Two cows have died of anthrax on a beef farm in south Wales, it has been confirmed by the assembly government.
Anthrax can lead to sudden death in animals with no obvious symptoms
Tests were carried out on the unnamed farm in Rhondda Cynon Taf after the sudden death of five cows in April.
The assembly government said all five carcasses had been burnt on site to ensure there was no risk to the public.
The anthrax was discovered through routine testing. It is the first case in Britain since 2002, when a cow died at a farm in Wrexham.
An assembly government spokeswoman confirmed the farm in the latest cases had once tested positive for anthrax 35 years ago.
Anthrax spores can persist in the environment, notably soil, for years. An anthrax infection can be treated successfully with antibiotics when the disease is identified early.
Anthrax is a highly infectious and contagious disease but uncommon in humans
Under certain conditions it forms spores that may persist for many years in the environment
Cutaneous anthrax is the most common type, accounting for 95% of cases
Before 2002, the last confirmed case of anthrax in cattle occurred in Lanarkshire in 1997
Local veterinary inspectors are involved in monitoring and all unexplained sudden deaths in livestock are reported
The small farm has been sealed off, with the remaining herd of suckler cows confined to their field while tests continue.
Chief veterinary officer for Wales Dr Christianne Glossop said: "The assembly government and state veterinary service have worked quickly to ensure that there is no threat from anthrax to the public, farmers or any other livestock in Rhondda Cynon Taff.
"Officials are liaising with the Environment Agency and medical authorities to ensure that all necessary precautions are being taken.
"Anthrax is very rare - it last occurred in Wales in 2002. We are working to trace the source of the current outbreak."
In a statement, the assembly government said no cattle from the farm had been sent for food for almost 12 months.
The Food Standards Agency has been informed of the outbreak.
The 2002 outbreak in Wrexham was considered to be a sporadic incident on a farm which had three anthrax cases in the previous two decades.
There was also a case in cattle in Clwyd in 1992 and pigs were confirmed with the disease at a farm in Wrexham in 1989.
Alan Morris, a spokesman for the Farmers' Union of Wales, said there was no need for the public to be anxious.
He said: "We are satisfied that the contingency plans put in place are working very, very effectively. We are pleased that the disease was identified quickly."