The news of a second virus-positive case detected in Beijing - first mentioned yesterday by Crof, and that I wrote in Newshounds On The Trail Of The Latest Beijing H7N9 Report – has the unusual twist that this 4-year old hasn’t shown clinical symptoms of infection.
Since the vast majority of H7N9 cases detected to date have exhibited severe symptoms, this latest finding confirms that the virus can also generate mild, or sub-clinical symptoms in humans (we already know of its low pathogenicity in birds).
And that not only makes it harder to identify (and by inference, contain), it also suggests there may already be more cases out there than we currently are aware of.
Delving into all this is one of our favorite flu journalists Jason Gale, who interviews Dr. Ian MacKay (see VDU: Updated H7N9 Charts) - associate professor of clinical virology at the University of Queensland – and others, on what this may mean.
A short excerpt, but follow the link to read Jason’s full article, which also includes statements by Sinovac Biotech Ltd. CEO Yin Weidong and Michael O’Leary, WHO’s China representative.
By Bloomberg News - Apr 15, 2013 3:46 AM ET
Bird flu was found in a 4-year-old Beijing boy who has no symptoms of the infection, health authorities said, suggesting more people may be catching the H7N9 influenza virus than reported.
The boy is under medical observation. The case suggests some H7N9 infections may be going unrecorded because of a lack of obvious symptoms. Almost all the 60 previous cases in eastern China were extremely unwell, with complications extending to brain damage, multi organ failure and muscle breakdown.
“With asymptomatic cases around, I think everything changes,” said Ian Mackay, an associate professor of clinical virology at the University of Queensland in Brisbane, in a telephone interview today. “There has been a spike in pneumonia cases that have drawn the health officials’ attention, but the virus may have been going around as a normal cold.”
Dr. Mackay goes on to state `“It’s essential that lab testing of contacts is carried out as soon as possible to give us some information about the denominator: how many cases are positive for this virus, whether they’re symptomatic or not.’
Writing on his own website – Virology Down Under – Ian notes:
Added 15.04.13. Multiple reports of the first asymptomatic case in a 4-year old male (4M) living across the street from the previously H7N9-POS, 7F. This may demystify a lot of H7N9 confusion as well as seriously increase the threat level for H7N9 spread...a stealth virus not only in poultry but humans is a new game.
As I've suggested earlier, the widespread use of sensitive molecular detection methods, not just on the cases with the most severe clinical signs and symptoms, is absolutely essential to detect mild or asymptomatic cases of infection. The use of PCR in this way seems to have done just that. I'll keep a close eye on this story but I suspect it will result in a drastic change to the landscape of detection numbers and epidemiology.
Symptoms alone tell only a small part of the story of any respiratory virus. This may strengthen the case for H7N9 having been in the community for much longer than the pneumonia cases officially commencing back in Feb, suggest.
You’ll find a lot more at his website, plus his H7N9 dedicated page has some of the best graphics and analysis going.
Mild or asymptomatic carriage of the H7N9 virus would seriously impact attempts to detect and contain the virus.
Asymptomatic infection with influenza is believed to be fairly common (albeit, by its very nature, difficult to quantify), and is something we’ve discussed before, most recently in PLoS One: Influenza Viral Shedding & Asymptomatic Infections .
This particular study was conducted in Germany over 4 flu seasons (2007-2011) and involved four flu strains; seasonal (A(H3N2), A(H1N1), influenza B, and pandemic (A(H1N1)pdm09.
Among their findings:
- Nearly 1/3rd of cases began shedding virus while pre-symptomatic
- Viral loads in (six studied) asymptomatic cases were similar to that to patients exhibiting ILI (influenza-like-illness) symptoms.
- Viral load among symptomatic patients peaked on illness days 1, 2 or 3 and declined steadily until days 7–9
Of course, how closely these results might align with how the H7N9 virus behaves, when (or if) it ever becomes more transmissible, is unknown.
In Branswell: Limitations Of Airport Disease Screening, we saw that it was asymptomatic and pre-symptomatic carriers of the 2009 H1N1 virus that largely thwarted attempts at detection at ports of entry during the opening months of the 2009 pandemic.
With the SARS outbreak of 2003, it was the lack of asymptomatic (or pre- symptomatic) transmission of the virus that has often been credited for making it possible to contain.
The one advantage that we still appear to have over the H7N9 virus is that based on the evidence to date (always subject to change), this virus does not yet appear to be transmitting efficiently in the community.
The World Health Organization is aware of a few `family clusters’ that may indicate human-to-human transmission of the virus, and therefore state:
Whether that bit of luck with this virus continues will determine just how much impact this virus will have outside of China.