Flu virus in pigs shows worrisome pandemic profile, study finds

December 30, 2015 by Lisa Schnirring
Credit: liz west / Flickr cc

Tests on the most common type of influenza found in Chinese pigs reveal that it has the potential to transmit easily in humans, posing a pandemic threat similar to the virus that triggered a pandemic in 2009 after jumping from swine to people.

A research team from China and Japan isolated 139 Eurasian avian-like H1N1 swine influenza viruses during surveillance in Chinese pigs from 2010 to 2013, then put the virus through its paces to assess its pandemic threat, including experiments in ferrets to gauge transmissibility in mammals. They reported their findings yesterday in Proceedings of the National Academy of Sciences.

One of two swine H1N1 lineages, Eurasian avian-like H1N1 (EAH1N1) swine influenza viruses (SIVs) has been circulating in pigs in several Eurasian countries since 1979 and has infected several humans in Europe and in China, one fatally in China in 2011. Little is known about its evolution and properties, however, which researchers said prompted the study.

The team noted that China is the world's largest pork-producing country and that can spread easily once introduced to the unvaccinated herds.

Tests reveal transmissibility, virulence

For the surveillance part of the study, investigators sampled more than 34,000 pigs from 24 Chinese provinces. Of 228 SIVs isolated from the pigs, EAH1N1 was by far the most common strain and was found in 10 of China's provinces.

Genetic sequencing found that the strains formed five genotypes and fell into two antigenic groups, both distinct from the 2009 H1N1 virus: A/swine/Guangxi/18/2011 and A/swine/Guangdong/104/2013.

Other tests on the EAH1N1 SIVs showed that they preferentially bind to human-type receptors. The team also found that 9 of 10 viruses they tested transmitted by respiratory droplets in ferrets, considered the best experimental model for human flu.

The authors said the virus might be able to replicate well in humans and cause notable disease, based on mutations the group found on the virus' PB2 protein genes. Like the 2009 H1N1 virus, EAH1N1 SIV doesn't cause severe disease in pigs but may cause more notable disease in humans, they observed.

Little cross-protection adds to threat

Experiments to assess whether humans have any immunity to the viruses showed a small degree of antibody response to A/swine/Guangxi/18/2011, but none of the 159 people tested had neutralizing antibodies against A/swine/Guangdong/104/2013 in their blood.

Antibody findings and an earlier study that found no substantial cross-protection from seasonal flu vaccine against EAH1N1 SIV suggest that humans aren't likely to have much preexisting immunity to the virus, the team concluded.

Using a US Centers for Disease Control and Prevention risk assessment tool to look at the pandemic potential of influenza viruses, the researchers found that EAH1N1 SIV scored the highest of six viruses, which also included H5N1, H9N2, variant H3N2, H7N9, and avian H1N1. The result suggests that EAH1N1 SIVs "may pose the highest pandemic threat among the avian currently circulating in animals," they wrote.

Wake-up call

Michael Osterholm, PhD, MPH, director of the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP), publisher of CIDRAP News, praised the study and said the findings are "very sobering."

He said it may be a wake-up call that alerts the world to a virus that has pandemic potential similar to the one that emerged in 2009. He said that although the research community has been watching flu viruses in and poultry since the 1990s, the emergence of the in 2009 caught it by surprise.

Based on the new findings, studies are urgently needed to see if current vaccines or vaccine seed stock show any protection against EAH1N1 SIV, Osterholm said.

"This is why we need game-changing influenza vaccines,"' he added, noting that if another pandemic emerged tomorrow, the world would likely be faced again with too little pandemic vaccine, too late, offering, at best, moderate protection.

Explore further: Iran reports 112 swine flu deaths since mid-Nov

More information: Huanliang Yang et al. Prevalence, genetics, and transmissibility in ferrets of Eurasian avian-like H1N1 swine influenza viruses, Proceedings of the National Academy of Sciences (2015). DOI: 10.1073/pnas.1522643113

Related Stories

Iran reports 112 swine flu deaths since mid-Nov

December 28, 2015
A swine flu outbreak in Iran has killed 112 people since mid-November and the country's first medical worker has died of the virus, media said on Monday.

Scientists 'must not become complacent' when assessing pandemic threat from flu viruses

October 15, 2014
As our ability to assess the pandemic risk from strains of influenza virus increases with the latest scientific developments, we must not allow ourselves to become complacent that the most substantial threats have been identified, ...

CDC preparing vaccine for new swine flu

August 4, 2012
(HealthDay) -- Only 29 human cases of a new strain of "swine" flu have been identified in two years, but the U.S. Centers for Disease Control and Prevention is making sure it's prepared should the H3N2 strain become more ...

Researchers find powerful swine flu strain in Korea

September 10, 2012
(HealthDay)—A new report shows that a deadly swine flu virus can infect ferrets, highlighting the importance of continuous surveillance of emerging flu strains.

Flu infections rising among Chinese pigs: study

May 7, 2013
Scientists said Wednesday that flu infections were rising among pigs raised for slaughter on farms in south and southeastern China, also plagued by bird flu.

Recommended for you

Google searches can be used to track dengue in underdeveloped countries

July 20, 2017
An analytical tool that combines Google search data with government-provided clinical data can quickly and accurately track dengue fever in less-developed countries, according to new research published in PLOS Computational ...

MRSA emerged years before methicillin was even discovered

July 19, 2017
Methicillin resistant Staphylococcus aureus (MRSA) emerged long before the introduction of the antibiotic methicillin into clinical practice, according to a study published in the open access journal Genome Biology. It was ...

New test distinguishes Zika from similar viral infections

July 18, 2017
A new test is the best-to-date in differentiating Zika virus infections from infections caused by similar viruses. The antibody-based assay, developed by researchers at UC Berkeley and Humabs BioMed, a private biotechnology ...

'Superbugs' study reveals complex picture of E. coli bloodstream infections

July 18, 2017
The first large-scale genetic study of Escherichia coli (E. coli) cultured from patients with bloodstream infections in England showed that drug resistant 'superbugs' are not always out-competing other strains. Research by ...

Ebola virus can persist in monkeys that survived disease, even after symptoms disappear

July 17, 2017
Ebola virus infection can be detected in rhesus monkeys that survive the disease and no longer show symptoms, according to research published by Army scientists in today's online edition of the journal Nature Microbiology. ...

Mountain gorillas have herpes virus similar to that found in humans

July 13, 2017
Scientists from the University of California, Davis, have detected a herpes virus in wild mountain gorillas that is very similar to the Epstein-Barr virus in humans, according to a study published today in the journal Scientific ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.