In 2011 a die off of seals in New England made headlines, which was eventually linked to an avian flu virus (see New England Seal Deaths Tied to H3N8 Flu Virus). While not a new revelation that seals were susceptible to influenza viruses, this did raise concerns as in 2012, in mBio: A Mammalian Adapted H3N8 In Seals, we saw the first hints that this virus had recently adapted to bind to alpha 2,6 receptor cells, the type found in the human upper respiratory tract.
Until it landed in seals, this H3N8 strain was an avian adapted virus. That is, that it bound preferentially to the kind of receptor cells commonly found in the digestive and respiratory tracts of birds; alpha 2,3 receptor cells.
Seals were suddenly on the radar as potential `mixing vessels’ for influenza, much in the same way as pigs have been for years. The good news being that seals have less opportunities to mingle with humans than do pigs.
Additional research, published this past September (see Nature Communications: Respiratory Transmission of Avian H3N8 In Ferrets), confirmed that this `virus has an increased affinity for mammalian receptors, transmits via respiratory droplets in ferrets and replicates in human lung cells.’
In recent weeks there have been reports of large die offs of seals in Denmark and Germany (My thanks to Fred de Vries for the emailed head’s up), and this past week it was determined that a combination of avian H10N7 influenza, pneumonia, and bacterial infections were behind these deaths.
This report from the Technical University of Denmark.
National Veterinary Institute have found the influenza virus in seals from Anholt, fjord and three locations on the west coast. For the first time, identified a major flu outbreak among seals in Europe.
In recent months, we have found several dead seals along the Danish coasts than normal, and the National Veterinary Institute studies show that the cause of an outbreak of influenza.
In early July this year showed the National Veterinary Institute for the first time influenza type H10N7 two seals from Anholt. In September, the same virus was detected in dead seals from the fjord, and in October, the influenza virus has also been detected in dead seals at White Sands, Sædding and Skallingen on the west coast. The latter virus is not yet typed, but there are probably talking about the same H10N7 virus. The same virus is also detected in dead seals along the Swedish west coast.
"There are previously reported outbreaks of influenza in seals in Asia and the United States, but this is the first time that a major outbreak of influenza virus is found in seals in Europe," says Professor Lars Erik Larsen Section of Virology at the National Veterinary Institute.
Influenza virus weakens the seals, thus becoming more susceptible to other infections which may contribute to the deterioration of the disease and possibly lead to seal door.
"Initially, the seals probably got the flu by being in contact with birds or their droppings, but subsequently there has probably been no suggestion that the virus has infected from seal to seal," explains Lars Erik Larsen.
Do not touch the seals
Discovery of influenza virus in wild ducks are common, without giving rise to infection of other animals and humans. There are no reports of infection in people with the virus identified in these outbreaks among seals in Denmark, but other influenza viruses of the same type have previously caused light infection in humans.
"If you found dead seals should not touch them, but contact Naturstyrelses local wildlife consultant," says Special Mariann Chriél from the Section of Diagnostics and Emergency at the National Veterinary Institute.
Although known human infections with avian H10N7 are limited, we’ve discussed them on several occasions in the past. In 2004, the first known human infections were reported among two Egyptian toddlers, as described in this report by WHO/CDS/CSR/RMD
The National Influenza Center (NIC) in Egypt and the WHO Influenza Collaborating Centre in the UK reported the isolation of Avian Influenza A (H10N7) from two human specimens. They refer to two one-year-old infants, residents of Ismaillia, who recovered after presenting a fever and cough. The father of one of them is a poultry merchant who frequently traveled between Isamillia and Damietta. In the latter town, five cases of the same virus were isolated from wild ducks between 18 and 22 April 2004, from samples taken from a market of hunted migratory birds. Additional preliminary investigation tested negative in 75 human samples collected in Ismaillia and in 13 samples from migratory birds from the same market. No influenza outbreak has been reported among poultry in Egypt. At present, there are no public-health implications from this event.
And again, in 2012, in EID Journal: Human Infection With H10N7 Avian Influenza, we looked at a limited outbreak among workers at a chicken farm in Australia. While their symptoms were mild and of short duration, the abattoir instituted enhanced PPE requirements for employees to try to prevent future infections.
Given its limited history of infecting humans, and the mild symptoms it has provoked, H10N7 seems an unlikely candidate to cause a serious public health threat.
Of course, you could have said the same thing about avian H7 viruses two years ago. All that changed when a new and deadly H7N9 emerged in China.
H10N7 – like all influenza A viruses – has the ability to drift, mutate, or reassort with other influenza viruses and – over time - continually re-invent itself.
Which makes surveillance of events – such as this seal die off – an important part of the world’s efforts to detect the next emerging disease threat – and perhaps even stop it - before it can pose a serious public health risk.