February 28, 2008

Satellites could play a part in controlling the spread of deadly African Horse Sickness (AHS) - a disease which has already affected parts of Europe and many believe will eventually hit Britain.

Danish researchers will explore whether data from satellites can be used to predict where in their country the small blood-sucking midges that spread a disease closely related to AHS, Bluetongue, are likely to be most abundant.

Bluetongue affects sheep and cattle while AHS attacks horses. The same millimetre-sized midges that carry and spread bluetongue (Culicoides species) carry AHS.

Using satellite information would allow ground-based teams to better focus their attack on midge populations or vaccination efforts.

Heat, humid soil and plant cover are known to be some of the conditions that determine whether midges can thrive in a particular area. These are also conditions that can be measured from satellites.

Danish scientists are therefore going to investigate if satellites can predict when and where the midges are present in numbers.

When the knowledge gathered about the midges and their preferred conditions for living and reproducing is combined with data covering soil types and farms, the scientists plan to develop a computer model to calculate risk areas for bluetongue in Denmark.

With an efficient computer model, the scientists have a tool which can help calculate how quickly the virus develops in midges and how fast the infection spreads in various locations and in different seasons.

A current outbreak of bluetongue has developed into one of the most widespread epidemics in cattle and sheep in Europe in modern times.

In just a few years the disease has spread from Africa and the Middle East to large parts of Europe, including Denmark. The disease spreads with great speed every nothern summer. In 2007 more than 50,000 farms were infected in Western Europe and when the outbreak was at its peak, one German farm was infected every 10 minutes. The spread of bluetongue to northern Europe may be an effect of global warming and climate change.

Bluetongue only affects ruminants and needs midges as vectors, and, like AHS, does not affect people.

Britain's Horse Trust has been campaigning for the country to be prepared for the arrival of AHS on its shores, with a mortality rate of up to 90% likely among infected horses.

It is backing an education and information campaign and a research programme to evaluate the likely impact of the disease and develop appropriate control measures in accordance with the aims of the country's Equine Health Welfare Strategy.

The only vaccines currently available are live attenuated preparations made in South Africa. These are not yet licensed for use in Europe, though they can be used as an emergency response when the disease has taken hold.

Infected midges can be blown by the wind for more than 100km and transported long distances in farm vehicles.

African Horse Sickness was diagnosed in Spain in 1987-90 and in Portugal in 1989, but was eradicated using slaughter policies, movement restrictions, vector eradication and vaccination. Were AHS to break out in Europe again, under current vector and climate conditions it is inevitable that it will have a much greater opportunity to establish itself - including in Britain.

Although the disease is notifiable in Britain and Europe, a British slaughter policy is unlikely to be viable once the disease is established in the midge vector population.

The British and European horse population is considered highly vulnerable to the disease, with vaccines that currently exist being either unavailable or unlicensed. Some are unsuitable for use where the disease is not endemic.