Thursday, October 31, 2019

EID Journal: Highly Pathogenic Avian Influenza A(H5N8) Virus in Gray Seals, Baltic Sea

Gray Seals - Credit Wikipedia


Highly pathogenic avian H5N8 (clade emerged over the winter of 2013-14 in South Korea, and over the next two years sparked major epizootics in North America (2014-2015) and Europe (2016-2017).
The European version proved to be a more virulent strain - the product of a reassortment over the summer of 2016 in either China or Russia - and was dubbed clade B (see EID Journal: Reassorted HPAI H5N8 Clade - Germany 2016).
While a few dogs were reportedly infected in South Korea by the initial strain  (see Korea Finds More Dogs With H5N8 Antibodies),  (AFAIK) we've not seen any confirmed mammalian infections with the reassorted H5N8 B clade outside of laboratory experiments (see Sci Rpts: H5N8 - Rapid Acquisition of Virulence Markers After Serial Passage In Mice).
Today, however, the EID Journal brings us evidence of HPAI H5N8 infection in two marine mammals - grey seals - recovered in the Baltic sea over the winter of 2016-17.
Seals, and other marine mammals are susceptible to a wide variety of influenza viruses, and over the years we've looked at a number of investigations involving H3N8, H10N7, and other (mostly avian) flu subtypes.
  • In 2014, a large outbreak northern Europe (mostly Denmark and Germany & Sweden) resulted in as many as 3,000 harbor seal deaths from avian H10N7 (see Avian H10N7 Linked To Dead European Seals), prompting warnings to the public not to touch seals.
While harbor seals have been the most commonly affected seal species, in 2016 we looked at a seroprevalence study intriguingly suggested that grey seals may be an unrecognized natural wild reservoir for influenza A viruses (see Emerg. Microbes & Inf.: Prevalence Of Influenza A in North Atlantic Gray Seals).

The full text of today's EID dispatch is well worth reading.  I've only included a few excerpts (bolding mine), so follow the link to read it in its entirety. 

Volume 25, Number 12—December 2019

Highly Pathogenic Avian Influenza A(H5N8) Virus in Gray Seals, Baltic Sea

Dai-Lun Shin, Ursula Siebert, Jan Lakemeyer, Miguel Grilo, Iwona Pawliczka, Nai-Huei Wu, Peter Valentin-Weigand, Ludwig Haas1, and Georg Herrler


We detected a highly pathogenic avian influenza A(H5N8) virus in lung samples of 2 gray seals (Halichoerus grypus) stranded on the Baltic coast of Poland in 2016 and 2017. This virus, clade B, was closely related to avian H5N8 viruses circulating in Europe at the time.


We report the case of a clade B group HPAI H5N8 virus able to infect marine mammals. The isolated H5N8 seal virus showed 99%–100% identity to the avian strains that were circulating in Europe during 2016–2017. HPAI H5N8 B virus infections are associated with severe symptoms in infected waterfowl or wild birds. The AIV AR8444 strain in the EpiFLU database with the highest homology to H5N8/seal was isolated from a dead tufted duck found in Lake Plön, Schleswig-Holstein, in northern Germany. Experimental infection of ducks with the AR8444 strain resulted in a mortality rate of 33% 4–8 days postinfection (9).


Studies have shown that some mutations known to enhance the transmissibility of H5N1 HPAI viruses may increase the ability of LPAI viruses to be transmitted from bird to marine mammal (1113). These factors include the change of sialic acid receptor binding affinity (11) and adaptive mutations in the vRNP complex for replication and virus spread in the seal population (12). In the H5N8/seal isolate, we detected no molecular markers previously associated with the transmission of avian-derived influenza viruses to marine mammals (13) in the viral PB2, PB1, PA or HA segments (Table). Thus, it appears that no adaptive mutations have occurred in the gray seal analyzed in this study.

Most reports on influenza viruses in seals are related to outbreaks in harbor seals and not gray seals. However, seroprevalences against H10N7 influenza A virus were described in gray seals in the Netherlands (14). In addition, influenza A virus matrix RNA (without further characterization) was detected in swab samples of 9.0% of apparently healthy weaned gray seal pups live-captured in the North Atlantic (15). In adult seals, seroprevalence was 50%; the authors suggest a possible role of gray seals as a wild reservoir of influenza A virus.
These reports indicate that the gray seal can be infected by influenza viruses. Because we describe a naturally occurring spillover of HPAI virus to a marine mammal, future surveillance programs should continue to monitor gray seals and harbor seals as possible reservoirs of AIV.
Dr. Shin is a veterinarian at the University of Veterinary Medicine, Hannover, Germany. His primary research interest is the pathogenesis of influenza virus infection in different animal species.
Admittedly there are fewer opportunities for marine mammals to infect humans with (potentially mutated or reassorted) flu viruses; at least compared to pigs, poultry, or companion animals.
But in 2014, a study published in - Nature Communications: Respiratory Transmission of Avian H3N8 In Ferrets - raised precisely those concerns (see USGS Avian Flu in Seals Could Infect People).
A more recent study in 2016 (see Sci Rpts: Receptor Cell Binding Of Seal H3N8) has rolled back some those concerns due to finding limited binding to cells in the human trachea (as opposed to deep lung tissues), but concerns over the future evolution and mammalian adaptation of H3N8 remain.
Although we look primarily to birds and pigs as being the most likely source of the next flu pandemic, over the past 2 decades we've learned of a growing array of species that can host novel flu viruses.
While most are long shots in the pandemic generation sweepstakes, nothing says that one of these couldn't help spawn the next novel virus. A few past blogs on some these `outlier' flu hosts include:
EID Journal: Equine Influenza - A Neglected, Reemergent Disease Threat
HPAI H5Nx Clade Shedding In Cottontail Rabbits

Back To The Bat Cave: More Influenza In Bats
mBio: Novel Reassortant Influenza A Viruses in Canines in Southern China
EID Journal: Avian H7N2 Virus in Human Exposed to Sick Cats

H9N2 Adaptation In Minks