The furor came amid questions about whether dogs can get and transmit the disease.
In the United States, a spokesman for the federal Centers for Disease Control and Prevention, Thomas Skinner, said Wednesday that studies had shown that dogs can have an immune response to Ebola, meaning that they can become infected. But he said there had been no reports of dogs or cats developing Ebola symptoms or passing the disease to other animals or to people.
The death of Excalibur, a 12-year-old rescue dog, was confirmed to reporters by Javier Rodríguez, an official from Madrid’s regional government, and the body is expected to be cremated.
The nurse’s husband had pleaded publicly with officials in Madrid to change their minds about euthanizing the dog. He told the Spanish newspaper El Mundo that there was no indication that Excalibur had been infected with Ebola. The nurse has been identified as María Teresa Romero Ramos.
The fate of the dog ignited a frenzy online. More than 350,000 people signed the petition to save his life. By comparison, about 150,000 people have signed a petition urging the Food and Drug Administration to fast-track research on a potential vaccine and treatment for Ebola.
Twitter erupted, with pleas in both English and Spanish to save Excalibur’s life.
Then, after Excalibur was euthanized, came tweets using the hashtag #RIPExcalibur.
Some also suggested that more attention was being focused on the dog than on Ebola’s human victims.
Nearly 4,000 people in West Africa have died during the current Ebola epidemic, and global health authories expect to see thousands more infections there. The Spanish nurse became the first person to become infected outside West Africa. The only case diagnosed in the United States has been that of a Liberian man who had traveled from Liberia to Dallas and died in a hospital there Wednesday. Three infected American aid workers were transferred from West Africa to American hospitals and treated successfully, and a freelance cameraman for NBC who became infected in Liberia has been transferred to a hospital in Nebraska, where he is undergoing treatment.
Mr. Skinner said the disease centers were recommending that Ebola patients with dogs or cats at home “evaluate the animal’s risk of exposure,” meaning they should assess how likely it is that the animal has ingested bodily fluids like blood, vomit and feces from the patient. If the animal has been exposed, it should be monitored for 21 days, the incubation period for the disease.
Mr. Skinner said the C.D.C. was working with the American Veterinary Medical Association to study the issue and develop guidance for pets in the United States.
In a 2005 study of dogs in Gabon done after an Ebola outbreak in 2001-02, researchers found that dogs can be infected with the virus, but that they show no symptoms.