dead crows from a roost were reported to the dutchess county department of health in december 2004 ( figure ) . the roost was located in coniferous and deciduous trees at the east end of the mid - hudson bridge , poughkeepsie , new york , usa . because winter surveillance in poughkeepsie had not previously confirmed wnv , the crows were not collected for testing . crow deaths associated with west nile virus ( wnv ) infection and maximum and mean temperatures for poughkeepsie , new york , usa ( december 1 , 2004march 31 , 2005 ) . roost area was checked for crow carcasses at least every 48 hours after february 10 , 2005 . temperature data were obtained from national oceanic and atmospheric administration , silver spring , maryland , usa . all 98 crow carcasses were tested for wnv by reverse transcription  pcr ( rt - pcr ) ( 2 ) , vectest , and rapid analyte measurement platform ( 3,4 ) . twelve were positive by all 3 tests ; 1 crow collected on march 7 , 2005 , was positive by rt - pcr only . however , after the third dead crow in january was reported , ground surveillance of the roost was initiated ( figure ) . thereafter , carcasses were collected 45 times per week at a radius of 1/4 mile around the roost and were transported for necropsy to the new york state department of environmental conservation . on march 1 , 2005 , the roost , culverts , and areas under the bridge were examined for overwintering mosquitoes . temperature data from december 1 , 2004 , to march 31 , 2005 , were obtained from the national oceanic and atmospheric administration , silver spring , maryland , usa . oral swabs were collected from carcasses and screened by using vectest ( medical analysis systems , freemont , ca , usa ) and rapid analyte measurement platform ( ramp ; response biomedical corp , burnaby , british columbia , canada ) ( 3,4 ) . brain tissue was submitted to the new york state department of health ( nysdoh ) for testing by taqman reverse transcription pcr ( rt - pcr ) and standard rt - pcr ( 2,5 ) . when possible , blood clots were collected from heart chambers for antibody testing by elisa ( 6 ) . ectoparasites were collected from some carcasses before necropsy and tested for wnv by taqman rt - pcr ( 2 ) . to characterize this wnv genotype , rna was extracted from the homogenate of a wnv - positive crow kidney ( strain 05000918 ) by using rneasy ( qiagen , valencia , ca , usa ) . the envelope coding region was amplified in 3 overlapping fragments by using qiagen one - step rt - pcr core kit . dna was sequenced at the wadsworth center molecular genetics core facility by using abi 3100 or 3700 automated sequencers ( applied biosystems , foster city , ca , usa ) . dq823132 ) by using the seqman module within lasergene ( dnastar , madison , wi , usa ) and compared it with previously characterized north american strains by using megalign within lasergene . we collected 45 fecal specimens from 12 sampling points in the roost and 10 from beneath 2 carcasses . specimens were tested for wnv rna by using taqman and standard rt - pcr ( 2 ) with minor modifications ; 100 mg of each specimen was diluted in 1.0 ml of ba-1 , homogenized , centrifuged , and sterile filtered . rna was extracted from the filtrate by using rneasy ( qiagen ) , and rt - pcr was conducted . from february 10 to march 29 , 98 carcasses were collected from the roost area ; of these , 12 ( 12.2% ) were wnv - positive according to vectest and ramp and 13 ( 13.3% ) were positive according to taqman rt - pcr ( figure ) . necropsy findings included low body weight ( 84.6% ) , enlarged spleen ( 23.1% ) , and enlarged liver ( 30.8% ) ; histopathologic findings included slight to moderate encephalitis with mild , diffuse gliosis and occasional small foci of necrosis in the gray matter of the brain . wnv - negative crows ( n = 85 ) died from traumatic injuries ( 51.8% ) , predation ( 16.5% ) , avian pox ( 14.1% ) , pneumonia ( 11.8% ) , and poisoning ( 5.9% ) . two pools of > 20 lice ( philopterus spp . : mallophaga ) from 6 wnv - positive birds and 1 pool from 1 wnv - negative bird were tested ; 6 positive pools were detected from 4 positive birds . all 56 blood clots collected were seronegative by elisa for flavivirus antibodies . of the 45 fecal samples , 3 were wnv - positive ; 2 of these ( 1 collected from beneath a wnv - positive crow ; 1 from a random roost sampling point ) had > 800 pfu / ml , according to extrapolation from taqman rt - pcr . no mosquito hibernacula were located in the areas examined , and no mosquito activity was observed by field workers . maximum daily temperatures were > 10c for 6 days in december , 4 days in january and february , and 5 days in march ; mean temperatures were < 10c throughout the epizootic ( figure ) . how wnv crow infections occurred during winter in new york when mosquito activity would have been limited is unclear ( figure ) . reporting of crow carcasses can be as low as 10% ; therefore , additional carcasses may have been observed and not reported before ground surveillance began ( 9 ) . initial crow infections could have occurred in november , when mean monthly temperature was > 10c and mosquito infection was more probable . maximum daily temperatures > 10c occurred sporadically from december through march . however , mean temperatures remained at < 10c ( figure ) and photoperiods at < 12 h / day . laboratory studies of wild - captured culex pipiens l. females , the primary wnv vector in the northeastern united states , have shown that cx . pipiens are unlikely to terminate diapause with photoperiods of < 12 h / day and temperatures < 10c ( 10 ) . pipiens remain in overwintering locations until mid - april , at which time photoperiods are > 12 h / day and mean temperatures > 10c ( c. drummond , nysdoh arbovirus laboratories , unpub . wnv has been detected in blood  feather pulp of crows ( 3 ) , and wnv - positive lice ( philopterus spp . ) research is needed on the risk for bird - to - bird viral transmission posed by ectoparasites , particularly to roost mates and nestlings . scavenging of infected birds as a risk factor is supported by laboratory studies demonstrating wnv infection in crows after they ingested infected house sparrows ( passer domesticus ) ( 11 ) and by chronic wnv infection in house sparrows and other bird species ( 12 ) . chronic infection in crows is unlikely given that laboratory studies have demonstrated 100% mortality rates within 5 days of infection ( 11 ) . crow - to - crow transmission of wnv is supported by laboratory findings of fecal - shed wnv and contact transmission ( 11,13 ) and by wnv - positive results from oral and cloacal swabs used in vectest and ramp ( 3,4 ) . in laboratory studies , crows shed wnv fecal titers as high as 10 pfu / g ( 13 ) . our study provides the first evidence of fecal - shed wnv in the wild . in illinois , healthy and wnv - infected crows roosted communally in summer ( 14 ) ; however , no additional evidence linked viremic crows and subsequent crow infections . further study is needed on the role of summer and winter roosts and feces in the wnv transmission cycle . no human cases are known to be related to exposure to crow feces , although avoiding feces and wearing gloves when handling live or dead birds are recommended . the role of birds in arbovirus overwintering and dissemination during migration has been suggested but is poorly understood . the last wnv - positive crow in this study was collected on march 29 as the roost was dispersing . radio - marked crows infected with wnv have traveled up to 4 km per night during the 5 days before they died ( 14 ) . thus , infected birds could transport the virus to new areas with active mosquitoes and contribute to the beginning of the wnv transmission cycle . we recommend additional study of winter wnv activity in crows and other bird species to determine their potential roles in arbovirus overwintering and the initiation of transmission when mosquitoes become active .
in new york , an epizootic of american crow ( corvus brachyrhynchos ) deaths from west nile virus ( wnv ) infection occurred during winter 20042005 , a cold season when mosquitoes are not active . 
 detection of wnv in feces collected at the roost suggests lateral transmission through contact or fecal contamination .