# 2229
Earlier this summer, our eyes were briefly diverted from the H5N1 virus by a report from the CDC suggesting that the H7 group of influenza viruses also posed a pandemic threat to humans.
I covered this story in early June:
CDC Press Release On Adaptation Of H7 Viruses
# 2059
The CDC gives us their summary of a PNAS article released on May 27th, indicating that some H7 viruses may be adapting to human receptor cells. Earlier coverage of this story can be found here, here and here.
This didn't come as a total surprise to flu observers, since we've seen (generally mild) human infections with H7 viruses in the past.
One of my earlier essays entitled It Isn't Just Bird Flu -archived on the Blasts from the Past section of my sidebar - explores a number of other pathogens that could potentially cause a pandemic.
This was written nearly 18 months ago, before the UK outbreak of H7 in humans last year:
Other influenza viruses with pandemic potential exist out there, among them are H9N2, which infected two children in Hong Kong in 1999 and another in 2003, H7N7 which infected 89 people (1 death) in the Netherlands in 2003, and H10N7 which infected two infants in Egypt in 2004.
Beyond Influenza we also watch for SARS, which broke out of China in 2003, and infected 8000 people worldwide, killing roughly 800. SARS wasn't as easily transmitted as influenza, but it does have pandemic potential. We hear very little about it today, but there is nothing to say that it couldn't jump back into the headlines tomorrow.
Today we get a new warning on one of those aforementioned influenza viruses, the H9N2 strain which infected the children in Hong Kong. This comes from a study published in open access journal PLoS One.
Reuters has a summary of this research:
New bird flu threat could be H9N2
WASHINGTON - COUNTRIES around the world may be preparing for a possible H5N1 bird flu pandemic, but another strain called H9N2 also poses a threat to humanity, researchers reported on Tuesday.
Tests on the H9N2 strain of the virus show it is capable of infecting and spreading with very few changes, a team from the University of Maryland, St. Jude's Children's Research Hospital in Memphis, and elsewhere reported.
'Our results suggest that the establishment and prevalence of H9N2 viruses in poultry pose a significant threat for humans,' the researchers wrote in the Public Library of Science journal PLoS ONE.
Most influenza experts agree that a pandemic - a deadly global epidemic - of some kind of flu is inevitable.
While this Reuters' report ends with the following paragraph:
There are hundreds of strains of avian influenza viruses, but only four - H5N1, H7N3, H7N7, and H9N2 - are known to have caused human infections, according to the World Health Organisation.
It should be noted that this isn't strictly true.
According to CIDRAP, and other sources, two 1-year-old infants, residents of Ismaillia, Egypt were found to have been infected by the H10N7 strain in 2004.
The PLoS One study is entitled:
Replication and Transmission of H9N2 Influenza Viruses in Ferrets: Evaluation of Pandemic Potential
Hongquan Wan1#¤, Erin M. Sorrell1#, Haichen Song1, Md Jaber Hossain1¤, Gloria Ramirez-Nieto1, Isabella Monne2, James Stevens3, Giovanni Cattoli2, Ilaria Capua2, Li-Mei Chen3, Ruben O. Donis3, Julia Busch4,5, James C. Paulson4,5, Christy Brockwell6, Richard Webby6, Jorge Blanco7, Mohammad Q. Al-Natour8, Daniel R. Perez1*
Abstract (reformatted)
H9N2 avian influenza A viruses are endemic in poultry of many Eurasian countries and have caused repeated human infections in Asia since 1998.
To evaluate the potential threat of H9N2 viruses to humans, we investigated the replication and transmission efficiency of H9N2 viruses in the ferret model. Five wild-type (WT) H9N2 viruses, isolated from different avian species from 1988 through 2003, were tested in vivo and found to replicate in ferrets.
However these viruses achieved mild peak viral titers in nasal washes when compared to those observed with a human H3N2 virus. Two of these H9N2 viruses transmitted to direct contact ferrets, however no aerosol transmission was detected in the virus displaying the most efficient direct contact transmission.
A leucine (Leu) residue at amino acid position 226 in the hemagglutinin (HA) receptor-binding site (RBS), responsible for human virus-like receptor specificity, was found to be important for the transmission of the H9N2 viruses in ferrets.
In addition, an H9N2 avian-human reassortant virus, which contains the surface glycoprotein genes from an H9N2 virus and the six internal genes of a human H3N2 virus, showed enhanced replication and efficient transmission to direct contacts.
Although no aerosol transmission was observed, the virus replicated in multiple respiratory tissues and induced clinical signs similar to those observed with the parental human H3N2 virus.
Our results suggest that the establishment and prevalence of H9N2 viruses in poultry pose a significant threat for humans.
Researchers discovered that a single mutation in the H9N2 virus could make it more virulent and pathogenic, as well as more easily transmissible in ferrets.
And a reassortment experiment - where they combined the H9N2 virus and an H3N2 (seasonal flu) virus - resulted in a virus more easily transmissible between ferrets.
An important reminder that our world hosts a number of potential pandemic pathogens, and that it isn't just the H5N1 bird flu virus that we need to keep our eyes on.
