New bird flu strain can cause serious disease after developing resistance

A virulent new strain of avian influenza appears to retain its ability to cause serious disease in humans even after developing resistance to antivirals, according to a study published on Wednesday in Nature Communications. Researchers at the Icahn School of Medicine at Mount Sinai found that a drug-resistant strain of the H7N9 virus retained its ability to replicate in human respiratory cells and was still able to produce severe disease in animal models. H7N9, an avian strain of influenza A that emerged in China last spring, infected at least 135 people and caused 44 deaths during the outbreak. There is currently no vaccine to protect against the virus. The researchers found that while H7N9 has a limited ability to transmit between humans, the transmissibility in animals was comparable between drug-resistant and drug-susceptible strains. "Transmission was inefficient for both of the H7N9 viruses that we tested in our experiments," Bouvier said. "But surprisingly, transmission of the drug-resistant virus was no less efficient than that of the drug-sensitive version." When flu viruses develop genetic mutations that makes them less susceptible to anti-flu drugs, the changes often come at a cost to the virus. The virus is usually less able to replicate and spread from person to person. "Many of the people infected with H7N9 during the outbreak in China were elderly or had other conditions that predisposed them to severe influenza illness," Bouvier said. "Nevertheless, our study suggests that flu viruses can indeed develop drug-resistant mutations without suffering a penalty in terms of their own fitness." Bouvier said the study highlights the need to develop more antiviral drugs and vaccines in an effort to defeat the adapting influenza virus.