Since we only rarely hear of it infecting humans, and it tends to produce mild to moderate illness when it does, the H9N2 avian influenza virus doesn’t get as much attention as it probably deserves. Despite its relatively benign reputation, H9N2 is a major driver of avian influenza evolution, and reassorts readily (and often) with other viruses.
Look at the internal genes of some of the most worrisome avian influenza viruses – H5N1, H7N9, H10N8, etc. – and you’ll find that H9N2 that has lent a good deal of its backbone – it’s internal genes – to the creation of these emerging threats.
Earlier this year, the WHO warned:
The emergence of so many novel viruses has created a diverse virus gene pool made especially volatile by the propensity of H5 and H9N2 viruses to exchange genes with other viruses. The consequences for animal and human health are unpredictable yet potentially ominous.
Early last year, The Lancet carried a report entitled Poultry carrying H9N2 act as incubators for novel human avian influenza viruses by Chinese researchers Di Liu a, Weifeng Shi b & George F Gao that warned:
Several subtypes of avian influenza viruses in poultry are capable of infecting human beings, and the next avian influenza virus that could cause mass infections is not known. Therefore, slaughter of poultry carrying H9N2—the incubators for wild-bird-origin influenza viruses—would be an effective strategy to prevent human beings from becoming infected with avian influenza.
We call for either a shutdown of live poultry markets or periodic thorough disinfections of these markets in China and any other regions with live poultry markets.
And just last January (see PNAS: Evolution Of H9N2 And It’s Effect On The Genesis Of H7N9) we looked at a study that found a new, better adapted genotype (G57) of the H9N2 virus had emerged – one that evades the poultry vaccines currently in use – and that it has become widespread among vaccinated Chinese poultry since 2010.
Globally, we’ve seen seen a fairly limited number of human infections, including a handful in China between 1998 & 1999, Hong Kong in 1999 (2 cases), 2003 (1 case), and 2007 (1 case), and December of 2013 (see Hong Kong: Isolation & Treatment Of An H9N2 Patient). In late 2014, two mild cases were reported out of China.
As this virus is most common in areas where testing and surveillance are less than optimal, we really don’t know how many people end up infected by it.
Although reporting out of Egypt has been inconsistent, last February (see An H9N2 Infection In Egypt & Updated H5N1 Count – FAO/EMPRES) we learned of Egypt’s first H9N2 infection. Late yesterday ProMed Mail carried the following report – gleaned from an FAO report – detailing Egypt’s third H9N2 infection.
Published Date: 2015-05-22 13:44:27
Archive Number: 20150522.3378923
AVIAN INFLUENZA, HUMAN (108): EGYPT, H9N2 AND INFLUENZA B
A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases
Date: Thu 14 May 2015
Source: FAO EMPRES-Animal Health, Global Early Warning System (GLEWS) [edited]
Animal Disease Threats Update
(Disease Events monitored by FAO AGAH/GLEWS between 10 May 2015 and 14 May 2015)
Egypt, confirmed additional infection with H9 LPAI in a human;
- on 29 Apr 2015, a 7-year-old male with high fever and cough tested positive for H9 on 7 May 2015;
- the sample tested positive for RNP gene, flu A, avian H9 and flu B and was negative for all other respiratory viruses;
- the investigation revealed a history of exposure to live bird market poultry. The case was cured and discharged. [MoH and FAO field officer, 12 May 2015]
Note: This is the 3rd case of H9N2 LPAI reported in humans in Egypt since January 2015. The other 2 cases were detected in 2015 in Aswan and Cairo Governorate. The latest case is the 1st recorded human case of co-infection with H9 and flu B in Egypt.
While the direct threat to human health from H9N2 is currently small, its promiscuity and history of reassorting with other avian viruses makes it a serious threat, and one very much worth keeping track of.
Warning: be prepared for surprises
Though the world is better prepared for the next pandemic than ever before, it remains highly vulnerable, especially to a pandemic that causes severe disease. Nothing about influenza is predictable, including where the next pandemic might emerge and which virus might be responsible. The world was fortunate that the 2009 pandemic was relatively mild, but such good fortune is no precedent.