Table Of ContentFrontmatter-X4047.qxd 8/13/07 10:26 AM Page v
Contributors
Mary E. Allen, PhD Marcus Clauss, MSc, DrMedVet
Center for Veterinary Medicine Senior Research Associate
Food and Drug Administration Division of Zoo Animals, Exotic Pets, and Wildlife
Rockville, Maryland Vetsuisse Faculty
University of Zurich
David E. Anderson, DVM, MS, DACVS Zurich, Switzerland
Professor and Head of Agricultural Practices
Clinical Sciences Robert A. Cook, VMD, MPA
College of Veterinary Medicine Chief Veterinarian and Vice President
Kansas State University Wildlife Health Sciences
Manhattan, Kansas Wildlife Conservation Society
Bronx, New York
Adjunct Assistant Professor
Kay A. Backues, DVM, DACZM
School of International and Public Affairs
Adjunct Professor
Columbia University
Zoo-Exotic Animal Medicine
Manhattan, New York
Oklahoma State University
Tulsa, Oklahoma
Graham Crawshaw, BVetMed, MS, MRCVS,
Adjunct Professor
DACZM
Lab and Exotic Pet Medicine
Senior Veterinarian
Tulsa Community College
Toronto Zoo
Tulsa, Oklahoma
Toronto
Staff Veterinarian
Ontario, Canada
Veterinary Health Department
Tulsa Zoo
Sharon L. Deem, DVM, PhD, ACZM
Tulsa, Oklahoma
Research Veterinarian
Department of Animal Health
Thomas A. Bailey, BSc, BVSc, MRCVS, MSc
Smithsonian National Zoological Park
(wild animal health), CertZooMed, PhD,
Washington, DC
DECAMS
Falcon and Wildlife Veterinarian
Mary C. Denver, DVM
Dubai Falcon Hospital
Director, Medical Department
Dubai
Maryland Zoo in Baltimore
United Arab Emirates
Baltimore, MD
Wayne Boardman, BVetMed, MRCVS, MACVSc Ellen S. Dierenfeld, BS, MS, PhD, Cert Nutr Spec
Head of Veterinary Conservation Programs Adjunct Professor
Zoological Society of South Australia Department of Animal Science
Adelaide Zoo Cornell University
Adelaide, South Australia Ithaca, New York
Australia Adjunct Professor
Department of Animal Science
Andrew C. Breed, BSc, BVMS, MSc, MRCVS University of Missouri
Project Officer Columbia, Missouri
School of Veterinary Science Nutritionist
Australian Biosecurity Cooperative Research Centre Department of Animal Health and Nutrition
University of Queensland Saint Louis Zoo
Brisbane, Australia Saint Louis, Missouri
v
Frontmatter-X4047.qxd 8/13/07 10:26 AM Page vi
vi Contributors
Peter Dollinger, DVM, PhD William B. Karesh, DVM
Executive Director Director
World Association of Zoos and Aquariums (WAZA) Field Veterinary Program
Lieberfeld-Berne, Switzerland Wildlife Conservation Society
Bronx, New York
Andrea L. Fidgett, BSc, MSc, PhD
Nutritionist Reimi E. Kinoshita, BVMS, MRCVS, MPhil
North of England Zoological Society Research Veterinarian and Specialist Advisor
Chester Zoo Zoological Operations and Education
Chester, United Kingdom Ocean Park Corporation
Hong Kong
Edmund Flach, MA, VetMB, MSc, DZooMed,
MRCVS James K. Kirkwood, BVSc, PhD, FlBiol, MRCVS
Veterinary Officer Chief Executive and Scientific Director
Veterinary Department Universities Federation for Animal Welfare
Zoological Society of London Wheathampstead, Hertfordshire, United Kingdom
Dunstable, Bedfordshire Gregory A. Lewbart, MS, VMD, Dipl ACZM
United Kingdom Professor of Aquatic Medicine
Department of Clinical Sciences
Laurie J. Gage, DVM North Carolina State University
Lecturer College of Veterinary Medicine
Department of Medicine and Epidemiology Raleigh, North Carolina
University of California at Davis
School of Veterinary Medicine Gregory A. Lewbart, MS, VMC, DACZM
Davis, California Department of Clinical Sciences
North Carolina State University
Jean-Michel Hatt, ProfDrMedVet, DECAMS College of Veterinary Medicine
Division of Zoo Animals, Exotic Pets, and Wildlife Raleigh
University of Zurich North Carolina
Zurich, Switzerland
Linda J. Lowenstine, DVM, PhD, DACVP
Sabine Hilsberg-Merz, Dr Professor of Veterinary Pathology
Zoo Animal Specialist (FTA) Department of Microbiology and Immunology
Trendelburg, Germany School of Veterinary Medicine
University of California at Davis
JoGayle Howard, DVM, PhD Davis, California
Adjunct Professor
Department of Animal and Avian Sciences Susan K. Mikota, DVM
University of Maryland Hohenwald, Tennessee
College Park, Maryland
Theriogenologist Melissa A. Miller
Department of Reproductive Services Marine Wildlife Veterinary Care and Research Center
Smithsonian’s National Zoological Park Department of Fish and Game
Washington, DC University of California at Davis
Davis, California
Wan Htun, BVS (Ygn)
Assistant Manager (Vet) Michael W. Miller, DVM, PhD
Deputy General Manager Office Senior Wildlife Veterinarian
East Bago Division Colorado Division of Wildlife
Myanmar Timber Enterprise Wildlife Research Center
Taungoo, Myanmar Fort Collins, Colorado
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Contributors vii
Michele A. Miller, DVM, PhD Edward C. Ramsay, DVM, DACZM
Veterinary Operations Manager Professor of Avian and Zoological Medicine
Department of Veterinary Services Department of Small Animal Clinical Sciences
Disney’s Animal Programs The University of Tennessee
Lake Buena Vista, Florida Knoxville, Tennessee
Sharon P. Redrobe, DVM
Hayley Weston Murphy, DVM
Head of Veterinary Services
Director of Veterinary Services
Bristol Zoo Gardens
Zoo New England
Bristol, United Kingdom
Boston, Massachusetts
Timothy A. Reichard, MS, DVM
Luis R. Padilla, DVM
Bird and Exotic Pet Wellness Center
Oklahoma City Zoo
Toledo, Ohio
Oklahoma City, Oklahoma
Thomas H. Reidarson, DVM, DACZM
Alberto Parás, MVZ Director of Veterinary Services
Professor, Wild Animal Medicine Sea World of California
Univercidad Nacional Autonoma de México San Diego, California
México City, México
Director, Animal Health Service Laura K. Richman, DVM, PhD, DACVP
Animal Health Service Smithsonian’s National Zoological Park
African Safari Department of Pathology
Puebla, México Washington, DC
Patricia G. Parker, PhD Nadia Robert, DVM, DACVD
Des Lee Professor of Zoological Studies Assistant Professor
Department of Biology Centre for Fish and Wildlife Health
University of Missouri—St. Louis Institute of Animal Pathology
St. Louis, Missouri Vet Suisse Faculty Berne
Senior Scientist Berne, Switzerland
Wildcare Institute
Saint Louis Zoo Anthony W. Sainsbury, BVetMed, CertZooMed,
St. Louis, Missouri MRCVS
Lecturer in Wild Animal Health
Institute of Zoology
Allan P. Pessier, DVM
Zoological Society of London
Zoological Society of San Diego
London, United Kingdom
San Diego, California
Juergen Schumacher, DrMedVet, DACZM
Joost D. Philippa, DVM
Associate Professor, Avian and Zoological Medicine
Institute of Virology
University of Tennessee
Erasmus Medical Center
College of Veterinary Medicine
Rotterdam, The Netherlands
Department of Small Animal Clinical Sciences
Knoxville, Tennessee
Romain Pizzi, BVSc, MSc, DZooMed, FRES,
MACVSc (Surg), MRCVS Francis T. Scullion, MVB, PhD, MRCVS
Zoo and Wildlife Pathologist Founder, Member, and Past President of the World
Veterinary Department Association of Wildlife Veterinarians
Zoological Society Ballygawley, County Tyrone
London, United Kingdom Northern Ireland
Frontmatter-X4047.qxd 8/13/07 10:26 AM Page viii
viii Contributors
Raghunath Shivappa, PhD William M. Switzer, MPH
Postdoctoral Research Associate Laboratory Branch
College of Veterinary Medicine Division of HIV/AIDS Prevention
North Carolina State University Centers for Disease Control and Prevention
Raleigh, North Carolina Atlanta, Georgia
James G. Sikarskie, DVM, MS, DACZM Maryanne E. Tocidlowski, DVM, DACZM
Zoo and Wildlife Veterinarian Associate Veterinarian
Small Animal Clinical Sciences Houston Zoo, Inc.
College of Veterinary Medicine Houston, Texas
Michigan State University
East Lansing, Michigan Dominic Travis, DVM, MS
Director, Davee Center for Epidemiology and
Jonathan M. Sleeman, MA, VetMB, DACZM, Endocrinology
MRCVS Department of Conservation and Science
Adjunct Professor Lincoln Park Zoo
Large Animal Clinical Sciences Chicago, Illinois
Virginia-Maryland Regional College of Veterinary
Medicine Raymund F. Wack, DVM, MS, DACZM
Virginia Technical University Senior Veterinarian
Blacksburg, Virginia Wildlife Health Center
Adjunct Assistant Professor University of California at Davis
Department of Small Clinical Sciences Davis, California
College of Veterinary Medicine Staff Veterinarian
University of Tennessee Sacramento Zoo
Knoxville, Tennessee Sacramento, California
Judy St. Leger, DVM Christian Walzer, DrMedVet
Sea World San Diego Professor for Wildlife Medicine and In-situ
San Diego, California Conservation
Research Institute for Wildlife Ecology
Cynthia E. Stringfield, DVM, BS University of Veterinary Medicine
Professor Vienna, Austria
Exotic Animal Training Management/Animal Science
Moorpark College Martha Weber, DVM
Moorpark, California Staff Veterinarian
Staff Veterinarian St. Louis Zoo
America’s Teaching Zoo at Moorpark College St. Louis, Missouri
Moorpark, California
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Preface
With the sixth volume of Zoo and Wild Animal are all subject to pressures from the same or similar
Medicine we return to the Current Veterinary Therapy infectious agents and environmental stresses. All ani-
format. Topics were selected to address current issues. mals interrelate with one another. Determining how
Authors were selected for their experience and disease agents circulate in the world requires a holistic
expertise in captive wild animal medicine or in the approach to medicine.
field with free-ranging wildlife. The medical management of species or groups of
The sixth volume reflects a world view of some animals that may not have been thoroughly discussed
of the special challenges that face wild-animal veteri- elsewhere includes bustards and chamois. A topic of
narians as they seek to assist in the preservation and vital concern to the world is the potential for a pan-
conservation of wild animals. Countries represented demic of avian influenza to wreak havoc on humans
include Australia, Austria, Canada, China, England, and domestic and wild animal populations. The avian
Germany, Mexico, The Netherlands, Northern Ireland, chapter has been continually updated throughout the
Scotland, United Arab Emirates, and the United States. production of this book to keep current on what is
Some of the topics address current problems, such as happening worldwide with avian influenza.
chronic wasting disease in cervids and tuberculosis in This volume discusses animal medical management
free-ranging deer and elephants. Other topics describe of selected species in all the major vertebrate groups. It
newly emerging or newly recognized diseases,such as is hoped that there will be chapters of interest to all
paramyxovirus in bats and protozoal encephalitis in readers who are concerned about the preservation and
marine mammals. conservation of the world’s fauna.
One topic that is addressed and needs to be con-
sidered by all medical professionals is the growing Murray E. Fowler
awareness that wildlife, domestic animals, and humans R. Eric Miller
ix
Frontmatter-X4047.qxd 8/13/07 10:26 AM Page xi
Acknowledgments and
Dedication
Our thanks to the more than 50 authors who con- Once again, we thank our wives, Audrey and Mary
tributed 57 topics to the sixth volume of Zoo and Wild Jean, for vocal and moral support while we took time
Animal Medicine. This is especially significant because away from family activities to complete the task of
all of the royalties support research for wild animals, editing and bringing it all together.
with none going to the authors or editors. Wild This volume is dedicated to all veterinarians who
animals deserve our support. Thanks are also due to use their time, talents, expertise, and finances to care
the many researchers who are gathering data on the for and study wild animals throughout the world.
biology and medicine of wild animals.
Acknowledgment and thanks are expressed to the
institutions that supported the authors as they com-
pleted their writing tasks.
xi
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1
C H A P T E R
West Nile Virus in Birds
and Mammals
DOMINIC TRAVIS
ETIOLOGY WNV was first found in North America in New
York City in humans, equines, and free-ranging and
West Nile virus (WNV) is an arthropod-borne virus captive wildlife in 1999.7,40,58,71 Since 1999 in the U.S.,
(arbovirus) in the family Flaviviridae, genus Flavivirus— more than 20,000 humans have been infected, causing
Japanese encephalitis antigenic complex—that includes more than 700 deaths, and more than 23,000 equine
Alfuy, Cacipacore, Japanese encephalitis, Koutango, cases and hundreds of thousands of avian cases have
Kunjin, Murray Valley encephalitis, St. Louis been reported. Most cases occur in North America
encephalitis, Rocio, Stratford, Usutu, West Nile, and during the summer and fall between July and October,
Yaounde viruses. Flaviviruses share a common size with peaks in August and September. Spread across
(40-60 nm), symmetry (enveloped, icosahedral nucleo- North America to all 48 contiguous states and seven
capsid), nucleic acid (positive-sense, single-stranded Canadian provinces has been documented in twice-
RNAof ~10,000-11,000 bases), and appearance on elec- weekly summary reports available on the U.S. Centers
tron microscopy. The close antigenic relationship of for Disease Control and Prevention (CDC) World Wide
the flaviviruses, particularly those belonging to the Web site* and by interactive maps collated by the U.S.
Japanese encephalitis complex, accounts for the cross- Geologic Survey.† In Canada, Health Canada summa-
reactions observed in diagnostic serologic assays.31 rizes WNV activity.‡Since 1999, surveillance data have
shown WNV activity in the Cayman Islands in 2001
(CDC); birds in Jamaica23 and Guadeloupe64 in 2002;
HISTORY AND DISTRIBUTION horses, humans, and wildlife in Mexico in 20026,24,49;
and birds in the Dominican Republic in 200341 and in
WNV has been described in Africa, Europe, the Puerto Rico and El Salvador in 2004.17
Middle East, West and Central Asia, Oceania (subtype
Kunjin), and most recently in the Western Hemisphere.
It was first isolated from a febrile adult woman in TRANSMISSION
the West Nile District of Uganda in 1937, and its
ecology was first characterized in Egypt in the 1950s. The arboviral encephalitides are zoonotic, being main-
The virus became recognized as a cause of severe tained in complex life cycles involving a nonhuman
human meningitis or encephalitis in Israel in 1957. primary vertebrate host and a primary arthropod
Equine disease was first noted in Egypt and France vector. Transmission occurs between susceptible verte-
in the early 1960s.33,40,57 Recent outbreaks of WNV brate hosts by blood-feeding arthropod mosquitoes,
encephalitis in humans have occurred in Algeria in sand flies, ceratopogonids, “no-see-ums,” and ticks.1,2,48,68
1994, Romania in 1996–1997, the Czech Republic Infection usually occurs as a result of a mosquito bite
in 1997, the Democratic Republic of the Congo in while taking a blood meal. Normal transmission cycles
1998, Russia in 1999, the United States (U.S.) in usually remain undetected until humans or other
1999–2003,7,10,19,58 and Israel in 2000.33 Epizootics have mammals become “accidentally” infected, potentially
occurred in horses around the Mediterranean
(Morocco in 1996, Italy in 1998, France in 2000),57 and
in the U.S. in 1999–2001.61,78 A thorough review of *http://www.cdc.gov/ncidod/dvbid/westnile/surv&control.
htm.
pre–North American WNV ecologic history was pub- †http://westnilemaps.usgs.gov/index.html.
lished by Komar.40 ‡http://www.hc-sc.gc.ca/english/westnile/.
2
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West Nile Virus in Birds and Mammals 3
as the result of some ecologic change. Humans and INTRODUCTION INTO WESTERN
domestic animals may develop clinical illness but HEMISPHERE
usually are incidental or “dead-end” hosts because
they do not produce significant viremia and thus The WNV strain first identified in New York was
do not contribute significantly to the transmission closely related to that recently isolated in Israel.33,46
cycle. Although the route of introduction is not known,
Since 1999, more than 60 separate species of hypotheses include release of infected vectors or hosts
mosquito have been positive (virus isolated, RNA or through international commerce or travel. Geographic
antigen detected) through national surveillance.* spread via introduction through migratory birds has
Although not all these are competent vectors, the pre- been hypothesized51,65,66 worldwide but is unlikely in
dominant species testing positive are Culex spp. The the case of introduction into North America. Aquanti-
discovery that hybrid Culex mosquitoes sometimes tative risk assessment of pathways by which WNV
feed on both humans and birds resulted in a focus could reach Hawaii suggests that the most viable hosts
on potential “bridge vectors.”27 One risk assessment for introduction are mosquitoes, rather than birds or
of mosquito feeding characteristics identified Culex other hosts. Viable routes of introduction include
pipiens and C. restuans as the most competent vectors transfer of infected hosts via plane or boat, and intro-
for humans.37 A 5-year analysis of mosquito data in duction through migratory birds could not be quan-
Connecticut revealed that Culex spp. were the most tified in this case.36
prevalent carriers from July to September, playing a
roll in early-season enzootic transmission and late-
season epizootic amplification in wild birds. Culex DIAGNOSIS
restuanswas most prevalent in June and July and may
play an important role in enzootic transmission and Cases are confirmed by combining clinical and labo-
amplification in wild birds early in the season. Culiseta ratory criteria. Standard clinical and laboratory case
melanura was found to be the major orniphilic species definitions have been derived for humans7,9,30,52,63 and
and may play a major role in amplification among are updated periodically on the CDC website.*
birds. Aedes vexansmay play a significant role in trans- Arboviral infections may be asymptomatic or may
mission to mammals.2 result in febrile illnesses of variable severity sometimes
Other, non–arthropod-borne routes of transmission associated with central nervous system (CNS) involve-
have been reported. New transmission routes in ment (aseptic meningitis, myelitis, and encephalitis).
humans include infection through contaminated blood Arboviral meningitis is usually characterized by fever,
products and transfusion13,63 and organ transplanta- headache, stiff neck, and pleocytosis in cerebrospinal
tion,14maternal transmission through breast milk and fluid (CSF). Arboviral myelitisis usually characterized
intrauterine transmission,12 and occupational expo- by fever and acute paresis or flaccid paralysis. Arboviral
sure through laboratory “sharps.”11 Experimentally, encephalitisis usually characterized by fever, headache,
infection has been demonstrated after oral exposure and altered mental status ranging from confusion to
in cats fed infected mice and birds.3,42 Oral exposure coma with or without additional signs of brain dysfunc-
to horse meat is the hypothesized route of transmis- tion. Nonneuroinvasive syndromes include myocarditis,
sion for infected alligators.55 Fecal shedding was pancreatitis, or hepatitis. In addition, arboviral infec-
identified as a potential route of transmission after tions may cause febrile illnesses (“West Nile fever”)
experimental direct transmission between cage mates with headache, myalgias, arthralgias, and sometimes
in crows (Corvus brachyrhynchos), blue jays (Cyanocitta accompanied by skin rash or lymphadenopathy.
cristata),black-billed magpies (Pica pica),and ring-billed Laboratory confirmation consists of one of the
gulls(Larus delawarensis).42,54Experimental and natural following criteria:
direct transmission also occurred between geese.4,75
The importance of these transmission routes is 1. Fourfold or greater increase in virus-specific serum
unknown but thought to be of secondary significance antibody titer.
compared with arthropod-borne transmission for 2. Isolation of virus from, or demonstration of specific
amplification and spread of the disease. viral antigen or genomic sequences in, tissue, blood,
CSF, or other body fluid.
*http://www.cdc.gov/ncidod/dvbid/westnile/ mosquitoSpecies. *http://www.cdc.gov/epo/dphsi/casedef/arboviral_current.
htm, accessed January 2006. htm, accessed January 2006.
Ch01-X4047.qxd 8/9/07 11:36 AM Page 4
4 CHAPTER1
3. Virus-specific immunoglobulin M (IgM) antibodies which may limit its use in many laboratories. IgM-
demonstrated in CSF by antibody-capture enzyme capture enzyme-linked immunosorbent assays (ELISAs)
immunoassay (EIA). have been developed for humans, equines, canines,
4. Virus-specific IgM antibodies demonstrated in serum and chickens and are useful for determining recent
by antibody-capture EIAand confirmed by demon- exposure to the virus.30The IgM ELISAmay be used as
stration of virus-specific serum immunoglobulin G a screening test, with PRNT performed to differentiate
(IgG) antibodies in the same or a later specimen by between St. Louis encephalitis and WNV as confirma-
another serologic assay (e.g., neutralization or tion. A blocking ELISA was developed for broad
hemagglutination inhibition). species use and is used to determine the origin of
antibody reactivity. A broadly reactive IgG-capture
Because closely related arboviruses exhibit sero- ELISA for bird serum has proved to be effective in
logic cross-reactivity, positive results of serologic tests a wide variety of birds but needs to be confirmed by
using antigens from a single arbovirus may be mis- PRNT.29,30 Antibody persistence in naturally and
leading, as in determining that antibodies detected experimentally exposed birds is variable. In a study
against St. Louis encephalitis virus are not the result of wild-caught rock pigeons (Columba livia) naturally
of an infection with West Nile (or dengue) virus, or infected with WNV, antibodies were found to
vice versa, in areas where both these viruses occur. In persist for longer than 15 months, as detected by
areas where WNV has circulated in the recent past, the ELISA and PRNT; maternal antibodies persisted for
coexistence of WNV-specific IgM antibody and illness an average of 27 days. Both tests outperformed the
in a given case may be coincidental and unrelated. HAI test.29
In those areas the testing of serially collected serum
specimens assumes added importance.
Most cases in animals are defined through isolation of HOST SUSCEPTIBILITY AND
the virus or detection of genetic material postmortem. CLINICAL PRESENTATION
Virus isolation is the “gold standard” but takes time,
which limits its use as a rapid surveillance tool. WNV has an extremely broad host range, replicating
Immunohistochemistry (IHC) and reverse-transcription, in birds, reptiles, amphibians, mammals, mosquitoes,
nested polymerase chain reaction (RT-PCR) tests are and ticks.30 Reviews of pathologic findings in various
used for detection of antigen, and an antigen-capture animal species are available.*
assay is also commercially available. No definitive list
exists for the most effective combination of tissue and
test methodology by species, but some optimal combi- Equine
nations have been reported.82,83In general, virus is best
detected in kidneys, brains, and hearts, as well as Cases of WNV disease in horses have been docu-
on oropharyngeal or cloacal swabs antemortem. The mented either by virus isolation or by detection of
success of IHC depends greatly on tissue selection WNV-neutralizing antibodies every year since 1999.
(heart, kidney, liver, lung); brain tissue is best for virus WNV infection in horses and other domestic equids
isolation; and RT-PCR is generally the most sensitive ranges from asymptomatic to fatal encephalitis.
test for all tissues, with few reported exceptions.* Common clinical signs include ataxia, incoordination,
Recently, feather pulp collected from bird carcasses lethargy, weakness, hind limb paresis, muscle tremors
has been shown to be useful in dead-bird surveillance and fasciculations, recumbency, and death. Experi-
when tested by RT-PCR.22 mental studies suggest that about 10% of infected
Standard antibody detection methods include horses develop clinical illness.41,61From 20% to 40% of
the hemaglutination inhibition (HAI) test and plaque equine WNV cases result in death or euthanasia.69,70,79,80
reduction neutralization test (PRNT). The HAI test Horses most likely become infected by the bite of
is hindered by nonspecific reactivity, whereas the infectious mosquitoes. In a review of 569 cases, the
PRNT is more specific and may differentiate between risk of death among nonvaccinated horses was 3 to
antibody reactivity from closely related viruses.30 In 16 times higher than in vaccinated horses after one or
the U.S. the PRNT requires biosafety level 3 facilities, two doses.70
*References 5, 16, 18, 21, 26, 28, 32, 38, 39, 46, 47, 50, 53,
*References 28, 30, 39, 41, 71, 83. 55, 60-62, 67, 69, 71, 75, 80, 81, 82, 83.
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West Nile Virus in Birds and Mammals 5
Avian species. Dogs and cats were found seropositive at
26% and 9%, respectively, in a large outbreak in
From 1999 to 2005, 284 bird species were reported to Louisiana.35 A Maltese terrier succumbed to WNV
the CDC’s WNV avian mortality database. Unlike in encephalitis in 2002.67 An Arctic wolf (Canis lupus)
traditional endemic areas, infected birds in North succumbed with clinical signs of vomiting, anorexia,
America have a spectrum of clinical outcomes ranging and ataxia before death; virus was demonstrated
from no disease to death. Because birds are the natural in the kidneys and cerebrum on necropsy.47 Two
reservoir species, they may act as dead-end hosts WNV-infected alpacas (Lama pacos) showed signs of
or viral amplifiers. Komar et al.42 showed that encephalitis, one severe and one mild. The severe case
Passeriformes and Charadriiformes such as the blue was euthanized after disease progressed to lateral
jay (C. cristata), common grackle (Quiscalus quiscula), recumbency and opisthotonos. The mild case recovered
house finch (Carpodacus mexicanus), American crow after 150 mLof llama plasma with antibodies against
(Corvus brachyrhynchos), and house sparrow (Passer WNV was administered intravenously on the first day
domesticus)are all competent reservoirs. Reisen et al.68 clinical signs were observed.45 Infection in four rein-
recently showed that Western scrub jays (Aphelocoma deer (Rangifer tarandus)resulted in encephalomyelitis,
coerulescens), house finches (C. mexicanus), and house representing the first known cases in Cervidae.62
sparrows (P. domesticus)have sufficiently high viremia A Barbary macaque (Macaca sylvanus) at the Toronto
to infect Culexmosquitoes. Zoo became infected with naturally acquired WNV
Some species, especially those of the family Corvidae, encephalitis and was euthanized.60 A polioen-
order Passeriformes, are highly susceptible.40,41,42 cephalomyelitis syndrome was observed in a harbor
Mortality has approached 100% in American crows (C. seal (Phoca vitulina).21 Small mammals, Eastern fox
brachyrhynchos)and loggerhead shrikes (Lanius ludovi- squirrels (Sciurus niger), gray squirrels (Sciurus caroli-
cianus migrans), causing potentially severe declines in nensis),a rabbit (Oryctolagus cuniculus),and an Eastern
the overall population in some areas.* Raptors are chipmunk (Tamias striatus) have all shown clinical
thought to be extremely susceptible, especially the signs and mortality associated with WNV infec-
family Stringidae.26,74,82Seroprevalence in free-ranging tion.32,38,43Morbidity and mortality occurred in farmed
raptor species has been documented from 2% to 88%, alligators (Alligator sp.) after being fed infected horse
suggesting wide ranges of exposure and susceptibility meat and in a captive crocodile monitor (Veranus sal-
in these species.74 One captive population in the epi- vadori) in North America with natural infection.
center of the original outbreak recorded a seropreva- Farmed crocodiles in Israel (Crocodylus niloticus) were
lence of 34% in all at-risk birds.50,71 A review of five seropositive after natural exposure.55,72,77
zoologic institutions in Kansas recorded disease in Serologic evidence of infection has been found
eight species of seven families in the face of emergence in many other captive and wild species, including
in the region.18 A North American zoologic surveil- black bears (Ursus americanus), marine mammals,
lance system identified serologic evidence in more and numerous genera of captive African and Asian
than 100 species from 2001 to 2005.76 In most species, mammals.25,50,71,77
common clinical signs included anorexia, weakness,
depression, weight loss, recumbency, and death with
no previous clinical signs of infection. Neurologic PREVENTION AND CONTROL
signs (ataxia, tremors, disorientation, circling, impaired
vision, abnormal head posture) have been widely Although WNV is most often transmitted by the bite
reported in most susceptible species as well.26,30,41,50,71 of infected mosquitoes, the virus may also be trans-
Hematologic abnormalities reported include leukocy- mitted through contact with infected animals, their
tosis and heterophilia, with infrequent monocytosis blood, or other tissues. Thus, laboratory, field, and
and reactive lyphocytes.18,50,71 clinical workers who handle tissues or fluids infected
with WNV or who perform necropsies are at risk of
WNV exposure. These workers include laboratory diag-
Other Species nosticians and technicians, pathologists, researchers,
veterinarians and their staff, wildlife rehabilitators,
In addition to equid and avian species, WNV has entomologists, ornithologists, wildlife biologists, zoo
caused clinical illness and mortality in many other and aviary curators, health care workers, emergency
response and public safety personnel, public health
*References 5, 8, 43, 53, 54, 81, 84. workers, and others in related occupations. To minimize
