Photo Credit: Rodrigo Ferrada Stoehrel/SVA.
#16,971
While marine mammals are known to be susceptible to avian influenza viruses (mostly seals, and very rarely whales), before today we'd never seen a confirmed report of bird flu in a porpoise.
But this has been a summer of H5N1 `firsts' (see HPAI Detected In Arctic (Svalbard) For the First Time).
The following (translated) report comes from Sweden's Statens Veterinärmedicinska Anstalt (National Veterinary Institute). I'll have a bit more after the break.
First case of bird flu confirmed in porpoises
Last updated: 2022-08-31
The Norwegian Veterinary Institute (SVA) has confirmed the first finding of avian influenza virus in a porpoise. The analysis shows that the porpoise died as a result of the same virus that was behind this summer's extensive bird flu outbreak among wild birds.
The young male porpoise stranded alive in Kämpersvik, in Tanum municipality, Västra Götaland 28 June 2022. Despite repeated attempts by private individuals to get it to swim out to deeper water again, it was too exhausted, got tangled in seaweed and died later in the evening. The porpoise was transported to SVA for an autopsy. The analysis now shows that bird flu virus was found in several organs and that the virus had caused brain and meningitis. The findings confirm that the bird flu virus was the cause of death.
- As far as we know, this is the first confirmed case in the world of bird flu in a porpoise. Unlike seals, where disease outbreaks caused by influenza viruses have been repeatedly demonstrated, there are only isolated reports of influenza viruses in cetaceans. It is likely that the porpoise somehow came into contact with infected birds, says Elina Thorsson, game veterinarian at SVA.
The same virus that is behind the big outbreak
The virus, H5N1, is the same virus that was also behind the extensive bird flu outbreak that is still ongoing among wild birds in Sweden, other parts of Europe and in North America. How the porpoise from Kämpersvik was infected is still unknown, but it was found at the same time as bird flu was causing high mortality among seabirds, especially gannets, on the west coast.
- It is an unusual find, and interesting because we get the opportunity to learn more about the virus. At the same time, this is about an individual case, and we have not seen any increased mortality among porpoises. We know that there is a risk that marine mammals can become infected, and have therefore included sampling for influenza in our surveillance program, says Elina Thorsson.
Monitoring of marine mammals
SVA examines stranded porpoises, other cetaceans and seals, in collaboration with the National Museum of Natural History. The aim is to find out how the animals are doing and what diseases and other threats they suffer from. In the long run, changes within populations, species and ecosystems can be detected. The work is carried out with support from Swedish environmental monitoring on behalf of the Swedish Maritime and Water Authority. Porpoises belong to the state's game and must be reported to the police if they are found dead.
Low risk of infection to humans
The risk of humans being infected with the variant of bird flu that is now circulating among wild birds is considered to be small.
Occasional cases of infection in other mammals
During the ongoing bird flu outbreak in Europe and North America, in addition to large numbers of dead wild birds, a smaller number of mammals have also been infected and died. The route of infection is suspected to be through close contact with infected birds. Single cases have been detected in red foxes, otters, lynxes and skunks. An increased mortality in both harbor seals and gray seals has been seen in connection with the outbreak in North America, but in Sweden there have been no increased reports of dead seals during the summer.
Once again, we learn of a mammalian infection resulting in the systemic spread of the virus, and severe (often fatal) neurological manifestations. While clade 2.3.4.4b H5N1 infections have been very mild in the few human cases detected so far, it has exacted a much greater toll among terrestrial and marine mammals in the wild.
Norwegian Veterinary Institute Reports Avian H5N1 Spillover Into Red FoxesJust over a month ago, in PrePrint: HPAI H5N1 Infections in Wild Red Foxes Show Neurotropism and Adaptive Virus Mutations, we saw evidence from the Netherlands that Europe's avian H5N1 virus was adapting to its new-found mammalian hosts by acquiring the PB2-627K mutation.
Two States (Michigan & Minnesota) Report HPAI Infection In Wild Foxes
Ontario: CWHC Reports HPAI H5 Infection With Severe Neurological Signs In Wild Foxes (Vulpes vulpes)
Netherlands DWHC Reports another Mammal (Polecat) Infected With H5N1
CDC EID Journal: Encephalitis and Death in Wild Mammals at An Animal Rehab Center From HPAI H5N8 - UK)
PB2-627K can enable the virus to replicate more efficiently at the lower temperatures (33°C) commonly found in the respiratory tract of mammals, rather than the higher temperatures found in avian gastrointestinal tracts.
Admittedly, H5N1 has loomed large several times before, only to recede. But clade 2.3.4.4b continues to evolve, and has become more widespread - and better adapted to year-round persistence - than past incarnations (see Study: Global Dissemination of Avian H5N1 Clade 2.3.4.4b Viruses and Biologic Analysis Of Chinese Variants).
This recent, rapid spread of HPAI H5 has a lot of scientists genuinely worried (see Nature Why unprecedented bird flu outbreaks sweeping the world are concerning scientists).
Where HPAI H5Nx goes from here is unknowable, but when a virus continually defies expectations, we ignore it at our own peril.
