Warm weather raises disease risk

Climate change is altering the way livestock are being farmed. Perhaps the most obvious example of this trend is the emergence of bluetongue in the UK.

According to Professor Philip Mellor of the Institute for Animal Health bluetongue was traditionally limited to a band across the middle of the earth stretching from 45° North (eg southern Spain) and 35° South (eg South Africa). The disease was limited to native African midges. But as the world has warmed up there has been a spread of the midge and the disease in the past 20 years.

“The disease jumped the Mediterranean taking hold in France and Spain,” says Prof Mellor, adding that an increase in the severity of winds may have helped blow bluetongue infected midges further than they would have travelled previously.

Bluetongue requires a temperature above 12°C to spread, increasing its virulence the higher the temperature. Therefore warmer weather in more northern parts of Europe, including the UK, France, Germany and the Netherlands, created the conditions for the spread of the Bluetongue 8 strain of the disease (BTV 8). Then animals infected by the African midge were bitten by native northern European midges and the disease was able to move north, infecting cattle and sheep in the near Continent in 2006 and the UK in 2007.

Prof Mellor warns that there are 24 strains of bluetongue and although it is unlikely all of them will affect the UK, farmers should be prepared for outbreaks of other strains. But he reassures producers that bluetongue can be controlled.

“A robust vaccine strategy is essential to control bluetongue,” says Prof Mellor. I estimate it accounts for 90% of control with restricted animal movements and on-farm measures accounting for the other 10%.”

There are other diseases that spread in a similar way to bluetongue and could threaten the UK. These include African Horse Fever and Rift Valley Fever. The latter is of concern as it affects humans as well as cattle and sheep.

Liver fluke is another disease that could increase with climate change as warmer and wetter weather provides breeding grounds for the parasite. There is no evidence that bird flu is a disease governed by climate change, although it has caused most problems in hot, humid and densely populated regions. Migrations of birds may also be influenced by changing climate in the future.

But the threat of some diseases may diminish with climate change. For instance, foot-and-mouth requires cold and wet weather to spread. Warmer winters may lessen the potential for outbreaks.

Impact of climate change in the uk

Animal disease threats

  • 21 new bluetongue strains (cattle and sheep)
  • African Swine Fever (pigs)
  • Swine Vesicular Disease (pigs)
  • Rift Valley Fever (cattle, sheep, goats and humans)
  • West Nile Virus (birds, horses and humans)

Crop disease threats

  • Phoma
  • Black stem rust
  • Leaf blotch
  • Fusarium
  • Brown rust

Climate change crop pests

  • Colorado beetle (potatoes)
  • Root knot nematodes (potatoes and field vegetables)
  • Japanese beetles (all crops)
  • Increase in aphids and sawflies affecting cereals, oilseed rape and brassicas

Wanted: Strong and robust crops

A changing climate is already being felt on British farms. Simon Oxley, senior pathologist at SAC, says that trials in the East of Scotland that began in 1983 show that flag leaf emergence in wheat is now two to four weeks earlier than it was then.

“While changes in variety and earlier drilling dates cannot be ruled out as having an effect, it does appear that the growing season is getting earlier.”

Earlier emergence does not necessarily mean earlier harvests as day length has a significant effect on crop maturity, explains Dr Oxley. But it does mean that the growing grain and its flag leaf is exposed to disease for longer periods.

“It is important that growers keep their upper leaves cleaner for longer,” he says, urging vigilance so that disease can be spotted and treated as soon as possible.

But climate change does not just mean a lengthening of the growing season, but also more unpredictability.

“For instance, we have noted a difference in temperature of between 0°C and 22°C at the crucial boot stage (early ear emergence),” says Dr Oxley, adding that this summer’s rain and lack of sunshine have also caused severe problems.

“There will be a need for more robust varieties and growing techniques.”

Another effect of a changing climate is a greater threat of disease, particularly as pathogens adapt to warmer and wetter weather. Dr Oxley cites yellow rust as an example.

It is posing more of a threat outside its traditional heartland of East Anglia while fusarium could be more of a problem as the weather gets warmer and wetter and more maize is grown.

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