Research Suggests H7N9 Has Serious Pandemic Potential

Microscopic view H7N9

A report that will appear in the October 2013 issue of The American Journal of Pathology suggests that the emerging influenza virus H7N9 has pandemic potential.

First reported in March 2023 in China it was though to be spread from infected poultry,and that human to human transmission was unlikely.

Research has found however that the virus attaches to the epithelium in both the upper and the lower respiratory tract. Usually the lower respiratory tract is infected which makes human to human transmission less likely. It’s the discovery of upper respiratory tract colonization that has worried the scientists. Virulence is increased in conditions where both the upper and lower respiratory tract are infected.

They found that like other avian influenza viruses, the H7N9 viruses attached more strongly to lower parts of the human respiratory tract than to upper parts. However, compared to other avian influenza viruses, the attachment to epithelial cells by H7N9 in the bronchioles and alveoli of the lung was more abundant and the viruses attached to a broader range of cell types. “These characteristics fit with increased virulence of these emerging avian H7 viruses compared to that of human influenza viruses,” says Dr. Kuiken.

A third notable finding was a more concentrated attachment of H7N9 viruses in ciliated cells of the nasal concha, trachea, and bronchi, suggesting the potential for efficient transmission among humans. “However, the fact that the emerging H7N9 virus has caused infection mainly in individual human cases suggests that it has not acquired all the necessary properties for efficient transmission among humans,” notes Dr. Kuiken. (source)

The research follows on from the findings from a University of Wisconsin team in July.

 H7N9 viruses have several features typically associated with human influenza viruses and therefore possess pandemic potential and need to be monitored closely,” says Kawaoka, one of the world’s leading experts on avian flu.

Normally, avian influenza viruses do not infect humans, with the exception of the highly pathogenic H5N1 strains. However, the H7N9 virus has so far infected at least 132 humans, killing more than 20 percent of those infected, and several instances of human-to-human infection are suspected.

The new study suggests that the ability of the H7N9 virus to infect and replicate in human cells may be due to just a few amino acid changes in the genetic sequence of the virus. “These two features are necessary, although not sufficient, to cause a pandemic,” says Kawaoka, explaining that the influenza virus depends on host cells, which it hijacks to make new virus particles and sustain the chain of infection.

In monkeys, the H7N9 virus was shown to efficiently infect cells in both the upper and lower respiratory tract. Conventional human flu viruses are typically restricted to the upper airway of infected nonhuman primates. (source)

With winter fast approaching scientists will be worried that H7N9 will infect someone suffering from a cold or seasonal influeza and will quickly spread through the population. Influeza viruses mutate readily and swap genetic material with circulating viruses. This gives them the improved transmissibility of the circulating virusand the complications associated with the emerging virus. With H7N9 already having the markers for a pandemic spread this could prove disasterous.