In 1865 a "virulent distemper" affected the farming stock of England to the extent that Queen Victoria composed a prayer for use in every church.
"Stay, we pray Thee," begged the queen, "this plague by Thy word of power; defend us from the pestilence with which many foreign lands are smitten, and keep it far from us." The queen's request, however, went unheeded up above, and some time later the Archbishop of Canterbury intervened to ask the Home Secretary to declare a Day of National Humiliation; it was assumed, one supposes, that this might improve the chances of divine intervention. More recently, the authorities have tended to look instead to meteorologists, inter alii, for help in coping with epidemics. Foot-and-mouth disease is a viral illness affecting cattle, pigs and other creatures with cloven hooves. Its symptoms include blisters in the mouth and on the feet of the affected animals. It is usually first imported accidentally, but once arrived the weather becomes an important factor which may help or hinder the spread of the disease. The viruses survive in tiny moisture droplets expelled from the respiratory systems of infected animals. These droplets may be carried along by the wind for several miles to infect otherwise healthy stock; moreover, the airborne virus thrives in conditions of high relative humidity, but becomes inactive if the humidity falls below 60 per cent or thereabouts.
The importance of meteorology lies in the way in which the disease may be controlled. The only effective method is to identify infected areas, prohibit the movement of livestock into or out of them, and slaughter all infected animals in the danger zone. The aim is to concentrate activity in the smallest areas consistent with isolation of the disease.
Given details of the initial outbreak, mathematical models run on a computer can be used to analyse the wind regime in the vicinity, and make useful estimates of the concentrations of the virus in zones surrounding an infected farm.
The existence or otherwise of vertical currents in the atmosphere, which would carry the virus upwards and out of harm's way, are taken into account. It is also possible to incorporate forecasts of relative humidity into the model, so that the rate of infection for a given concentration of the virus can be assessed.
Using this information, veterinary authorities can then identify specific areas in which to concentrate the eradication effort, avoiding unnecessary and expensive action in zones where the risk is very small.