New cases of bird flu detected in Europe will likely hit other bird populations and may infect a few people, though the virus is highly unlikely to spread in the human population, the World Health Organization (WHO) said on Tuesday.

The H5N8 form of the virus has hit a Dutch chicken farm and a German turkey farm and is suspected - but not yet confirmed - as the strain that infected ducks on a British farm.

Asked if more bird populations were likely to be infected, WHO expert Elizabeth Mumford said: "Absolutely, I would say."

"I think we will probably see some human cases," she told reporters. "I don't see why we wouldn't. If it's really circulating widely, there's no reason we shouldn't see human cases."

H5N8 bird flu has never been known to infect humans before, and many experts in flu virology say the risk to people from this subtype is minimal.

"The risk for humans is always a possibility because of the massive shedding of these viruses by infected chicken flocks, however in my opinion the chances are very low," said Linda Klavinskis, a specialist in immunobiology at King's College London.

Mumford said there was a possibility of "a few sporadic cases", but people who have caught other H5 subtypes have not passed on the illness to others.

"We believe any time that humans are in close contact with poultry, there's a possibility of transmission to humans," she added.

H1 and H3 bird flu subtypes tend to be more transmissible to humans but cause less severe illness, she said.

"All of the genes in this virus (H5N8), everywhere we have looked so far, are all avian genes - there's no swine component and there's no human component to the genome," she said. "Genetic analysis shows that it prefers to bind to avian receptors. It very much remains an avian virus."

If there is a human case, the H5N8 strain has been shown to be susceptible to Roche's flu medicine oseltamivir, also known as Tamiflu, she said.

The outbreak of the disease has grabbed headlines in Europe and Mumford said the media reaction was "absolutely appropriate" because all countries should be vigilant for outbreaks.

"The first thing I always say is that flu viruses are unpredictable. That's the caveat of influenza."