It’s a Dog-Eat-Dog World Out There

Thanks to an outbreak of avian influenza around the world, chickens and other captive birds have been on house (coop?) arrest for the past few months – or “flockdown,” as many have called it (a term I’ve deemed my Word of the Month for May).

In the UK, birds were released from their latest bout of solitary confinement on May 2, but the looming influenza threat doesn’t stop there. Experts have warned that a “dog flu” virus is becoming increasingly geared up to make the jump into humans. Notably, the H3N8 and H3N2 strains of canine influenza virus are both believed to have originated from avian influenza viruses. Scientists have traced H3N8 back to an equine influenza virus that jumped to dogs; it was first reported in the US in greyhounds in 2004 (1).

H3N2 – the focus of a recent study – is believed to have originated from an avian influenza virus that was transmitted to dogs in Asia around 2006 (2). Could man’s best friend be the stepping stone between bird and humans? Bird flu is not currently transmissible between humans; however, if the virus can establish itself in mammals and become more like a mammalian virus, there are concerns that it could then transmit between mammals – including humans.

A recent study by Mingyue Chen and colleagues found that the H3N2 strain of dog flu has adapted to better recognize the human-like SAα2,6-Gal receptor and better replicate in human airway epithelial cells (3). The strain also demonstrated a 100 percent transmission rate via respiratory droplets in a ferret model. Moreover, they found that humans lacked immunity to H3N2 canine influenza viruses – and human seasonal flu doesn’t provide protection against infection.

The authors suggest that dogs may serve as intermediaries that allow bird flu to adapt and jump to humans. To be clear, there is no evidence of dog flu infecting humans at this time, but, as with any potential threat, enhanced surveillance and awareness are the name of the game.