Officials at the Centers for Disease Control and Prevention in Atlanta also said the virus strains have potential to spread from human to human.

The study, published in the Proceedings of the National Academy of Sciences, found avian influenza A H7 viruses are fairly common in birds, but rarely infect humans. Most cases of avian influenza in humans have resulted from contact with infected poultry or contaminated surfaces.

"We know that influenza viruses are constantly changing and that is why it′s so important to watch them carefully," lead author Dr. Jessica Belser of the CDC said in the statement.

"We discovered that some recently identified avian influenza A H7 viruses have some properties that could enhance their potential to infect people and possibly spread among people."

The study′s findings suggest these North American avian influenza A H7 viruses are partially adapted to recognize sugar receptors preferred by human influenza viruses found in the human upper respiratory tract.