H7N9 is having a big season...Happy New Year!

My how things can change in 5 weeks. 

If you look back a few posts you'll see that in late December, the data suggested avian influenza A(H7N9) virus was having a wimpy season - its slowest to date. 

Well, thanks to 100+ cases in China which have been bulk reported by the ever vigilant Hong Kong Centre for Heath Protection (CHP) - and captured and listed by FluTrackers - the situation has changed dramatically. 

Never take your eye off influenza virus - especially during its favourite season. And this season is a particularly active one for avian influenza all over the world.[4]

H7N9 is an avian influenza virus (hence the  "bird flu" moniker) that to date has been localised to China - especially but not exclusively to its eastern coast provinces - and it's a flu virus that doesn't make the birds it infects noticeably sick. 

These "low pathogenic" influenza viruses can sneak silently through poultry flocks because infections are mild - they don't cause infected birds to get sick or die. 

Data on human infections with avian influenza A(H7N9) virus. Data from [1]
Click on image to enlarge.

The H5 avian influenza viruses on the other hand - H5N1, H5N8, H5N5 or H5N6 for example - are called "high pathogenicity" avian influenza viruses because they kill off infected birds. Thankfully, H5N1 is the only H5 avian influenza that has caused a sizable number of human infections. H5N6 is gaining some ground though. The other H5s do not reportedly cause much impact in humans. Whether this is because they are not found or not sought in humans who have had contact with infected animals is unclear.

Disease in an H5-infected flock can serve as a sentinel for an outbreak of the virus. 

With H7N9 though, it's humans falling ill that set of the alarm that H7N9 (or another influenza virus) is in the house...or the market. And there are a sizable number of deaths among those - often male - who already have some sort of underlying illness and then acquire an H7N9 infection.

Most human cases of H7N9 result from contact with a "wet" market, also called a live bird market (LBM) in which chickens and ducks can be chosen, killed and dressed to provide a super-fresh meal. These tasty treats are especially in demand around this time of year as Chinese New Year is upon us. 


Chinese New Year is also a time when we observe the largest seasonal migration of humanity in the world. [2] Loved ones travel across a massive country to visit each other, share stories, traditions, meals - and the occasional respiratory virus like influenza. 

From [3].

In the coming weeks, as the gatherings disperse, it will be very interesting to see whether the current spike in human H7N9 infections is reflected by a steep rise in human cases acquired during the New Year celebrations - some of which include contact (direct or indirect) with infected poultry in backyard farms or LBMs.

Stay tuned. And don't forget to wash your hands often and cough/sneeze into the crook of your elbow.

References...

1. http://virologydownunder.blogspot.com.au/2014/11/influenza-ah7n9-virus-detection-numbers.html
2. https://www.nytimes.com/2017/01/26/world/asia/chinese-new-year-home-lunar.html?_r=0
3. https://www.cdc.gov/flu/protect/covercough.htm
4. http://news.trust.org/item/20170126150919-05z2c/