Professor Ian Brown, head of virology at the Animal and Plant Health Agency (APHA), said it was not known exactly why there have been record outbreaks for two years in a row, as well as a rare human case this winter.
But he told The Independent these events suggest something is changing and “we need to understand what is driving it”.
Bird flu has been detected at more than 70 premises in the UK over the past few months, which the government says is the country’s largest outbreak to date.
It tops the previous record of 26 set the year before, which Prof Brown said “now pales into insignificance”.
Events were increasing in both scale and frequency, he said.
“We’ve got into a cycle in the last few years of incursions of bird flu into Europe and the UK almost getting to annual,” he told The Independent.
“So the frequency of events increased and when those events are happening, they’re translating into bigger outbreaks than we’ve seen in the past.”
Christine Middlemiss, the UK’s chief veterinary officer, said last month bird flu was at a “phenomenal level” and further research was needed to prevent it worsening.
She said a “reasonably sized outbreak” would usually be followed by two or three quiet years, adding: “But that’s not happening [this time.]”
Experts are considering whether the climate crisis is playing a role in rising infections.
“The birds migrate to the north of Russia over the summer and mix with other birds on other global flight pathways and exchange the viruses. So it’s quite plausible that with climate change and change in pathways that different mixing is going on,” Dr Middlemiss told BBC Radio 4’s Today programme.
Scientists told The Independent the climate crisis could theoretically lead to increased infections, but there was no evidence of this at the moment.
Mark Fellowes, an ecology professor at the University of Reading, said: “There’s little doubt that climate change is altering both the timing and patterns of bird migration.”
He added: “As migration becomes disrupted, the risk may increase of wild bird populations mixing and disease spreading, but how these dynamics will play out is not clear.”
Prof Brown said he would be cautious about linking the climate crisis to worsening outbreaks at the moment, but added: “What I would say is we need to consider all possible factors.
“Anything that affects how a wild bird lives its life and behaves, and climate could be a factor in there, we do need to try and understand that. Because clearly, it doesn’t feel like we are going to reverse out of this problem occurring on an annual basis any time soon.
“It feels like we are going to be in this space for a while, which means we do need to understand what is driving it.”
The head of virology at the APHA, an executive agency of the Department for Food, Environment, and Rural Affairs, called for a “multinational, collaborative effort to understand and track what is happening with wild birds”.
As well as scores of premises being infected during the current outbreak, a man in his 70s has become the first Briton to contract a strain of bird flu.
Experts said this case was extremely rare and that he had “very close, regular contact with a large number of infected birds” kept inside and around their house.
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