Midges

Wind-borne virus

18 July 2012

In summer 2011, a new wind-borne disease broke out in the town of Schmallenberg in Germany, affecting livestock in the region. Carried by midges, the virus has since spread and even hit the UK. Laura Burgin, Atmospheric Dispersion Research and Response Scientist at the Met Office, has been studying its reach — and helping farmers plan ahead.

Laura Burgin

"Schmallenberg is an orthobunya virus found in Germany, Belgium, Denmark, the Netherlands and now the UK," says Laura.

Transmitted by particular certain species of midges the disease produces mild cold symptoms in adult cattle, goats and ewes. However, the implications for their unborn calves and lambs are far more serious. In fact, when lambing season started in November, farmers across Germany and the Netherlands reported severe deformities in new-borns and, in some cases, late abortion.

Forecasting the spread

On their own, midges have limited ability to travel. Their normal patterns of flight mean they are usually restricted to moving only between fields in the same local region. But in warm, dry, light-wind conditions, they can cover much larger distances. With the right prevailing wind, they can even travel across the channel - thus making the leap from mainland Europe to the UK.

Predicting the spread of this kind of disease has, historically, been notoriously difficult. But Laura and the Met Office Atmospheric Dispersion team employed the Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME) to help show how far, and in which direction, the midges are likely to travel - blown by the prevailing wind.

However, NAME is not used solely for tracing wind-borne diseases. It has previously been used to model volcanic ash - and during the Fukushima nuclear incident in Japan last year. But the principles of particles being spread by the wind (or in this case midges) are the same. The process involves using NAME to calculate the movement of particles when the conditions are right for midges to take off. The system then tracks their most probable movement.

Plume map The Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME) helps to show how far, and in which direction, the midges are likely to travel - blown by the prevailing wind.

Warnings in advance

The Met Office's work in predicting the spread of wind-borne diseases is used by a range of organisations - from farmers to the government.

"We're trying to give advanced warning to the Department for Environment, Food and Rural Affairs (Defra). That way they can tell the vets in the field who will, hopefully, identify the symptoms quicker," says Laura.

"We're trying to give advanced warning to the Department for Environment, Food and Rural Affairs (Defra). That way they can tell the vets in the field who will, hopefully, identify the symptoms quicker."

With enough warning, vets and farmers can start putting restrictions in place and, if vaccines are available, begin inoculating animals. The right information at the right time can influence decision-making at every stage of the chain, from government right down to local farmers.

What's more, the Met Office has partnerships with various other organisations who, together, work to help stem the spread of wind-borne diseases. For example, the Met Office works closely with the Institute for Animal Health and Defra.

This collaborative way of working already proved successful during the bluetongue outbreak of 2007.

"By predicting when the virus was most likely to arrive, we were able to inform the government well ahead of time, enabling them to prevent widespread bluetongue," Laura says.

The future for Schmallenberg

With wind-borne viruses such as Schmallenberg, there are several possible outcomes following an outbreak. A worst-case scenario could be the virus spreading into the local midge population in the UK, allowing it to move north from the affected areas, even as far as Scotland. Another, much more positive, possibility is that a vaccine will be developed quickly or animals could naturally become more immune to the virus, causing it to die out in a couple of years.

Should this happen on a wider scale, with livestock across Europe also developing immunity, the virus could completely die out, alleviating future risk for the UK. Unfortunately, at this stage, it is not known which is the more likely outcome.

The good news about Schmallenberg is that the latest evidence suggests it is very unlikely to affect humans - either through direct infection or through eating affected meat. With that knowledge and the Met Office's careful monitoring of the movement of the disease, the expectation is it will soon be contained and its impact will be minimised.

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