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Influenza A virus transmitted from swine to humans at 2012 agricultural fairs
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At agricultural fairs in Ohio during 2012, influenza A viruses circulated widely among exhibition swine, and genome testing confirmed that some of these viruses were zoonotically transmitted to humans, according to recent findings.
The findings suggest that more thorough preventive strategies are needed at swine-human interfaces such as agricultural fairs.
As part of an ongoing virus surveillance project, researchers enrolled 40 agricultural fairs located across Ohio. At the end of each fair, investigators visually examined exhibition swine for signs of respiratory illness and took nasal swab samples from at least 20 swine not selected based on apparent health status. The swab samples were screened by real-time reverse transcription PCR for influenza A virus.
As part of an investigation of a 2012 outbreak of subtype H3N2 virus, human specimens of suspected infection were also collected and sent to the Ohio Department of Health for influenza testing. Samples with preliminary positive results were sent to the CDC for confirmation.
The researchers identified influenza A(H3N2) virus from at least one swine at 10 (25%) of the 40 fairs in the study. Of the 834 swine sampled, influenza virus was identified in 161 (19.3%). The researchers isolated influenza A(H3N2)pdm virus from swine at all seven fairs associated with human cases of subtype H3N2. None of the 30 fairs in which influenza A virus was not identified in swine were associated with human cases of subtype H3N2 virus.
Analysis of the genome sequences revealed that at five of the seven fairs at which human cases of subtype H3N2 virus were identified, the nucleotides of the matched subtype H3N2 isolates from swine were 99% identical.
According to the researchers, these findings provide molecular verification of the epidemiological link between cases of subtype H3N2 virus infection and exposure to exhibition swine at the fairs evaluated.
“Influenza A virus infections in exhibition swine represent an unquantified public health risk,” the researchers wrote. “Rigorous efficacy evaluations and expanded risk assessments of adopted mitigation strategies to protect public and animal health are needed to help animal and public health experts make evidence-based recommendations for reducing intraspecies and interspecies transmission of influenza A virus in this setting.”
Disclosure: The researchers report no relevant financial disclosures.
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