 -- A mix breed dog named Excalibur that was euthanized today has set off a controversy about whether pets can carry and transmit the deadly Ebola virus to their owners or other humans.

Excalibur was owned by the Spanish nurse’s aide who is believed to be the first person to contract the disease outside of West Africa. Spanish authorities obtained a court order to euthanize the dog and incinerate its body as a precaution against the further spread of Ebola, despite a worldwide outcry.

The Spanish government said there is scientific evidence suggesting that dogs may transmit the virus to humans.

Research is scant on this subject but one 2005 study by French and African researchers observed dogs eating Ebola-infected dead animals during a 2002 outbreak in the African country of Gabon. Among the 159 dogs tested from highly infected areas, about 30 percent of the animals carried traces of Ebola antibodies in their blood, suggesting that they had been infected at some point.

However, none of the dogs got sick and the researchers could not say whether the dogs transmitted Ebola to humans. It isn’t known if Excalibur had ingested any infected biological material such as blood, feces or vomit.

Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said in a news conference Tuesday that scientists had not identified dogs as a means of Ebola transmission.

“We know in rural areas of Africa, Ebola can infect mammals,” Frieden said, though he declined to comment specifically on the Spanish case.

Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center, said he couldn’t understand what Spanish authorities are thinking.

“There is no biological reason for the dog to be infected that we understand,” he explained. “Pets and other domesticated animals in rural areas have not played a role in Ebola transmission that we know of.”

Schaffner said that wild animals have definitely contributed to the spread of the virus, which has killed 3,500 people in this latest outbreak in West Africa. Fruit bats have been shown to infect great apes and jungle antelopes, he explained. When people in the area hunt and kill these animals for food, humans become infected from eating the meat of sick animals.

So far, dogs and pigs seem to be the only domesticated animals that can be infected by Ebola. A 2013 study found that infected pigs could transmit the Ebola virus to other pigs and macaques, a monkey species, though they couldn’t determine if there was any transfer to humans.

Among all this debate, Excalibur’s fate hung in the balance. There were over 300,000 signatures on a Change.org petition asking clemency for the dog, but to no avail.

Additional reporting by Anshu Abhat