EASTON -- An outbreak of avian cholera that has killed hundreds of sea ducks in the Chesapeake Bay this week could destroy tens of thousands of birds before it runs its course, state waterfowl experts said yesterday.
The highly contagious disease is lethal to waterfowl, capable of killing them six to 12 hours after exposure, but it is not considered to be a high-risk malady for people.
Teams of state Department of Natural Resources workers are combing the Chesapeake shoreline to collect contaminated duck carcasses in hopes of slowing the spread of the disease to other migratory birds.
But a dramatic die-off of waterfowl caused by the the highly infectious bacterium Pasteurella multocida apparently is under way and cannot be stopped.
"We've probably got dead birds all along the shoreline," said Larry Hindman, the state migratory bird program specialist.
"It's too early to tell the magnitude, and this thing could last two or three weeks. It's likely to become a major outbreak."
Wildlife specialists are trying to discover what causes the disease and how it can turn lethal so abruptly that, in past outbreaks, afflicted birds have fallen dead out of the sky.
"You don't like to see this happen," Mr. Hindman said. "In some ways we feel helpless, but this is one of those things that occurs to our birds now and then."
The disease is transmitted from bird to bird through ingestion of food or contaminated water. In some cases, scavengers, such as sea gulls, can spread the bacterium from open waters to land populated by other species of birds.
Mr. Hindman recommended that pets be kept away from areas where carcasses have been spotted. He also said anyone picking up a dead duck should wear plastic gloves, hold the carcass by the bill and place the bird inside a double-lined plastic bag. Carcasses should be burned or buried above mean high water.
Before an infected duck dies, it is lethargic, produces a clear liquid from its bill and often has diarrhea. Its discharges can contaminate surrounding areas and can be picked up easily by other waterfowl.
The genesis of the bacterium remains a mystery -- although wildlife biologists believe it may exist in small amounts in many mammals and birds -- and scientists are uncertain what prompts to turn fatal.
One theory is that the bacterium becomes activated when birds experience stressful environmental conditions such as harsh winters, said Dr. Kathy Converse, a disease specialist with the Department of the Interior's National Wildlife Health Research Center in Madison, Wis.
Dr. Converse said a die-off attributed to the disease occurred in the Chesapeake Bay area in 1970, beginning on Feb. 21 -- almost the identical date of this latest outbreak.
During March and April 1978, a massive die-off took place throughout the Chesapeake. Estimates of the number of birds killed range from 50,000 to 200,000. A smaller kill was recorded in 1975 near the Maryland-Virginia border.
vTC The winters of 1970 and 1978 were similar to current weather conditions, which may have contributed to the three outbreaks.
"It's a bacterium that likes cold weather," said Dr. Converse. Similar outbreaks have occurred this winter among migratory birds in northern California and Texas, she said.
So far, the disease has had the greatest effect on oldsquaws and scoters -- diving ducks that prefer to feed in deep waters -- although carcasses of goldeneye and bufflehead ducks also have been recovered, Mr. Hindman said.
Dead ducks were first spotted in Eastern Bay in Queen Anne's and Talbot counties on Sunday during a routine aerial survey of sea ducks by natural resources employees.
On Monday, several hundred dead birds were seen at the mouth of the Choptank River and along the Calvert County shore. Since then, dead waterfowl have been sighted from the vicinity of the Bay Bridge south to Smith Island and into Virginia. waters.