The USGS National Wildlife Health Center in Madison, Wisconsin, today reported that it had detected the virus in cormorant samples taken from the inland sea during a recent die-off that has killed about1,600 of the black waterbirds to date. The laboratory cautioned that the particular strain of Newcastle virus in this outbreak has yet to be identified, so it is unknown at this time what risk its appearance in the Salton Sea poses to other birds or to domestic poultry.
Samples have been sent to the U.S. Department of Agriculture's National Veterinary Services Laboratory in Ames, Iowa, and analysis is already under way to characterize which of several strains of Newcastle disease caused the cormorant deaths. Certain varieties of Newcastle disease pose threats to domestic poultry, while other varieties pose only a minimal threat. Similar analysis of tissue samples is being performed by the State of California's Veterinary Diagnostic Laboratory in San Bernardino.
Newcastle disease was first identified in the United States in 1944 and is now found virtually worldwide. Human health implications from Newscastle disease virus are considered to be minimal.
As a part of today's announcement, the U.S. Fish and Wildlife Service and the USGS laboratory have recommended that wild birds not be transported beyond the Salton Sea area until such time as the viral strain has been identified. No sick or diseased birds will be taken outside the immediate area for rehabilitation; if birds require additional care and treatment, that will be performed locally at a site to be established by Salton Sea National Wildlife Refuge. The refuge advises private citizens to notify Fish and Wildlife Service staff in the area of any sick birds, but not to attempt to recover or move birds themselves. Also, the California Department of Fish and Game has declared the appearance of this virus in birds at the Salton Sea as an "incident" under its "incident command system," and will undertake efforts with its Federal counterpart agency to limit the spread of the disease.
Identification of the virus in cormorants occurs as wildlife biologists contend with other maladies affecting two other species of birds in sections of the remote 380-square-mile sea, which is the last stop in the United States for many species of birds migrating along the Pacific Flyway. Small numbers of deaths in brown and white pelicans, attributed to avian botulism, have been reported over the past 2 months, as well as undiagnosed deaths in eared grebes, another species of waterbird. Last year, the Salton Sea was the site of the largest recorded die-off of pelicans, diagnosed as avian botulism, a recurrent disease of birds in the wild.
In the current situation, deaths of nestlings in a cormorant and Caspian tern colony on Mullet Island in the Salton Sea were first reported in early May 1997. At that time, about 1,600 nestlings and young birds were found dead and no active nests remained on the island, though about 200 cormorants remained active in the waters surrounding the site, some of them showing signs of illness.
Review of clinical signs in ill cormorants and microscopic analyses performed by the USGS facility determined that the Salton Sea die-off was similar to that seen in die-offs of cormorants from Newcastle disease in the Great Lakes and St. Lawrence region in1990 and 1992 and in Saskatchewan in1995. The USGS laboratory and the Fish and Wildlife Service recently have urged wildlife biologists and natural resource managers in the United States and Canada to report instances of unusual neurological behavior in cormorants -- wing or leg paralysis or the inability to maintain balance -- to the Interior Department agencies or state fish and wildlife agencies for further investigation.
The doubled-crested cormorant is a common species of bird found throughout the United States, always associated with water and increasing in population in many places. The bird stands up to 30 inches tall and can frequently be seen on rocks and coastal outcroppings.