The First Lethal and Transmissible Avian Virus

By Akari Miki

In 2013, a previously unknown avian virus, H7N9, began infecting poultry in China, and by late July 2017, 1,600 people contracted the virus. Of the infected people, 40 percent died, prompting researchers at the University of Wisconsin-Madison School of Veterinary Medicine to immediately begin investigation. According to the principal investigator, Professor Yoshihiro Kawaoka, this is the first case of an avian virus that is lethal and transmissible between animals.

His team received a sample of the H7N9 from a deceased patient and performed genomic analysis on it. Their most significant finding was that the virus had two different populations: one that was vulnerable to Tamiflu, a common flu drug, and another that was resistant. This observation suggested that after infecting the patient, the virus was accumulating mutations, improving its resistance to the drug.

The next step was to determine whether H7N9 is transmissible among ferrets, the most accurate animal model for studying human infections. Each experimental trial consisted of two ferrets, a healthy one and one that was deliberately infected with H7N9. Each ferret was placed in two adjacent cages with a barrier in between them that allowed the passage of respiratory droplets. All of the previously healthy ferrets became infected, and the deliberately infected ferrets as well as the ferrets to which they transmitted the virus died, confirming the lethality and infectiousness of the virus.

Professor Kawaoka predicts that H7N9 will continue to accumulate mutations that enhance their pathogenicity and transmissibility, a phenomenon known as gain-of-function. Prior to this study, he published a commentary that emphasizes the importance of research on gain-of-function of viruses in transmissibility, drug resistance, pathogenicity, and ability to replicate, because it would facilitate the development of pre-pandemic vaccines and antiviral drugs. As gain-of-function studies get underway, the best measure for global public health is to improve close surveillance on the circulating virus.


University of Wisconsin-Madison. (2017, October 19). H7N9 influenza is both lethal and transmissible in animal model for flu. ScienceDaily. Retrieved October 29, 2017 from