Vet. Microb.: Detection Of Non-notifiable LPAI H4N6 In Poultry In Great Britain

Credit NIAID

#13,557

 
There are scores of  HPAI and LPAI avian influenza subtypes that circulate in wild birds - and occasionally infect poultry flocks - but only HPAI viruses and LPAI H5 & H7 subtypes are considered `Notifiable' by the OIE.

From the 2015 OIE regulations:

For the purposes of the OIE Terrestrial Animal Health Code, avian influenza is notifiable to OIE and is defined as an infection of poultry caused by any influenza A virus with high pathogenicity (HPAI) and by H5 and H7 subtypes with low pathogenicity (H5/H7 LPAI). Influenza A viruses with high pathogenicity in birds other than poultry, including wild birds, are also notifiable.

Low pathogenicity non-H5 and non-H7 influenza A viruses (i.e. H1–4, H6 and H8–16) are not defined as avian influenza and are not notifiable.

H5 and H7 LPAI viruses are included because they have shown the ability to mutate spontaneously into HPAI viruses when introduced into poultry flocks.

HPAI viruses have been generated in the lab by repeated passage of LPAI viruses through chickens (cite FAO) but exactly how and why this occurs naturally is poorly understood (see JVI  Emergence of a Highly Pathogenic Avian Influenza Virus from a Low Pathogenic Progenitor). 

The most important LPAI subtype not captured by this surveillance system is arguably LPAI H9N2, which not only causes rare human infection, it reassorts easily with many other avian subtypes, and its internal genes are found in HPAI H5N1, H5N6, H7N9 and H10N8 (see Vet. Sci.: The Multifaceted Zoonotic Risk of H9N2 Avian Influenza).

But there are other LPAI viruses that - while much farther down our list of avian flu concerns concerns - nevertheless show signs (including hints of mammalian adaptation) that they could one day become bigger players in the avian flu world. 

• One of the most visable candidates is H6N1, which in 2013 infected a woman who was hospitalized with mild pneumonia in Taiwan. 
• Two years later, in the EID Journal: Seropositivity For H6 Influenza Viruses In China, we saw researchers reported a low - but significant - level of H6 antibodies,  particularly among live bird handlers.
• A few days after that, in Study: Adaptation Of H6N1 From Avian To Human Receptor-Binding, we looked at another study, published in the EMBO Journal, that found recent and worrisome changes in the receptor binding characteristics of the H6N1 virus. Changes they maintain have steadily moved the virus towards an affinity towards human receptor cells instead of avian receptor cells.

Another virus increasingly on our `suspect list' has been LPAI H4N6 - which while common in wild and migratory birds - has also been found in Chinese, Canadian (1999) and American swine (see Virology: Detection & Characterization Of Avian H4N6 In Midwestern Swine (2015)).

Just over a year ago, in Cell: Avian-to-Human Receptor-Binding Adaptation by Influenza A Virus Hemagglutinin H4, researchers presented evidence that avian H4N6 viruses can adapt to human receptor cells while in a swine host (using the 1999 Canadian isolate), warning:

These results clearly implicate the potential threat posed by H4 viruses to public health. Therefore, early-warning study of H4 subtype human receptor-binding property is highly appreciated.

H4N6 has also been detected in other mammals, including seals.  In 2017's PLoS One study Isolation and characterization of H4N6 avian influenza viruses from mallard ducks in Beijing, China, the authors warned: 

All of our isolates belonged to a novel genotype that was different from other H4N6 viruses isolated in China. We further evaluated the virulence and transmission of two representative H4N6 strains in mammalian models. We found that both of these H4N6 viruses replicated efficiently in mice without adaptation.

Additionally, these two strains had a 100% transmission rate in guinea pigs via direct contact, but they had not acquired respiratory droplet transmissibility.

These results reveal the potential threat to human health of H4N6 viruses in migratory birds and the need for enhanced surveillance of AIVs in wild birds.

None of this is to suggest that H4N6 is on the verge of becoming a pandemic threat, but it does illustrate some of the gaps in our surveillance and overall knowledge of LPAI viruses.

Helping to fill in those gaps, we have the following report on recent discoveries of non-notifiable LPAI H4N6 in poultry in Great Britain.

Veterinary Microbiology
Volume 224, October 2018, Pages 107-115

Detection of non-notifiable H4N6 avian influenza virus in poultry in Great Britain

Scott M.Reida1 Sharon M.Brookesa1 Alejandro Núñezb Jill BanksaC. DanielParkerc Vanessa Ceeraza Christine Russella Amanda Seekingsa Saumya S.Thomasa Anita Puranika2 Ian H.Browna

https://doi.org/10.1016/j.vetmic.2018.08.026

Highlights

• H4N6 LPAIV isolated from broiler breeder chickens from the first submission to the NAD ‘testing to exclude’ (TTE) scheme.
• A second H4N6 LPAIV case in June 2014 affected free-range laying chickens in GB, reflecting a different clinical presentation.
• The two H4N6 LPAIVs were genetically very similar but not identical (overall ≥ 99.7% identity).
• Stalk deletion in the neuraminidase sequence indicated viral adaptation to poultry.
• Viral genome analyses implied that the virus had not recently transferred from wild birds, indicating spread within the poultry sector.
  

Abstract

A 12-month pilot project for notifiable avian disease (NAD) exclusion testing in chicken and turkey flocks in Great Britain (GB) offered, in partnership with industry, opportunities to carry out differential diagnosis in flocks where NAD was not suspected, and to identify undetected or undiagnosed infections.

In May 2014, clinical samples received from a broiler breeder chicken premises that had been experiencing health and production problems for approximately one week tested positive by avian influenza (AI) real-time reverse transcription polymerase chain reaction (RRT-PCR). Following immediate escalation to an official, statutory investigation to rule out the presence of notifiable AI virus (AIV; H5 or H7 subtypes), a non-notifiable H4N6 low pathogenicity (LP) AIV was detected through virus isolation in embryonated specific pathogen free (SPF) fowls’ eggs, neuraminidase inhibition test, cleavage site sequencing and AIV subtype H4-specific serology. 

Premises movement restrictions were lifted, and no further disease control measures were implemented as per the United Kingdom (UK) legislation. Phylogenetic analysis of the haemagglutinin and neuraminidase genes of the virus revealed closest relationships to viruses from Mallard ducks in Sweden during 2007 and 2009. 

In June 2014, clinical suspicion of NAD was reported in a flock of free-range laying chickens elsewhere in GB, due to increasing daily mortality and reduced egg production over a five-day period. An H4N6 LPAIV with an intravenous pathogenicity index of 0.50 was isolated. This virus was genetically highly similar, but not identical, to the virus detected during May 2014.

Full viral genome analyses showed characteristics of a strain that had not recently transferred from wild birds, implying spread within the poultry sector had occurred. A stalk deletion in the neuraminidase gene sequence indicated an adaptation of the virus to poultry. Furthermore, there was unexpected evidence of systemic spread of the virus on post-mortem. 

No other cases were reported. Infection with LPAIVs often result in variable clinical presentation in poultry, making detection of disease more difficult.

While the discovery of H4N6 circulating in British poultry isn't exactly a `Stop the presses!' type moment, it does provide another important piece of the overall avian influenza puzzle.  

Information that could prove invaluable should H4N6 begin to flex its malleable genome.

Three months ago, in Reassortment After Co-infection Of Chickens With H4N6 and H9N2 influenza Viruses - also published in Veterinary Microbiology - we looked at a report that showed how easily LPAI H4N6 reassorts with LPAI H9N2 in co-infected chickens, and that some of those reassortants showed signs of increased virulence.

The authors - including  Chen Hualan, director of China's National Avian Influenza Reference Laboratory. - wrote:

Our results indicate that co-infection of an avian individual with the H4N6 and H9N2 viruses leads to a high frequency of reassortment and generates some reassortants that have higher virulence than the wild-type viruses in mammals.

These results highlight the potential public risk of the avian influenza reassortants and the importance of surveillance of the co-existence of the H4N6 and H9N2 viruses in avian species and other animals.

While LPAI H9N2 is not currently a problem in Great Britain, it has recently made substantial geographic leaps into the Middle East, Africa, and Northern Europe. 

While H4N6 sits far down on our worry list, the more we know about these non-notifiable (and presumably innocuous) LPAI viruses. the less likely we are to be blindsided by an avian flu threat coming at us from out of left field.