Bilgic Huseyin Bilgin, Aksulu Ayça, Bakırcı Serkan, Unlu Ahmet Hakan, Kose Onur, Hacılarlıoglu Selin, Weir William, Karagenc Tulin
Aydin Adnan Menderes University, Faculty of Veterinary Medicine, Department of Parasitology, 09016, Isıklı, Aydın, Turkey.
Van Yuzuncu Yil University, Vocational high School of Gevas, Department of Veterinary Medicine, Programme of Laboratorian and Veterinary Health, 65700, Van, Turkey.
Vet Parasitol. 2019 Jan;265:63-73. doi: 10.1016/j.vetpar.2018.11.012. Epub 2018 Dec 7.
Tropical theileriosis is a tick-borne haemoparasitic disease of cattle caused by the protozoan parasite Theileria annulata. Globally, the economic impact of the disease is immense and enhanced control measures would improve livestock production in endemic regions. Immunisation with a live attenuated vaccine is an effective and widely used control method, however, the repeated use of live vaccines may have an impact on the field parasite population at a genetic level. Additionally, there has been an increasing number of reports of vaccine breakthrough cases in recent years. Thus, the present study was designed to evaluate the genetic composition of a parasite population over a disease season in a locality where live cell line vaccination is practised. A diverse range of parasite genotypes was identified and every T. annulata positive cattle blood sample harboured multiple parasite genotypes. An alteration in the major genotype and an increasing multiplicity of infection in individual animals was observed over the course of the disease season. Vaccination status was found not to effect within-host multiplicity of infection, while a significantly higher number of genotypes was detected in grazed cattle compared to non-grazed ones. A degree of genetic isolation was evident between parasite populations on a micro-geographic scale, which has not been reported previously for T. annulata. Analysis of parasite genotypes in vaccinated animals suggested only a transient effect of the vaccine genotype on the genetic diversity of the T. annulata population. The vaccine genotype was not detected among clones of two vaccine 'breakthrough' isolates and there is no suggestion that it was responsible for disease. The obtained data indicated that in the system studied there is no apparent risk of introducing the vaccine genotype into the population with only a transient effect on the genetic diversity of the parasite population during the disease season.
热带泰勒虫病是由原生动物寄生虫环形泰勒虫引起的一种牛蜱传血液寄生虫病。在全球范围内，该病的经济影响巨大，加强防控措施将改善流行地区的畜牧业生产。使用减毒活疫苗进行免疫是一种有效且广泛应用的防控方法，然而，重复使用活疫苗可能会在基因水平上对田间寄生虫种群产生影响。此外，近年来疫苗突破病例的报道越来越多。因此，本研究旨在评估在一个实施活细胞系疫苗接种的地区，一个疾病季节内寄生虫种群的基因组成。鉴定出了多种寄生虫基因型，每一份环形泰勒虫阳性牛血样本都含有多种寄生虫基因型。在疾病季节过程中，观察到主要基因型发生了改变，个体动物的感染复数增加。发现疫苗接种状态不影响宿主体内的感染复数，而与非放牧牛相比，放牧牛中检测到的基因型数量显著更多。在微观地理尺度上，寄生虫种群之间存在一定程度的基因隔离，这在环形泰勒虫中此前尚未见报道。对接种疫苗动物的寄生虫基因型分析表明，疫苗基因型对环形泰勒虫种群的遗传多样性仅产生短暂影响。在两株疫苗“突破”分离株的克隆中未检测到疫苗基因型，也没有迹象表明它与疾病有关。所获得的数据表明，在所研究的系统中，没有明显的风险将疫苗基因型引入种群，并且在疾病季节对寄生虫种群的遗传多样性仅产生短暂影响。
