The first case of the deadly blue tongue livestock disease has been discovered in West Sussex.
The virus, which has devastated the farming industry, has been found in Haywards Heath.
The Department for Environment, Food and Rural Affairs (Defra) has limited the transportation of livestock and movement of agricultural vehicles in the region.
And experts have warned further cases in the county could be detected in the coming weeks as animals are tested.
The blue tongue virus, which affects mainly sheep but also cattle and goats, is transmitted by midges.
Tonight the National Farmers' Union (NFU) blamed the recent mild weather for the spread of the disease because midges have not been killed by the cold.
The NFU also warned blue tongue would continue to devastate the industry, with Sussex farmers also having to pay for expensive blood tests and vaccines.
In October blue tongue disease was found in East Sussex when it was diagnosed at a farm in Northiam, near Rye.
An NFU spokeswoman said: "It is not a surprise there has been a case found in West Sussex because it has been in East Sussex for a while.
"We have had some mild days this winter and people will have noticed there have been lots of midges around.
"We don't know the exact financial impact of blue tongue because it came at a time when foot and mouth broke out.
"The combined cost of blue tongue and foot and mouth nationally is £100 million and there are further costs to consider."
The infected animals were found after testing when it was deemed there were not enough midges around to spread the infection.
Sussex farmers will have to pay for a blood test, costing between £3 and £15, for every animal they wish to transport.
A vaccine for the virus, which is available from May, will cost farmers £60 per dose, with some animals needing two shots.
Three other cases of infected premises have been discovered in the south east.
The Haywards Heath case takes the total number of infected premises in the UK to more than 70.
A Defra spokeswoman said: "The most recent cases were found as a result of pre-movement testing currently required.
"Through the course of surveillance work and pre-movement testing it is possible that other new cases will be identified."
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