A strain of bird flu spreading in China has raised concerns among experts due to its potential to cause a pandemic. Known as H3N8, this particular strain differs from the H5N1 strain, which has already been identified as having pandemic potential in humans. The H3N8 strain has fueled fears of a new bird flu outbreak and has been found in birds, horses, dogs, and even seals. While it has rarely infected humans in the past, a Chinese woman in March became the first confirmed fatality from H3N8.
After conducting laboratory tests on ferrets and mice infected with the H3N8 strain, UK and Chinese scientists have issued a warning about the potential vulnerability of humans to infection at epidemic or pandemic proportions. The researchers published their findings in the journal Cell, stating that human populations, even when vaccinated against human H3N2 virus, appear to have little immunity to emerging mammalian-adapted H3N8 avian influenza viruses.
To assess the virulence of the mammal-spread H3N8 strain, the scientists infected mice with various diseases and monitored them for two weeks. They found that clinical symptoms were clearly evident at a dose of 50 percent of the H3N8 virus. In contrast, mice infected with chicken-derived H3N8 viruses or the human seasonal flu showed no clinical signs or mortality.
Further experiments on ferrets, chosen for their similar respiratory makeup to humans, revealed that those infected with the human-derived H3N8 strain suffered severe symptoms, including wheezing, difficulty breathing, and coughing. The virus was found in the animals’ nasal tissue, tracheae, lungs, and even brains. Notably, the H3N8 human viruses were found to be capable of airborne transmission, while the chicken-derived H3N8 viruses could not transmit between ferrets.
The researchers emphasized that the H3N8 strain has acquired properties that allow it to more easily transmit through the air. They warned that even vaccinated populations may be susceptible to infection at epidemic or pandemic levels.
In addition to the H3N8 strain, the H5N1 strain has also been causing concern. Over 700 cases of H5N1 have been detected among wild birds in England since September 2022. A Chinese woman became the first person to die from the H3N8 strain, likely from exposure at a wet market where live animals are sold. Wet markets have been identified as high-risk environments for the transmission of pathogens.
Symptoms of bird flu in humans include fever, fatigue, nausea, and other flu-like symptoms, as well as potential complications such as pneumonia. The H5N1 strain has been found to cause lethal disease in multiple mammalian species, raising concerns about its potential impact on humans.
While some countries, including China, have been vaccinating against the H5N1 strain, chickens in the UK are currently not vaccinated. However, the Animal and Plant Health Agency in the UK is exploring potential candidate vaccines for humans in case the virus spreads to people.
The bird flu death rate is estimated to be around 50 percent globally, according to the European Centre for Disease Prevention and Control. The UK Health Security Agency has set the threat level to level three due to evidence of changes in the virus genome that could lead to mammalian infection.
Overall, the emergence of the H3N8 and H5N1 strains highlights the ongoing risk of bird flu and the potential for these viruses to cause widespread illness and mortality in humans. Vigilance, research, and preparedness are crucial in addressing this threat and protecting public health.
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