New concerns over pandemic threats are rising in China, as a novel flu variant stirs significant disruption.

Experts are closely observing the trajectory of a cattle flu strain, cautioning that its ongoing dissemination could lead to a new pathogen capable of human transmission.

A recent investigation spearheaded by Chinese scientists has revealed that the Influenza D virus (IDV), which typically targets livestock, is undergoing mutations. These changes may enable it to evolve from an animal-restricted virus to one that can spread among people.

Researchers at China’s Changchun Veterinary Research Institute have identified a particular influenza strain, D/HY11, which surfaced in cattle in northeastern China in 2023.

Their lab tests revealed that this strain could replicate in human respiratory cells and animal tissues, sparking fears that human transmission may already be occurring.

Additionally, the study illustrated that the virus could be effectively transmitted via airborne particles between cows and ferrets, a common method used to predict how a virus might spread among humans.

Blood tests revealed 74 percent of people in Northeast China had been exposed to the virus, based on an analysis of archived blood samples, proving it has jumped from animals to humans. The rate rose to 97 percent in those with respiratory symptoms; however, it remains unknown whether it can spread between people or if these were all isolated infections from animals.

The team concluded: ‘In summary, it is likely that IDV outbreak has metastasized into an ongoing problem for cattle and humans.’

Nearly three-quarters of people tested in Northeast China had antibodies for the D/HY11 virus, a figure that jumped to 97 percent among those who had recently been sick with respiratory symptoms (stock)

A virus’s potential to cause a pandemic often hinges on its ability to spread easily through the air. To assess this threat, researchers have been studying an IDV strain isolated in Northeast China.

Researchers began by growing the virus in cells from dogs and humans, which are standard tools for studying flu strains.

They also tested it on cells specially designed to mimic the airway linings of humans, cows, pigs and dogs to get a more realistic picture.

The virus efficiently infected and multiplied in all of those lab-grown cells.

The core of the study involved infecting mice to study the virus’s ability to cause disease and spread to different organs, including the brain.

They infected dogs, who were monitored for symptoms to see how much virus they shed, indicating their potential to spread it; as well as ferrets, the gold-standard model for human flu transmission. 

The animals were used in specially designed cages to test whether the virus could spread through the air from an infected animal to a healthy one.

The virus spread from infected ferrets to healthy ones through the air, without any direct contact; a significant finding, as it is a trait associated with viruses that can easily spread among humans.

Finally, the team checked if the virus was vulnerable to existing antiviral drugs and analyzed one of the polymerase complexes, the virus’s internal machinery for replication, to understand its potential for replication.

The graph quantifies the virus’s ability to infect cells from pigs, cows, humans and dogs. For each species, it shows the infection rate in lab-grown cells that mimic three different parts of the respiratory tract: the nasal passage, trachea and lungs (alveolar)

The line graphs track the growth of the D/HY11 virus over 96 hours in lab-grown cells from the nasal passage (A), windpipe (B) and lungs (C) of four different species. They show the virus replicated efficiently in human, cow and pig cells across all three respiratory regions, reaching high concentrations

The virus was susceptible to newer antiviral drugs that target the virus’s RNA polymerase, such as baloxavir. However, it was resistant to common flu medications, such as Tamiflu.

The D/HY11 polymerase showed heightened activity, a characteristic sometimes linked to more efficient spread between mammals.

Nearly three-quarters of people in both urban and rural Northeast China tested were found to have a high percentage of antibodies against the virus, indicating widespread exposure to the virus. 

That rate was far higher among those who had sought medical care for respiratory symptoms.

‘This raises the possibility of cryptic transmission in humans with mild or asymptomatic infections via the emerging D/HY11-like viruses,’ the researchers said.

‘Our retrospective serum analyses (2020–2024) indicate IDV may have been circulating in northeastern China since at least 2020… Currently, no routine IDV testing is carried out anywhere in the world, facilitating concerns about the silent spread of this panzootic virus and the potential emergence of new varieties.’

Their findings were published in the journal Emerging Microbes & Infections.

Given the massive human toll of the multi-year Covid pandemic, a global network of researchers and public health officials is now hyper-vigilant, closely tracking the evolution of animal viruses and other pathogens that show the hallmarks of pandemic potential, namely, efficient spread and significant risk to humans.

Scientists are leveraging new tools, from advanced genetic sequencing of viruses in wildlife to blood serum testing in humans, all aimed at buying time to develop potential treatments and vaccines before the next pathogen takes over.