Three people were bitten by a rabies-infected puppy dog in British quarantine, a Health Protection Agency (HPA) spokeswoman said Saturday.
The Department for Environment, Food and Rural Affairs (Defra) announced that a case of rabies had been confirmed in the puppy.
The dog died Thursday and had been held in quarantine in south-east England since April 18 after being brought into Britain from Sri Lanka.
The last human death from indigenous classical rabies in Britain occurred in 1902, while the disease was eradicated from the island kingdom in 1922.
Officials said Britain remained rabies-free and the risk of it spreading was highly unlikely, while those bitten required swift treatment.
"This animal died whilst in quarantine, which has effectively contained any public health risk," said Doctor Dilys Morgan, an HPA rabies expert.
"We understand that three individuals connected to the quarantine centre and rescue centre were bitten by the animal and all have received or will be receiving prompt protective treatment with appropriate vaccination.
"Even if someone has been bitten by an animal with rabies, prompt post-exposure treatment following the bite is highly effective in preventing rabies."
Checks were underway on animals which might have come into contact with the puppy, Defra said, including those which have since left the centre. A full investigation is underway.
"While initial tests show that this puppy has tested positive for rabies, this shows that the system is working and the case has been picked up while the animal is in quarantine," said Acting Chief Veterinary Officer Alick Simmons.
"This means it is contained and the UK's rabies free status remains in place.
"We are now tracing animals that have moved from the kennels to ensure that all animals that have come into contact with the puppy are monitored.
"However, any risk of the disease having spread to other animals is highly unlikely."
A lawmaker revealed the quarantine centre was in his suburban north-east London constituency.
Cases were found in nearby France and Belgium late last year.
Rabies can be transmitted to humans through animal bites and is nearly always fatal for those who have not been vaccinated and contract symptoms.
The rabies virus infects the central nervous system. Symptoms include fever and headache and can progress to partial paralysis, hallucinations and fear of water. Death usually occurs within days of the symptoms appearing.
The World Health Organisation estimates that between 40,000 and 70,000 people die from rabies each year, with most in south and south-east Asia.