A strain of bird flu spreading in China has ‘pandemic potential’, experts have warned.
Called H3N8, it is different to the H5N1 strain, which experts have already identified as having pandemic potential in humans, sparked fears of a fresh pandemic after fuelling the world’s biggest ever bird flu outbreak.
The variant is common in birds, horses and dogs and has even been found in seals, but it has rarely infected people.
But in March a Chinese woman became the first confirmed H3N8 fatality.
UK and Chinese scientists issued their warning after their laboratory tests on ferrets and mice infected with the bird flu strain showed humans could be ‘vulnerable to infection at epidemic or pandemic proportions’.
UK and Chinese scientists have issued a warning about the variant after their laboratory tests on ferrets and mice have showed humans could be ‘vulnerable to infection at epidemic or pandemic proportions’
Called H3N8, it is different to the H5N1 strain, which experts have already identified as having pandemic potential in humans, sparked fears of a fresh pandemic after fuelling the world’s biggest ever bird flu outbreak. The variant is common in birds, horses and dogs and has even been found in seals, but it has rarely infected people. But in March a Chinese woman became the first confirmed H3N8 fatality
Writing in the journal, Cell, the team of researchers said: ‘Human populations, even when vaccinated against human H3N2 virus, appear immunologically naive to emerging mammalian-adapted H3N8 AIVs [avian influenza viruses] and could be vulnerable to infection at epidemic or pandemic proportion.’
To test how deadly a mammal-spread H3N8 virus could be, researchers first infected a group of mice with one of five diseases then monitored them for 14 days.
The viruses included two H3N8 viruses collected from infected people, two H3N8 viruses from chickens and a human seasonal flu virus as a baseline.
They found clinical symptoms — decreased activities, body weight loss and ruffled fur — were ‘clearly evident’ at a mammal-spread H3N8 virus dose of 50 per cent.
In contrast, no clinical signs, body weight loss, and mortality were observed in mice infected with the same doses of the chicken viruses or the human seasonal flu.
Scientists discovered all H3N8 viruses replicated well in tissues inside the mice’s noses as well as their lungs.
But mice infected with the human-derived H3N8 viruses were found to have a ‘significantly higher’ level of the virus in both areas compared to regular flu.
Experts also observed that abnormalities on the lung were also ‘more severe’ than those caused by the chicken-derived H3N8 and seasonal flu.
The experiment was then replicated on groups of two ferrets.
Ferrets were chosen for the study as they have a similar respiratory makeup to humans, providing experts with an idea of how a virus would interact in people.
Researchers found the animals infected with seasonal flu and chicken H3N8 ‘showed few clinical signs’ of being ill.
Ferrets with human-derived H3N8 however suffered serious symptoms including wheezing, difficulty breathing and coughing.
High virus levels were also found in the their nasal tissue, as well as the animals’ tracheae, lungs, and even brains.
Infection with this bird flu strain also triggered peribronchiolitis — a dangerous inflammation of lung tissue — and bronchopneumonia.
Concerningly, scientists discovered the H3N8 human viruses were airborne, capable of spreading between animals with no direct contact.
In comparison, the chicken-derived H3N8 viruses failed to transmit between ferrets at all.
Paper co-author Professor Jinhua Liu, an expert in veterinary microbiology at the China Agricultural University in Beijing, said the team discovered the virus had acquired properties enabling it to more easily transmit via the air.
He added: ‘Human populations, even when vaccinated against human H3N2 virus, appear immunologically naive to emerging mammalian-adapted H3N8 avian influenza viruses and could be vulnerable to infection at epidemic or pandemic proportions.
Professor Kin-Chow Chang, an expert in veterinary molecular medicine at the University of Nottingham, who was involved in the study, also said: ‘We demonstrate that an avian H3N8 virus isolated from a patient with severe pneumonia replicated effectively in human bronchial and lung epithelial cells [which line the airways and make mucus].’
He added that the virus was ‘extremely harmful in its effects in laboratory mammalian hosts and could be passed on through respiratory droplets’.
UK scientists tasked with developing ‘scenarios of early human transmission’ of bird flu have warned that 5 per cent of infected people could die if the virus took off in humans (shown under scenario three). Under another scenario, the scientists assumed 1 per cent of those infected would be hospitalised and 0.25 per cent would die — similar to how deadly Covid was in autumn 2021 (scenario one). The other saw a death rate of 2.5 per cent (scenario two)
Over 700 confirmed cases of H5N1 have been detected among wild birds in England since September 2022, according to the UKHSA. Pictured above, a bird flu outbreak in February in Queens Park, Heywood, Rochdale
In March, a Chinese woman became the first person to ever die from the H3N8 strain.
Health officials believe she caught the virus from a wet market, where live animals are bought and sold, which she spent time before becoming ill.
Experts have long warned of the mounting disease threat such markets pose, labelling them ideal grounds for transmission of pathogens.
The unidentified woman was only the third person ever to officially be diagnosed with H3N8 – one of the most common strains in birds.
Two young boys were struck down with the same virus in April and May last year in China in unlinked cases, but both survived.
Like other forms of bird flu, human infections can occur when enough of the virus gets into a person’s eyes, nose, mouth or is inhaled, usually in the form of infected droppings or other material from the animals.
Such cases are usually the result of ‘direct or indirect exposure to infected live or dead poultry or contaminated environments’, according to the World Health Organization.
Although there have only been a limited number of cases of this strain globally, the illness is believed to be similar to other bird flus in people.
Usual symptoms include fever, fatigue, nausea and other flu-like symptoms.
Sufferers may experience diarrhoea, sickness, stomach pain, chest pain and bleeding from the nose and gums, and pink eye.
It comes as research in April, yet to be peer-reviewed found the H5N1 strain could also ’cause lethal disease in multiple mammalian species’.
Canadian researchers, including some from Government health bodies, infected ferrets with one of four strains of H5N1.
In March, a Chinese woman became the first person to ever die from the H3N8 strain. Health officials believe she caught the virus from a wet market, where she spent time before becoming ill
Wet markets are large collections of open-air stalls where sellers flog live animals, raw meat and fish, as well as fruits and vegetables, herbs and spices. Experts have long warned of the mounting disease threat such markets pose, labelling them ideal grounds for transmission of pathogens
They found that ‘direct contact’ with one strain of H5N1 isolated from an infected bird, resulted ‘in lethal outcomes’, the paper added.
It raises the prospect that the strain may have developed ‘certain adaptations that allow for a higher degree of replication, pathogenicity, and transmission’.
At the time they warned that if such a strain made the leap to humans, the consequences could be catastrophic.
‘Because there is little to no H5-specific population-wide immunity, if an H5N1 isolate capable of sustained transmission made a species jump into humans, this would likely represent a destructive infection in immunologically naïve population,’ they wrote.
Some nations, including China, have been vaccinating against the H5N1 strain for years.
Birds are vaccinated either via an injection into the egg or a spray onto chicks when they are still in boxes.
Under UK health policy however, vaccinating chickens is currently illegal.
But the Animal and Plant Health Agency, an arm of DEFRA, is currently looking at potential candidate vaccines for humans in the UK, if the virus spills over into people.
According to the European Centre for Disease Prevention and Control, the bird flu death rate is believed to be around 50 per cent globally.
In the UK, the Animal and Plant Health Agency, an arm of DEFRA, is reviewing the bird flu risk to humans every week.
The UK Health Security Agency (UKHSA) has currently set the threat level to level three, given there is ‘evidence’ of changes in the virus genome that could trigger ‘mammalian infection’, it said.
Any ‘sustained’ mammal-to-mammal transmission of the pathogen would raise the threat level to four, while human-to-human would push it to five.
