from the Field
West Nile Virus and Other Diseases Threatening Our Birds
We sat in the darkened auditorium, watching the grainy video footage play silently on the screen. "There are 16 crows," said the speaker softly. We watched the healthy birds flying and hopping in an enclosed laboratory with central perches of PVC pipe. "Seven were inoculated with the virus, nine are controls." We watched the birds move around and eat. A man in a space suit came into the room and changed the food and water. "Hmmm," said someone in the audience, "I thought it was transmitted by insects. That guy's wearing a lot of protection, but maybe it's routine for them."
Along with other Project Wildlife volunteers, I was attending a wildlife conference and watching a video showing the effects of the West Nile virus on American Crows. Like others in the auditorium I wondered if we would be attempting the rehabilitation of species that might be affected. Crows (and corvids in general) are highly susceptible, but the virus isn't choosy, having caused the deaths of over 70 species of birds: bitterns and blackbirds, cormorants and cowbirds, ducks, herons, hummingbirds and hawks have all died of it.
West Nile virus, first described in the West Nile region of Uganda in 1936, is one of many diseases infecting wildlife in the U.S. The list of disease outbreaks in the reports of the National Wildlife Health Center in Madison, Wisconsin, makes amazing reading with its thousands of wildlife deaths, mainly of birds.
Seven hundred Atlantic Brants died on the Edwin B. Forsythe National Wildlife Refuge in coastal New Jersey in the fall of 2000, their cause of death still undetermined. Thirteen Bald Eagles and numbers of American Coots died on 10 lakes in four southern states, most of avian vacuolar myelinopathy (AVM). One hundred seabirds died in Baldwin County, Alabama, cause so far undetermined. Seventeen hundred waterfowl in North Dakota died of botulism in five weeks, and an estimated 5000 Blue Jays and American and Fish Crows died in eleven eastern states between May and October 2000 of West Nile virus. Avian cholera, which affects birds in our own Salton Sea, killed over 11,000 birds in the first few months of 2000 in California alone.
These statistics are the sobering entries summarized from reports from the public, veterinarians, wildlife refuges, parks, and wildlife rehabilitators. Diagnoses are made by examination of carcasses and tissues shipped to the center. Undoubtedly other epidemics strike, unnoticed by people.
Back at the conference, the video continued, moving to day three, then four. One bird started to drag its legs along the floor, vainly flapping its wings. Its eyes blinked slowly, it gradually weakened, fluttered, and closed its eyes. Time of death was noted on screen; the guy in the space suit came in and removed the bird. Another crow began experiencing similar symptoms, followed by another. The speaker intoned, "all the inoculated crows but one died in four days, the healthy control crows showed signs of symptoms within 10 days, and all died in 14 days."
Bird diseases are generally neglected unless they affect the poultry industry, commercial farming, or human health. Duck plague or duck viral enteritis (DVE), a contagious herpesvirus affecting most species of waterfowl, was first reported in domestic ducks in 1967 in the duck-producing areas of Long Island. There is no treatment for DVE, but a vaccine is available for domestic ducks in commercial flocks or valuable zoo specimens. Sick or exposed wild birds are euthanized en masse to protect other wild populations and, ironically, to protect poultry operations. In 1973, 43,000 waterfowl (mostly Mallards) died of DVE at Lake Andes National Wildlife Refuge in South Dakota, while some years ago at Eastlake in Chula Vista many ducks were euthanized when the birds showed signs of the disease.
Avian cholera was first reported in wild waterfowl in the 1950s. When the severe form of the illness strikes, ducks have actually been seen falling dead from the sky. Outbreaks (such those at the Salton Sea) are managed by removal of carcasses to prevent scavenging and water contamination. This process also helps prevent the spread of botulism, a problem in shallow, warm, nutrient-rich water. Driving the remaining birds away from the area is controversial since it may stress the birds further and spread the infection.
In 1994, a strange neurologic disease killed a few Bald Eagles in Arkansas. By 1998, Bald Eagles and coots were dying of a similar disease at Strom Thurmond Lake on the Georgia/South Carolina border. Now found on 10 lakes in four southern states, the disease causes changes in brain tissue resembling those of BSE or "mad cow disease." In birds it is known as avian vacuolar myelinopathy (AVM). The disease has also been confirmed in a Killdeer, a Great Horned Owl, and two Canada Geese. Pathologists have not yet found the causative agent, and the disease spreads a little further each year.
The video ended. The speaker explained that there was still no information on how the viral infection had passed from crow to crow. Investigators were still attempting to determine whether it was transferred in the food, water, aerosolized droppings, or by contact. Mosquitoes were obviously not the sole means of transmission--a chilling thought to those of us who would be handling and possibly attempting to save some of these birds in our rehab centers.
It is ironic that many of the disease outbreaks take place at what are known as "refuges." Even in our own back yards we bird lovers may help spread certain diseases. Songbirds (particularly goldfinches and siskins) suffer outbreaks of salmonellosis, possibly because of contaminated bird feeders, and House Finches infected with Mycoplasma suffer conjunctivitis, blindness, sinusitis, and death. Treatments attempted in a rehabilitation center failed to cure the disease. Some birds remained carriers or relapsed after treatment. The disease is spreading from the eastern states across the U.S., and the Cornell Lab of Ornithology's Feederwatch program has helped monitor its spread.
What causes these disease outbreaks? Some suggest overcrowded, degraded habitats, migrants crowded in polluted coastal lagoons, ocean/global warming, or more UV radiation reaching the earth. And how do diseases reach our shores? A growing contributor has to be global trade (used tires incubating mosquito larvae brought from countries with humid climates), imports of pet birds, and people carrying all kinds of viruses from various parts of the world. Dirty bird feeders or contaminated bird baths spread bacterial infections locally.
One factor mentioned by the media during the start of the West Nile virus outbreak was the underfunding of the public health system and disease surveillance in New York. Neglect allowed a new mosquito-borne disease to establish itself in bird populations and spill over into other species. When the infection failed to die out the first winter as hoped, there was an attempt at control, but by then it was too late. The virus was already traveling in its feathered hosts through New Jersey, toward Cape May where the migrants fly through on their southward journey.
But birds fly west as well as south. The estimated time of arrival for West Nile virus in California is five years. The California Department of Health Services, other state health departments, the National Wildlife Health Center, and Centers for Disease Control are cooperating in a surveillance program, but attempted prevention and controls (insecticides) may not be popular with the public.
Our jays, crows, and ravens may be in a lot of trouble.
Meryl A. Faulkner
Web sites with more information on West Nile virus and other wildlife diseases: