A puppy had to be put down by a Keighley vets due to a rabies alert.
The young Shih Tzu had been illegally imported into the UK.
Now Keighley Vets4Pets is warning people against the dangers of buying puppies online.
Veterinary surgeon Lara Clarkson said the Shih Tzu had been bought in good faith by a Keighley family, which travelled to Cambridgeshire to collect it after seeing an advert.
But when the pup was taken for a check-up on Sunday at Vets4Pets, in Hard Ings Road, a potential rabies risk was spotted.
It transpired the animal had been born in Lithuania and brought into this country under a false passport, without a proper vaccination.
"Rabies is a disease that kills people,” said Lara.
“Smuggling puppies into the country puts not just dogs in danger, but human lives too.
“Luckily we spotted the potential risk and isolated the puppy before it came into contact with any other dogs or people."
She added: “We strongly advise anyone thinking of getting a puppy to ask to see the rest of the litter and the puppy's mother, so you know for sure that it has been bred in this country.
“There is absolutely no need to be putting puppies through such a cruel experience when rehoming centres are crying out for owners to adopt a dog."