Background Information
I am the Director of the USGS National Wildlife Health Center in Madison, Wisconsin, which provides federal and state resource management agencies across the nation with information, technical assistance, and research on national and international wildlife disease and health issues. Our Center monitors disease and assesses the impact of disease on wildlife populations; defines ecological relationships leading to the occurrence of disease in free ranging wildlife; provides on site investigation and control for wildlife disease emergencies; and provides guidance, training, and technical information for reducing wildlife losses when outbreaks occur. Current investigations include the causes of deformities and disease in amphibians; tumors in green sea turtles; the mysterious eagle mortality in Arkansas and elsewhere; and management strategies to control avian botulism and avian cholera in migratory waterfowl. Major studies are underway at the Salton Sea in California.
The staff provides technical support, knowledgeable guidance, and timely intervention to wildlife managers who are regularly confronted with sick and dead wild animals, frequently on a large scale. Due to the mobility of wildlife and the potential for the spread of disease, timely and accurate determination of the causes of wildlife illness and death is a prerequisite to achieving effective disease control and prevention. The expertise and resources of our disease diagnostic laboratory are crucial in providing this rapid response to wildlife mortality events.
West Nile Virus Background: The West Nile virus (WNV) is a mosquito-borne virus belonging to the Flavivirus taxonomic group that also includes St. Louis encephalitis virus, Kunjin virus, Murray Valley encephalitis virus, and others. These viruses are structurally and genetically similar making them difficult to separate by traditional virological and serological procedures. West Nile virus was first isolated in the West Nile district of Uganda in 1937 and subsequently isolated in Egypt in the early 1950s. The normal distribution of West Nile virus is Africa, the Middle East, western Asia, and Europe. In September, investigators discovered West Nile virus in the New York City area. This is the first known occurrence of this virus in the Western Hemisphere.
West Nile Virus can infect a wide variety of vertebrate animals, but birds are the primary natural hosts for this virus. It can be transmitted from birds to other birds and animals, including humans, through the bite of mosquitoes. Human epidemics were first recorded in Israel during 1950-1954 and later in parts of Africa and Europe. An epidemic occurred in Volgograd, Russia, during the summer of 1999. The virus usually produces either asymptomatic infection or mild fever in humans, but WNV has not been documented to cause epizootics (epidemics) in birds throughout its known geographic range. Natural antibody to WNV was commonly found in crows and other birds in Africa and Israel suggesting asymptomatic or mild infection usually occurs in those regions. St. Louis encephalitis virus in the United States commonly infects wild birds which can become reservoirs for the virus, but are normally not harmed by it. Therefore, the disease in birds in the New York area producing high mortality in crows and other bird species is unusual for these viruses suggesting that this introduced West Nile virus is more virulent to the native bird species or represents a new virulent strain of the virus. Resident and migratory birds may play an important role in natural transmission cycles of this virus and in maintaining the virus in the United States. Migratory birds could also disseminate the virus to new states outside of the New York City area. Enhanced monitoring through surveillance for early and rapid detection of WNV in those states outside of the affected area will be important to guide prevention measures.
Current Status of West Nile Virus in the United States
West Nile virus infection has been detected in humans in the New York City area only; in mosquitoes in New York, Connecticut, and New Jersey; and in birds (mostly crows) in New York, Connecticut, New Jersey, and one crow in Baltimore, Maryland. Birds testing positive for the virus have been reported almost entirely from within about a 50-mile radius of the initial affected area in New York City except for one crow from upstate New York, one from southern New Jersey, and the crow from Maryland. As of November 5, 1999, 392 birds have been tested for WNV by the Centers for Disease Control and Prevention (CDC) and 192 were positive. The virus has infected 18 species of birds, including exotic and native birds at zoos, and about four species of mosquitoes. Mortality from the virus has been predominantly in American and fish crows. Bird mortality has been reported in multiple states in the region and may represent thousands of birds. The finding of the infected crow in Maryland extends the affected area a considerable distance southward. It is unknown if this crow was infected in the New York City area and moved to Baltimore before it died or if it was infected locally in Maryland. USGS and CDC have increased sampling of wildlife in that area in cooperation with the Maryland and Delaware wildlife agencies to determine if local transmission has occurred. Enhance wildlife surveillance for detection of West Nile virus by USGS, CDC, U.S. Department of Agriculture (USDA), and other agencies is continuing and will expand to other Atlantic and Gulf Coast states. These agencies are continuing to collaborate on enhanced surveillance and what specific surveillance methods are needed for each region.
Efforts are underway by CDC to determine the source of the virus by conducting molecular comparisons with known strains from other continents. Several federal and state agencies and private groups, including USGS are searching for stored human and animal specimens to test for West Nile virus or antibody to determine if the virus was present before 1999. Results from these investigations should provide more insight into how, where, and when the virus was introduced.
Additional Research Needed for Wildlife
Additional wildlife research is needed to determine the principal wildlife host species of West Nile virus in the U.S., and to determine if wildlife species can maintain the virus in New York and other states and serve as an overwintering source for resurgence next summer. We need to determine the best wildlife species to be used as sentinels for detection of West Nile virus activity in surveillance programs. We need to determine the current distribution of the virus in bird populations in the eastern U.S., and if the virus distribution has been expanded by migratory birds. We want to know the impact of West Nile virus on bird populations, particularly for the American and fish crow species and to determine the susceptibility of other native wildlife species to this virus. Finally, we need to determine if threatened and endangered species and zoo animals can be protected from exposure and infection.
USGS Collaboration and Interaction with Other Agencies
USGS regularly interacts with other federal and state agencies in providing diagnostic assistance and consultations on wildlife diseases nationwide. That interaction brought our lab into the West Nile virus investigation when we were asked to provide diagnostic assistance on crow mortality to the New York State Department of Environmental Conservation. I was personally contacted early in the outbreak for information and advice because of my expertise in avian mosquito-borne diseases, specifically St. Louis encephalitis. I also have experience from working with three of the federal agencies involved in the investigation. USGS and CDC quickly established collaborative efforts to investigate the avian aspects of West Nile virus in the New York City area. This effort led to increased collaboration with CDC on multi-state surveillance for detection of the virus in birds. USGS later established further surveillance efforts with USDA's Wildlife Services and Veterinary Services. We increased our cooperative interactions with state agencies. We are using their staff to assist with bird sample collections. We are providing increased diagnostic support and an avian pathologist to assist at the New York state laboratory.
USGS was successful in establishing and maintaining these collaborations and cooperative efforts with the federal and state agencies and they are working well. The combined expertise and resources of each agency are complementary to each other. This combined investigation by three federal agencies will far exceed any effort that could have been accomplished alone by any one of the agencies. This completes my statement. I will be pleased to answer any questions you may have.