H7N9 Virus Retains Unusual Strength Even After Mutating

A new strain of bird flu can still cause serious illness in humans even after developing resistance to antiviral medications - a process that usually weakens the virus's ability to breed as well as spread from one person to another.

The finding, reported in the journal Nature Communications, centers on the H7N9 virus that wreaked havoc in China last spring, infecting at least 135 people and killing 44.

Initial observations suggested the virus could quickly adapt so as to become more resistant to antiviral medication Tamiflu. Antiviral medication, the researchers note, are the only form of defense against a flu virus for infected patients in the absence of a vaccine, which has yet to be developed for the H7N9 strain. Even in patients in whom drug resistance developed, however, severe infections were reported.

"In this outbreak, we saw some differences in the behavior of H7N9 and other avian influenza strains that can infect humans, beginning with the rapid development of antiviral resistance in some people who were treated with oseltamivir and the persistence of high viral loads in those patients," said lead investigator Dr. Nicole Bouvier, assistant professor at the Icahn School of Medicine at Mount Sinai.

The scientists discovered that a drug-resistant H7N9 virus was still able to replicate in human respiratory cells and cause similarly severe illness in animal models when compared to non-resistant virus forms. What's more, drug-resistant strains were able to spread with relative ease between animal subjects, although it has yet to adapt so as to transmit between humans.

"Transmission was inefficient for both of the H7N9 viruses that we tested in our experiments," Dr. Bouvier said. "But surprisingly, transmission of the drug-resistant virus was no less efficient than that of the drug-sensitive version."

Bouvier said the study's results highlight the need to "develop a bigger arsenal" when it comes to antiviral drugs and vaccines. Currently, researchers from Mount Sinai are working to develop new targets for drugs in order to create a vaccine that could prevent a range of influenza strains.