Concern grows as more horses in the US have tested positive for West Nile virus, a disease which causes brain inflammation

The number of cases of West Nile virus in horses in the United States has risen. The virus, which causes brain inflammation, first appeared in the United States in 1999.

The disease, which can be fatal, lives in birds and is transmitted by mosquitoes. However, there is no evidence it is transmitted from horse to horse or from horse to people.

According to the National Veterinary Services Laboratory in Iowa, the virus has appeared in 12 states this year.

In Virginia alone, three horses have tested positive. The first two cases were reported to have been confirmed in September.

A spokesman for the Department for Environment, Food and Rural Affairs said there had been no reported cases in the UK, although there had been some in France.

Asked if there would be any implications for theWorld Equestrian Games in Spain in 2002, he said: “With the normal quarantine regulations in place, the Games should not be disrupted.”

But he said the department would be “monitoring” the situation closely.

Almost half the horses infected with the virus recover with no long-term effects, but there is no cure for the disease.

The most common signs of infection in horses are stumbling, weakness, partial paralysis and muscle twitching.