3O2. possible to project decreased virus activity in the ed Ansari MZ, ShopeRE, Malik S. 1993.Evaluation of Vero northeastem related Niffo episodes. USA to El cell lysate antigen for ELISA of .J Clin Lab La Nifla events represent the opposite extreme of Anal 7:230-237. the El Niffo/Southern Oscillation (ENSO) cycle and Armstrong P, Borovsky D, Shope RE, Morris CD, Mitch- often closely follow El Nifro episodes. The La Nifia ell CJ, KarabatsosN, Komar N, SpielmanA. 1995.Sen- event that began in mid to late 1998 has been the sitive and specific colorimetric dot assayto detect east- 188 JoURNALop rse AvenrcAN Moseurro Coxrnol AssocrenoN Vor-. 19, No. 3

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