Psoroptes ovis mites are the causative parasites of sheep scab disease. It is a contagious disease which causes intense pruritus, wool loss and the development of lesions. These lesions are exacerbated by secondary bacterial infections. Bacteria appear to play an integrated role in the pathogenicity of this disease and are found in the internal cavities of P. ovis. The aim of this study was to investigate these bacterial associations, with the aim of identifying a microbial target for sheep scab control. The microbial communities associated with sheep scab were investigated using both molecular and bacteriological techniques. Several environmental niches were targeted: scab-infected fleece, internal mite cavity and excreted faecal trails. Microbial communities were very complex, with a variety of species and bacterial groups identified. Some bacteria were common to all environments, whereas others were isolated from one sample. Both natural and in vivo cultured mites were investigated in an attempt to identify universal and potentially beneficial bacteria. In addition, P. ovis mites were screened using PCR to detect potential endosymbiotic bacteria. Positive identification was made of Comamonas sp. in both natural and in vivo cultured mites; this species has been identified as an endosymbiont in other arthropods and its role in P. ovis requires further investigation. In vitro feeding experiments were carried out with P. ovis mites in the laboratory. Initially mite chambers were constructed and optimised to encourage maintenance of P. ovis off-host. A number of diets were tested and antibiotics were compared for their effect on bacteria within P. ovis. In vitro experiments revealed that P. ovis survival was significantly reduced with the administration of antibiotics and there was also evidence that they altered internal bacterial densities. The potential of bacteriophage therapy for the microbial control of bacteria associated with P. ovis was investigated. Bacteria isolated from P. ovis faecal trails were used to isolate bacteriophage from environmental samples. Sixteen bacteriophage were successfully isolated, which were infective against three mite faecal bacteria. Isolated bacteriophage were characterised by a number of methods including their response to chemicals, enzyme and infection dynamics in both solid and liquid phases. In vitro experiments with bacteriophage were also investigated, resulting in a significantly reduced mite lifespan seen with some bacteriophage lysates. The potential for using bacteriophage for the control of P. ovis mites is discussed.

Psoroptic mange, caused by the Astigmatid mite Psoroptes ovis, is an ectoparasitic disease of significant economic importance to agriculture on a global scale and poses a serious welfare concern. With the current chemotherapeutic controls considered unsustainable, there is pressing need for novel control strategies. RNA interference has been proposed as a potential high throughput approach for the identification of novel therapeutic targets with high specificity, speed and at a relatively low cost compared to the existing methods. The presence of the components of the RNA interference (RNAi) pathway in P. ovis was first confirmed through in silico analyses of the P. ovis transcriptome and, following development of a non-invasive immersion method of double stranded RNA (dsRNA) delivery, gene silencing by RNAi was demonstrated in P. ovis. Statistically-significant reduction of transcript level was measured for the three genes targeted: P. ovis mite group 2 allergen (Pso o 2), P. ovis mu class glutathione S-transferase (PoGST-mu1) and P. ovis beta tubulin (Poβtub). This is the first demonstration of gene silencing by RNAi in P. ovis and provides a key mechanism for mining transcriptomic and genomic datasets in the future for novel targets of intervention against P. ovis. The first assessment of gene silencing was also performed in two related Astigmatid mites of high medical importance; the European house dust mite Dermatophagoides pteronyssinus and the scabies mite Sarcoptes scabiei. A statistically-significant reduction in expression of a D. pteronyssinus mu class glutathione S-transferase (DpGST-mu1) transcript was observed. No significant reduction in expression of a S. scabiei mu class glutathione S-transferase (SsGST-mu1) transcript was observed. Additionally, microRNAs (miRNAs) from the related miRNA pathway were identified in a P. ovis small RNA sample and were sequenced and annotated.