Evidence of equine influenza A (H3N8) activity in horses from Eastern and Central Saudi Arabia: 2013-2015

Background: Equine influenza virus (EIV) is one of the main causes of viral respiratory affections in horses. Little is known about the prevalence of EIV in Saudi Arabia especially the H3N8 serotype. Objectives: To assess prevalence of equine influenza in horse populations in Eastern and Central Saudi Arabia. Study design: Cross-sectional study. Methods: We collected 145 sera, 323 nasal and 323 rectal swabs from horses from six major cities in Eastern and Central regions. None of the horses were vaccinated against EIV. Sera were tested in ELISA assays for influenza A type-specific antibodies and by haemagglutination inhibition (HI) tests using equine H3N8. The swabs were tested by RT-qPCR assay targeting a conserved region of the influenza A matrix gene that detects influenza A viruses of all subtypes. Results: None of the swabs had detectable influenza A virus RNA. Of the 145 serasamples tested by ELISA, 81 (55.9%) were positive and 98 (67.6%) of 145 sera tested by HI tests were positive for equine H3. Main limitations: Our failure to detect and sequence any EIV prevents identification of the lineage of virus that circulates in the Kingdom of Saudi Arabia. Conclusions: These results confirm that EIV H3N8 is circulating in Saudi Arabia and should be considered as a possible cause when investigating horses with respiratory disease in Saudi Arabia.