Bad Bentheim, Germany
#18,358
Prior to the summer of 2013, avian H7 influenza viruses were thought to be less of a human health concern than H5Nx, despite several notable outbreaks including:
- 3 mild cases of LPAI H7N7 in Italy in 2013 (see ECDC Update & Assessment: Human Infection By Avian H7N7 In Italy).
- In 2006 1 person in the UK was confirmed to have contracted H7N3, and the following year, 4 people tested positive for H7N2 – both following local outbreaks in poultry.
- The Fraser Valley H7N3 outbreak of 2004 resulted in at least two human infections, as reported in this EID Journal report: Human Illness from Avian Influenza H7N3, British Columbia.
- In 2003 the Netherlands suffered a major outbreak, resulting in the loss of 30 million birds across 1,000 farms, and scores of mild human infections and the death of a veterinarian (see Eurosurveillance Human-to-human transmission of avian influenza A/H7N7, The Netherlands, 2003).
That perception changed abruptly after an LPAI H7N9 virus emerged in China which was asymptomatic in poultry, but produced severe - often fatal - illness in humans. More than 1,500 human infections were reported over 5 years, killing roughly 40% of those hospitalized.
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| 5 Epidemic Waves - Credit FAO |
While we continue to see sporadic H7 outbreaks in poultry (see Australia: 11th Avian H7 Outbreak, Now Reported in ACT), human infections have become rare the past few years.
Last July Germany reported an unusual outbreak of a novel HPAI H7 virus in two farms in Bad Bentheim (see Germany: Avian Influenza Outbreak Identified As HPAI H7N5). Although Germany had never detected a LP (Low Path) H7N5 virus in wild birds, the assumption was the HPAI version was the result of a spontaneous mutation following introduction into a poultry flock.
Today we have a detailed research letter by researchers from the Institute of Diagnostic Virology, Friedrich Loeffler Institut - published in Emerging Microbes & Infections - which details their investigation into this unusual outbreak.
I've only posted some excerpts, so those looking for a deeper dive will want to follow the link to read it in its entirety.
Beyond the scientific data presented, this report is a reminder that Nature's laboratory is open 24/7, and that HPAI H5 isn't the only pandemic contender out there tossing the genetic dice.
I'll return with a brief postscript after the break.
Research Letter
Out of the blue: Detection of a unique highly pathogenic avian influenza virus of subtype H7N5 in Germany.
Ann Kathrin Ahrens, Anne Pohlmann, Christian Grund, Martin Beer & Timm C. Harder
Article: 2420723 | Accepted author version posted online: 22 Oct 2024
https://doi.org/10.1080/22221751.2024.2420723
Main Text
The current situation of an avian panzootic caused by highly pathogenic avian influenza viruses (HPAIV) of the goose/Guangdong lineage, subtype H5N1, clade 2.3.4.4b, is attracting significant attention and resources from both operational animal disease control and infectious disease research forces [1]. Consequently, the scrutiny of the scientific community may, at least temporarily, shift away from other avian influenza viruses.
The occurrence of low and high pathogenicity H7N9 AIV in China between 2013 and 2018 provides compelling evidence of the significant zoonotic potential of subtypes other than H5 [2]. We report here the isolated instance of an infection with a unique HP H7N5 AIV subtype in a chicken layer farm in Germany during the summer of 2024 also to highlight the continuing presence and potential importance of AIV subtypes other than H5.
Case report: In late June of 2024, a commercial poultry enterprise in Germany keeping about 90,000 chicken layers was affected by a sudden rise in mortality. Clinical signs in affected animals included reduced feed intake, listlessness and edematous head appendages prior to acute death within hours to 2-3 days after onset. Within two days mortality amounted to 6.000 hens (7%) before the remaining birds were culled and safely disposed of without delay [3].
Examination of combined nasal and cloacal swab samples of 80 clinically affected or dead birds gave evidence for presence of an influenza A virus that was immediately subtyped as H7N5 with a polyclonal cleavage site (PEIPKRKKRGLF) by real time-RT-PCR and Sanger sequencing [4,5]. This cleavage site is identical to that of two older HP H7 isolates from outbreaks in laying hens in Germany and Australia (A/ck/Leipzig/137-8/1979 [GenBank L43913], A/ck/Victoria/224 /1992 [GenBank CY025078])(https://www.offlu.org/wp-content/uploads/2022/01/Influenza-A-Cleavage-Sites-Final-04-01-2022.pdf).
No further AIV subtypes have been detected by whole genome sequencing or by an RT-qPCR assay specific for 16 HA and 9 NA subtypes [4]. Virus isolation attempts readily yielded isolates from two samples with high virus loads in the first passage in embryonated chicken eggs. Clinical and virological investigations in the restriction zone did not give evidence for further spread of this virus or circulation of its presumed precursor.
To date, sources and incursion routes of this outbreak remain enigmatic: no evidence for H7N5 viruses in wild birds or poultry has ever been obtained before in Germany and a report of the detection of an LP H7N5 virus in a mallard in neighboring Netherlands (EPI_ISL_267186) dates back to 2014. Yet, wild birds seem to be the most likely source of introduction. It should be mentioned, that a similar outbreak, but featuring an unrelated HP H7N7, had occurred in 2015 in a layer farm in the same region; however, at that time, an LP precursor had been identified in a neighboring layer farm [6].
(SNIP)
Discussion
We report an isolated outbreak of HPAIV H7N5 in chicken layers that is unique globally and came “out of the blue” for the affected farm as well as for the related authorities. Failure to identify closely related, sympatric viruses of the same sub- and genotype in the databases re-emphasizes the underrepresentation of LPAIV in public databases. LPAIV of subtypes H5 and H7 may act as progenitors to HP phenotypes, and all subtypes may donate internal segments to HP viruses.
Enrichment of sequence databases with LPAIV sequences requires enhanced surveillance, detection and sequencing activities which, in turn, must be based on intensified active monitoring programs of wild birds. So far, surveillance efforts in the European Union have mainly focused on passive monitoring, which is inept to detect viruses such as LP H7N5, that presumably replicate in wild birds without severe clinical correlates. A similar example is the recently described novel subtype H19, whose few (n = 3) representatives also originate from active monitoring studies [13, 14] .
Nevertheless, this episode of a spontaneous, solitary HP H7N5 outbreak provides compelling evidence that, despite the current HP H5N1 panzootic, other AIVs with significant pathogenic potential continue to circulate and can emerge.
A little over 2 months ago the WHO unveiled a revised 38-page Pathogens Prioritization report that detailed more than 30 PHEIC High Risk disease threats. Despite this expansion, this is not an exhaustive list, and will probably grow over time.
Included are 7 different influenza A subtypes (H1, H3, H3, H5, H6, H7, and H10), 5 bacterial strains that cause cholera, plague, dysentery, diarrhea and pneumonia, several Coronaviruses (including MERS-CoV), along with a number of hemorrhagic viruses.
A reminder that even if we get lucky - and HPAI H5 fizzles - the world will face another pandemic threat.
It's only a matter of time.
