New pig flu strain may be going undetected on farms

Scientists have discovered the standard surveillance test for flu in livestock is ineffective for strains of H3N8 in pigs, meaning cases of the illness may be going undetected on farms. 

A study, led by Dr Maria Montoya from The Pirbright Institute in Surrey and the Centre for Research in Animal Health (CReSA) in Barcelona, also revealed that two different strains of the H3N8 influenza A virus (IAV) are able to infect and replicate in pigs – one strain was isolated from seals and a second avian strain which is circulating in poultry in the US.

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Researchers are concerned that with H3N8 being difficult to detect in the pig population and being able to cross the species barrier it could become the cause of future outbreaks.

It has already been shown that the H1N1 strain, which caused a pandemic in 2009, had been circulating in the population before the outbreak.

However, Dr Montoya said there was no need for pig producers to panic at this stage.

She added: “There is no need for any alarm, but if farmers are suspicious of flu symptoms they should contact their vet and send samples for more detailed analysis.

“There is no need for any alarm, but if farmers are suspicious of flu symptoms they should contact their vet and send samples for more detailed analysis”
Dr Maria Montoya

“The virus may be circulating without being noticed and it’s important to keep an eye on what is circulating on our farms,” she explained.

As the virus is very promiscuous and can infect many species, it can easily adapt and infect pigs, said Dr Montoya.

A single case of the H3N8 virus has been isolated on a pig farm in China, though in the UK its ability to cross species and infect pigs and cause clinical disease had only been proven under experimental conditions, she added.

According to the Pirbright Institute H3 viruses, in particular H3N8, are highly adaptive since they are found in multiple avian and mammal hosts. 

A report from the institute added that while human cases have not yet been found, the strain is known to be able to infect people following an early study in the 1950s.

As humans are more closely related to pigs than other livestock carriers of the virus, the institute said there was a concern that avian and pig strains may come together create a highly pathogenic virus more readily able to infect people.

The institute warned that if H3N8 is able to cross the species barrier and circulate undetected in pigs, then the chance of it coming together with circulating strains of avian influenza A viruses would be increased.