A deadly bug that claims thousands of lives a year has been passed between two British dogs for the first time - forcing one to be put down.
Leishmaniasis is a tropical disease caused by a parasite spread through the bite of infected female sand flies.
It is behind up to 40,000 deaths annually, mainly among the poorest people in the world. It causes lesions, weight loss and kidney failure.
Dogs have been known to pick it up the infection after being wounded by an infected animal. But up to now, this has not been reported in the UK.
Cases to date have involved blood transfusions, breeding programmes or overseas travel to an area where the infection is endemic.
But a three year old neutered male shih tzu cross has been diagnosed with leishmaniosis in Hertfordshire.
It had been with its owner since a puppy and had none of the known risk factors. Dog to dog transmission is the most likely explanation.
Another dog in the household that had been imported from Spain had to be put down six months earlier after developing the disease.
Reporting the case in Vet Record, experts warned extra vigilance is now needed to guard against the spread of the infection.
The dog was taken to the Queen Mother Hospital for Animals at the Royal Veterinary College, Hatfield, Hertfordshire, with a three-week history of weight loss, vomiting and diarrhoea.
Dr Myles McKenna and colleagues said: "This dog had been in the owner's possession since it was a puppy, had no travel history outside of the UK and had never received a blood transfusion or been used for breeding.
"However, another dog in the household, that had been imported from Spain, had been euthanased six months previously due to severe leishmaniosis.
"Given the previous diagnosis of leishmaniosis in another dog in the same household, direct transmission between these dogs is considered the most likely route of infection."
To their knowledge, they said it is the first case of its kind in the UK and vets should consider leishmaniosis as a diagnosis when appropriate symptoms are present.
This applies even if the dog has no travel history, but might have been in contact with one that has travelled from an endemic area.
The researchers said: "In an era of increased foreign travel of dogs and increased importation of dogs to the UK, it is likely that the number of dogs positive for leishmaniosis will continue to increase.
"Infected dogs may present a risk to other dogs, even in the absence of natural vectors, as direct transmission between dogs is possible."
They said this is not the usual route for this potentially fatal infection which is zoonotic - meaning it can also be passed on to people.
They called for further research to determine the risk and potential routes of direct dog-to-dog transmission.
Dr McKenna added: "It is important to take note of this first reported case of likely dog-to-dog transmission of Leishmania infantum in the UK.
"Historically we had considered this to be a condition affecting dogs with a travel history to areas where Leishmania infantum is endemic.
"Dog-to-dog transmission in non-endemic areas has previously been reported, for example in the USA, but this case serves as a reminder to UK veterinary surgeons that we must be vigilant for conditions such as Leishmania in non-travelled dogs and that alternative transmission mechanisms do exist."
A recently published letter in the same journal revealed a second case diagnosed in another dog with no obvious risk factors - in a different part of the UK.
Vets said the three year-old fully vaccinated male neutered English pointer was struck down even though it had never travelled beyond the borders of Essex, where it lived.
But its owners had lived in Spain and visited the Jalon Valley, between Alicante and Valencia, last summer - without their pet.
Unlike the first case, this dog was not living, or in regular contact, with another infected dog.
It may be infected sand flies were inadvertently brought back in the owners transport, luggage, or clothing.
Ian Wright, a veterinary surgeon and the UK and Ireland head of the non-profit group of European vets specialising in parasitology, said: "This case demonstrates it cannot be assumed that because a dog has no history of travel, leishmaniosis can be ruled out.
"It also serves as a reminder that we should not be complacent about the risk of leishmaniosis establishing in the UK, even in the current absence of the sand fly vector."