Equine flu findings in Britain back currently recommended vaccine strains

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The influenza virus viewed under an electron microscope. Image: Centers for Disease Control and Prevention
The influenza virus viewed under an electron microscope. Image: Centers for Disease Control and Prevention

Researchers who examined changes in the equine flu viruses circulating in Britain in recent years found no evidence of significant antigenic drift away from the recommended vaccine strains.

The study team from Britain’s Animal Health Trust and the London-based Crick Worldwide Influenza Centre set out to learn more about the evolution and divergence of H3N8 equine flu virus circulating in the country from 2013 to 2015.

Equine influenza viruses are a major cause of acute respiratory disease in horses worldwide and occasionally also affect vaccinated animals.

Like other influenza A viruses, they can undergo changes, which highlights the importance of monitoring the virus to ensure that vaccine strains are kept up to date.

As well as checking for any genetic and antigenic changes in the virus circulating in Britain, the researchers also wanted to identify any evidence of vaccine breakdown in the field.

Sixty-nine outbreaks of equine influenza in Britain were reported by the Animal Health Trust between January 2013 and December 2015. These affected 28 counties in England, 8 in Scotland and 2 in Wales, with multiple outbreaks in some areas.

Forty-seven viruses were successfully isolated in eggs from 41 of the outbreaks for subsequent DNA analysis.

Gene sequencing revealed that all of the viruses belonged to the Florida clade 2 sub-lineage of H3N8.

Further analysis showed that the two known sub-populations previously identified within clade 2 − − 144-group and 179-group − continued to circulate and had accrued further amino acid substitutions.

However, antigenic characterisation tests failed to detect any marked antigenic differences between the isolates.

“These findings show that Florida clade 2 equine influenza virus continue to circulate in the UK and support the current OIE [World Organisation for Animal Health] recommendation to include an example of Florida clade 2 in vaccines,” Adam Rash and his colleagues reported in the journal Pathogens.

No clade 1 viruses were isolated during the time period studied in Britain.

The viruses, they noted, had acquired further mutations in both the haemagglutinin and neuraminidase genes. “Therefore careful monitoring is required to identify antigenic drift at an early stage.”

The researchers said only three cases of vaccine breakdown were identified and in each case the vaccine used contained a virus antigen not currently recommended for equine flu vaccines.

The study team concluded that Florida clade 2 had continued to diverge, noting that the 144-group viruses predominated in Britain and the 179-group viruses in Europe. However, they said there was a shortage of sequence data available from Europe for recent years.

“There is no evidence of significant antigenic drift away from the recommended vaccine strains.

“The current recommendations to include coverage in Florida clade 2 as well as Florida clade 1 therefore still stand.”

The study team comprised Rash, Rachel Morton, Alana Woodward, Olivia Maes, Neil Bryant and Debra Elton, all from the Animal Health Trust; and  John McCauley, from the Crick Worldwide Influenza Centre.

Evolution and Divergence of H3N8 Equine Influenza Viruses Circulating in the United Kingdom from 2013 to 2015
Adam Rash, Rachel Morton, Alana Woodward, Olivia Maes, John McCauley, Neil Bryant and Debra Elton
Pathogens 2017, 6(1), 6; doi:10.3390/pathogens6010006

The study, published under a Creative Commons License, can be read here

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