With the country’s near-total return to normalcy after years of quarantine and isolation measures, the Covid pandemic increasingly feels like a distant memory for many.
But infectious disease experts are far less forgetful and have remained on their toes since the novel coronavirus was first identified in 2019, continuously looking for signs of mutations or other emerging threats.
Now, they believe to have found one in influenza A subtype H5N1, known as the ‘bird flu,’ which has sickened at least 66 people across 10 states. These cases resulted from people coming into contact with infected poultry and cattle or from drinking unpasteurized milk.
There has been no human-to-human transmission.
However, with every new cross-species infection, there is an increasing risk the virus will mutate to better infect humans.
Dr Conor Meehan, a professor at Nottingham Trent University, studies how bacteria spread and evolve, with a focus on the genetic makeup of microbial communities.
He said: ‘Compared with only two cases in the Americas in the previous two years, this is quite a large increase. Coupling this with a 30 percent mortality rate from human infections, bird flu is quickly jumping up the list of public health officials’ priorities.’
This week, the US reported its first severe human case of H5N1 in Louisiana and California, where 36 of the country’s bid flu cases have been diagnosed, declared a state of emergency over the virus just hours later.
At least 66 people have been infected with avian flu. Cases in California have exceeded 35, prompting a state-wide emergency declaration
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H5N1 bird flu doesn’t seem to transmit from person to person, Dr Meehan said, ‘which greatly reduces its likelihood of causing a pandemic in humans… in its current form, H5N1 can’t easily spread in humans.’
However, he added, ‘a recent study showed that a single mutation in the flu genome could make H5N1 adept at spreading from human to human, which could jump-start a pandemic.’
Bird flu cases in humans have generally been relatively mild, primarily manifesting as conjunctivitis (pink eye), cough or difficulty breathing, sore throat, muscle or body aches, diarrhea, and vomiting.
But last week, a Louisiana patient became the first to become hospitalized with the virus. Investigators said they likely caught the disease after handling sick and dead birds in a backyard poultry flock.
No further details on their symptoms have been revealed, except that they are ‘severely ill’ with the bird flu.
The CDC has not changed its overall assessment that the risk to the public from bird flu is low.
However, H5N1 has been shown to have the ability to mutate rapidly and spread between mammals.
The virus from a Michigan patient had gene segments closely related to those from dairy cows, but there were no significant changes that would improve its ability to spread between humans.
Despite that, experts did note a mutation in that patient associated with an ability to better infect and spread in mammals and increased virus replication in animals.
So while the risk of spread from person to person remains low, the risk that more people could become sick as it transmits among animals is ticking up.
The human cases of avian flu have been due to exposure to infected cattle and poultry. Human to human transmission risk remains low
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Scientists at Scripps Research Institute revealed earlier this month that just one gene mutation in the strain of bird flu virus spreading in dairy cows would allow it to latch on to human cells.
The researchers altered one of H5N1’s proteins called hemagglutinin, which is what latches on to cells in humans and allows the virus to infect.
The team generated viral proteins from the genes of the virus taken from a person in Texas who developed bird flu after contact with an infected cow.
Then, they engineered different mutations into the hemagglutinin and discovered that just one small change in H5N1’s genetic makeup allowed it to switch from infecting bird cells to infecting human cells in the upper respiratory tract.
Dr Ian Wilson, a computational biologist at Scripps and co-author of the study said: ‘This was surprising. It was just this single mutation [that] was sufficient to switch the receptor specificity.’
Governments are already showing signs of preparing for this rising threat. The UK has bought 5million doses of H5 vaccine that can protect against bird flu.
In June this year, Finland became the first country to offer bird flu vaccinations to humans, providing two injections to 10,000 people. The vaccinations were given to workers who have been exposed to animals.
This map shows cases of the virus detected in wild mammals, such as red foxes and seals
And the US government has bought vaccines and commissioned Moderna to create an mRNA bird-flu vaccine
Dr Meehan said: ‘Even without the potential ability to spread between humans, bird flu is likely to affect animal health even more in 2025.
‘By understanding and preventing disease in our environment and the animals around us, we can better prepare and combat those diseases entering humans. Similarly, by surveying and disrupting infectious diseases in humans, we can protect our animals and the environment’s health too.’
