Abstract
In 2012, equine influenza (EI) virus was confirmed as the cause of outbreaks of respiratory disease in horses throughout South America. In Uruguay and Argentina, hundreds of vaccinated thoroughbred horses in training and racing facilities were clinically affected. To characterise the EI viruses detected during the outbreak in Uruguay and Argentina. Virus was detected in nasopharyngeal swabs by a pan-reactive influenza type A real-time RT-PCR. The nucleotide sequence of the HA1 gene was determined and analysed phylogenetically using mega 5 software. Amino acid sequences alignments were constructed and virus was antigenically characterised with specific ferret antisera. Paired serum samples were tested by haemagglutination inhibition and single radial haemolysis. The diagnosis of EIV was confirmed by real-time RT-PCR, virus isolation and serological testing. The phylogenetic analysis of HA1 gene sequences of 18 EI viruses indicated that all of them belong to clade 1 of the Florida sublineage of the American lineage and are closely related to viruses isolated in the United States in 2012. The HA1 of viruses identified in horses in racing facilities in Maroñas, Uruguay, and in Palermo, Argentina, displayed 100% amino acid sequence identity and were identical to that of a virus isolated in Dubai in 2012, from vaccinated endurance horses recently imported from Uruguay. The surveillance data reported illustrate the international spread of EI viruses and support the recommendations of the OIE expert surveillance panel to include viruses of the Florida sublineage in vaccines.
Highlights
Subsequent evolution within the Florida sublineage has resulted in the emergence of two distinct clades, designated as Florida clade 1 and Florida clade 2.11,12 Florida clade 1 viruses are endemic in the United States (USA) but have caused outbreaks in South Africa,[13] Japan,[14] Australia 15 and Europe.[11,16,17,18,19]
In February 2012, several horses suffering an acute respiratory disease were observed by private veterinarians in Maron~as thoroughbred racing and training facilities, in Montevideo, Uruguay
The phylogenetic analysis of HA1 gene sequences of 18 Equine influenza (EI) viruses detected in South America indicated that all of them belong to clade 1 of the Florida sublineage of the American lineage (Figure 2) and are closely related to viruses isolated in the United States in 2012
Summary
Equine influenza (EI) is one of the most economically important respiratory diseases of horses, due to its contagious nature and rapid spread among susceptible horses.[1,2,3] Equine influenza virus (EIV) is endemic in the European and American continents, and large outbreaks of the disease are often associated with the congregation of horses for equestrian events and competition.[3,4] Two subtypes of influenza A virus, H7N7 and H3N8, have been associated with this disease in horses.[5,6] Equine influenza viruses currently circulating in horses belong to the H3N8 subtype and are responsible for widespread outbreaks of disease in both vaccinated and unvaccinated horses.[2,7] Phylogenetic analysis of the haemagglutinin (HA) gene revealed that equine H3N8 viruses diverged during the mid-1980s and early 1990s into two distinct evolutionary lineages namely the Eurasian and the American lineages.[8]. In 2012, equine influenza (EI) virus was confirmed as the cause of outbreaks of respiratory disease in horses throughout South America. In Uruguay and Argentina, hundreds of vaccinated thoroughbred horses in training and racing facilities were clinically affected
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