Feeling kinda blue

Last year bluetongue hit the UK - until that time, this livestock disease was completely unknown to Western Europe. Vaccination is one form of defence - but there is another way 

MIDGE vectors have become another beneficiary of global warming. Different species are displaying increased ranges of activity with deadly consequences for livestock (sheep and cattle) from the bluetongue virus they carry and transmit. Bluetongue disease is endemic in Asia and Sub Saharan Africa but until relatively recently the nearest it ever got to Europe was the North African Mediterranean coastline and some Balkan countries. 
Vector distribution was largely confined to the sub tropical midge Culicoides imicola which started to move northwards, apparently under the influence of global warming. Bluetongue disease moved into Spain, Italy and Greece, the Mediterranean islands of Sardinia and Sicily and eventually the northern coastline of the Mediterranean Sea on the back of this vector
The blue tongue serotypes carried and transmitted into Southern Europe were those endemic in North Africa (BTV 2, 4, 9 and 16) and confined to C. imicola, spread of which was limited by climate. Things started to change when BTV serotypes from North Africa were successfully carried and transmitted by temperate midge species, including C. obsoletus and C. pulicanis, allowing Bluetongue to establish in Central Europe including Hungary and Bulgaria.
What happened next for Bluetongue was a surprise as a completely new serotype designated BTV8 ‘parachuted’ into the Netherlands in August 2006 close to the border with Belgium and Germany, probably arriving on a zoo animal.
Such was the shock of a completely unknown livestock disease in Western Europe that initial reaction was “blue what?” Temperate midge species like C. obsoletus which were already spreading the Mediterranean BTV serotypes picked up BTV8 with relish and began to disseminate it with speed. Scientists instinctively knew this serotype was different, even before laboratory identification as BTV8, because the ‘Mediterranean’ strains had only seriously affected sheep, whereas this serotype was already killing both cattle and sheep in large numbers.
The disease hit sheep farming in Belgium hard killing 30,000 animals, half of all the infections which affected 15% of the national flock. Germany with 20,000 farms infected lost 10,000 sheep (2% of the national flock), as well as 1,500 cattle, 8% of the 17,000 infected. Comparable losses occurred in the Netherlands and France with 6,400 and 12,700 farms infected. BTV8 is lethal to cattle and sheep whereas other serotypes have reserved their most deadly consequences for sheep.
BTV8 appeared in the United Kingdom (UK) in late summer 2007. Meteorologists were able to pin-point arrival on UK soil, down to the day and the hour, by plotting offshore winds from the continent that carried midges into East Anglia. There were 136 outbreaks up to 27 June 2008. All future hopes for bluetongue management in the UK were pinned on the dedicated BTV8 vaccine, first available in May 2008, and administered to livestock in bluetongue protection zones which were extended westwards and northwards across the United Kingdom. 
Reports from France in summer 2008 showed bluetongue had survived another northern European winter and farmers were vaccinating livestock in a race against time. According to a report by New Scientist the disease began to surface in July 2008 with France reporting more than 260 cases by the end of the month. Most said the reports were found along front line of the 2007 outbreak, suggesting the epidemic was spreading into new areas despite a compulsory vaccination policy in France.
Voluntary vaccination was rolled out in the UK from East Anglia starting in May 2008 where the virus had arrived in 2007. The ‘vaccination front’ moved steadily westwards and northwards reaching Wales in the west and Yorkshire in the north and alarmingly close to the UK’s main sheep producing areas towards the end of July 2008. Experts were concerned because sheep just outside the vaccinated zone were clearly more at risk but would probably not be vaccinated until autumn 2008. All depended, they said, on whether sufficient farmers south of the vaccination front line had vaccinated their livestock to slow down spread of the disease. That said, the high number of new outbreaks already recorded in France in 2008 suggested this could be difficult to achieve. 
Modelling research by Camile Szmaragd and others at IAH (Institute of Animal Health) Pirbright (UK) predicted the extent of bluetongue spread in the UK by October 2008 in the absence of this vaccine. There was an 80-100% chance of the virus covering most of southern, central and eastern England and 10-20% chance of western England, Wales and parts of lowland Scotland becoming infected. The question still on everyone’s lips concerned the native Scottish midge (C. impunctatus) and would it start to carry and transmit BTV8, thus putting huge highland sheep flocks and prime beef cattle in Scotland at risk.
Midge pest monitoring is urgently required to pin-point all potential midge-species vectors and any pattern of spread. The European Reference Laboratory for bluetongue at IAH Pirbright in the United Kingdom (UK) and  led by Professor Philip Mellor, has so far only recommended use of light traps but these clearly have limitations. They will catch 100's of midges but are they the ones responsible for vectoring blue tongue virus?
Experiments carried out at Pirbright have shown up the potential limitations of light traps and deficiencies in their catch profile for midges associated with sheep. Catches from penned sheep covered with nets to secure all midges on animals were compared with catches in light traps sited nearby. Comparative trap catches did not match up so scientists are now viewing with some urgency midge monitoring using dedicated traps loaded with animal host odour lures proven for target midge attraction.
Most prominent and appropriate for midge monitoring is the BG Sentinel Trap patented by BioGents (Germany), and loaded with the lure from AgriSense-BCS (UK) containing carbon dioxide (CO2) and key synergistic components identified from animal host odours.
The trap mimics convection currents created and generated during heat exchange by the animal body, as well as displaying attractive visual (black and white) cues, and releasing attractant chemicals from the lure over an extensive surface area. Traps used for general midge monitoring are supplied with an integral light at the top-located orifice to complement midge catches. It is hoped that as chemical attractants become more finely tuned for BTV vectors the need for light will be obviated, thus eliminating catch of non BTV vectors.
An integral fan blows volatile chemicals from the lure upwards through the fabric gauze on top of the trap in a convection-like current, thus mimicking scents continually emitted by sweat on the surface of the animal body. Any midges following the scent trail are visually attracted to the edge of the black suction column centrally placed in the top of the trap and surrounded by the white fabric gauze. Insects are subsequently forced into a net inside the trap by the downward suction forces generated by the trap’s fan.  
Key component and synergist in the AgriSense lure is the R (-) isomer of 1-octen-3-ol, an optically-active isomer (enantiomer) with proven midge attraction. The lure is already well established for monitoring and control of Scottish midge in its current role as a nuisance biting insect.
Research has shown how light or CO2 as stand-alone factors are too much of a

“Reports from France in summer 2008 showed bluetongue had survived another northern European winter and farmers were vaccinating livestock in a race against time”

blunt instrument, attracting all sorts of other insects as well as target midges. The addition of 1-octen-3-ol synergises the main CO2 plume, allowing target midges to distinguish between CO2 plumes from the trap lure and others such as those from fermenting fruit. Target midges are therefore more likely to follow this plume from the trap, which consequently provides more selective catches giving a clearer picture of the target midge profile in the surrounding environment.
Re-evaluation of C. obsoletus and other closely related midge species as potential vectors of the BTV8 serotype is required as a matter of urgency. The situation is complicated by 24 different BTV serotypes, varying widely in virulence and mortality, and the ‘complex classification’ of C. obsoletus. This ‘species’ comprises a number of different biotypes morphologically similar but genetically different and only distinguishable by PCR technology. The complex includes C. chiopterus, C. scoticus and C. dewulfi as well as C. obsoletus. Highly specific midge monitoring only achieved using host odour lures is required. 
AgriSense-BCS is willing to collaborate with anyone over their semio-chemical lures which they believe are the most appropriate, pulling in those species of midge that specifically respond to animal cues. This willingness extends to any appropriate trap testing procedure, although their lures should ideally be used in the BG Sentinel trap for which they are custom-designed.