When the influenza burden is high during certain years, the amount of antiviral oseltamivir used will be high. Much of it enters the water system and will end up driving antiviral resistance in avian viruses. Previous work has demonstrated that influenza virus can develop resistance to oseltamivir carboxylate (OC) when the virus infects wild ducks that are exposed to environmental-like OC concentrations suggesting that environmental resistance is a concern.
Avian influenza strain H1N1 with the OC resistance mutation (NA-H274Y) has been found to retain resistance even when the environment did not contain oseltamivir carboxylate, suggesting maintained fitness of the virus. If wild birds, wild ducks in particular, are the first to be infected by influenza virus brought in by migratory birds, domestic poultry act as an important amplifying host, and a source of influenza virus evolution. The virus that has evolved can then spread from poultry birds to humans.
A study recently published in the Journal of General Virology has demonstrated that oseltamivir-resistant strain can transmit from wild ducks to chickens and then spread between chickens, while retaining the resistance mutation in an experimental setting mimicking conditions suitable for natural transmission.
“Our results demonstrate that regardless of the oseltamivir-resistance mutation, infection was detected in experimentally-infected chickens and chickens in contact with infected mallards,” the authors write. However, none of the virus strains established sustained transmission in chickens.
According to the authors, this may be due to poor species adaptation of the virus. “We demonstrated limited interspecies transmission, with no differences between wild-type and resistant virus,” they write. However, neither oseltamivir-resistant strain nor the wild type was able to establish a sustained transmission in chickens in the two different experiments.
They found that mutation (NA-H274Y) that renders the virus resistant to oseltamivir carboxylate can remain stable in an environment even when oseltamivir carboxylate was not present. And there is no barrier to interspecies transmission of the antiviral-resistant virus per se, thus demonstrating a risk of an oseltamivir-resistant pandemic virus.
The study turns the spotlight on responsible use of oseltamivir and surveillance for resistance development to limit the risk of an oseltamivir-resistant pandemic strain.
