Influenza A persists in environment during swine pen outbreaks

Numerous investigations of influenza A outbreaks at swine commercial production facilities revealed significant levels of the virus in the air and on surfaces in barns, representing an exposure hazard to both swine and people.

“Despite evidence that reassortment can happen in various species, swine is often labeled as the ‘mixing vessel’ since swine have receptors capable to replicate influenza viruses of avian, human and swine origin,” Montserrat Torremorell, DVM, PhD, an animal health expert from the University of Minnesota, and colleagues wrote. “Because these viruses can infect humans, understanding transmission of swine-origin [influenza A viruses (IAVs)] should be a priority.”

According to Neira and colleagues, 11 investigations of influenza A virus outbreaks were conducted at six swine farms across southern Minnesota and northern Iowa between 2012 and 2013. Investigators identified the farms after asking veterinarians to report swine herd respiratory symptoms that resembled development of influenza A virus. These included sneezing, rhinorrhea, dry hacking cough, and lethargy. Within 1 to 3 days of being contacted by a veterinarian, the investigators visited the farms to collect air and surface samples — both inside and outside of barns — as well as pig oral fluids.

During five confirmed outbreaks of IAV, 48% of oral fluid samples (n = 98) tested positive for the virus, while 38% of samples taken from pen railings (n = 84) and 43% of indoor air samples (n = 82) were positive, according to the researchers. Specifically, oral fluid and indoor air samples yielded a mixture of influenza A subtypes, including H1N1, H1N2 and H3N2. The researchers noted that maximum levels of influenza A RNA detected in the air during outbreaks occurred between 7 days and 11 days of onset.

Previous research has shown that pig-human interactions, including at live animal markets and agricultural fairs, represents a potential source for novel influenza A viruses and interspecies transmission.

“Further studies are needed to evaluate the viability of IAV in the environment, evaluate strategies to mitigate the risk of indirect transmission of IAV, confirm the impact of personal protective equipment on exposure risk to people and explore strategies to prevent bidirectional transmission of IAV between humans and swine,” the researchers wrote. “Information from this study should help to develop evidence-based guidelines to minimize the impact of IAV infections on swine production.” – by Jeff Craven

References:

Bowman AS, et al. Emerg Infect Dis. 2014;doi:10.3201/eid2009.131082.

Choi MJ, et al. Clin Infect Dis. 2015;doi:10.1093/cid/civ618.

Neira V, et al. PLoS ONE. 2016;doi:10.1371/ journal.pone.0146616.

Disclosure: The researchers report no relevant financial disclosures.