Genomic sequencing and characterization of Theiler's disease-associated virus identified in commercial equine sera in China.

Abstract

Theiler's disease-associated virus (TDAV) could be the aetiological agent of Theiler's disease. Horses experimentally inoculated with equine plasma containing TDAV develop acute and chronic infections with viraemia. Since its first identification in 2013, TDAV has not been detected in equines in the epidemiological studies that have been conducted. Until now, only one genome sequence of TDAV (HorseA1_serum) had been obtained. In this study, we sequenced the genome of four TDAV strains (A/China, F/China, H/USA and I/USA) in commercial equine sera used for cell culture propagation in China using three rounds of RT-PCR. The PCR primers were designed based on the HorseA1_serum genome sequence. All four TDAV strains had a polyprotein gene that was 9567 nt long, the same nucleotide length as the polyprotein gene of HorseA1_serum. Sequence analysis demonstrated the genetic diversity of TDAV. The nucleotide similarity of the polyprotein genes of the TDAV strains ranged between 90.3 and 93.6 %, with a high amino acid similarity that ranged from 98.2 to 98.8 %. Phylogenetic analysis using the polyprotein gene showed that A/China, F/China, H/USA and I/USA were clustered together with HorseA1_serum in the genus Pegivirus D. This study enriches our knowledge of the genetic diversity of TDAV.