Abstract: [Objective] To investigate the infection status of equine influenza virus in large-scale donkey farms in Liaocheng City of Shandong Province, and to identify the possible sources of the virus. [Method] Clinical samples were collected from the large-scale donkey farms in Liaocheng City. The positive rate of serum antibodies against H3N8 subtype of equine influenza virus was determined by HI test. RT-PCR was used to amplify the M gene of equine influenza virus in lungs and nasal swabs. The obtained M gene was sequenced and compared with the M gene of different influenza viruses to infer its origin. [Result] HI test showed that the positive rate of equine influenza virus H3N8 subtype in 120 serum samples was 33.3% （40/120）. The positive rate for female donkeys, male donkeys and donkey foals was 42.5% （17/40）, 32.5% （13/40） and 25.0% （10/40）, respectively. RT-PCR assay demonstrated that 32.3% （21/65） of the samples was detected as positive for the presence of M gene. The M gene obtained in this study is highly homologous to H3N8 subtype influenza virus of equine （CY032222, CY032318, CY028821, etc.）, with the highest homology of 99.8%. [Conclusion] Equine influenza virus is prevalent in several large-scale donkey farms around Liaocheng City. The M gene of influenza virus obtained from donkeys in this study belongs to the M gene of H3N8 subtype of equine influenza virus.

Key words: large-scale donkey farms, equine influenza virus, H3N8 subtype, RT-PCR, antibody