A new strain of lethal bird flu needs to be monitored closely as health officials don't yet know how easily it can spread from human to human, a Hamilton Health Sciences infectious disease expert says.

"It's a very serious infection and a very serious problem right now in China," said Dr. Mark Loeb, an infectious disease physician at Hamilton Health Sciences and professor at McMaster University.

"In terms of a global pandemic problem — it's too early to tell."

This new strain of bird flu, dubbed H7N9, emerged in China over the last month. The World Health Organization's top influenza expert, Dr. Keiji Fukuda, told reporters at a briefing in Beijing Wednesday that people seem to catch the H7N9 virus from birds more easily than the H5N1 strain that began ravaging poultry across Asia in 2003.

The H5N1 strain has since killed 360 people worldwide, mostly after contact with infected fowl.

A high infection severity

Scientists are watching the virus closely to see if it could spark a global pandemic, but say there is little evidence so far that it can spread easily from human to human.

Loeb says that because this strain of virus hasn't been known to cause infections in people until now, humans have no preexisting immunity towards it.

"And because of that, the severity of the infection is pretty high," he said. "There have been a number of deaths and severe illness due to this virus."

The H7N9 bird flu virus has infected more than 100 people in China, seriously sickening most of them and killing more than 20, mostly near the eastern coast around Shanghai. On Wednesday, Taiwan confirmed its first case, a 53-year-old man who became sick after returning from a visit to the eastern Chinese province of Jiangsu.

"This is definitely one of the most lethal influenza viruses we have seen so far," Fukuda said. But he added that experts are still trying to understand the virus, and that there might be a large number of mild infections that are going undetected.

In comparison, the earlier bird flu strain, H5N1, is known to kill up to 60 of every 100 people it infects.

An emerging picture

Part of the issue researchers are facing is facts on how the virus spreads and exactly where it came from are still emerging.

Some people who are infected with it were potentially exposed to birds, but others were not, Loeb says.

"It's an emerging picture," he said. "We're not at this point seeing evidence of rapid spread from human to human, but we don't even know if that's happening or not."

"The key message is that public health officials need to keep their eyes on this and watch it very carefully to see how it evolves."

WHO experts say they still aren't sure how people are getting infected but said evidence points to infections at live poultry markets, particularly through ducks and chickens. They said it was encouraging that reported infections appeared to slow down after the closure of live poultry markets in affected areas.

With files from the Associated Press