Laboratoire de Parasitologie, Ecole Nationale de Médecine Vétérinaire, Institution de la Recherche et de l'Enseignement Supérieur Agricoles and La Manouba University, 2020 Sidi Thabet, Tunisia.
Vet Parasitol. 2012 Nov 23;190(1-2):230-40. doi: 10.1016/j.vetpar.2012.05.017. Epub 2012 May 23.
The ixodid ticks from the Hyalomma genus are important pests of livestock, having major medical and veterinary significance in Northern Africa. Beside their direct pathogenic effects, these species are vectors of important diseases of livestock and in some instances of zoonoses. Anti-tick vaccines developed in Australia and Cuba based on the concealed antigen Bm86 have variable efficacy against H. anatolicum and H. dromedarii. This variation in vaccine efficacy could be explained by the variability in protein sequence between the recombinant Bm86 vaccine and Bm86 orthologs expressed in different Hyalomma species. Bm86 orthologs from three Hyalomma tick species were amplified in two overlapping fragments and sequenced. The rate of identity of the amino acid sequence of Hm86, He86 and Hdr86, the orthologs of Bm86, respectively, in H. marginatum marginatum, H. excavatum and H. dromedarii, with the Bm86 proteins from Rhipicephalus microplus (Australia, Argentina and Mozambique) ranged between 60 and 66%. The obtained amino-acid sequences of Hmm86, He86 and Hdr86 were compared with the Hd86-A1 sequence from H. scupense used as an experimental vaccine. The results showed an identity of 91, 88 and 87% for Hmm86, He86 and Hdr86, respectively. A specific program has been used to predict B cells epitopes sites. The comparison of antigenic sites between Hd86-A1 and Hm86/Hdr86/He86 revealed a diversity affecting 4, 8 and 12 antigenic peptides out of a total of 28 antigenic peptides, respectively. When the Bm86 orthologs amplification protocol adopted in this study was applied to H. excavatum, two alleles named He86p2a1 and He86p2a2 were detected in this species. This is the first time that two different alleles of Bm86 gene are recorded in the same tick specimen. He86p2a1 and He86p2a2 showed an amino acid identity of 92%. When He86p2a1 and He86p2a2 were compared to the corresponding sequence of Hd86-A1 protein, an identity of 86.4 and 91.0% was recorded, respectively. When compared to He86, Hdr86 and Hm86, Bm86 used in commercial and experimental vaccines, showed a greater extent of diversity than noted when the same Hyalomma orthologs were compared to Hd86-A1. Although significant, these variations were less extensive within the Hyalomma genus. Accordingly, thus suggesting that Hd86-A1 vaccine candidate might be more appropriate to target Hyalomma tick species than corresponding Bm86 commercial vaccines. However, vaccination trials with both antigens are required to validate this hypothesis.
属钝缘蜱的璃眼蜱是重要的家畜害虫，在北非具有重要的医学和兽医意义。除了直接的致病作用外，这些物种还是重要家畜疾病的媒介，在某些情况下还是人畜共患病的媒介。基于隐蔽抗原 Bm86 在澳大利亚和古巴开发的抗蜱疫苗对 H. anatolicum 和 H. dromedarii 的有效性各不相同。疫苗效力的这种变化可以用重组 Bm86 疫苗和不同钝缘蜱物种中表达的 Bm86 同源物之间的蛋白质序列的可变性来解释。从三种钝缘蜱物种中扩增了两个重叠片段并进行了测序。Hm86、He86 和 Hdr86 的氨基酸序列的同一性，分别是 Bm86 的同源物，在 H. marginatum marginatum、H. excavatum 和 H. dromedarii 中，与来自 Rhipicephalus microplus（澳大利亚、阿根廷和莫桑比克）的 Bm86 蛋白的同一性在 60%至 66%之间。获得的 Hmm86、He86 和 Hdr86 的氨基酸序列与用作实验疫苗的 H. scupense 的 Hd86-A1 序列进行了比较。结果表明，Hmm86、He86 和 Hdr86 的同一性分别为 91%、88%和 87%。使用了一个专门的程序来预测 B 细胞表位位点。比较 Hd86-A1 与 Hmm86/Hdr86/He86 的抗原位点显示，总共 28 个抗原肽中有 4、8 和 12 个抗原肽受到多样性影响。当在这项研究中采用 Bm86 同源物扩增方案应用于 H. excavatum 时，在该物种中检测到两个等位基因，分别命名为 He86p2a1 和 He86p2a2。这是第一次在同一蜱标本中记录到 Bm86 基因的两个不同等位基因。He86p2a1 和 He86p2a2 的氨基酸同一性为 92%。当将 He86p2a1 和 He86p2a2 与 Hd86-A1 蛋白的相应序列进行比较时，记录到 86.4%和 91.0%的同一性。与 He86、Hdr86 和 Hm86 相比，商业和实验疫苗中使用的 Bm86 表现出比与 Hd86-A1 同源物比较时更大的多样性程度。尽管差异显著，但在钝缘蜱属内的这种变化范围较小。因此，这表明 Hd86-A1 候选疫苗可能比相应的 Bm86 商业疫苗更适合针对钝缘蜱物种。然而，需要进行两种抗原的接种试验来验证这一假设。
