Influenza variant in farm fair pigs infects humans

Human influenza viruses developed new variants in pigs before infecting humans again at several Midwest agricultural fairs, according to researchers.

The infections show how novel viruses can evolve in an agricultural fair setting and how quickly influenza — and possibly other diseases — can spread from pigs to humans, they wrote in Emerging Infectious Diseases.

“In addition to the zoonotic risks of influenza A virus, this pattern serves as a warning of possible dissemination of other emerging or high-consequence diseases in swine,” study researcher Andrew S. Bowman, DVM, MS, PhD, an assistant professor in the department of veterinary and preventive medicine at The Ohio State University College of Veterinary Medicine, and colleagues wrote.

A separate study documented several outbreaks of H3N2 influenza in July and August of 2016. That study’s authors detected the virus in 18 humans who reported attending at least one of seven agricultural fairs at that time in Michigan and Ohio.

In the present study, Bowman and colleagues assessed samples from 161 pigs displayed in those fairs (A-G). Fair G’s share consisted of a lab submission from a pig with respiratory disease.

Among Fairs A through F, an average of 77.5% of pigs were infected by influenza A, the researchers said. Despite that, only two fairs had extensive influenza-like illness among pigs, “suggesting that subclinical influenza infections in pigs remain a threat to public health,” they added.

The viruses found in pigs were “nearly identical” to those found in the humans, the researchers said. In addition, a virus relatively new to pigs — an H3 influenza A virus — was detected in 16 of the 18 human influenza cases.

It contained a gene descended from a human seasonal virus that circulated in 2010 and 2011. That virus reassorted with pig influenza viruses to develop new variants, the researchers said.

The compatibility and the wide dispersal of the H3 virus suggest the need for vigilance, they added.

“The path traversed by this human-like H3, from initial introduction from humans to swine until the zoonotic transmission events of 2016, demonstrates how novel viruses can be generated and maintained in animal populations and, subsequently, can infect humans through specific ecologic niches like swine exhibitions or live-animal markets,” Bowman and colleagues wrote. “Therefore, continued surveillance in swine populations is imperative for detecting novel influenza A viruses that threaten swine and human health.” – by Joe Green

Disclosure: Bowman reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.