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Persistently infected African buffalo not a likely cause of new FMD outbreaks say Pirbright scientists

12 August 2020

Scientists at The Pirbright Institute have shown that African buffalo persistently infected with foot-and-mouth disease (FMD) are unlikely to be the source of new outbreaks in other buffalo and cattle.

African buffalo do not usually present any clinical signs of infection and can carry FMD for years and can therefore act as an important reservoir for the disease which can spill over into livestock populations and cause severe productivity losses. Previously it was thought that buffalo with long term infections could generate new genetic variations of FMD virus enabling outbreaks in neighbouring buffalo and cattle herds.

Dr Bryan Charleston, Director of The Pirbright Institute and Head of the Viral Immunology Group, said “Genetic changes during persistent infection are important to analyse as they allow us to understand how the virus alters over the course of infection. If mutations occur that alter the virus significantly enough for it to evade the buffalo immune system, this could give rise to virus variants that have the potential to generate new outbreaks”.

New variants of FMD are more likely to occur due to mutation in the early acute phase of infection when viral replication levels are at their highest. To assess if new variants could arise during persistent infection scientists analysed genomes of FMD viruses isolated from multiple tissues of buffalo up to 400 days after infection.

The results, published in the Journal of Virology, show that only a small number of mutations had accumulated over this time period. Most of these changes are known as ‘silent mutations’, meaning that they made no change to the structure or function of the virus. The findings show that the virus does not mutate sufficiently enough during persistent infection to evade the immune response and become a major source of new outbreaks.

FMD incurs large economic costs and is recognized as an important constraint to international trade of animals and animal products. This research increases knowledge about the way FMD persists in carriers and provides clarity about the potential sources of new outbreaks, which is important for FMD prevention and control.

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