After Spanish authorities ordered the euthanization of the dog of an Ebola patient on Wednesday, questions emerged over whether the action was necessary. Can Ebola actually be transmitted from a dog to a human?

Possibly, according to an academic study of dogs exposed to the virus.

While the case has animal activists up in arms, it has also caused confusion over the protocol for domestic animals who come into contact with Ebola. Some, including the dog’s owner, have called for him to be quarantined, while others see the pooch as a public health threat.

Spanish health officials have said the killing of the dog was a preventative measure, to ensure that he does not spread the disease. The action raised one key question: Can a dog that is exposed to Ebola be a threat to human health?

Although academic research on Ebola in canines is limited, a 2005 study published in the Centers for Disease Control and Prevention’s Emerging Infectious Diseases journal suggests that dogs are susceptible to the virus, just like humans.

“Given the frequency of contact between humans and domestic dogs, canine Ebola infection much be considered as a potential risk factor for human infection and virus spread,” the study noted. “Human infection could occur through licking, biting or grooming. “

Conducted during an Ebola outbreak in Gabon in 2001 and 2002, the study focused on dogs who were highly exposed to Ebola by eating infected dead animals or coming into contact with humans carrying the virus.

Forty of 159 dogs tested during the study in Gabon had detectable levels of Ebola in their blood, indicating an infection or anti-body stimulation. Of the dogs from villages where both animals and humans had Ebola, 31.8% were discovered to be infected with the virus, as seen in the following chart. (Note: Dogs in France were used as the control group in the study.)

“These findings strongly suggest that dogs can be infected by Ebola virus, and that some pet dogs living in affected areas were infected during the 2001-2002 human Ebola virus outbreak,” the study concluded.

It also pointed out that noticeable symptoms of Ebola did not develop in any of the dogs in the study, which supports the notion that they were asymptomatic. However, this does not mean that the dogs cannot transmit the disease. Even dogs exhibiting no symptoms of Ebola “may excrete infectious viral particles in urine, feces and saliva for a short period before virus clearance”, which has been observed in other animals, according to the study.

While the study focused on dogs in villages in Gabon, it is important to note that those animals are typically not fed exclusively by their owners, and instead scavenge and hunt for food.

Sharon Curtis Granskog, a spokesperson for the American Veterinary Medical Association, told the Associated Press that the risk that dogs might spread Ebola is very small in the U.S. or other places where dogs aren’t near corpses, or are eating infected animals.

While the deadly Ebola virus is known to cause widespread infections in humans and other primates , its effect on other animals is unclear, the BBC reported.

The generalized guidelines on Ebola prevention issued by the CDC does not explore the possibility for domesticated animals to contract or transmit the disease. According to the guidelines, Ebola can be spread to humans if they come into contact with infected animals. However, it does not specifically mention whether dogs can transmit the virus to humans:

Ebola is spread through direct, unprotected contact with the blood or body fluids of an infected symptomatic person, contact with the body of someone who has died from Ebola, contact with infected animals and exposure to objects (such as needles) that have been contaminated with infected blood or other body fluids and tissues.

Human-to-human transmission does not occur until people exhibit symptoms of the disease, so it is unclear if dogs would have to be exhibiting Ebola symptoms in order to pass on the virus.

According to a statement from the Texas Department of State Health Services, which was responsible for coordinating the response to the first U.S. Ebola patient in Dallas, the CDC is working to establish guidelines for dealing with pets of Ebola patients in the U.S.

Studies have shown that dogs can have an immune response to Ebola, but there have been no reports of pet dogs or cats becoming sick with Ebola or of passing the disease to other animals or people. In a situation where there is a dog or cat in the home of an Ebola patient, CDC recommends public health officials evaluate the animal’s risk of exposure. And, if it is determined that the pet had exposure (consistent with CDC’s definition of exposure for people, public health officials should recommend that the pet be monitored for a period of 21 days. This is an unprecedented outbreak and there are still many details to be worked out. CDC is working with the American Veterinary Medical Association to look at this issue and develop guidance for the U.S. pet population.

People for the Ethical Treatment of Animals criticized Spain’s decision to euthanize the dog.

“PETA is not aware of any evidence that dogs can transmit Ebola, but even if they can, it seems contrary, unfair and upsetting that while all efforts are being made to save the afflicted woman, none will be made to save Excalibur, a dog who has not contracted the disease and may indeed be unable to do so,” said PETA UK director Mimi Bekhechi. “If the woman survives, her heart will be broken to find that authorities have killed a beloved member of her family.”

Mashable reached out to the CDC to determine if the U.S. has a protocol for dealing with domesticated animals of Ebola patients, but did not receive an immediate response.

Check out the study, below:

Ebola Virus Antibody Prevalence in Dogs and Human Risk by Brian Ries

Have something to add to this story? Share it in the comments.