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Washington, Jun 30: Researchers in China have discovered a new type of swine flu that is capable of triggering a pandemic, according to a study published Monday in the US science journal PNAS.

Named G4, it is genetically descended from the H1N1 strain that caused a pandemic in 2009.

It possesses "all the essential hallmarks of being highly adapted to infect humans," say the authors, scientists at Chinese universities and China's Center for Disease Control and Prevention.

The researchers then carried out various experiments including on ferrets, which are widely used in flu studies because they experience similar symptoms to humans -- principally fever, coughing and sneezing. 

G4 was observed to be highly infectious, replicating in human cells and causing more serious symptoms in ferrets than other viruses.

Tests also showed that any immunity humans gain from exposure to seasonal flu does not provide protection from G4.

According to blood tests which showed up antibodies created by exposure to the virus, 10.4 percent of swine workers had already been infected.

The tests showed that as many as 4.4 percent of the general population also appeared to have been exposed.

The virus has therefore already passed from animals to humans but there is no evidence yet that it can be passed from human to human -- the scientists' main worry.

"It is of concern that human infection of G4 virus will further human adaptation and increase the risk of a human pandemic," the researchers wrote.

The authors called for urgent measures to monitor people working with pigs.

"The work comes as a salutary reminder that we are constantly at risk of new emergence of zoonotic pathogens and that farmed animals, with which humans have greater contact than with wildlife, may act as the source for important pandemic viruses," said James Wood, head of the department of veterinary medicine at Cambridge University.

A zoonotic infection is caused by a pathogen that has jumped from a non-human animal into a human.

The current physical distancing guidelines provided by the World Health Organisation (WHO) and by the US Centers for Disease Control and Prevention (CDC) may not be adequate to curb the coronavirus spread, according to a research which says the gas cloud from a cough or sneeze may help virus particles travel up to 8 metres. The research, published in the Journal of the American Medical Association, noted that the the current guidelines issued by the WHO and CDC are based on outdated models from the 1930s of how gas clouds from a cough, sneeze, or exhalation spread.

Study author, MIT associate professor Lydia Bourouiba, warned that droplets of all sizes can travel 23 to 27 feet, or 7-8 metres, carrying the pathogen.

According to Bourouiba, the current guidelines are based on "arbitrary" assumptions of droplet size, "overly simplified", and "may limit the effectiveness of the proposed interventions" against the deadly pandemic.

 She explained that the old guidelines assume droplets to be one of two categories, small or large, taking short-range semi-ballistic trajectories when a person exhales, coughs, or sneezes.

However based on more recent discoveries, the MIT scientist said, sneezes and coughs are made of a puff cloud that carries ambient air, transporting within it clusters of droplets of a wide range of sizes.

Bourouiba warned that this puff cloud, with ambient air entrapped in it, can offer the droplets moisture and warmth that can prevent it from evaporation in the outer environment.

"The locally moist and warm atmosphere within the turbulent gas cloud allows the contained droplets to evade evaporation for much longer than occurs with isolated droplets," she said.

"Under these conditions, the lifetime of a droplet could be considerably extended by a factor of up to 1000, from a fraction of a second to minutes," the researcher explained in the study.

The MIT scientist, who has researched the dynamics of coughs and sneezes for years, added that these droplets settle along the trajectory of a cough or sneeze contaminating surfaces, with their residues staying suspended in the air for hours.

"Even when maximum containment policies were enforced, the rapid international spread of COVID-19 suggests that using arbitrary droplet size cutoffs may not accurately reflect what actually occurs with respiratory emissions, possibly contributing to the ineffectiveness of some procedures used to limit the spread of respiratory disease," Bourouiba wrote in the study