June 5, 2018

expert reaction to paper looking at the genomics of dog flu, published in mBio

A study was published in the journal mBio looking at the genomics of dog flu and whether in future it’s possible dogs could share flu with other mammals such as pigs and possibly people.

Prof Paul Digard, Chair of Virology and Head of the Infection & Immunity Division, The Roslin Institute, University of Edinburgh, said:

“So far ‘dog flu’ hasn’t been a problem in people (the old H3N8 strain that went from horses into dogs has actually been put into human volunteers with no ill effects) but the more times the dice are rolled the higher the chance of it becoming a problem.  And we know that pig strains of influenza can infect humans, and although this doesn’t always lead to a pandemic, it can.  However, a virus that went directly from bird to dog would probably be less able to spread between dogs or to other species (including us) than a pig-derived virus that has already adapted to mammals.

“It’s hard to predict the behaviour of a virus that (probably) doesn’t exist yet, but in all likelihood, the problem would certainly be smaller in parts of the world without populations of wild dogs.  The equine H3N8 flu that has jumped into dogs on several occasions has only been a long-term problem in the US where it got into some of the animal shelters, where large and transient populations of dogs mix.  Contrast that with the UK where it’s only been seen in one or two isolated cases of fox hound packs, or Australia where it was a short-lived episode following on from an outbreak of equine influenza.

“There are no cases of human flu being caught from dogs that I am aware of.  But there is certainly evidence of us giving flu to dogs.

“Vaccines are already available in the US for two strains of dog influenza.  If there were an outbreak of a new strain of dog flu then we’d face the same problems that we face for human pandemics – making a new vaccine in time.  Even with the inevitable delay until a vaccine is available, and even in the worst case hypothetical future scenario of it being a virulent virus capable of infecting humans, if you can control access of your dog to other dogs, you can drastically cut the risk of it getting infected.

“The bottom line here is that this is an important piece of work identifying something that could potentially turn out to be a problem in the future.  There’s no need to ring alarm bells right now, but it’s something that should be followed up by further surveillance, especially in the wider non-pet dog population.”

Prof Sally Cutler, Professor of Medical Microbiology, University of East London, said:

“This is interesting work that builds upon that of others.  The work highlights a realistic possibility that in future dogs could potentially share flu viruses with pigs and possibly humans.  However, it is not time to press the panic button yet as recombinant virus will show variable ability to transmit within and between species and also different abilities to cause disease.  So far, there are no cases I’m aware of of people catching flu from dogs.

“The conclusions of this study appear valid, but some of the extrapolations are not yet supported by evidence, such as the suggestion for vaccination in dogs.

“Such mixing of viruses in different species is likely to have been on-going through time, but our intensification might influence the speed of newly emerging re-assortments.  This study is worthy of observation, but is not sufficient to merit a massive emergency responses at this time.  Reverse zoonosis (from humans to animals) appears to be a larger risk!”

Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“There is no evidence that the strains of influenza virus that circulate in dogs can infect humans.  Virologists think that other animals are a far more likely source of a new influenza virus pandemic and this view is based on a number of factors including the properties of the animal viruses and how easy it would be for them to infect a new human host, the severity of the infection, the level of human exposure to the animals harbouring the novel virus and, perhaps the most important, whether or not there is evidence of spillover infections into humans.

“But of course we know that influenza viruses in animals and birds have made the jump in the past, and we certainly expect new strains of virus to emerge in the future.  Humans have lots of interaction with dogs, and we know that dogs can be infected with influenza.  What this study provides is evidence that dogs can be naturally infected with multiple strains of viruses, most notably viruses from pigs, which are a known reservoir of influenza viruses that can infect us.  This increases the potential threat of dogs acting as mixing vessels for the production of new strains of virus that might, just might, in the future spill-over into humans.  This is a really neat bit of genetic sleuth work, which tells us much about influenza infection in dogs.  But let’s face it – viruses always have the ability to surprise and no matter how good we think we are at predicting the unknown, we will never be able to second-guess where the next outbreak virus will come from.”

Prof Wendy Barclay, Chair in Influenza Virology, Imperial College London, said:

“This interesting paper reveals there is a surprising and previously unanticipated amount of influenza virus in dogs in China.  Pets and rural dogs were swabbed and 15% had evidence of influenza infection.  Most of the viruses found in dogs were related to swine influenza strains, including strains like the swine flu of 2009 that crossed into people and caused the 2009 pandemic.  This tells us that dogs could in the future act as a conduit for influenza viruses into humans from pigs and bearing in mind that most people have more contact with dogs than with pigs this could be important.

“It is unlikely that the dogs in other parts of the world are carrying this much influenza and there has not been a case of a person catching flu from their dog.  Going forward from here it will be important to really understand whether by adapting to circulate in dogs, the viruses become more or less likely to cross into humans.

“It would be possible to vaccinate dogs against influenza viruses, for example using the same type of vaccines that are used in pigs.”

* ‘Emergence and evolution of novel reassortant influenza A viruses in canines in southern China’ by Ying Chen et al. was published in mBio on Tuesday 5 June 2018. 

Declared interests

Prof Paul Digard: “No interests to declare though I have done consultation work for vaccine manufacturers in the past.”

Prof Sally Cutler: “No conflict of interest to declare.”

Prof Wendy Barclay: “Wendy Barclay has received money for giving advice to influenza vaccines manufacturers.”

None others received.