By Pallab Ghosh
Science correspondent, BBC News
Livestock farms in the UK will again be at risk from bluetongue from the second half of April, predict scientists.
Researchers have produced a map showing when farms in different parts of England and Wales are at most risk.
They say midges that could spread the virus will become active from the middle of March, but could begin infecting livestock just weeks later.
Last year, only a small number of farms were affected, but scientists warn many more are at risk during 2008.
The head of the team feared that a vaccine would not be ready until after the first animals had become infected.
Philip Mellor of the Institute for Animal Health warned that the disease, if left unchecked, would spread across the country this year.
"In the UK in 2007, the disease involved between 60 or 70 farms," he told BBC News.
"But with the sort of increase in infection we've seen in northern Europe, we'd be expecting thousands of farms to be infected this year."
Professor Mellor's team has been studying the lifecycle of midges and what happens to them when they are infected with the bluetongue virus.
The researchers have discovered that if the temperature doesn't drop below 15C (59F), it would take about two weeks for the insects to build up a sufficient amount of the virus to infect livestock.
Assuming that this year's weather follows the same pattern as 2007, they have built up a picture of how they think bluetongue could spread.
Current estimates suggest that animals in Kent will be the first to be at risk from 21 April.
Scientists studied midges' lifecycles to predict when farms are at risk
But days after, midges in other parts of southern England could begin spreading infection.
By May, outbreaks could be happening in Wales and the Midlands; towards the end of the month and early June, the disease is predicted to have made its way to northern England.
According to one of the scientists involved, John Gloucester, who is on secondment from the Met Office, the projections should help the government contain the disease.
"At the end of the day, we can't stop the midges from flying from one area to another," he told BBC News.
"But clearly we can target the vaccines and general surveillance in the areas that are first likely to become infected."
The government's acting chief vet Fred Landeg has ordered 22.5 million doses of vaccine.
"Almost certainly the disease will re-emerge because that's been the experience of northern Europe," he said.
"Unlike last year in northern Europe, we hope that vaccine will be available and should limit clinical signs in herds and protect them from infection.
"But I think if people don't vaccinate you will see the disease re-emerge with a vengeance and slowly spread."
Professor Mellor's and his team's projections suggest that the first infections could begin before the first batches of vaccine are available to farmers.
"This vaccine is supposed to arrive in May this year - that's the time that virus transmission should be getting underway," he explained.
"So it's a race between the delivery of vaccine and transmission of the virus - it is going to be a very close race."