Determining the epidemiology and immune responses of UK cattle to natural challenge with Dictyocaulus viviparus

The nematode Dictyocaulus viviparous is the causative agent of Bovine parasitic bronchitis (BPB) in grazing cattle. Infection causes disease ranging from sub-clinical, to severe pneumonia and death. Outbreaks are widely reported annually across the UK, with evidence to suggest prevalence is increasing due to changing weather patterns. In addition to its impact on animal health and welfare, BPB is estimated to cost £100-140 per case or £5.2m per annum nationally, making it the sixth most costly infectious disease in UK cattle.
Current evidence concerning host immune responses to D. viviparus indicate a strong, Th2-dominated response to primary challenge, a feature which can be successfully exploited through administration of a live oral vaccine. To date, the majority of these investigations have focussed on responses to experimental challenge. Whilst this has led to a number of important findings, the significance of these in the context of natural challenge and their epidemiological consequences are unclear. For example, immunity to D. viviparus is short-lived. Animals require natural exposure post-vaccination to develop full protection, whilst adult cattle may be susceptible to "re-infection syndrome" due to waning immune memory. Understanding how and why such issues affect disease status under natural "field" conditions will help improve control measures in the future.
The aim of this project is to further our understanding of the epidemiological and immunological profile of BPB in UK cattle. Discrete research chapters will follow the proposed outline:
1. Development of immunological tools and reagents. This Includes preparation and evaluation of general and stage-specific D. viviparus antigens (native and recombinant). These products will be used to develop diagnostic and research-focussed immunoassays (eg. ELISA and ELIspot) for evaluating immune responses of cattle to natural D. viviparus infection.
2. Determining herd-level sero-prevalence of D. viviparus in the UK. Using the tools and reagents developed, the candidate will answer this important but presently unknown question. Serological data will be collected longitudinally from herds distributed across the UK to determine prevalence, distribution and variation in risk over the grazing season. This investigation will also help to provide valuable data for ongoing work being conducted by the CASE partner NADIS into development of a predictive risk model for BPB (see Section 6), and facilitate identification and recruitment of BPB-affected farms for subsequent investigations.
3. Determining immune responses of cattle naturally exposed to D. viviparus. BPB-affected herds experiencing outbreaks of disease will be visited. Individual animals classified as clinically affected, asymptomatic infected and uninfected will be sampled for serum, whole blood and faeces. Levels of antibody isotypes capable of binding to our previously prepared repertoire of D. viviparous antigens and peripheral leukocyte responses measured in collected serum and whole blood, respectively. Parasitological data on larval pasture burdens and faecal counts will be collected to determine level of challenge and stage of infection, respectively to give a comprehensive overview of disease status for each farm and provide context to aid analysis of observed immune responses.
4. Functional assays to determine mechanisms and importance of D. viviparus immune responses. To investigate how immune responses measured ex vivo relate to effector function, we will perform additional in vitro assays using bovine leukocyte cultures. These will include larval killing assays using serum collected from animals grouped as described above and stimulation with D. viviparus antigens, with particular focus for the latter on memory B-cell ELIspot assays.
Overall, this study will improve our understanding of BPB in the UK. Firstly, by improving the quality of epidemiological information available, then determining