Ali A M, Salih D A, Njahira M N, Hassan S K, El Hussein A M, Liu Z, Yin H, Pelle R, Skilton R A
Biosciences eastern and central Africa-International Livestock Research Institute (BecA-ILRI) Hub, P.O. Box 30709-00100, Nairobi, Kenya; University of Khartoum, Faculty of Veterinary Medicine, Khartoum, Sudan.
Biosciences eastern and central Africa-International Livestock Research Institute (BecA-ILRI) Hub, P.O. Box 30709-00100, Nairobi, Kenya; Central Veterinary Research Laboratory, P.O. Box 8067, Khartoum, Sudan.
Vet Parasitol. 2017 May 30;239:7-14. doi: 10.1016/j.vetpar.2017.04.005. Epub 2017 Apr 4.
Theileriosis, caused by parasitic protozoa of the genus Theileria parasites, are among the major tick-borne diseases of ruminant livestock. The largest economic losses are attributed in particular to those caused by the leukoproliferative species of Theileria: T. parva, T. annulata and T. lestoquardi. Theileria lestoquardi is transmitted by Hyalomma ticks and causes malignant ovine theileriosis (MOT), a disease that is particularly prevalent in Sudan. The disease is considered of a high economic importance in Sudan, where export of sheep is a major component of the national economy. A live vaccine based on a Sudanese isolate of T. lestoquardi (Atbara strain) was previously developed for the control of MOT in Sudan, but not yet deployed in the field. The present study aims to genetically characterize and compare samples of T. lestoquardi circulating in Sudan as well as the live vaccine isolate in order to understand vaccine breakthroughs and failure that may occur. Sheep and goats blood samples were collected from six regions in Sudan that are known to be endemic for T. lestoquardi infection or have experienced outbreaks of MOT. Blood samples infected with T. lestoquardi were identified by PCR or RLB. Genotyping was carried out by (1) sequencing the homologues of two T. parva CD8 T cell antigen genes, Tp1 and Tp2, and (2) using a panel of seven micro- and mini-satellite markers. A total of 100 T. lestoquardi positive field samples and the T. lestoquardi (Atbara) vaccine were genotyped. The results showed that all samples had mixed genotypes, with several alleles identified at one or more loci. The gene diversity ranged from 0.7840 (TS8) to 0.2133 (TS12) with mean values of 0.5470. PCA revealed three clusters of the parasite in Sudan; interestingly one independent cluster was clearly seen, corresponding to the vaccine isolate. The T. lestoquardi Tp1 homologue showed higher homology with T. annulata than with T. parva sequences included the defined single CD8 T cell target epitope region. The result indicates that multiple genotypes are a common feature of T. lestoquardi infection in Sudan. Both genotyping and the sequencing results clearly showed that the vaccine isolate is highly distinct from the field samples. This finding raised the question whether vaccination with the prepared lived vaccine will effectively protect animals against challenges by the field isolates of T. lestoquardi. The results of this work will inform on the best approach for controlling MOT in Sudan.
泰勒虫病由泰勒虫属的寄生原生动物引起，是反刍家畜主要的蜱传疾病之一。最大的经济损失尤其归因于泰勒虫的白细胞增生种类：小泰勒虫、环形泰勒虫和莱氏泰勒虫。莱氏泰勒虫通过璃眼蜱传播，引起恶性绵羊泰勒虫病（MOT），该病在苏丹特别流行。在苏丹，绵羊出口是国民经济的一个主要组成部分，因此该病被认为具有很高的经济重要性。此前已开发出一种基于莱氏泰勒虫苏丹分离株（阿特巴拉株）的活疫苗，用于控制苏丹的MOT，但尚未在实地部署。本研究旨在对苏丹流行的莱氏泰勒虫样本以及活疫苗分离株进行基因特征分析和比较，以了解可能出现的疫苗突破和失败情况。从苏丹已知莱氏泰勒虫感染流行或曾发生MOT疫情的六个地区采集绵羊和山羊血样。通过PCR或RLB鉴定感染莱氏泰勒虫的血样。基因分型通过（1）对两个小泰勒虫CD8 T细胞抗原基因Tp1和Tp2的同源物进行测序，以及（2）使用一组七个微卫星和小卫星标记来进行。共对100份莱氏泰勒虫阳性野外样本和莱氏泰勒虫（阿特巴拉）疫苗进行了基因分型。结果表明，所有样本均为混合基因型，在一个或多个位点鉴定出多个等位基因。基因多样性范围从0.7840（TS8）到0.2133（TS12），平均值为0.5470。主成分分析揭示了苏丹寄生虫的三个聚类；有趣的是，明显可见一个独立聚类，对应于疫苗分离株。莱氏泰勒虫Tp1同源物与环形泰勒虫的同源性高于与小泰勒虫序列的同源性，包括定义的单个CD8 T细胞靶表位区域。结果表明，多种基因型是苏丹莱氏泰勒虫感染的一个共同特征。基因分型和测序结果均清楚表明，疫苗分离株与野外样本高度不同。这一发现提出了一个问题，即使用制备的活疫苗进行接种是否能有效保护动物免受莱氏泰勒虫野外分离株的挑战。这项工作的结果将为苏丹控制MOT的最佳方法提供信息。
