Although avian H9N2 is an LPAI (Low Path) virus, where ever it goes, trouble just seems to follow. Regarded as having only moderate pandemic potential on its own (see CDC IRAT score), H9N2 more than makes up for that by its promiscuity and genetic generosity.
Over the years H9N2 has lent its internal genes (via reassortment) to a long list of successful and often dangerous HPAI & LPAI viruses, including H5N8, H5N6, and H7N9 (see graphic below).
|H7N9 Genetic Structure - Credit Eurosurveillance|
H9N2's contributions to the creation of novel HPAI/LPAI strains has not been a one shot deal either. In 2014's Eurosurveillance:The Evolving Threat From New, Reassorted H7N9 Viruses, researchers reported finding ongoing and `dynamic reassortments between influenza A(H7N9) and A(H9N2) viruses since the outbreak of A(H7N9) virus infection in March 2013.'
This continual participation in the evolution of H7N9 (and other) avian viruses has led to the creation of new lineages, and dozens of new genotypes, a pattern that makes identifying any changes in H9N2's genetic structure, behavior, or geographic spread of considerable interest.In early 2014 The Lancet carried a report entitled Poultry carrying H9N2 act as incubators for novel human avian influenza viruses where researchers warned that `reassortment between the prevalent poultry H9N2 viruses (providing genetic segments) and the influenza virus from wild birds could make the influenza evolve to adapt to domestic hosts.'
Three years ago, in PLoS Path: Genetics, Receptor Binding, and Transmissibility Of Avian H9N2 researchers found evidence of Chinese H9N2 viruses binding preferentially to alpha 2,6 receptor cells - the type commonly found in the human upper respiratory tract - rather than to alpha 2,3 receptor cells which are found in the gastrointestinal tract of birds.
Endemic in Asia, and the Middle East, H9N2 continues to evolve and diversify. And along the way it has been a significant catalyst for the generation of new subtypes and genotypes of avian, canine, and swine flu viruses.H9N2 has begun to appear in North Africa in recent years, sparking concerns that it could eventually spread down the continent, and potentially reassort with other avian viruses.
Today we've a report from the EID Journal detailing the detection of H9N2 in the West African Nation of Burkina Faso - a region which has reported numerous outbreaks of HPAI H5N1 since early 2014.
Volume 23, Number 12—December 2017
Since their detection in China in 1992, influenza A(H9N2) viruses have caused large economic losses to the poultry industry and have occasionally been transmitted to mammalian species, including humans. Three main genetic lineages were described among the Eurasian H9N2 subtype viruses: G1, Y280, and Y439 (Korean) lineage (1). In the past decade, the G1 lineage has spread mostly in gallinaceous birds across Asia, the Middle East, and eventually North Africa, where H9N2 outbreaks were reported in Libya (2006 and 2013) (2), Tunisia (2010–2012) (3), Egypt (2011–present) and Morocco (2016) (4).
AbstractWe identified influenza A(H9N2) virus G1 lineage in poultry in Burkina Faso. Urgent actions are needed to raise awareness about the risk associated with spread of this zoonotic virus subtype in the area and to construct a strategy for effective prevention and control of influenza caused by this virus.
The Veterinary Services of Ouagadougou, Burkina Faso, submitted 30 tracheal swab specimens and 10 organ samples collected in January 2017 in Burkina Faso to the World Organisation for Animal Health/Food and Agriculture Organization of the United Nations Reference Laboratory for Avian Influenza, Istituto Zooprofilattico Sperimentale delle Venezie (Legnaro, Padova, Italy). All samples were collected from a layer farm that was experiencing decreased egg production and respiratory signs among its flock; the animals were suspected to have infectious bronchitis virus (IBV).
Molecular analyses of the animal samples showed negative results for IBV and indicated that animals from the farm were infected with avian influenza A(H9N2) virus. The 8 gene segments were obtained for 1 representative virus by using a MiSeq Platform (Illumina, San Diego, CA, USA). Sequences were submitted to GenBank under accession numbers MF510849–F510856.
Identification of H9N2 subtype virus in West Africa, where highly pathogenic H5 strains of the A/goose/Guangdong/1/1996 lineage (Gs/GD) have been widely circulating since the beginning of 2015, is a concern because of animal health implications, negative effects on local economies, and possible emergence of reassortant viruses with unknown biological properties.
Reassortment events between H9N2 and highly pathogenic H5N1 subtype viruses were reported in China in 2005 and 2016 (7,8) and in Bangladesh in 2012 (9). In December 2013, an H5N1 subtype virus that had an H9N2 subtype polymerase basic 2 gene was reported in a patient in Canada who had returned from China (10). Moreover, H5N6 subtype reassortant viruses belonging to clade 184.108.40.206, which contain H9N2 subtype–like internal genes, were identified in China in 2015–2016 (8).
H5 strains belonging to clades 220.127.116.11c and 18.104.22.168 are currently circulating in West Africa. This finding, combined with detection of human-like receptor specificity and 2 mutations typical of human influenza viruses in the H9N2 subtype virus from Burkina Faso, might indicate emergence of a strain capable of infecting humans and warrants additional attention to the avian influenza situation in West Africa. Furthermore, identification of H9N2 subtype viruses in Morocco and Burkina Faso in chickens suggests that commercial poultry trade between North and West Africa might have played a key role in spread of the virus.
Involvement of wild birds in long-distance spread of H9N2 subtype G1 virus seems unlikely because this lineage is strongly adapted to poultry. These observations highlight the difficulty in tracing and containing circulating H9N2 subtype G1 virus and underline the need to review current approaches of disease reporting to understand spread and effects of this virus, which are probably underestimated. Thus, it is imperative to provide strategic guidance to countries in West Africa on technical and policy options for cost-effective surveillance and prevention and control of multiple cocirculating influenza virus strains.
Dr. Zecchin is a biotechnologist at the Istituto Zooprofilattico Sperimentale delle Venezie, Padova, Italy. Her primary research interests include studying the molecular phylogeny and the evolutionary dynamics of viruses.