New strain of swine flu virus with ‘pandemic potential’ found in China

G4, the strain found by researchers in China, is a descendant of the H1N1 influenza A virus, hasn’t shown evidence of human-to-human transmission so far.

A wholesale market of pigs in Nanning, Guangxi province, China | Qilai Shen | Bloomberg

Bengaluru: Researchers in China have discovered a new strain of the H1N1 swine flu virus that can potentially trigger a pandemic, though hasn’t yet shown evidence of human-to-human transmission. The peer-reviewed findings have been published in the journal, PNAS.

Researchers have said the new strain of swine flu is a descendant of the H1N1 virus, with properties similar to the European avian-like (EA) H1N1 virus that had caused the 2009 pandemic in Mexico (pdm09). It is also a triple reassortant virus, which means its genetic sequence is a different combination of three of the eight segments of H1N1 RNA.

The new strain of virus is called the G4 genotype, and the paper states that swine workers or people working with farm animals and handling meat have shown evidence for this virus in their bloodstream.

Pigs are one of the most important “mixing vessels” or hosts for novel viruses that could mutate inside their bodies before getting transmitted to humans. They are the only known mammal species that are susceptible to both avian and human influenza viruses as they have receptors in their bodies for both types of virus.

Pigs’ bodies become a laboratory dish where different viruses come together to mutate and form a deadlier, more infective virus, that is capable of causing pandemics.

Pigs and influenza

Influenza is extremely common among pigs, and can easily be transmitted among a herd through the air. Multiple human outbreaks of swine flu strains in the recent past have been associated with humans coming in direct contact with pigs due to animal husbandry and farming practices. There have been many types of swine flu, which are caused by the subtypes of influenza A, such as the H1N1, H1N2, H3N1, H3N2, and H7N9, which are also the most common strains worldwide.

Pigs have always been thought to hold significance in generation of newer strains of influenza, which could potentially be more virulent and infective, and also have the potential to jump across species, including to humans.

The last big pandemic caused by a strain of swine flu was the outbreak that began in Mexico in 2009. The country shut down schools for two to three months as the flu also spread to the US where it was seemingly less deadly than it had been in Mexico.

The virus was officially called the A/H1N1pdm09 and is now covered by the annual flu vaccine.

G4 H1N1 detection and prevalence

To detect the G4 H1N1 virus, as many as 338 swine workers were tested between 2011 and 2018. Out of these, 35 individuals, or 10.4 per cent of the workers, tested positive for occupational exposure to the virus. The prevalence was higher (20.5 per cent) in the age group of 18 to 35, and the virus has become more common since 2016. The study also stated that 4.4 per cent of the general population is also likely to have been exposed to the virus.

A total of 30,000 nasal swabs were also taken from pigs in slaughterhouses and veterinary hospitals in ten different cities in China, obtaining 179 influenza viruses.

When ferrets were infected with these viruses and studied in the lab, the researchers found that the virus also transmits via aerosols. The researchers, based in Beijing, have indicated in the paper that the virus shows a propensity to multiply rapidly in human epithelial cells that line the lungs and nasal passages.

Upon studying for immunity, the authors found that existing immunity against other strains of swine and avian flu does not offer protection against G4 viruses. Treatment for swine flu strains is typically available in the form of prescription drugs, and flu vaccines are not thought to be effective for more than a year or two.

The researchers warn that the G4 virus’ infectivity increases the opportunity for it to mutate and adapt to humans, triggering a potential pandemic. The authors urge that “systematic surveillance of influenza viruses in pigs is essential for early warning and preparedness for the next potential pandemic”.