Bluetongue outbreaks set to rise with climate change

19 July 2011 by Tamera Jones

Scientists have found the first concrete evidence that recent outbreaks of bluetongue disease across Europe are linked to climate change. What's more, they warn that as the climate continues to change, the risk of outbreaks is likely to rise.

CowsThe researchers also found a link between a devastating outbreak of bluetongue disease that hit the northern European countries of Belgium, the Netherlands and Germany during 2006, and recent changes in our climate.

Until recently, the disease was restricted to Africa, Asia, Australia and the Americas. But it spread to southern Europe from Africa in 1998, before moving to northwest Europe in 2006. Since 1998, more than 80,000 outbreaks of bluetongue have been reported across Europe, with millions of farm animals dying as a result.

Bluetongue disease is caused by a virus which affects animals like sheep, cattle and goats and is spread by midges from animal to animal, similar to the way malaria is spread by mosquitoes. The disease doesn't infect people.

The disease spreads most rapidly when it's warm and wet, and scientists are concerned that climate change could make outbreaks more common.

We think a run of warm autumns through the early part of the twenty-first century has driven its spread.

- Dr Andy Morse, University of Liverpool

There are a number of diseases which many scientists think are climate-related, such as malaria, Rift Valley fever, and even seasonal influenza. But whether or not they really are driven by changes in our climate is a controversial topic among researchers right now.

"Bluetongue is often cited as an example of climate's impact on the emergence of disease, but, until now, there was no study that supported this," says Dr Andy Morse from the University of Liverpool, co-author of the study published in the Interface, a journal of the Royal Society.

So, he and a team of European researchers decided to investigate the likelihood of future bluetongue outbreaks by developing a mathematical model to tell them how the disease would spread under different climate conditions.

They looked at the effect of past climate of the changing risk of outbreaks over the last 50 years, to get a handle on the triggers for disease outbreak. They then combined their model with 11 climate models to project forward to the year 2050. By doing this, they could see how the disease might react to climate change.

They found a clear connection between the climate and the emergence of the disease.

"A clear climate signal in northern Europe has allowed the virus to replicate," says Morse.

They also found a difference in the likelihood of outbreaks in northern and southern Europe. Over the next few decades in northern Europe, they predict a 17 per cent increase in incidence of the virus, compared with just seven per cent in the south of the continent.

"This is because it's already warm in the south. Northern Europe is likely to see more warming than the south as the climate changes," explains Morse.

"Bluetongue isn't endemic in the UK; it has to be reintroduced to get an outbreak. But we think a run of warm autumns through the early part of the twenty-first century has driven its spread," says Morse.

"The climate seems to be important for both the emergence and spread of bluetongue," he adds. "But climate is only one factor; there are lots of other things to think about such as land-change, human behaviour and farming techniques."

Morse says the team's framework could be applied to other climate-driven diseases.

'Modelling the effects of past and future climate on the risk of bluetongue emergence in Europe' - Helene Guis, Cyril Caminade, Carlos Calvete, Andrew P. Morse, Annelise Tran, and Matthew Baylis. Interface, a journal of the Royal Society, Published online before print 22 June 2011, doi: 10.1098/rsif.2011.0255