Tuesday, June 10, 2014

EID Journal: Mutations Of A(H10N8) Virus in Chicken Eggs and MDCK Cells

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Jiangxi Province – Credit Wikipedia – Site of 3 H10N8 Cases

 

# 8723

 

As part of the growing `alphabet soup’ of novel flu viruses, H10N8  sprang into the limelight last December when it was detected for the first time in a human host in Jiangxi Province, China (see HK CHP Notified Of Fatal H10N8 Infection In Jiangxi). 

 

Previously, (related versions ofH10N8 had only been seen in wild and domestic birds in China,  Italy, Canada, South Korea, Sweden, Japan, and the USA (cite).

 

In the `close, but no cigar category’,  two years ago in EID Journal: Human Infection With H10N7 Avian Influenza, we learned that the H10N7 avian flu virus had been detected in two poultry abattoir workers in Australia from 2010. Although 7 abattoir workers reported symptoms, only 2 tested positive for the H10 virus.

 

While a one-off detection of a novel influenza virus infection is of interest, the plot thickened in January – and again in February – when two more (epidemiologically unrelated) cases of H10N8 infection emerged in Jiangxi Province (see  Jiangxi Province Reports Second H10N8 Infection & Jiangxi Province Reports 3rd H10N8 Case).

 

Reports of cases stopped after three, likely as the result of the closure of live markets in China to contain the much larger H7N9 avian flu epidemic last winter.

 

Last month we saw reassuring media reports suggesting that the H10N8 virus – while worthy of watching – wasn’t `currently’ considered a big pandemic threat (see H10N8 bird flu unlikely to threaten public health), based on receptor binding testing done by the MRC National Institute for Medical Research (MRC-NIMR).

 

The operative word was `currently’, as it is axiomatic that the only true constant with influenza viruses is that they continually change.

 

Most often, change comes about gradually, through a process called antigenic drift which produce small, incremental changes in the virus over time. Drift is the standard evolutionary path of influenza viruses, and comes about due to replication errors that are common with single-strand RNA viruses (see NIAID Video: Antigenic Drift).

 

More abrupt changes come from antigenic shift, also called reassortment.  For shift to happen, a host (human, swine, bird) must be infected by two influenza different viruses at the same time.  Shift occurs when one virus swap out chunks of their genetic code with gene segments from another virus.

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The three avian flu viruses we are watching with particular interest in China – H5N1, H7N9, and H10N8 – all  share several important features (see Study: Sequence & Phylogenetic Analysis Of Emerging H9N2 influenza Viruses In China):

 

    • They all first appear to emanate from Mainland China
    • They all appear to have come about through viral reassortment in poultry
    • And most telling of all, while their HA and NA genes differ - they all carry the internal genes from the avian H9N2 virus

 

What we are finding is that the relatively benign and ubiquitous H9N2 virus, is actually fairly promiscuous; bits and pieces of it keep turning up in new reassortant viruses.  And perhaps even more ominously, these reassortants continue to reassort again and again (see EID Journal: H7N9 As A Work In Progress).
 

 

All of which serves as prelude to a new EID study, published yesterday, that looks at the evolution and mutations picked up by the H10N8 virus when passaged through Chicken eggs and MDCK cells.  MDCK (Madin-Darby canine kidney) are a line of mammalian epithelial cells often used in research. 

 

(Note link below now fixed)

 

Volume 20, Number 9—September 2014
Dispatch

Mutations of Novel Influenza A(H10N8) Virus in Chicken Eggs and MDCK Cells

Jian Yang1, Ting Zhang1, Li Guo1, Yongfeng Hu1, Jinlin Li, Haoxiang Su, Yan Xiao, Xianwen Ren, Jie Dong, Lilian Sun, Yan Xiao, Li Li, Fan Yang, Jianwei Wang2, Hui Yuan2, and Qi Jin2Comments to Author

Abstract

The recent emergence of human infection with influenza A(H10N8) virus is an urgent public health concern. Genomic analysis showed that the virus was conserved in chicken eggs but presented substantial adaptive mutations in MDCK cells. Our results provide additional evidence for the avian origin of this influenza virus.

Influenza A virus remains a major threat to public health worldwide. The 2000s witnessed the epidemic of human infections with the avian influenza A(H5N1) and A(H7N9) viruses in China (1,2) and a global pandemic of human influenza caused by a novel swine-origin influenza A(H1N1) virus (3). More recently, the first human case of a novel influenza A(H10N8) virus infection was reported in China, and 2 additional human cases have been confirmed in the same province (4,5). The emergence of the novel influenza A(H10N8) virus has become an urgent public health concern (6).

 

A preliminary genomic analysis showed that the emerging influenza virus was genetically distinct from the avian influenza A(H10N8) viruses previously identified in China, and scientists have postulated that the virus resulted from multiple reassortments of subtype H9N2 strains that circulated widely in poultry in China (4).

Nevertheless, no identical influenza A(H10N8) virus was detected in the live-poultry market visited by the first patient before the onset of her illness, and the origin of the novel A(H10N8) virus remains unclear. We compared the genomic mutations of the virus cultured in embryonated chicken eggs and in MDCK cells in an attempt to find additional evidence to support the possible avian origin of the virus.

<SNIP METHODS & MATERIALS>

Conclusions

We investigated the genomic mutations and heterogeneities of the novel influenza A(H10N8) virus during culture in embryonated chicken eggs and MDCK cells compared with the genome sequence obtained directly from the clinical specimen. The viral genome was highly conserved during culture in embryonated chicken eggs, and no mutations were identified. This result suggests that the novel A(H10N8) virus might have been highly adapted to an avian-like host before it was transmitted to the human host (i.e., the first patient). In contrast, substantial genetic mutations were observed in the viral genome during culture in MDCK cells; this finding implies an ongoing adaptive microevolution of the virus in a mammalian environment.

Taken together, our results favor the proposal that the novel influenza A(H10N8) virus has an avian origin; however, more research is required to establish the definite origin of the emerging influenza virus. Furthermore, the substitutions E627K (in the PB2 protein) and R292K (in the NA protein) observed in the cultures of the MDCK cells indicate that the virus might be undergoing rapid adaptation to mammals and developing antiviral drug resistance. Although only 3 human cases of infection with the novel A(H10N8) virus have been reported, the potential for this virus to threaten public health should not be underestimated.

 

The bottom line is that H10N8 sample remained stable when passaged through chicken eggs, suggesting it is highly adapted to – and likely emerged from – an avian source.

 

When passaged through mammalian cells, however, the virus quickly picked up mutations, suggesting it `might be undergoing rapid adaptation to mammals and developing antiviral drug resistance’.

This obviously makes H10N8 a concern, but perhaps of equal interest is the fact that we continue to see new, `oddball’ flu viruses turn up – particularly in Asia.

 

While most reassortant viruses end up as evolutionary failures, and are ultimately unable to compete with the existing wild viruses, every once in awhile a new one will appear that is biologically fit enough to carve out a niche of its own.

 

Although none of these oddball viruses has shown the ability to transmit efficiently from human to human, as long as they circulate in poultry or wild birds along side H9N2 (or any other compatible flu strains), they will continue to get more opportunities to roll the genetic dice. 

 

And while failure is the most common result, one of these viruses only has to get `lucky’ once, to be a game changer.

 

For more on all of this you may wish to revisit:

 

EID Journal: Predicting Hotspots for Influenza Virus Reassortment 

Viral Reassortants: Rocking The Cradle Of Influenza

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