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

This research article discusses a study on Theiler’s disease-associated virus (TDAV) in horses, where the genomes of four different strains of the virus were sequenced and compared to increase the understanding of TDAV’s genetic diversity.

Introduction to Theiler’s Disease and TDAV

• Theiler’s disease is a disease in equines, potentially caused by Theiler’s disease-associated virus (TDAV).
• It has been observed that horses experimentally infected with TDAV through equine plasma tend to develop acute and chronic infections and viraemia, a condition where the virus enters the bloodstream and hence has access to the rest of the body.
• Despite its initial detection in 2013, the virus has not been found in horses in subsequent epidemiological studies.

Sequencing and Analysis of TDAV Genomes

• In this study, the researchers sequenced the genome of four different TDAV strains (A/China, F/China, H/USA, and I/USA) that were found in commercial equine serum, a component used for the propagation of cell cultures.
• The reverse transcription-polymerase chain reaction (RT-PCR) technique was used over three rounds to complete the sequencing. The PCR process amplifies specific DNA samples to large amounts, and when combined with reverse transcription, can be used to convert RNA into DNA, which can be sequenced.
• The primers for the PCR were designed based on a previously obtained TDAV genome sequence, HorseA1_serum.

Comparison and Implications of Findings

• All the four strains had a polyprotein gene of the same length (9567 nt) as that in the HorseA1_serum strain.
• Analysis of the different sequences helped demonstrate the genetic diversity between the different TDAV strains, with the nucleotide similarity of the polyprotein genes ranging from 90.3 to 93.6% and the amino acid similarity ranging from 98.2 to 98.8%.
• Phylogenetic analysis, which is typically used to understand the evolutionary relationships between different species, was carried out using the polyprotein gene. The result showed that the four new strains were closely related to the HorseA1_serum strain and belonged to the Pegivirus D genus.
• The study overall enriches the current understanding of TDAV, providing further insights into its genetic make-up and diversity.