UK APHA: Detection of Avian H7N1 In Grey Seal

 
Credit UK APHA

#18,791

We've known for decades that marine mammals (seals, whales, sea lions, otters, etc.) are susceptible avian, and other types, of influenza viruses. The emergence and spread of HPAI H5Nx clade 2.3.4.4b around the globe has killed tens - perhaps hundreds - of thousands of pinnipeds over the past 2 years.

Preprint: Pathology of Influenza A (H5N1) Infection in Pinnipeds Reveals Novel Tissue Tropism and Vertical Transmission.

Nature Reviews: The Threat of Avian Influenza H5N1 Looms Over Global Biodiversity

But other avian viruses have been documented in marine mammals for decades. A few (of many) reports include: 

• During the winter of 1979-1980 seals were found suffering from pneumonia on the Cape Cod. In that instance, the culprit turned out to be an H7N7 influenza. (see Isolation of an influenza A virus from seals G. Lang, A. Gagnon and J. R. Geraci)
• In November of 2011 a die off of seals in New England that was eventually tied to an H3N8 avian Flu Virus. 2012's mBio: A Mammalian Adapted H3N8 In Seals, presented  evidence that this virus had recently adapted to better bind to alpha 2,6 receptor cells, the type found in the human upper respiratory tract. 

• A large outbreak was reported from northern Europe (mostly Denmark and Germany & Sweden) in 2014, when as many as 3,000 harbor seals reportedly died from avian H10N7 (see Avian H10N7 Linked To Dead European Seals), prompting warnings to the public not to touch seals.
• In 2017, during the HPAI H5N8 epizootic in Europe, that emerging subtype (clade 2.3.4.4.B) was found in Grey seals in the Baltic Sea (see EID Journal: Highly Pathogenic Avian Influenza A(H5N8) Virus in Gray Seals, Baltic Sea). 

Earlier this year the UK reported (two) outbreaks of clade 2.3.4.4b HPAI H5N5 in Grey seals (see here, and here). They reported finding the mammalian adaptive mutation PB2-E627K mutation in some of these isolates.

This amino acid substitution has been seen in other mammalian spillovers (see Cell Reports: Multiple Transatlantic Incursions of HPAI clade 2.3.4.4b A(H5N5) Virus into North America and Spillover to Mammals).

This week the UK's APHA/Defra is reporting the detection of a low-path avian H7N1 virus in a grey seal pup, which was found dead near Cornwall.  While H7 viruses have been (rarely) reported in pinnipeds, this (AFAIK) appears to be the first confirmed H7N1 virus. 

First the brief report, after which I'll have a bit more on H7 viruses. 

Note 2: findings in a grey seal in Cornwall

Sampling of a dead 8-month-old grey seal reported in Cornwall confirmed the presence of influenza A of subtype H7N1. The potential source of infection is wild birds, although very few seal sequences are available and the diversity of influenza A viruses in seals is poorly understood as is the dynamic of virus exchange between seals and birds. The cleavage site sequence indicated a motif consistent with a low pathogenicity virus if this virus had been found in poultry. However, the relevance of that cleavage site for seals is less clear.

The sequence generated from this positive seal sample included a mammalian adaptive mutation (E627K) in one gene (PB2) but this mutation has been observed in numerous positive samples from mammals detected previously both in Great Britain and globally, and in isolation isn’t considered to represent an increase in zoonotic risk. We cannot determine with certainty whether influenza A was the sole cause of death, and it is possible other factors may have contributed.

While H5 avian viruses have captured most of our attention over the past 25 years, for 5 years during the last decade China's H7N9 epidemic showed us that H7 viruses has genuine pandemic potential, producing > 1600 infections in China.

H7N9 Epidemic Waves - June 14th 2017 - Credit FAO

Other human spillovers include:

• In December of 2016, at least two veterinarians caring for sick cats at a NYC shelter were mildly infected with H7N2 (see J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016).

• 3 mild cases were reported in Italy in 2013 (see ECDC Update & Assessment: Human Infection By Avian H7N7 In Italy).

• Mexico reported a couple of mild human H7N3 infections back in 2012 (see MMWR: Mild H7N3 Infections In Two Poultry Workers - Jalisco, Mexico), resulting in conjunctivitis without fever or respiratory symptoms.

• Twenty-two years ago (2003) world's attentions were focused on a different avian flu virus - HPAI H7N7 - which spread rapidly across hundreds of poultry farms in the Netherlands, infecting scores of farmers, and which killed a local veterinarian (see Human-to-human transmission of avian influenza A/H7N7, The Netherlands, 2003).

A follow up investigation of the 2003 outbreak by the RIVM found the spread of the virus to be far greater than originally reported, suggesting as many as 1,000 human infections occurred. 

So, while H7 viruses are generally thought of as being less dangerous than H5 viruses - and primarily an agricultural concern - that reputation is not entirely warranted.

That said, the detection of H7N1 in a single seal pup in the UK is mostly likely a one-off, or incidental finding. Obviously, if more turn up, it will warrant additional scrutiny. 

But this is another reminder that much of what happens with viral evolution goes on outside of our view.  While we focus on our current  HPAI H5 threat, we could easily be blindsided by something brewing unseen out in left field. 

Which is why we need to treat pandemic preparedness as integral to our national security, not as something we hastily ramp up whenever a new threat appears.