The National Surveillance System for West Nile Virus in Zoological Institutions
In June 2001, the Lincoln Park Zoo in Chicago co-hosted a meeting with the Centers for Disease Control and Prevention (CDC) that brought zoo professionals together with human and veterinary public health experts from local, state and federal agencies in order to discuss the design and implementation of a nationwide surveillance system for WNV in zoos accredited by the American Zoo and Aquarium Association (AZA). The result of this meeting was a set of guidelines entitled Surveillance for West Nile Virus in Zoological Institutions and the implementation of a 1-year pilot study. Objectives of the system are paradigm-based and twofold. Zoo veterinarians need access to affordable, reliable diagnostic testing in order to assess and protect the health of collection animals that often include endangered or threatened species. Public health officials recognize that zoos are ideal sentinels for monitoring the spread of zoonotic infectious diseases and that reliable data gathered from this system could be a useful addition to national surveillance.
The reporting structure for this system is unique. Participating institutions submit samples to the Cornell Animal Health Diagnostic Laboratory. To preserve confidentiality, test results are reported directly to the submitting institution and to the centralized zoo database at the Lincoln Park Zoo Davee Center of Veterinary Epidemiology. Submitting institutions are required to share results, both positives and negatives, with local public health officials; public health officials code zoo data for confidentiality and enter it as local data. Summary statistics are compiled and reported from the central zoo database at Lincoln Park Zoo.
The objective of phase I was to detect geographic spread of the virus. In phase I, we solicited samples from suspect animals (neurologic, systemically ill or undiagnosed problem in animals exposed to mosquitoes) in institutions along the front edge of the spread of disease in the United States. The objective of phase II was to detect positive animals in zoological institutions that would predate the first positive in the immediate area. Over the winter months of 2002, a retrospective serosurvey of institutions in the endemic area of the eastern United States was performed. The objective of phase III involves redirecting the system from surveillance, the detection of cases in previously negative areas, to monitoring trends in captive wildlife now that WNV is endemic throughout most of the United States.
As of December 2002, 120 of the institutions accredited by the American Zoo and Aquarium Association were full participants in the system. Participants were distributed over 41 states and the District of Colombia. Over 5,200 animals were tested at the Cornell University Veterinary Diagnostic Laboratory; of these, 77% were avian, 3% were equine, 19% were other mammals and 1% were reptile/amphibians. Over 754 different species were tested, and 11.5% of all animals tested were free-range wild animals (90% avian) found on zoo grounds. Animal histories were coded into six categories (serosurvey, suspect-live, found dead, other clinical signs, no information, vaccine titer check). Serosurvey (45%) and live or dead clinical suspects (25%) accounted for the majority of samples. A poorly designed submission form probably accounted for a high percentage of samples without histories (25%), and an increase in extra-label vaccine use in avian species accounted for 5% of the samples submitted.
Preliminary results as of December 2002 included 152 virus positives confirmed by RT-PCR and virus isolation. Seventy-four (49%) positives were wild animals (mostly crows) found on zoo grounds from seven institutions. Of the 78 collection animals from 14 institutions, 74 (95%) were avian representing 32 spp., and three were mammals (one gray squirrel, one addax, one alpaca). One reptile (crocodile monitor) was positive, representing the first WNV confirmed positive, clinically ill reptile with neurologic signs at that time. No zoo animal case was the first found in a nonendemic area (objective I), and no positive animal from a zoo predated confirmed viral activity in any endemic area (objective II). We are currently redesigning the system to accommodate objective III.
In the September 2000 GAO report, “West Nile Virus Outbreak—Lessons for Public Health Preparedness” (GAO/HEHS-00-180), investigators concluded that the WNV events illustrated “the value of communication between public and animal health communities, the latter including those dealing with domestic animals, wildlife, and other animals such as zoo animals.” However, they noted that although zoo animals had served as important sentinels for WNV, zoos were, by and large, “left out of the animal and public health paradigm.” This project was launched in an effort to bridge the gap between the zoo and public health communities and enhance national surveillance for WNV.
This program has: created/strengthened working relationships between zoos and local/state health officials for the detection/reporting of a zoonotic disease threat; provided data to the public health system by tapping into the strengths of the zoo community (veterinary expertise; routine pathology programs; medical records; serum/tissue banks; commitment to active disease surveillance year round); and provided a framework that may be applied to other biologic threats of concern.