A protein found in egg, could be used to help control the spread of the devastating livestock disease bluetongue (BT), say scientists from The Pirbright Institute. Bluetongue affects livestock including sheep (which are most severely affected), cattle and goats along with wild animals such as deer.
The bluetongue virus (BTV) that causes the disease is mainly spread by Culicoides biting midges. Controlling BT is a challenge as Culicoides midges are tiny and are easily carried on the wind. Pirbright scientists, working closely with weather experts at the Met Office, produce modelling maps for the UK and other governments to predict the spread of midges. However, knowledge gaps on how far and fast the insects fly means it is tricky to accurately predict exactly how an outbreak will spread.
The use of ovalbumin, a protein in egg white, to mark insects has previously been used to track and study crop pests. The technique is sensitive enough to show if even a single insect has been exposed and enables them to be marked without the need for collection.
Dr Chris Sanders, a senior post-doctoral entomologist at Pirbright and lead author of a new study, published today in the Journal of Applied Ecology explored whether the approach could also be used to track Culicoides midges. The research is the first to measure how many midges might travel between farms, and could help countries that are threatened by BTV to respond more rapidly in an outbreak to control the spread of the virus.
Culicoides prefer to rest and breed on damp organic matter such as cattle dung and Dr Sanders’ and his colleagues sprayed ovalbumin on to dung and straw in a barn, to ensure the insects would pick up the protein marker when they emerged or landed on it. Traps for the midges at various distances from the barn were set up to measure how far they travelled. Five trials were conducted which collected 9,000 midges in total. 600 midges tested positive for the protein and had travelled up to 3.1km from the treated barn.
Dr Sanders said, “By combining this data with information from on-site weather stations, we found that the Culicoides midges had flown upwind and downwind towards the traps, and we think that a significant number are actively moving between farms.
“Midges are too small to track by eye or with cameras or radar technology. People have tried capture-mark-recapture, but this is very hard work for small insects because so few marked insects are usually recovered. This research means we now have a much better understanding of the movement of the Culicoides midge species that transmits BTV and have the data we need to estimate the likely spread of the disease between farms more accurately.
“BT has a huge social and economic impact globally – the last outbreak in northern Europe, (which affected in the UK in 2008), cost an estimated £800 million. As well as BTV, Culicoides biting midges also transmit other costly virus diseases such as Schmallenberg virus which infects domestic livestock and African horse sickness virus which infects equine species. The outcomes of this research will provide governments with crucial insight to enable them to put control measures in place for these diseases more quickly, saving animals’ lives and helping reduce the losses to farmers”.
There is no treatment for BT and animals can only be effectively protected by vaccination. There are 27 serotypes (types) of BTV however and each requires a different vaccine. For over 40 years, Pirbright has played a major role in helping contain and prevent outbreaks of BTV across the world. The Reference Laboratories at Pirbright receive samples from Europe and the rest of the world as well as the UK, where they diagnose the emergent strain so the correct vaccine can be produced.