The global spread of bird flu and the number of viral strains currently circulating and causing infections have reached unprecedented levels, according to disease experts.
According to the experts, the number of viral strains currently circulating raises the risk of a potential human outbreak.
The experts added that multiple outbreaks have been reported in poultry farms and wild flocks across Europe, Africa and Asia in the past three months.
While most involve strains that are currently low risk for human health, the sheer number of different types and their presence in so many parts of the world at the same time increases the risk of viruses mixing and mutating – and possibly jumping to people.
Michael Osterholm, an infectious disease specialist at University of Minnesota, said: “this is a fundamental change in the natural history of influenza viruses”.
He described as “unprecedented”, the proliferation of bird flu in terms of geography and strains.
But Osterholm said wild birds could be “shedding” more of the virus in droppings and other secretions, increasing infection risks.
Global health officials are worried another strain could make a jump into humans like H5N1 did in the late 1990s.
It has since caused hundreds of human infections and deaths but has not acquired the ability to transmit easily from person to person.
The greatest fear is that a deadly strain of avian flu could then mutate into a pandemic form that can be passed easily between people – something that has not yet been seen.
While avian flu has been a prominent public health issue since the 1990s, ongoing outbreaks have never been so widely spread around the world, something infectious disease experts put down to greater resilience of strains currently circulating, rather than improved detection or reporting.
While there would normally be around two or three bird flu strains recorded in birds at any one time, now there are at least half a dozen, including H5N1, H5N2, H5N8 and H7N8.
The Organisation for Animal Health (OIE) says the concurrent outbreaks in birds in recent months are “a global public health concern”.
The World Health Organisation’s director-general warned on Monday that the world “cannot afford to miss the early signals” of a possible human flu pandemic.
The precise reasons for the unusually large number and sustained nature of bird outbreaks in recent months, and the proliferation of strains, is unclear – although such developments compound the global spreading process.
Bird flu is usually spread through flocks through direct contact with an infected bird.
Also, Mr Ian MacKay, a virologist at Australia’s University of Queensland, said the current proliferation of strains means that “by definition, there is an increased risk” to humans.
“You’ve got more exposures, to more farmers, more often, and in greater numbers, in more parts of the world – so there has to be an increased risk of spill over human cases,” he told Reuters.
Nearly 40 countries have reported new outbreaks of highly pathogenic avian influenza in poultry or wild birds since November, according to the WHO.
In Africa – which experts say is especially vulnerable to missing flu outbreak warning signs due to limited local government capacities and weak animal and human health services – H5N1 outbreaks have been reported in birds in Burkina Faso, Cameroon, Ghana, Niger, Nigeria and Togo.
H5N8 has been detected in Tunisia and Egypt, and H7N1 in Algeria.