International health officials are saying that the new bird flu virus is the most deadly of any other flu virus. Since March, the new strain of influenza has killed 22 people and infected 108, said health experts Wednesday.

Officials from the World Health Organization (WHO) expressed concerns about how easily the bird flu can be caught by humans from infected birds. With the new H7N9 strain, monitoring of the virus is difficult, since there are no initially recognizable symptoms.

"This is definitely one of the most lethal influenza viruses we have seen so far. We are at the beginning of our understanding of this virus," Assistant Director-General for Health Security for WHO, Dr. Keiji Fukuda, said at a press conference in Beijing Wednesday.

Ten years ago, the SARS virus killed an estimated 800 people and in comparison, the new strain of bird flu is much more dangerous and easily spread. Fukuda called the virus "unusually dangerous" for humans.

Many of the cases are located near the Yangtze River in the eastern part of China and there is no evidence of transfer of the virus human-to-human.

"Evidence so far is not sufficient to conclude there is person-to-person transmission. Moreover, no sustained person-to-person transmission has been found," Yangtze said.

A poultry market where live poultry is sold is most likely the source of infection, according to health officials. Earlier this month, thousands of birds were destroyed and many poultry markets were closed when some birds tested positive for H7N9. Health officials from around the world are working together to gain a better understanding of the new bird flu virus.

"We are at the very early stages of this investigation. There's a lot to be learned," said the head of the Influenza Division at the Center for Disease Control and Prevention in Atlanta, Dr. Nancy Cox.