Whatever the cause of the foot-and-mouth outbreak in Surrey, weather can play a key role in spreading the disease.

The foot-and-mouth virus survives in tiny moisture droplets breathed out by infected animals. Those droplets can be swept up by the wind and carried for miles before infecting healthy animals. In the epidemic of 1968 in the UK, the Met Office traced how the infection fanned out from the first outbreak in Shropshire on a southwesterly wind, and when the wind changed direction the disease changed tack.

Humidity is crucial because water droplets give the virus a vehicle. Unfortunately, the humid, windy weather this summer is ideal for spreading the disease, although heavy rains wash the virus to ground. However, hot, dry sunny weather is best because low humidity and strong ultraviolet light help to kill off the virus.

Another feature of previous outbreaks is how the disease travels in clouds of dust. Bouts of foot-and-mouth in Korea in 2000 and 2001 followed dust storms from China, and in 1993 three outbreaks in Italy followed a dust cloud from the Sahara. In the UK, the outbreak of February 2001 in Northumberland came soon after a shower of dust from the Sahara fell over northeast England.