Emerging Infectious Diseases Volume 7 Issue 4

161 Pages·2001·3.1 MB·English

by  CDC

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West Nile Virus
West Nile Virus: A Reemerging Global Pathogen L.R. Petersen and
...................................................................................................611 J.T. Roehrig
Crow Deaths as a Sentinel Surveillance System for West M. Eidson et al.
Nile Virus in the Northeastern United States, 1999............615
Serologic Evidence for West Nile Virus Infection N. Komar et al.
in Birds in the New York City Vicinity during an
Outbreak in 1999 .....................................................................621
West Nile Virus Isolates from Mosquitoes R.S. Nasci et al.
in New York and New Jersey, 1999........................................626
Cover: The Mosquito Net (ca. 1912) by Dead Bird Surveillance as an Early M. Eidson et al.
John Singer Sargent. The White
House Collection, copyright White Warning System for West Nile Virus.....................................631
House Historical Association. West Nile Virus Surveillance in Connecticut J. Hadler et al.
See p. 766.
in 2000: An Intense Epizootic without High Risk
for Severe Human Disease......................................................636
Letters
Mosquito Surveillance and Polymerase Chain D.J. White et al.
Treatment of West Nile Virus Reaction Detection of West Nile Virus,
Encephalitis with Intravenous New York State ........................................................................643
Immunoglobulin............. 759 Partial Genetic Characterization of West Nile G.D. Ebel et al.
Z. Shimoni et al. Virus Strains, New York State, 2000.....................................650
Nipah Virus InfectionAmong Clinical Findings of West Nile Virus Infection D. Weiss et al.
Military Personnel Involved in in Hospitalized Patients, New York and
Pig Culling during an Outbreak New Jersey, 2000 .....................................................................654
of Encephalitis in Malaysia, West Nile Encephalitis in Israel, 1999: M. Giladi et al.
1998-1999 .......................759 The New York Connection.......................................................659
R. Ali et al.
Dead Crow Densities and Human Cases of M. Eidson et al.
Integrated Mosquito West Nile Virus, New York State, 2000.................................662
Management: No New Thing Equine West Nile Encephalitis, United States .....................665 E.N. Ostlund et al.
......................................... 761
Mosquito Surveillance for West Nile Virus in T.G. Andreadis et al.
H.R. Rupp
Connecticut, 2000: Isolation from Culex pipiens,
Integrated Mosquito Cx. restuans, Cx. salinarius, and Culiseta melanura............670
Management—Reply to Dr. Rupp
Clinical Characteristics of the West Nile Fever M.Y. Chowers et al.
......................................... 761 Outbreak, Israel, 2000.............................................................675
R.I. Rose
West Nile Virus Infection in Birds and Mosquitoes, K.A. Bernard et al.
Enteric Fever Treatment New York State, 2000..............................................................679
Failures: A Global Concern
West Nile Fever Outbreak, Israel, 2000: M. Weinberger et al.
......................................... 762
Epidemiologic Aspects.............................................................686
D.S. Chandel and R. Chaudhry
West Nile Outbreak in Horses in Southern France, B. Murgue et al.
The opinions expressed by authors contributing 2000: The Return after 35 Years ............................................692
to this journal do not necessarily reflect the The Relationships between West Nile J.H. Scherret et al.
opinions of the Centers for Disease Control and
Prevention or the institutions with which the and Kunjin Viruses..................................................................697
authors are affiliated.
(cid:13)(cid:7)(cid:14)(cid:15)(cid:15)(cid:16)(cid:17)(cid:18)(cid:15)(cid:19)(cid:20)(cid:15)(cid:21)(cid:15)(cid:22)(cid:7)(cid:23)(cid:2)(cid:24)(cid:16)(cid:25)(cid:26)(cid:3)(cid:7)(cid:27)(cid:16)(cid:26)(cid:28)(cid:29)(cid:20)(cid:25)(cid:30)(cid:7)(cid:26)(cid:25)(cid:22)(cid:7)(cid:13)(cid:25)(cid:26)(cid:3)(cid:31) (cid:20)(cid:25)(cid:30)(cid:7)!(cid:20)"(cid:15)(cid:26)"(cid:15)(cid:7)(cid:27)(cid:16)(cid:15)(cid:25)(cid:22)" (cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)(cid:8)(cid:2)(cid:4)(cid:9)(cid:6)(cid:7)(cid:10)(cid:11)(cid:11)(cid:12)
Letters, cont’d West Nile Virus, cont’d.
Enteric Fever Treatment Rapid Determination of HLA B*07 Ligands from A.S. De Groot et al.
Failures—Reply to Drs. the West Nile Virus NY99 Genome........................................706
Chandel and West Nile Virus Infection in the Golden Hamster S-Y Xiao et al.
Chaudhry........................763 (Mesocricetus auratus): A Model for West Nile
E.J. Threlfall and L.R. Ward Encephalitis..............................................................................714
Mycobacterium tuberculosis West Nile Virus Infection In Mosquitoes, V.L. Kulasekera et al.
Beijing Genotype, Thailand— Birds, Horses, and Humans, Staten Island,
Reply to Dr. Prodinger New York, 2000........................................................................722
......................................... 763
Experimental Infection of Chickens as Candidate S.A. Langevin et al.
D. van Soolingen et al.
Sentinels for West Nile Virus .................................................726
Widespread West Nile Virus Activity, A.A. Marfin et al.
Commentary Eastern United States, 2000...................................................730
Exposure of Domestic Mammals to West Nile Virus N. Komar et al.
Identification of Arboviruses during an Outbreak of Human Encephalitis,
and Certain Rodent-Borne New York City, 1999................................................................736
Viruses: Reevaluation of Detection of North American West Nile Virus D.J. Johnson et al.
the Paradigm..................756 in Animal Tissue by a Reverse Transcription-Nested
American Committee on Polymerase Chain Reaction Assay.........................................739
Arthropod-Borne Viruses West Nile Virus in Overwintering Culex R. S. Nasci et al.
Mosquitoes, New York City, 2000...........................................742
News and Notes West Nile Virus Outbreak Among Horses in S.C. Trock et al.
New York State, 1999 and 2000 .............................................745
Isolation and Characterization of West Nile Virus M. Hindiyeh et al.
Fifth International Conference
from the Blood of Viremic Patients During
of the Hospital Infection Society
......................................... 765 the 2000 Outbreak in Israel....................................................748
Fatal Encephalitis and Myocarditis in Young D.E. Swayne et al.
Inaugural EIDIOR Workshop
Domestic Geese (Anser anser domesticus)
......................................... 765
Caused by West Nile Virus .....................................................751
4th European Health
Comparative West Nile Virus Detection in N.A. Panella et al.
Forum—Gastein 2001
Organs of Naturally Infected American Crows
......................................... 765
(Corvus brachyrhynchos) .........................................................754
International Conference on
Emerging Infectious Diseases
......................................... 765 The Cover
Erratum, Vol.7, No. 2..... 765
Obituary: Vulimiri The Mosquito Net by John Singer Sargent
Ramalingaswami............766 (ca. 1912)...................................................................................766
West Nile Virus
West Nile Virus: A Reemerging Global Pathogen
envelope that has been modified by the insertion of two
integral membrane glycoproteins, E (53 kDa) and prM (18-20
kDa). The virion is 45 nm to 50 nm in diameter (Figure 2).
Late in virus maturation, the prM protein is cleaved to M
protein (8 kDa) by a cellular protease, and the M protein is
incorporated into the mature virion. The genome also encodes
seven nonstructural proteins (NS1, NS2a, NS2a, NS3, NS4a,
NS4b, and NS5) that make up the intracellular replication
machinery of the virus. E-glycoprotein, the most immunolog-
ically important structural protein, is the viral hemagglutinin
Lyle R. Petersen John T. Roehrig
Guest Editor, Guest Editor,
Series on West Nile virus Series on West Nile virus
Dr. Petersen is Deputy Dr. Roehrig is chief of
Director for Science, Division of the Arbovirus Diseases Figure 1. Genomic structure of flaviviruses. The flavivirus genome is
Vector-Borne Infectious Diseases, Branch, Division of Vector- 11,000 to 12,000 nucleotides long. Both the 5'- and 3'- ends contain
Centers for Disease Control and Borne Infectious Diseases, noncoding (NC) regions. The genome encodes 10 proteins, 3 of which
Prevention. He has been active Centers for Disease Control are structural proteins (C, M, and E), and 7 of which are
in developing ArboNet, a new and Prevention. His re- nonstructural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and
surveillance system to monitor search interests focus on the NS5). The M protein is synthesized as a precursor (prM) protein. The
the spread of the West Nile vi- immunology of vector-borne prM protein is processed to pr + M protein late in the virus
rus in the United States. His re- viral diseases; protein bio- maturation by a convertase enzyme (furin).
search focuses on the epidemiol- chemistry; and specific dis-
ogy and prevention of vector- ease interests—equine and
borne infectious diseases in the human encephalitides, den-
United States and abroad. gue fever, and rubella.
The recognition of West Nile (WN) virus in the Western
Hemisphere in the summer of 1999 marked the first
introduction in recent history of an Old World flavivirus into
the New World (1,2). The United States is not alone, however,
in reporting new or heightened activity in humans and other
animals, and incursions of flaviviruses into new areas are
likely to continue through increasing global commerce and
travel. Similar expansion of other flaviviruses has been
documented. Dengue viruses, perhaps the most important
human flaviviral pathogens, have spread from roots in Asia to
all tropical regions (3-5). Japanese encephalitis (JE) virus has
recently encroached on the northern shores of Australia and
may soon become endemic in that continent (6-9). This issue of
Emerging Infectious Diseases focuses on current understand-
ing of the biology, ecology, and epidemiology of WN virus.
WN virus, a member of the family Flaviviridae (genus
Flavivirus) (10), was first isolated in 1937 in the West Nile
district of Uganda (11). Flaviviruses have a 30- to 35-nm
icosahedral core composed of multiple copies of a 12-kDa
capsid protein. The capsid encloses a single-stranded,
positive-sense RNA of approximately 12,000 nucleotides
Figure 2. Diagram of the flavivirus virion. An icosahedral
(Figure 1). The capsid is enclosed in a host cell-derived
nucleocapsid (half shown here) encloses the virion RNA. The virion
has an envelope derived from the host cell membranes. E-
Address for correspondence: Lyle R. Petersen, Centers for Disease glycoprotein (E), an integral membrane protein, is arranged as
Control and Prevention, P.O. Box 2087, Fort Collins, CO 80522, USA; homodimers (head-to-tail) and associates with the other integral
fax: [phone]; e-mail: [email protected] membrane proteins prM protein (in immature virions).
Vol. 7, No. 4, July–August 2001 611 Emerging Infectious Diseases
West Nile Virus
and also mediates virus-host cell binding. It elicits most of the virus (26). Lineage 2 WN viruses are maintained in enzootic
virus neutralizing antibodies. WN virus is a member of the JE foci in Africa and have not been associated with clinical
virus serocomplex (Table) (12), which contains a number of human encephalitis. Among lineage 1 WN viruses, the
viruses also associated with human encephalitis: JE, St. viruses causing the recent human and equine outbreaks
Louis encephalitis (SLE), Murray Valley encephalitis, and throughout Europe and Asia have been most closely related to
Kunjin (a subtype of WN). All flaviviruses are closely related a WN virus first isolated in Romania in 1996 (ROM96) and
antigenically, which accounts for the serologic cross-reactions subsequently in Kenya in 1998 (25,30,31). The WN virus
observed in the diagnostic laboratory. Members of the JE responsible for the U.S. outbreak (NY99) is genetically
complex are even more closely related, often needing distinguishable from the ROM96-like viruses. The closest
specialized tests (e.g., virus neutralization assays) to relative of NY99 virus was a virus circulating in Israel from
differentiate the infecting flavivirus (13). Because of the close 1997 to 2000 (Isr98). Only the United States and Israel have
antigenic relationships between the flaviviruses, acute- and reported illness and death in humans and animals caused by
convalescent-phase serum specimens from patients are this Isr98/NY99 variant of WN virus (18,28). The reason for
required to fully assess antibody response. A useful this is not known. The genotype of NY99 WN virus in the
outgrowth of the recent WN virus activity has been the United States has remained stable. Very few genomic changes
development, standardization, and implementation of rapid occurred in the NY99 WN virus between the 1999 and 2000
techniques for antibody and virus detection (14-16). These WN virus outbreaks (32; Lanciotti, pers. comm.).
rapid, sensitive techniques permitted identification of The 2000 WN virus outbreak in humans and birds in
overwintering mosquitoes in New York City in 2000 and two Israel was caused by cocirculation of both the ROM96 and the
human WN encephalitis cases in Israel in 1999 (17,18). Isr98 variants of WN virus (33; C. Banet, manuscript in
Since the original isolation of WN virus, outbreaks have preparation). Although these are the first reports of two
occurred infrequently in humans, those in Israel (1951-1954 genetic variants of WN virus causing a single WN
and 1957) and South Africa (1974) being most notable. Since encephalitis outbreak in humans and birds, similar mixed
the mid-1990s, however, three disturbing epidemiologic human flavivirus outbreaks have been documented for
trends for WN virus have emerged: 1) increase in frequency of dengue virus (34).
outbreaks in humans and horses (Romania 1996; Morocco The close genetic relationship between WN virus isolates
1996; Tunisia 1997; Italy 1998; Russia, the United States, from Israel and New York suggests that the virus was
and Israel 1999; and Israel, France, and the United States imported into North America from the Middle East. The
2000)(19-23); 2) apparent increase in severe human disease means of its introduction (infected bird, mosquito, human, or
(2,19,20,22,24,25) (confirmed human infections in recent another vertebrate host) will likely remain unknown. A
outbreaks: Romania, 393 cases; Russia [Volgograd], 942 striking feature of the initial human epidemic in New York
cases; United States, 62 cases in 1999 and 21 in 2000; Israel, City in 1999 was the high number of avian deaths in the
2 cases in 1999 and 417 in 2000); and 3) high avian death rates accompanying epizootic, particularly in American Crows
accompanying the human outbreaks, in outbreaks in Israel (Corvus brachrhynchos) and other corvids (35,36). Subse-
and the United States. quent work demonstrating near 100% death rates among
Recent outbreaks of WN virus have been accompanied by experimentally infected American Crows with NY99 WN
an apparent evolution of a new WN virus variant. WN virus virus has confirmed this observation (R. McLean, pers.
can be divided genetically into two lineages (26-29). Only comm.). Although one early study showed high death rates
members of lineage 1 WN viruses have been associated with among Egyptian Hooded Crows (Corvus corone) and House
clinical human encephalitis (the lineage of the WN virus Sparrows (Passer domesticus) experimentally infected with
causing the human outbreak in South Africa in 1974 is under the prototype Egypt 101 WN virus strain (37), the epizootic in
contention). Lineage 1 WN viruses have been isolated from Israel in 1997 to 2000 was the first in the Old World
Africa, India, Europe, Asia, and North America. In addition, demonstrating high avian death rates (38). Whether high
Kunjin virus, an apparent subtype of lineage 1 WN viruses, avian death rates in the United States are due to higher
cocirculates in Australia with a second encephalitis virus virulence of the circulating strains or to higher susceptibility
member of the JE virus complex, Murray Valley encephalitis in North American birds requires further evaluation.
High avian death rates during the 1999 epizootic in the
New York City area prompted an avian mortality surveillance
Table. Distribution of Japanese encephalitis (JE) virus serocomplex viruses system to track the spread of WN virus in the eastern and
southern United States. Surveillance showed expansion of
Virus Abbreviation Geographic location
viral activity to 12 states in 2000, extending from the
Cacipacore CPC South America
Canadian border to North Carolina, a distance of 900 km (39).
Koutango KOU Africa
Japanese encephalitis JE Asia, Oceania, Pronounced northward spread of the virus from New York
Australiaa City was noted in the late spring and early summer and
Murray Valley encephalitis MVE Australia southward spread in the late summer and fall—a pattern
Alfuy ALF Australia consistent with bird migration. Through 2000, avian
St. Louis encephalitis SLE North America,
mortality rate surveillance has documented WN virus
South America
infection in 76 North American native and captive bird
West Nile encephalitis WN Africa, Asia, Europe,
species. Although American Crows were by far the most
North America
Kunjin KUN Australia commonly identified species, this may reflect the lethality of
Yaounde YAO Africa infection in this species, rather than its importance as a
aJE virus has occasionally been introduced into Australia. Classification from (12). reservoir host.
612
Emerging Infectious Diseases Vol. 7, No. 4, July–August 2001
West Nile Virus
Despite the substantial geographic expansion of WN suggest that hot, dry summers may promote human
virus activity documented by avian mortality surveillance in outbreaks caused by these two viruses (25,40,47,48). The
2000, human infections were noted only in New York City and mean July temperature in the New York City area in 1999
surrounding counties in New Jersey and Connecticut (39). was among the highest on record, while 2000 was compara-
Ten of the 21 infected persons identified in 2000 lived on tively cool. However, climate and weather influence mosquito
Staten Island, the only part of New York City without populations and arboviral recrudescence in complex ways;
documented WN virus infections in humans in 1999. The simple generalizations about weather have had poor predic-
reason that the 2000 human epidemic remained focal despite tive value for SLE forecasting and will likely be equally un-
a widely geographically expanding epizootic is unknown. predictive for WN virus forecasting in any given area (48,49).
Extensive spring and early summer larval mosquito control In the United States, first attempts have been made to
efforts in urban areas of the Northeast likely contributed to predict WN virus human epidemics in a county on the basis of
decreased human exposure to mosquitoes. avian mortality data (50); efforts to interpret avian mortality
In addition to high mortality rates of 5% to 14% among or other surveillance data at a more local level for more
persons with neurologic symptoms in the recent U.S., Romanian, focused emergency mosquito control are at an even earlier
Russian, and Israeli outbreaks, other clinical aspects (e.g., stage of development (46,51). To prevent WN virus infection
profound motor weakness and infrequency of skin rash and in humans, extensive early season larval control has been
lymphadenopathy) differ from those of earlier outbreaks recommended and undertaken, as have the development and
(19,20,22,25,39,40). Serologic surveys accompanying the dissemination of public health messages for reducing
Romanian (1996) and two U.S. outbreaks (1999 and 2000) personal exposure to mosquito bites (52). The efficacy and
indicated that severe neurologic illness developed in <1% of cost-effectiveness of these prevention measures, along with
persons infected with WN virus, with systemic febrile illness application of pesticides to control adult mosquitoes, require
developing in approximately 20% of those infected (40,41). further evaluation. These evaluations are likely to be
In the United States in both 1999 and 2000, infections in hindered by the sporadic nature of human WN epidemics.
humans peaked in August and in horses in September (39,42), Given our incomplete and evolving knowledge of the ecology
suggesting either different mosquito species transmitting the and public health impact of WN virus in the Americas, as well
virus to humans and horses or temporal differences in as the efficacy of control efforts, the virus will remain an
exposure to the same species. In 2000, 14 mosquito species in important public health challenge in the next decade.
five states had evidence of WN virus infection (by culture or
nucleic acid amplification) (39). Since mosquitoes of the genus References
Culex are the principal maintenance vectors in the Old World, 1. Asnis DS, Conetta R, Teixeira AA, Waldman G, Sampson BA. The
not surprisingly, Cx. pipiens and Cx. restuans—common, West Nile Virus outbreak of 1999 in New York: the Flushing
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Outbreak of West Nile virus infection, New York City area, 1999. N
identified species with WN virus in 2000 (39). However, which
Engl J Med 2001;344:1807-14.
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virus in the Americas may provide clues to the eventual
Hurk AF, et al. Japanese encephalitis in north Queensland,
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614
Emerging Infectious Diseases Vol. 7, No. 4, July–August 2001
West Nile Virus
Crow Deaths as a Sentinel Surveillance System
for West Nile Virus in the
Northeastern United States, 1999
Millicent Eidson,* Nicholas Komar,† Faye Sorhage,‡ Randall Nelson,§
Tom Talbot,* Farzad Mostashari,¶ Robert McLean,# and the West Nile Virus
Avian Mortality Surveillance Group1
*New York State Department of Health, Albany, New York, USA; †Centers for Disease Control
and Prevention, Fort Collins, Colorado, USA; ‡New Jersey Department of Health and Senior
Services, Trenton, New Jersey, USA; §Connecticut Department of Public Health, Hartford,
Connecticut, USA; ¶New York City Department of Health, New York City, New York, USA;
#National Wildlife Health Center, Madison, Wisconsin, USA
In addition to human encephalitis and meningitis cases, the West Nile (WN) virus
outbreak in the summer and fall of 1999 in New York State resulted in bird deaths
in New York, New Jersey, and Connecticut. From August to December 1999,
295 dead birds were laboratory-confirmed with WN virus infection; 262 (89%)
were American Crows (Corvus brachyrhynchos). The New York State
Department of Health received reports of 17,339 dead birds, including 5,697
(33%) crows; in Connecticut 1,040 dead crows were reported. Bird deaths were
critical in identifying WN virus as the cause of the human outbreak and defining
its geographic and temporal limits. If established before a WN virus outbreak, a
surveillance system based on bird deaths may provide a sensitive method of
detecting WN virus.
West Nile (WN) virus (family Flaviviridae) causes National Wildlife Health Center and the U.S. Department of
inapparent infection, mild febrile illness, meningitis, Agriculture’s National Veterinary Services Laboratory was
encephalitis, or death in humans and horses in Europe, Africa, identified as WN virus by the Centers for Disease Control and
Asia, and Australia (1). Wild birds are considered the Prevention (CDC) on September 23 (5). The virus was also
principal hosts of WN virus, and mosquitoes, particularly recovered by the Connecticut Agricultural Experiment
Culex species, are the primary vector (1). Bird deaths had not Station in specimens from a Connecticut bird on September
been frequently documented in previous human WN virus 13 (6). A West Nile virus genomic sequence identical to that
outbreaks, although infected carcasses of a variety of bird species derived from the bird isolates was then observed in a brain
were found in Israel in 1998 (1,2), and deaths were observed specimen from a human encephalitis case (7).
after experimental infection in crows and sparrows (3). In response to the initial indications of WN virus in bird
As early as the end of June 1999, an unusual number of specimens, surveillance systems for bird deaths and
dead and dying crows were noted by residents of northern laboratory testing were established and used in the
Queens in New York City (NYC). In July, a local veterinarian assessment and control of the outbreak. We reviewed data
noted neurologic illness in some birds with unstable gait. from systems in New York State, New Jersey, and
Although not then recognized, the earliest cases of human Connecticut to describe how surveillance of bird deaths was
illness due to West Nile virus occurred in this area, beginning used in 1999 to guide public health action, as well as the
in the first week of August (4). After initial evaluation of dead advantages and disadvantages of using dead birds as
birds by the New York State Department of Environmental sentinels for West Nile virus in a given geographic area.
Conservation’s Wildlife Pathology Unit and the Wildlife
Conservation Society, a virus isolated from specimens by the Methods
Address for correspondence: Millicent Eidson, Zoonoses Program, New Sightings of Ill or Dead Birds
York State Department of Health, Rm. 621 ESP Corning Tower,
Local health departments were requested to collect and
Albany, NY 12237, USA; fax: [phone]; e-mail:
report dead birds to the state health departments of New York
[email protected]
1Ward Stone, New York State Department of Environmental Conservation; Madhu Anand, Rockland County (NY) Department of Health; Annie Fine, Nancy
Jeffery, New York City Department of Health; Ada Huang, Christine Falco, Westchester County (NY) Department of Health; Steve Kopian, Nassau County (NY)
Department of Health; Clare Bradley, Suffolk County (NY) Department of Health Services; Kate Schmit, Amy Willsey, Yoichiro Hagiwara, Dennis White, Barbara
Wallace, Perry Smith, Hwa-Gan Chang, New York State Department of Health; local and county agencies in New Jersey and Connecticut; Eddy Bresnitz, Colin
Campbell, New Jersey Department of Health and Senior Services; Doug Roscoe, New Jersey Department of Environmental Protection; Theodore Andreadis, John
Anderson, Charles Vossbrinck, Connecticut Agricultural Experiment Station; James Hadler, Connecticut Department of Public Health; Herbert Van Kruiningen,
Antonio Garmendia, Richard French, University of Connecticut; Jenny Dickson, Connecticut Department of Environmental Protection; Lou Sileo, National Wildlife
Health Center; and Amy Kerst, Robert Lanciotti, Nicholas A. Panella, Centers for Disease Control and Prevention.
Vol. 7, No. 4, July–August 2001 615 Emerging Infectious Diseases
West Nile Virus
and Connecticut. Sighting reports for ill or dead birds that Results
were not submitted for laboratory testing were not
systematically maintained in New Jersey in 1999. Data Ill or Dead Bird Sightings
collected included date of the report, date of death or sighting New York State received 13,654 reports of 17,339 dead
of the birds, whether the birds were dead or appeared ill, birds from 32 county health departments and from the New
street address where the birds were seen or found, number of York City Department of Health, which represents five
birds, and species of birds. Mapping was based on the earliest boroughs (counties). Dates of death ranged from May 1 to
date provided for the death or sighting. New York State’s November 30. The predominant species reported was the
surveillance data for bird deaths were collected prospectively American Crow (Corvus brachyrhynchos) (5,697 sightings,
from September 23, 1999, through November 30, 1999, and 33%). Before August, there were few retrospective dead crow
retrospectively through May 1, 1999. Connecticut’s reporting sightings, and these were confined primarily to the NYC
system was active from September 30, 1999, through boroughs of Queens and the Bronx and to lower Westchester
November 4, 1999. County. Continued geographic spread of dead crow sightings
In New York State, a geographic information system was was noted in August (Figure 1a). Reported sightings peaked
used to geocode locations of WN virus-positive birds and to in September (Figure 1b), with the largest numbers from NYC
generate maps. Because of incomplete address information, and lower Westchester County and wide distribution into
dot-density mapping was used with random placement of the Long Island and north along the Hudson River. Although
birds within townships for dead crow sightings in New York dead crow reports did not dramatically decrease until
State and WN virus-positive birds in Connecticut and New November, they began to decline in number and density in
Jersey. To assess changes in crow populations, the National October (Figure 1c). Later reports were also distributed
Audubon Society’s Christmas Bird Count (8), adjusted for farther north along the upper Hudson Valley. Most of the dead
party-hours (sum of hours spent counting by each group bird sightings were of single dead birds, rather than clusters
performing the count), was used. of dead birds found together.
Specimen Collection
Recently dead birds with no other obvious causes of death
were submitted for testing in all three states. Although
initially New York State requested submission only of birds
found within 1 mile of each other within 72 hours, that
requirement was soon dropped. Connecticut prioritized the
submission of birds based on towns with multiple reports of
dead birds and then in areas near the towns where WN virus
was confirmed. WN virus testing was limited to birds
collected from September 13 through October 29, 1999. New
Jersey initially accepted all dead bird specimens but later
reduced the testing of specimens from several counties where
numerous positives had been identified. Mapping was based
on the date the dead bird was found.
In their respective states, dead birds were necropsied and
specimens were processed for virus testing by the New York
State Wildlife Pathology Unit, the New Jersey Department of
Health and Senior Services Public Health and Environmental
Laboratory, and New Jersey Division of Fish and Wildlife
Pathology Laboratory, as well as the Department of
Pathobiology at the University of Connecticut.
Laboratory Testing
Methods for detecting WN virus in avian tissues at CDC
have been described (9). Briefly, tissue samples were prepared
by macerating approximately 0.5 cm3 of brain tissue in 1.8 mL
of BA-1 diluent in a glass TenBroeck tissue grinder (Bellco
Glass, Inc., Vineland, NJ). These homogenates were clarified
by centrifugation. Virus isolation was attempted in duplicate
100-µL aliquots of the supernatant by Vero plaque assay in 6-
well plates. A 75-µL aliquot from each sample was tested by
either the traditional or TaqMan reverse-transcriptase-
polymerase chain reaction (RT-PCR) assays or both.
In Connecticut, brain tissue was assayed for WN virus as
described (6), using cytopathic effect in Vero culture to screen
for viruses and specific WN virus RT-PCR for identification. A
similar strategy was used at the National Wildlife Health Center, Figure 1. Dead crow sightings, August-October, 1999, New York
but kidney or spleen suspensions were used in place of brain. State.
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Emerging Infectious Diseases Vol. 7, No. 4, July–August 2001