The Institutional Implications of West Nile Virus
American Association of Zoo Veterinarians Conference 2000
Robert A. Cook1, VMD; Bonnie Raphael2, DVM, DACZM; Paul P. Calle2, VMD, DACZM; Michael Linn3, DVM; Tracy Clippinger2, DVM, DACZM; Patrick Thomas4, PhD; Tracey McNamara3, DVM, DACVP
1Wildlife Health Sciences, Wildlife Conservation Society, Bronx, NY, USA, 2Department of Clinical Care, Wildlife Conservation Society, Bronx, NY, USA, 3Department of Pathology, Wildlife Conservation Society, Bronx, NY, USA, 4Department of Mammalogy, Wildlife Conservation Society, Bronx, NY, USA



In August 1999 the Wildlife Conservation Society’s (WCS) Health Sciences staff became concerned about an increasing number of reports of wild crow deaths throughout the New York City (NYC) region. On 12 August 1999, WCS submitted wild crow specimens to the Department of Environmental Conservation’s (DEC) Wildlife Pathology Unit (WPU). Initial investigations by the DEC revealed no common cause of death between the crows. WCS pathologists, led by Dr. Tracey McNamara, discovered consistent findings of myocarditis, calvarial hemorrhage and subtle brain lesions. Subsequently, Bronx Zoo (BZ) birds began to die on 10 August 1999 and these animals presented with similar lesions of myocarditis and encephalitis. On 3 September 1999, the Centers for Disease Control and Prevention (CDC) announced a human outbreak of St. Louis encephalitis in NYC. Health agencies initially made no link between avian and human disease, despite the temporal, clinical, and pathologic similarities. WCS pathologists were instrumental in prompting action at the state and federal level that resulted in the diagnosis of West Nile virus (WNV) in birds, and subsequently as the cause of human illnesses and deaths.

WNV was first isolated in the West Nile Province of Uganda in 1937.4 The virus has widespread distribution in Africa, West Asia, the Middle East, and occasionally causes epidemics in Europe that are thought to be initiated by viruses introduced by migrant birds.7 The NYC area outbreak was the first report of this disease in the Western Hemisphere and its discovery resulted in a marked media response. As this outbreak has moved from the diagnosis of an emerging disease, surveillance and control methods have been established and both the clinical and pathology staff have mobilized to assist in answering critical scientific questions. In addition, WCS responses have included tremendous time and resource commitments by the animal departments and communications staffs.

Responses to the Initial Findings

Concerns that the agent of this epornitic was a reportable disease not normally present in the region, nor a foreign animal disease, prompted contact with the New York State Department of Agriculture and Markets (NYS Ag & Mkt) and the U.S. Department of Agriculture (USDA) veterinarians. Initial contact was proactive and preliminary as no diagnosis had been made, but there were real and potentially alarming concerns. Early exchange of information with animal health regulatory agencies by WCS is standard and has fostered a high level of trust between the Wildlife Health staff and agency personnel. These agencies were very supportive and facilitated sample analysis at the National Veterinary Services Laboratory (NVSL).

WCS administration was informed of a potentially serious situation with additional progress updates.

WCS pathologists began expanded crow necropsy examinations. Communication was established with the CDC. They were unable to evaluate biomaterials due to pre-existing commitments to analyze samples related to the human outbreak of encephalitis. In addition, none of the Western Hemisphere flaviviral infections were known to cause avian mortalities.

The WCS Communications and Marketing Department (C&M) was apprised of the situation.

Avian movement (between WCS exhibits as well as from WCS to other institutions) was halted prior to a diagnosis due to the uncertain diagnosis and the potential for reportable disease involvement.

Meetings were held with WCS curatorial and husbandry staffs to apprise personnel of the potential severity of the situation as well as to develop and institute preventive and protective measures.

Responses to the Diagnosis

NVSL isolated, and via electron microscopy, identified a 40 nm diameter flaviviral type virion from materials submitted by WCS. Repeated communication with CDC resulted in their evaluation of previously submitted BZ bird samples.

Despite repeated requests, the confidentiality standards for human medical information were not extended to the veterinary patients, despite the fact that specific locations or species of the affected birds were not essential reporting factors.

The media response vastly exceeded expectations. WCS had requested CDC to keep the source of the samples anonymous. CDC’s initial press release misrepresented the sequence of events and did not recognize the valuable role of either NVSL or WCS. This resulted in press misinterpretations that erroneously linked the emergence of the WNV with the BZ collection. WCS C&M clarified the released information by creating a brief and accurate statement that correctly reflected events: “Wild crows died in July and August, then people became ill and died, and lastly zoo birds had died. All were infected by an insect vector, likely a species of mosquito.” Although initial media requests were addressed by a WCS C&M spokesperson, as more information became available and the requested scientific detail increased, Dr. McNamara became the WCS spokesperson.

Mosquito control measures were instituted at all NYC WCS parks through a contract with a licensed pest control company. No aerial spraying was conducted by WCS institutions. Efforts concentrated on focused ground spraying primarily utilizing resmethrin, a synthetic pyrethrin believed to be the safest option for the collections. In areas in which fish exposure was a concern, Malathion was selected as a safer option and was also applied in a very focused manner to minimize exposure of both collection animals and the public.

Further WCS staff informational meetings were held for those with animal or park responsibilities.

An intensive mosquito surveillance program was established at the BZ with the assistance of Dr. Durland Fish, an entomologist from the Yale School of Medicine. Light and CO2 mosquito traps as well as mosquito larval traps, were strategically placed throughout the 250 acre BZ grounds.

Through the efforts of WCS pathologists, scientific collaborations were established with numerous governmental laboratories. The U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) and other branches of the United States Army arranged for the loan of a portable biocontainment unit. This was utilized by WCS pathologists for necropsies, alleviating potential zoonotic disease exposure. The loan was made possible by prompt written support of the NYC Office of Emergency Management and the USDA Emergency Programs office. USAMRIID also performed WNV specific testing of tissues and blood samples. The USDA provided a skilled veterinary pathologist, Dr. Terry Wilson, to assist with wild crow necropsies. WCS provided support for the National Wildlife Health Laboratories vaccine and virus challenge studies of wild crows to determine both vaccine safety and efficacy.

The Department of Clinical Care conducted a large scale WNV serologic surveillance program of WCS birds and mammals. Over 400 animals were tested in the ensuing months, with samples analyzed by USAMRIID. A review of avian shipment records for summer 1999 was performed. All receiving institutions were informed of the WNV outbreak, and samples from these birds were requested from recipient institutions for serologic screening. All internationally imported birds arriving at WCS New York facilities in 1999 were also tested.

Over Winter Efforts

WCS continues to respond to regular media requests that have increased as mosquito season approached.

WCS hosted the West Nile Virus Action Workshop funded by the New York State Assembly. This 2.5-day meeting brought together leading United States experts in entomology, arbovirology, human and animal health to interact with local, state, and federal agency specialists. This workshop was closed to the press during working sessions. A separate, concurrent forum for special interest groups and concerned members of the public was provided for their input, and which were later addressed by the workshop participants as future action recommendations were developed. A workshop proceedings was produced and forwarded to participants to augment on-going planning efforts.

Potential mosquito over wintering sites were examined by WCS Animal Department staff along with Dr. Durland Fish. Control measures were instituted.

Retrospective Information

The epornitic of free-ranging birds, especially crows in NYC and surrounding regions affected thousands of individuals.1 Loss of captive bird specimens at the BZ and the Queens Wildlife Center (QZ) between 10 August 1999 and 23 September 1999 included the deaths of at least 27 birds, minimally representing 8 orders and 14 species.5 Twenty-five (25) privately owned domestic horses on Long Island were clinically ill with neurologic signs; 16 recovered and nine died.6 The 1999 WNV epidemic in the NYC metropolitan area resulted in 61 human cases (55 confirmed and six probable), including seven deaths.3 The New York WNV isolate was most closely related to an isolate from a dead goose in Israel in 1998.2

Preparations for Spring

A multi-departmental working group was established that represented all NY WCS institutions. Six response areas were addressed:

1.  Mosquito surveillance

2.  Mosquito control

3.  Collection animal movement

4.  Public relations and education including

a.  Television, radio and print

b.  School education programs

c.  Staff education programs

i.  Wetlands policy

ii.  Legal issues

Pathology Suite modifications- A permanent BL-3 safety hood was scheduled for May or June 2000 installation. The pathology staff was trained by Dr. Keith Steele of USAMRIID to perform a rapid immunohistochemical diagnostic test on potentially infected avian samples.

  • Criteria for avian movements between zoos were reviewed and finalized
  • Mosquito netting was scheduled for installation in May or June 2000 on key avian holding areas at the BZ and QZ
  • An employee and volunteer WNV education program was prepared for all parks. The focus included informational updates, plans for the coming season, personal protection steps, and mosquito habitat reduction efforts.
  • Mosquito larval biologic control, utilizing the introduction of fat-head minnows to permanent bodies of water, was instituted
  • Mosquito larvicides were distributed in potential mosquito breeding sites
  • WCS staff provided input to the development of New York State and NYC protocols. Relationships were established with regional laboratories developing WNV diagnostic tests
  • WCS C&M prepared draft press releases for a variety of potential scenarios

Further Considerations

The appearance of a new emerging disease threat to the Western Hemisphere in NYC, a media rich environment, resulted in news reports and public perceptions that greatly affected agency interactions, funding opportunities, and ultimately resource utilization. However, one fact appears clear: habitat destruction, environmental degradation, and disease will continue to have an increasing impact on the health of our world. Zoo and wildlife veterinarians are uniquely qualified to monitor the health of free-ranging and captive wild animals and have the opportunity to play a critical role in protecting both animals and people.


Appreciation is extended to Drs. Sharon Deem, Rose Manduca, and Marie Rush for their assistance in clinical and pathology studies. Also of particular note were the efforts of Histotechnologist Alfred Ngbokoli and the Veterinary Technicians: Pamela Manning, Peter Psillas, Nina Palmer, and Barbara Schwartz. We thank Drs. Jonathan Smith, Keith Steele, George Ludwig, T. Larsen, Tom Geisbert, and Maj. John Nerge of USAMRIID for their tremendous scientific collaborations. We thank NVSL for their support and in particular, Dr. Panigraphy who first isolated the virus and Mr. Gary Gustafson who performed the electron microscopic identification. We recognize the efforts of the CDC, especially Dr. R. Lanciotti for identifying the virus isolate. Many at the USDA provided support, of special note was Drs. Joseph Anelli of Emergency Programs. A special thanks goes to Drs. John Huntley and Susan Trock of the New York State Department of Agriculture and Markets for their support. Lastly, many others at WCS provided valuable support including Ms. Linda Corcoran and Ms. Alison Power of the WCS Communication and Marketing Department.

Literature Cited

1.  Anderson JF, Andreadis TG, Vossbrinck CR, Tirrell S, Wakem EM, French RA, et al. Isolation of West Nile virus from mosquitoes, crows, and a Cooper’s hawk in Connecticut. Science. 1999;286:2331–2333.

2.  Lanciotti RS, Roehrig JT, et al. Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States. Science. 1999;286:2333–2337.

3.  Morbidity and Mortality Weekly Report. Jan 21, 2000. Guidelines for surveillance, prevention, and control of West Nile virus infection-United States. 2000;49(02):25–28.

4.  Smithburn KC, Hughes TP, Burke AW, Paul JH. A neurotropic virus isolated from the blood of a native of Uganda. Am J Trop Med Hyg. 1940;20:471.

5.  Steele K. Pathology of West Nile virus in birds during the 1999 New York outbreak. In: Cook RA, ed. Proceedings of the West Nile Virus Action Workshop. 19–21 January, 2000, Tarrytown, NY. 2000:62.

6.  Trock SC. 2000. West Nile virus equine summary as of Jan 18th, 2000. In: Cook RA, ed. Proceedings of the West Nile Virus Action Workshop January 19–21, 2000, Tarrytown, NY. 2000:61.

7.  Tsai TF, Popovici F, Cernescu C, Campbell GL, Nedelcu NI. West Nile encephalitis epidemic in southeastern Romania. Lancet. 1998;352:767–771.


Speaker Information
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Robert A. Cook, VMD
Wildlife Health Sciences
Wildlife Conservation Society
Bronx, NY, USA

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