Credit NIAID
# 7314
Helen Branswell has the details today on a new study which appears in the Journal Science, that looks at the ability of the avian H7N9 virus – recently emerged in China – to infect and transmit among ferrets.
Ferrets are considered a reasonable mammalian substitute for humans when testing respiratory viruses because their lung physiology is similar, and because they cough and sneeze when infected, very much as humans do.
As Helen reports, researchers found signs that the H7N9 virus has already made adaptations to mammalian hosts not normally seen in `wild’ avian flu viruses, and as such, must be considered `a serious threat’.
First, I’d invite you to follow the link to read Helen’s article, then I’ll return with more.
H7N9 bird flu virus spreads among mammals, inches closer to human-to-human transmission, experts warn
Helen Branswell, Canadian Press | 13/05/23 2:50 PM ET
TORONTO — A new study shows that the H7N9 flu virus can pass between ferrets, even sometimes spreading by airborne transmission.
While the airborne spread wasn’t highly efficient, the work suggests this virus is more closely adapted to spread among mammals than other bird flu viruses.
The study can be found at:
Published Online May 23 2013
Science DOI: 10.1126/science.1239844Infectivity, Transmission, and Pathology of Human H7N9 Influenza in Ferrets and Pigs
H. Zhu, D. Wang, D. J. Kelvin, L. Li, Z. Zheng, S.-W. Yoon, S.-S. Wong, A. Farooqui, J. Wang, D. Banner, R. Chen, R. Zheng, J. Zhou, Y. Zhang, W. Hong, W. Dong, Q. Cai, M. H. A. Roehrl, S. S. H. Huang, A. A. Kelvin, T. Yao, B. Zhou, X. Chen, G. M. Leung, L. L. M. Poon, R. G. Webster, R. J. Webby, J. S. M. Peiris, Y. Guan,Y. Shu
The emergence of the H7N9 influenza virus in humans in Eastern China has raised concerns that a new influenza pandemic could occur. Here, we used a ferret model to evaluate the infectivity and transmissibility of A/Shanghai/2/2013 (SH2), a human H7N9 virus isolate. This virus replicated in the upper and lower respiratory tracts of the ferrets and was shed at high titers for 6 to 7 days, with ferrets showing relatively mild clinical signs.
SH2 was efficiently transmitted via direct contact, but less efficiently by airborne exposure. Pigs could be productively infected by SH2 and shed virus for 6 days but were unable to transmit the virus to other animals. Under appropriate conditions human-to-human transmission of the H7N9 virus may be possible.
Today the NIH published a press release on this study, portions of which I’ve excerpted below:
Ferrets, Pigs Susceptible to H7N9 Avian Influenza Virus
NIH-Funded Study Examined Transmissibility of Emerging Virus
WHAT:
Chinese and U.S. scientists have used virus isolated from a person who died from H7N9 avian influenza infection to determine whether the virus could infect and be transmitted between ferrets. Ferrets are often used as a mammalian model in influenza research, and efficient transmission of influenza virus between ferrets can provide clues as to how well the same process might occur in people. The research was supported, in part, by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.
The researchers dropped H7N9 virus into the noses of six ferrets. A day later, three uninfected ferrets were placed inside cages with the infected animals, and another three uninfected ferrets were placed in cages nearby. All the uninfected ferrets inside the cages became infected, while only one of three placed in nearby cages became infected. The team concluded that the virus can infect ferrets and be transmitted between ferrets both by direct contact and, less efficiently, by air. The scientists detected viral material in the nasal secretions of the ferrets at least one day before clinical signs of disease became apparent. The potential public health implication of this observation is that a person infected by H7N9 avian influenza virus who does not show symptoms could nevertheless spread the virus to others.
The researchers also infected pigs with the human-derived H7N9 virus. In natural settings, pigs can act as a virtual mixing bowl to combine avian- and mammalian-specific influenza strains, potentially allowing avian strains to better adapt to humans. New strains arising from such mixing have the potential to infect humans and spark a pandemic, so information about swine susceptibility to H7N9 could help scientists gauge the pandemic potential of the avian virus. Unlike the ferrets, infected pigs in this small study did not transmit virus to uninfected pigs, either through direct contact or by air. All the infected ferrets and pigs showed mild signs of illness, such as sneezing, nasal discharge, and lethargy, but none of the infected animals became seriously ill.
ARTICLE:
H Zhu et al. Infectivity, transmission and pathogenesis of human-isolated H7N9 influenza virus in ferrets and pigs. Science DOI: 10.1126/science.1239844 (2013).
