Case Report of Equine Influenza in Italy, in 2014

Equine influenza (EI) is a highly contagious respiratory disease presently caused by subtype H3N8. As no active surveillance is ongoing in Italy, clinical observations of veterinary practitioners would indicate the infection as endemic. This study reports the isolation and genetic characterization of an EI virus (EIV) from a stable of Thoroughbred race horses. The episode was characterized by fever and dry cough and involved eleven, 2- to 3-year-old, flu vaccinated horses, four of which were found positive for EIV, by reverse-transcriptase real-time polymerase chain reaction (RRT-PCR) targeting the matrix gene. The EIV of two of the four RRT-PCR positive samples was successfully passaged in embryonated chicken eggs. Analysis of amino acid (AA) sequences of hemagglutination (HA) residues detected seven substitutions in the Italian isolate when compared with the prototype strain A/eq/Richmond/1/2007 (H3N8 American lineage, Florida clade 2). The constructed phylogenetic tree locates the present strain within the Florida clade 2, together with viruses isolated between 2011 and 2014 in Algeria, China, Eire, Germany, Japan, Mongolia, and the United Kingdom. Within this cluster, the Italian isolate presents 100% AA identity with A/eq/North Rhine Westphalia/1/2014, responsible of an outbreak in Germany around the same period. Even if vaccinated, only two of the 11 clinically involved animals, different from the EIV-positive animals, reacted positive in HA inhibition. Monitoring of the circulating strains of EIV is essential especially for verifying the appropriateness of the vaccine virus composition, as recommended by the OIE Panel of experts, on the basis of the genetic and antigenic characteristics of emerging strains.