An outbreak of a duck plague that led to the deaths of more than 400 of the fowl at a state-run hatchery on Maryland's Eastern Shore and may have caused the deaths of about 50 ducks at a private shooting reserve nearby has state officials worried that the disease may spread to wild birds.

The disease, duck viral enteritis, has been limited to captive birds, but it is highly contagious and could quickly spread to wild birds, said Steven Snyder, a spokesman for the Maryland Forest, Park and Wildlife Service. Wild ducks often mix with captive ones because of the easy access to food, he said.

Officials are worried because of the large number of wild birds that migrate to the state for the winter.

"Maryland is without a doubt the most important over-winter estuary site on the East Coast, maybe in North America," Snyder said, adding that "we are doing everything we can to prevent the disease from spreading" to wild birds.

Scare devices have been placed around the public facility on Wye Island and the pond used by ducks is to be drained. Lime has been spread on the ground to reduce the acid level of the soil and make it difficult for the virus that causes the disease to grow, Snyder said.

The disease, which causes internal bleeding and severe diarrhea, did not affect the recent two-day "short hunting season," yesterday Snyder said.

He said the outbreak first was detected last month, when hundreds of ducks, including mallards, pintails, redheads and black ducks, died at the Wye Island facility, a temporary duck hatchery being used by the Forest, Park and Wildlife Service to augment Maryland's declining duck population.

Examiners from the Maryland Department of Agriculture and from the National Wildlife Health Laboratory in Madison, Wis., confirmed the diagnosis of duck plague, and 86 other birds at the hatchery were destroyed.

Snyder would not disclose the name of the private shooting reserve in Queen Anne's County, but said that lesions characteristic of the disease appeared on more than 50 mallards there. Officials will not know if it is duck plague until this week, he said.

Dr. Archibald Parks, a veterinarian with the Department of Agriculture, said that duck viral enteritis affects only ducks, geese and swans and cannot harm humans. It is transferred mainly through contact with a bird carrying the disease, as well as through contact with the food or feces of a carrier, he said, and it generally affects captive birds rather than wild birds.

"Any time you congregate birds in large numbers, they become susceptible to diseases that they ordinarily would not be," Parks said. "And if you keep them in close quarters -- look out."

Wild flocks usually number 30 to 100, he said, while as many as 2,000 birds can be confined together. There were about 500 birds at the Wye Island facility, he said.

Parks said the Wye Island outbreak is probably the largest number of birds to have died of duck plague in Maryland. Normally, the disease is limited to one flock, he said, so the possibility that more than one flock may be involved "worries everyone intensely."