The authors have declared that no competing interests exist.
In the pre-virological era equine flu outbreaks were described based on clinical signs and on disease spreading pattern. Human flu cases were also described concomitant with those animal outbreaks. By that time there was none/or little knowledge about the agent that was causing those clinical signs in humans and animals. The equine influenza (EI) would cause serious impact in cities where horses were the major type of transportation
With science evolution, the agent that was causing flu was first identified from pigs
The techniques HA - hemagglutination assay, HI - inhibition of hemagglutination assay and virus isolation in embryonated chicken eggs, are deeply used to study EIV outbreaks
Initially, the EIVs H3N8 subtypes were defined in a single phylogenetic group
In South America, EIV outbreaks caused by the H3N8 subtype were described in Brazil in 1963, 1969, 1985, 1988, 2001, 2012 and 2015
In 2012, outbreaks occurred in the United States, Argentina, Brazil, Uruguay and Dubai. The strains had high nucleotide identity and belonged to FC1
An outbreak occurred in Brazil in 2015 in a veterinary hospital in the city of São Paulo (State of São Paulo) and different variants were found suggesting the evolution the virus suffered during the same outbreak
Before 2012, only a few studies about the circulating EIVs in South America were described. The surveillance studies of EIV in South America provide information about which strains are causing the outbreaks and control/prevention actions that might be applied such as the use of epidemiologically relevant strains in EIV vaccination