PORTLAND (AP) – A University of Delaware professor has pleaded guilty to taking part in a scheme to smuggle a poultry virus from Saudi Arabia into this country to create a vaccine for it.

John Rosenberger, one of the world’s top researchers on avian diseases, collaborated with Maine Biological Laboratories in Winslow in its efforts to manufacture a vaccine, Assistant U.S. Attorney Toby Dilworth said.

Rosenberger pleaded guilty Wednesday in U.S. District Court to aiding and abetting the receipt and concealment of a smuggled poultry virus. His plea agreement calls for six months of house arrest and two years of probation. No sentencing date was set.

Four former executives of Maine Biological Laboratories pleaded guilty earlier this year to conspiracy, mail fraud and other federal charges in connection with the scheme. Authorities said the events, which took place in 1998 and 1999, put domestic chicken flocks at risk of contracting a potentially devastating disease.

The four executives, who are scheduled to be sentenced this fall, could face years in prison and hundreds of thousands of dollars in fines. Two other executives pleaded guilty last year to other federal charges linked to the case and received fines and probation sentences.

“The investigation is still ongoing and other charges may be brought,” Dilworth said Thursday.

The case began when an American veterinarian working for a large poultry producer in Saudi Arabia was concerned that chickens there were sick with what he suspected was avian influenza, according to prosecutors. To prevent Saudi authorities from learning about the outbreak, they said, a sample was smuggled into this country to Rosenberger in 1998.

Rosenberger knew that the virus had been brought into the country without the necessary permits and licenses but helped identify its type and test the sample vaccines that Maine Biological Laboratories eventually produced, prosecutors say.

Court documents say the scheme resulted in about $895,000 in sales for the company. Rosenberger did not receive any money or compensation from the Saudi poultry producer for his work, prosecutors say.

Neither Rosenberger nor his lawyer could be reached for comment Thursday. Dilworth said Rosenberger got involved because he was “loyal to some of the people involved,” including the American vet in Saudi Arabia. “He wanted to help him out.”

The University of Delaware had no previous knowledge of the case and Rosenberger’s involvement until contacted by a reporter Thursday, said Neil Thomas, a university spokesman.

Rosenberger, an award-winning researcher who has been with the university since 1972 and is chairman of its Department of Animal and Food Sciences, is on leave and will retire Jan. 1, university Provost Dan Rich said in a statement.