An investigation of endemic and emerging tick-borne Protozoa and Rickettsia in Scottish livestock

Q Science (General);SF600 Veterinary Medicine

Gray, Alexander Geoffrey ; Weir, William

University:University of Glasgow

Department:Institute of Biodiversity Animal Health and Comparative Medicine

关键词: Tick-borne disease, Babesia divergens, B. divergens, Anaplasma phagocytophilum, A. phagocytophilum, tick-borne fever, TBF, livestock, sheep, cattle, red deer, Cervus elaphus, C. elaphus, roe deer, Capreolus capreolus, C. capreolus, Babesia sp. EU1, Babesia venatorum, B. venatorum, Sarcocystis, Sarcocystis tenella, S. tenella, Babesia odocoilei-like, B. odocoilei-like, polymerase chain reaction, PCR, 18S rRNA gene, 16S rRNA gene, msp4, Scotland, Scottish, Scottish Agricultural College Consulting, SAC Consulting, SAC, Scotland’s Rural College, SRUC, survey of large animal veterinary surgeons.;   

Others  :  http://theses.gla.ac.uk/8750/1/2017grayphd.pdf

来源: University of Glasgow

【 摘 要 】

This project set out to determine the importance of tick-borne protozoan and bacterial pathogens in Scottish livestock. The study comprised several aspects including a national survey of large animal veterinary surgeons, an appraisal of cases of tick-borne disease observed by Scottish Disease Surveillance Centres, the development of a novel assay to detect piroplasms and a targeted cross- sectional study of livestock and deer in the north of Scotland.A survey of the experiences of veterinary surgeons treating livestock in Scotland revealed cases of babesiosis (Babesia divergens) in cattle and tick-borne fever (Anaplasma phagocytophilum) in sheep. Examination of the records of the Scottish Agricultural College Consulting Disease Surveillance Centres for the years 2000 - 2013 revealed cases of babesiosis in cattle (n = 55) along with tick- borne fever and related disease in sheep (n = 116) and cattle (n = 6). Taking a combined passive and active surveillance approach, clinical material was obtained from a large number of healthy sheep, cattle and wild red deer (Cervus elaphus) together with a number of cattle and sheep suspected or confirmed as having a tick-borne disease. All samples were examined using a genus-specific nested PCR targeting the v4 region of the Babesia/Theileria 18S rRNA gene, which was developed and validated in the course of this study. This gene segment was confirmed as being capable of differentiating a diverse range of Babesia and Theileria spp. based on direct sequencing of PCR amplicons. A nested PCR assay targeting the 16S rRNA gene of A. phagocytophilum was also applied to each clinical sample and, if positive, the msp4 locus was also amplified and sequenced.Babesia ventatorum, a parasite typically associated with the roe deer (Capreolus capreolus) in Europe, was detected in 9 % of healthy sheep. Significantly, this is the first description of this parasite in sheep or in a vertebrate host in the United Kingdom. Babesia divergens was found in 11 % of wild red deer, confirming the presence of this parasite in this host species by molecular means for the first time in Scotland. Additionally a Babesia odocoilei-like parasite was found in 15 % of wild red deer, again for the first time in Scotland and only the second time in Europe. In cattle, B. divergens was confirmed as the cause of three clinical cases of babesiosis and was also found in the blood of 6 % of healthy cattle in December.Anaplasma phagocytophilum was found at a high prevalence in healthy sheep (73 %) and red deer (40 %) and at lower levels in healthy cattle (2.8 %). Comparison of msp4 gene sequences confirmed identical or highly similar msp4 genotypes in sheep and deer. Red deer were infected with larger numbers of msp4 genotypes than sheep and infection with multiple genotypes increased over the course of a grazing season on tick-infested hill land. Anaplasma phagocytophilum is zoonotic and can also have negative welfare and economic impacts in both sheep and, to a lesser extent, cattle and so these findings are highly significant. An incidental finding was Sarcocystis sp. similar to S. tenella in 3 % of healthy sheep.These results of this work clearly show what can be achieved by an active surveillance approach, using a ‘catch all’ molecular assay. In summary, this study discovered a novel, zoonotic pathogen in Scottish livestock and demonstrated that an endemic and arguably largely overlooked bacterium, A. phagocytophilum, is highly prevalent in the sheep population in tick-risk areas. Moreover, genotyping of this pathogen and B. divergens in both livestock and deer has provided new insights into potential reservoirs of infection for these organisms.