FACTBOX: Foot and mouth disease

(Reuters) - Following are facts about foot and mouth disease after an outbreak was reported on a farm near London:

Foot and mouth is a highly infectious disease affecting mostly sheep, pigs and cattle in which fever is followed by the development of blisters, chiefly in the mouth or on the feet.

The disease is rarely fatal, except in very young animals, but causes lameness and reduced milk yields. Culling remains the basic control policy used to stop the spread of the virus.

The interval between exposure to infection and the appearance of symptoms usually varies between 24 hours and 10 days, but can be longer. The average is three to six days.

It is very rare in humans and even then is mild, short-lived illness requiring no medical treatment.

Heat, sunlight and disinfectants will destroy the virus whereas cold and darkness tend to keep it alive.

Animals pick up the virus either by direct contact with an infected animal or by contact with feed that has been infected by such an animal.

Airborne spread of the virus can happen and under favorable climatic conditions it can spread several miles by this route.

Trucks, market places and loading ramps, in or on which infected animals have traveled, should be disinfected. Roads may also become contaminated and the virus may be picked up and carried on the wheels of passing vehicles.

Boots and clothing can also spread the disease. Dogs and cats, poultry, wild game and vermin also carry infection.

Signs of the disease in cattle: excess salivating, shivering, reduced milk yield, sores and blisters on feet, raised temperature

Signs in sheep: sudden, severe lameness, reluctance to move, blisters around feet, blisters in the mouth

Signs in pigs: sudden lameness, prefers to lie down, blisters around the feet, blisters on the snout or the tongue

An outbreak in 2001 was the largest in Britain since proper records began. There were 2,030 cases spread across the country.

More than six million animals were culled, of which almost five million were sheep. Many were burnt on funeral pyres.

Ban on livestock and meat exports estimated at the time to be costing the industry 8 million pounds ($16.3 million) a week.

Value of British sheep, beef and pigs exports (live animals and meat) was more than 500 million pounds in 2006.