Bluetongue (BT) is a seasonal vector-borne, viral, disease that causes significant economic and welfare problems in ruminants. It is transmitted by species of Culicoides midges (Diptera: Ceratopogonidae), and as such, the distribution of the disease is restricted to regions where the vectors are present. Once restricted to tropical and subtropical regions of the world, serotypes of BT have been causing outbreaks in southern Europe, following its introduction in 1998, and in 2006, BT serotype-8 emerged in northern Europe, causing devastating economic, welfare and production consequences. The northwards expansion of BT has been attributed to a shift in the geographic limit of the Culicoides imicola Meigen vector, and the involvement of the newly implicated Palaearctic vectors, the Obsoletus and Pulicaris Groups. Little is known about the ecological characteristics of the newly implicated vectors, or indeed those believed to be non-vectors, including their distribution and abundance, making disease risk assessment and management difficult. Within this thesis, a series of field experiments were initiated on a group of farms to gain insight into the distribution and abundance of Culicoides species. The results highlighted that a very high level of variation is seen when trapping Culicoides at the local-scale, yet it is possible to build a strong model explaining this variation using a mixture of host and environmental variables, with satellite-derived ecological correlates. This high level of variation in midge catches present between farms undermines attempts to record their nationwide distribution in larger scale models. The results uniquely model Obsoletus Group abundance, and highlight a difference in host involvement between vector and non-vector models. Further field studies which showed a lack of significant variation both between years and at the within-farm level highlight the robustness of this model in predicting the distribution of the BT vectors species, such that it could prove useful for exploring targeted surveillance and control methods. Culicoides distributions do not remain static, therefore an understanding of their flight behaviour is critical to determining the distance over which an insect may transmit a disease agent and the size of the area over which control should be applied. Laboratory studies were undertaken to validate the use of commercial fluorescent dusts as a quick and effective method of marking Culicoides for both field and laboratory studies, and a ‘self-marking’ technique was conceived. Dispersal studies, using the dusts, determined the distances that Obsoletus Group females and males, as well as C. pulicaris females, are able to disperse over a set period of time. This knowledge of flight speed and distance is of utmost value as a critical component in the modelling of BT disease and other Culicoides-borne diseases. The Obsoletus Group contains four members (C. obsoletus, C. scoticus, C. chiopterus and C. dewulfi¬) which are difficult to differentiate down a microscope. Using morphometric analyses, female C. obsoletus and C. scoticus individuals could be separated under a stereomicroscope based on abdominal measurements. Studies such as those contained in this thesis, therefore, are of utmost value in providing information on critical components in the modelling of BT disease and other Culicoides-borne diseases.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:617563 |
| Date | January 2014 |
| Creators | Kluiters, Georgette |
| Contributors | Baylis, Matthew; Read, Jonathan |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://livrepository.liverpool.ac.uk/18893/ |
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