Why was one 'Ebola dog' killed and the other saved?

TL;DR version: No one really knows

The dog belonging to Spanish Ebola patient Teresa Romero Ramos, Excalibur, was put down last week for fears it may transmit the disease, while Bentley, the dog belonging to US patient Nina Pham, was rehoused and given a fresh batch of toys.

Excalibur being put down came despite a petition signed by 390,000 people, but why was the Spanish dog euthanised while its American counterpart was spared?

What do the official guidelines say?

There are no guidelines on how to treat Ebola in domestic animals in the US. As the Washington Post reports, the Centre for Disease Control & Prevention (CDC) is currently working on new guidelines on how to treat Ebola in pets.

Can dogs actually get Ebola?

There's no definitive answer. Although, after an outbreak of the virus in Gabon in 2001-02 one major study suggested that dogs could get Ebola but didn't show any symptoms and it was unclear if they could transmit.

What do we know about transmission from other animals to humans?

We do know that other mammals transmit the disease to humans. Ebola is a "zoonotic" disease, one that spreads between animals and humans. In fact, that was how the disease was first transferred to the human population - with fruit bats thought to be the most likely cause.

So what happens to Bentley now?

Spanish authorities put Excalibur down because there was an unknown risk, however small it may have been, that the dog could transmit the disease to other humans. But because we do not know if dogs can transmit the disease US authorities cannot really estimate when it will be safe to release Pham's dog from quarantine. Which leaves them in an interesting Catch-22 situation. Meanwhile, the two women are continuing to be treated.

More: The fate of Excalibur and everything you need to know about Ebola