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Molecular and Phylogenetic Study of Bm86 Gene Ortholog from Hyalomma excavatum Tick from Tunisia: Taxonomic and Immunologic Interest

Mourad Ben Said, Moez Mhadhbi, Mohamed Gharbi, Yousr Galaï1, Limam Sassi, Mohamed Jedidi and Mohamed Aziz Darghouth

In order to assess the taxonomic and immunologic interest of Bm86 orthologs of Hyalomma ticks, partial sequence of Bm86 gene was amplified and sequenced. The sequences were isolated from three engorged Hyalomma excavatum females (Ariana strain, Tunisia). The analysis of nucleotide sequences showed increasing diversity rates of 0.26, 2.36, 4.97 and 6.02% between analyzed sequences and those isolated from H. excavatum specimen from a laboratory colony (Sousse strain, Tunisia), H. anatolicum, H. marginatum and H. scupense, respectively. The phylogenetic study showed a perfect agreement with recent data of systematic of ticks. This proves that genetic analysis of Bm86 orthologs isolated from Hyalomma ticks could be used to assist morphological diagnosis. In addition, amino-acid sequence comparison showed a high diversity rate (33-34%) between Bm86 and He86-A1/A2/A3 (Ariana strains) which can decrease the effectiveness of vaccination by commercial and experimental vaccines based on Bm86 against H. excavatum. Amino-acid diversity between Hd86-A1 used in an experimental vaccine against H. scupense and He86-A1/A2/A3 (Ariana isolates) was more limited (10.2%), thus suggesting that Hd86-A1 vaccine candidate might be more appropriate to target H. excavatum tick than corresponding Bm86 vaccines.