Avian flu has been detected in mallard ducks on a farm on the Eastern Shore, though officials caution that the low-pathogenic strain poses no risk to humans and is not the type that has been blamed for more than 140 deaths around the world.
Experts said the presence of the virus likely would not affect the $1.5 billion Delmarva poultry industry. Samples taken from chicken houses in the vicinity of where the ducks were found have tested negative for the virus, and though it is not known if the strain could infect chickens, such a scenario remains unlikely, they said.
It is the third case of avian flu infections detected in the U.S. since heightened testing began in April. Birds have tested positive in Michigan and Pennsylvania in recent weeks as a result of increased monitoring.
In the Maryland case, scientists detected the strain last week in nine fecal samples collected in early August from mallards at a Queen Anne's County farm. The samples were not immediately tested because the birds appeared healthy.
Though a strain of the avian flu, which in its high-pathogenic form is known as Asian H5N1, the recent findings were not the deadly version, said Guy Hohenhaus, the state veterinarian and chief of animal health for the Maryland Department of Agriculture.
"There is no evidence that this represents a human health problem," Hohenhaus said. "It's a run-of-the-mill duck problem with no human health implications."
Richard D. Slemons, a researcher with the Ohio State University team that collected the Maryland samples, said the virus attacks ducks in a digestive form but is a respiratory disease in domestic poultry. Only if the virus were able to circulate long enough among birds could it mutate to the higher strain - an unlikely event with stringent monitoring standards.
"These viruses go across the species barrier to domestic birds with great hesitancy," Slemons said. "Wild birds obviously are a reservoir for the type-A influenza virus, but it's a very different virus, and not as simple as it seems at first blush."
Poultry is the largest sector of agriculture in Maryland, which has about 1,200 chicken farms. Sales throughout Delmarva totaled $1.5 billion last year.
Maryland began strengthening its poultry regulations this year to guard against an outbreak of diseases such as avian flu to permit officials to rapidly respond to potential problems. The rules require the registration of all chicken flocks, along with pet birds including parakeets, canaries and parrots if there are four or more in a household.
An outbreak of avian flu in 2004 prompted the destruction of more than 300,000 chickens in the Delmarva region.
"Commercial poultry operations are designed to prevent exposure to other birds that may carry diseases," said Julie DeYoung, a spokeswoman for Perdue Farms in Salisbury. "This is further evidence of that monitoring and surveillance."
Fearing that the avian flu virus could mutate and become transmissible among humans and trigger a pandemic, Congress approved $29 million for additional monitoring last month. Samples from 75,000 to 100,000 wild birds a year are expected to be collected nationwide.
Sherrill Davison, an associate professor of avian medicine and pathology and director of the Laboratory of Avian Medicine and Pathology at the University of Pennsylvania School of Veterinary Medicine, said that mallard ducks are among the species most commonly found to have the avian influenza virus present in their system. But it is not the virulent strain has killed millions of birds and more than 140 people in Asia and the Middle East.
In August, a wild pair of mute swans nesting near Lake Erie became the first wildlife in this country to test positive for the non-lethal strain since 1986. On Saturday, federal agricultural officials said they found the strain in wild ducks in Crawford County, Pa.
Slemons, however, said he has personally encountered more than 400 birds with the lower-strain virus. "It's been detected only a few times, but we haven't looked very hard until now," he said.
On the Eastern Shore, fecal samples were collected Aug. 2 from resident wild ducks as part of a research project conducted by Ohio State University. Because there was no sign of illness in the birds, the samples were not given a high priority for testing and were received at an Iowa lab Aug. 24. A week later, tests came back positive for an H5N1 subtype.
Hohenhaus would not elaborate on where the Maryland waterfowl were located. He said the birds were on private property and the landowner, "out of civic duty," has allowed the state to test the birds periodically.
Some farms keep ducks as part of agriculture tourism that allows school groups to visit farms to see animals and learn about farming, he said. Others keep ducks to accommodate hunters.
John L. Chew Jr., Queen Anne's County's director of emergency management, said the county's large populations of poultry and migratory waterfowl magnify the risk of an outbreak. "Our risk is substantial given that environment," he said.
State Agriculture Secretary Lewis R. Riley said that properly cooked poultry meat remains safe to eat. He encouraged hunters, poultry growers, and bird owners to maintain a high level of biosecurity on farms and in their everyday handling of birds.
Recommendations included restricted access to poultry farms, wearing protective clothing and shoes in poultry houses, and keeping commercial poultry indoors and away from migratory birds.
Justin Fenton is a Sun reporter. Ted Shelsby is a free-lance writer.