Dogs are a potential reservoir for a future influenza pandemic, according to a new study, which was published on Tuesday in the journal mBio, which is affiliated with the American Society for Microbiology. Influenza virus can jump from pigs into canines and that influenza is becoming increasingly diverse in canines, the study found. “The majority of pandemics have been associated with pigs as an intermediate host between avian viruses and human hosts. In this study, we identified influenza viruses jumping from pigs into dogs,” said study investigator Adolfo García-Sastre, who is director of the Global Health and Emerging Pathogens Institute and principal investigator at the Icahn School of Medicine's Centre for Research on Influenza Pathogenesis (CRIP). Influenza can be carried among animal reservoirs where many different strains are located. These reservoirs serve as mixing bowls for the genetic diversity of strains, according to the paper. Pandemic influenza occurs when viruses are carried from animal reservoirs to humans who have no prior exposure to the virus. Most people do not have immunity to such viruses. The main animal hosts for influenza are wild birds, poultry, and other domestic birds of a certain species; pigs, and horses. Some of the viral genes from the 2009 pandemic H1N1 virus originated in birds. That avian virus then jumped to pigs, which exchanged some of their genes with previously circulating swine viruses and then jumped from pigs into humans. Birds and pigs are major reservoirs of viral genetic diversity, whereas equines and canines have historically been restricted to one or two stable influenza type A virus lineages with no or very limited transmission to humans. About 15 years ago, researchers documented an influenza virus in a horse jumping into a dog, and this created the first circulating canine influenza viruses. Five years ago, researchers identified an avian-origin H3N2 canine influenza virus circulating in farm dogs in Guangdong, China. “In our study, what we have found is another set of viruses that come from swine that are originally avian in origin, and now they are being carried into dogs and have been reassortant with other viruses in dogs. We now have H1N1, H3N2, and H3N8 in dogs. They are starting to interact with each other. This is very reminiscent of what happened in swine ten years before the H1N1 pandemic,” said García-Sastre. In the study, the researchers sequenced the complete genomes of 16 influenza viruses obtained from canines in Southern China (Guangxi autonomous region) during 2013-2015. The researchers found that the genomes contained segments from three lineages that circulate in swine in China: North American triple reassortant H3N2, Eurasian avian-like H1N1, and pandemic H1N1. In addition, the swine-origin H1N1 viruses were transmitted onward in canines and reassortant with the CIV-H3N2 viruses that circulate endemically in Asian dogs, producing three novel reassortant CIV genotypes: H1N1r, H1N2r, and H3N2r. The viruses in the study were collected primarily from pet dogs with respiratory symptoms at veterinary clinics. Dogs in certain regions of China, including Guangxi, are also raised for meat and street dogs roam freely, creating a more complex ecosystem for canine influenza virus transmission. García-Sastre added, “the new virus we have identified in our study is H1N1, but it comes from swine and is of avian origin, so it is different antigenically from the new H1N1s that were seen in the pandemic and a different origin as the previous H1N1 seen in humans," adding, “if there is a lot of immunity against these viruses, they will represent less of a risk, but we now have one more host in which influenza virus is starting to have a diverse genotypic and phenotypic characteristics, creating diversity in a host which is in very close contact to humans.”
