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Experts say the new swine flu strain can jump from pigs to people, but so far there hasn’t been person-to-person transmission. Getty Images
  • A new flu strain, called the G4 virus, has been identified in pigs in China, and it may have the potential to become pandemic.
  • Although the virus, which is a version of swine flu, doesn’t spread between people, the researchers say it could potentially adapt to become transmissible between humans.
  • The G4 virus isn’t an immediate threat, but health officials will need to monitor it to prevent and prepare for a potential pandemic.

A new flu strain has been identified in pigs in China, and it may have the potential to become pandemic.

That’s according to a new study published in Proceedings of the National Academy of Sciences.

Although the virus, which is a version of swine flu, doesn’t spread between people, the researchers say it could potentially adapt to become transmissible between humans.

If that happens, the researchers said it could cause a global outbreak.

However, health experts say the strain, called the G4 virus, isn’t an immediate threat.

Christine Johnson, VMD, MPVM, PhD, a University of California, Davis professor of epidemiology and researcher on the U.S. Agency for International Development’s Emerging Pandemic Threats PREDICT project, says zoonotic diseases that pass from animal to human emerge all the time.

The transmission varies from pig to human, bat to human, or other wild animal to human.

It’s going to be tough to predict if and when the virus could mutate and become human-to-human transmissible, Johnson says, but it’s something we need to keep an eye on.

“Obviously, the big step the virus has to take to become pandemic is it has to be human to human. It’s not going to cause an epidemic of notable size while it is constrained to being transmitted from pig to human only,” Johnson told Healthline.

From 2011 to 2018, Chinese researchers collected and evaluated more than 30,000 nasal swab samples from pigs in slaughterhouses and veterinary teaching hospitals.

According to the researchers, pigs are considered to be “mixing vessels” for pandemic flu viruses, as they make great hosts for multiple viruses to recombine with one another and produce a new strain.

“Pigs are susceptible to some bird and human flu viruses, so they are an animal where different viruses can mix and potentially infect people,” said Benjamin Neuman, PhD, a virologist and the head of the biology department at Texas A&M University-Texarkana.

It’s therefore crucial to track what strains pigs carry to prevent and prepare for future outbreaks.

Through their surveillance, the research team identified 179 swine flu viruses in the pigs. Many of these viruses dwindled over the years, but one strain kept popping up, even increasing, year after year: the G4 virus.

The G4 virus has blended characteristics of the H1N1 virus that triggered the 2009 flu pandemic, the 1918 influenza pandemic flu, and a North American H1N1 flu strain containing genes from avian, human, and pig influenza.

According to the researchers, the virus’s widespread occurrence in pigs increases the risk of exposure to humans.

It also has the potential to evolve and become able to spread between humans, which could trigger a pandemic.

“This flu virus is made up of pieces from bird flu, pandemic H1N1, and swine flu, and seems to grow well in human cells. That adds up to a lot of potential, but we haven’t seen this virus emerge and cause any real trouble yet,” Neuman said.

Neuman adds that it’s tough to predict whether a virus would or even could turn into a pandemic.

It’s common for viruses to jump from one host to another. It’s seen in nature, but pandemics are rare.

The researchers identified a handful of people who contracted the G4 virus directly from infected pigs and found that the virus is able to bind to a receptor in humans and replicate itself in people’s airways.

However, people with an infection didn’t spread it to other people. They were dead-end infections.

G4 currently doesn’t spread person to person, but some health experts are concerned the virus could mutate and become transmissible among people.

This sort of mutation is a big shift, but erratic and spontaneous mutations are common with flu viruses.

“That’s the problem with influenzas. It’s called reassortment and recombination, and so they’re constantly swapping out different parts of their genes with other functional genes in other influenza viruses,” Johnson said.

It’s happened before. Just look at the H1N1 swine flu outbreak of 2009. That virus became human-to-human transmissible and caused a pandemic.

It’s worth noting that not all flu viruses will spill over to humans and start spreading between people.

According to Johnson, some get stuck in animal-to-human mode.

One such example is the H5N1 strain. It had health experts worried it might trigger a pandemic.

When H5N1 jumps from chickens to people, as it sometimes does, it causes a severe illness with a high death rate.

“Decades ago, everyone was quite concerned that this could get human-to-human transmission capabilities, and it never did. And it’s been decades,” Johnson said.

It’s tough to estimate if and when a virus could start spreading person to person.

“There are so many other viruses lurking out there in other kinds of animals that it’s very hard to predict which ones to watch,” Neuman said.

Another concern is that humans may not have much immunity to the new strain — not from a previous flu infection or flu shot.

Usually, some level of immunity that spills over from previous infections or immunizations helps reduce the severity of the infection, if not prevent it altogether.

“The concerning part about this virus is they’re saying people don’t have immunity to it, not even partial immunity to it,” Johnson said.

If a population has no immunity, the disease can get around quickly, Johnson adds.

That said, it’s not a guarantee people will have zero immunity.

Neuman suspects since so many people have dealt with an H1N1 infection in the past, they may have at least some degree of protection.

“Some of the parts [of G4] are similar enough to past common flu strains that they might easily be recognized by a person’s immune system,” Neuman said.

The fact that scientists are already collecting so much knowledge about this new strain is a good sign.

The more insights they have about the virus’s characteristics, the better they’ll be able to monitor the virus and prevent an outbreak from occurring.

People who are in close contact with the pigs will need to be monitored for infection. They’ll also need to get vaccinated against other flu viruses so the G4 virus can’t recombine itself with others and become more transmissible.

“That’s about as good as it gets — to have advance knowledge and have people monitored, and have it potentially be able to be contained that way is good news,” Johnson said.

The knowledge will also help scientists understand how to prepare a vaccine against the G4 virus if the need ever arises in the future.

Neuman says making a new flu vaccine is pretty straightforward, especially once scientists know the genetic makeup of a flu strain (as they do in this case).

Health officials will need to continue to keep an eye on the G4 virus. Even if it’s not an immediate threat, it could eventually become one.

“It’s probably more potential than real threat, but I am absolutely OK with that,” Neuman said. “One pandemic at a time, please.”