Since the middle of March, the United Kingdom’s Animal Health Trust (AHT) has confirmed influenza in 20 racing yards (stables) in Newmarket, located in different areas of the town, and in a single breaking/holding yard just outside Newmarket. Most of these diagnoses have been made on the basis of nucleoprotein ELISA positive swab samples but two have been diagnosed on the basis of seroconversions on paired blood samples. The last yard was diagnosed on April 28, with a positive ELISA on a nasopharyngeal swab from a coughing horse.

Consistent with previous influenza outbreaks among Thoroughbred racehorses, clinical signs have been relatively mild compared to infections among non-vaccinated horses. Signs in the current outbreak have included acute coughing, mainly at exercise, with some horses developing a nasal discharge. Fever has been seen but is not a consistent sign. An unusual feature of the current outbreak is that, in most affected yards, the first horses to develop disease have been three-year-olds or older horses