Highly pathogenic influenza viruses (H5N1) mostly impact birds but can sometimes cross the species barrier and infect people.
H5N1 flu outbreaks have been reported in domestic poultry as well as wild birds in 63 countries and territories since 2003, the authors explained.
South Korea, for instance, confirmed a H5N1 bird flu outbreak in 2006, and in 2007, authorities in Japan confirmed that a bird flu outbreak was caused by H5N1.
There have been over 600 cases since H5N1 virus infections were first reported in humans in 1997. Of those cases, over 60% resulted in death.
The experts said:
"H5N1 influenza viruses continue to evolve and have the potential to cause sustained human-to-human transmission and pandemic virus spread."
Although antiviral drugs can help restrain flu viruses from spreading, the emergence of drug-resistant viruses can restrict the successfulness of this control measure.
Until now, there has been no large-scale analysis of drug resistance in H5N1 influenza. However, the new research found that 62.2% of human H5N1 viruses and 31.6% of avian viruses are resistant to the drug amantadine, which is no longer effective for the treatment of seasonal flu.
A small incidence of resistance to the drugs oseltamivir and zanamivir, which are two common treatments for flu, was also seen in the results, according to the scientists.
The authors explained:
"Total resistance was found in 2.4% of human and 0.8% of avian viruses, reduced susceptibility to the drugs was detected in 0.8% of human and 2.9% of avian isolates."
The resistance to common treatments in H5N1 viruses that spread around the world between 2002 and 2012 were also observed in the current research.
Some resistance to treatment was detected, however, the resistance has not increased over time, the researchers said.
The report emphasizes the need for continued surveillance. The acquisition of drug resistance is a severe public health problem, and the scientists believe that monitoring drug resistance is critical in evaluating the possibility of a pandemic.
"Continued antiviral susceptibility monitoring of H5N1 viruses is needed to maintain therapeutic approaches for control of disease," the authors concluded.
Written by Sarah Glynn