Cracking the problem: using egg whites to predict bluetongue outbreaks

Culicoides biting midges are vectors of arboviruses such as bluetonguevirus, which causes a potentially fatal disease in sheep, cattle and otherruminants. Quantification of the range and probability of Culicoidesdispersal is essential to inform policy responses during outbreaks. Avariety of methods have been used to quantify Culicoides dispersalat a local scale, including capture-mark-recapture (CMR) usingfluorescent dusts; however, a key assumption of CMR studies is thatthe marking process does not effect the survival and behaviour of theinsect. An alternative technique that addresses some of the limitationsof CMR is the use of protein-based immunomarking, which allowsthe marking of insects without needing to collect them. This studyused an ovalbumin (protein in egg white) immunomarking techniqueto quantify the within- and between-farm dispersal of Culicoides insouthern England.A mixed sheep and beef cattle farm in southern England wassprayed with liquid egg white solution so that insects were exposedto the immunomarker when they passed through the area (habitatimmunomarking). Insects were then collected for three or fourdays after treatment at 14 trap locations during two trial replicatescompleted in 2013; and 24 trap locations during three trial replicatesin 2015, where some of the traps extended out from the egg-markedarea to a maximum distance of 3876 m. An ovalbumin-specific ELISAwas used to detect ovalbumin-positive Culicoides.Both within- and between-farm dispersal of Culicoides wasobserved. Of the 9058 Culicoides collected over 22 nights of trapping,600 ovalbumin-positive Culicoides, of 12 species including thoseimplicated as arbovirus vectors, were collected with a maximumdispersal distance of 3125 m. Analysis of this data with informationcollected from on-site weather stations indicated that midges hadflown upwind and downwind towards the traps, and that a significantnumber are actively moving between farms.The authors conclude that the use of this novel immunomarkingtechnique will enable improved, data-driven modelling of the spreadof Culicoides-borne arboviruses which could inform the policyresponse to incursions and outbreaks.