Renewed pandemic fears are escalating in China, where a new flu variant is causing widespread chaos.
Scientists are tracking the evolution of a cattle flu variant, warning that its continued spread raises the prospect of a new pathogen adapted to circulate among humans.
A new study, led by a team of researchers in China, has identified that the Influenza D virus (IDV), a variant seen to primarily infect in livestock, is accumulating changes that could potentially enable it to transition from an animal-only pathogen to being able to spread among humans.
A team of researchers at the Changchun Veterinary Research Institute in China has zeroed in on a specific strain of the influenza virus, known as D/HY11, which emerged in cattle in northeast China in 2023.
Their laboratory analysis indicated that this strain was capable of replicating in human airway cells and in animal tissue, raising concerns that the variant could already be spreading among humans.
The study further demonstrated that the virus could be transmitted efficiently through the air between cows and ferrets, a standard model for estimating transmission potential in 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.
