August 10, 2015
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Animal markets facilitate emergence of novel influenza A viruses

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Live animal markets where people and swine were in proximity represented a potential source of novel influenza A viruses and interspecies transmission, according to recently published data.

“If efficiently transmitted among humans, novel [influenza A viruses (IAVs)] might have pandemic potential, prompting the need for public health and agriculture agencies to work with community groups, market employees and market customers to develop culturally appropriate messaging about the risk for variant IAV infections in these settings,” Mary J. Choi, MD, of the CDC, and colleagues wrote in Clinical Infectious Diseases. “Encouraging seasonal flu vaccination, educating customers about prevention measures against IAV and promoting the use of [personal protective equipment] among employees is also important.”

Over 12 weeks, Choi and colleagues conducted surveillance at two live animal markets in St. Paul, Minnesota. Both markets purchased swine with unknown influenza A vaccination status from multiple supplies several times a week, the researchers wrote. The researchers collected respiratory and environmental samples and performed real-time reverse transcription PCR (rRT-PCR), viral culture and whole genome sequencing on the samples. In addition, they collected paired serum samples from employees at the start and end of surveillance.

Seventeen employees participated, and 15 employees had direct contact with swine.

Nasal swabs from 65% of these employees were positive for influenza A viruses. One employee reported being ill the week before sample collection. On multiple occasions, seven employees tested positive for influenza A viruses by rRT-PCR.

Among the employees with direct swine contact, 73% had baseline hemagglutination-inhibition antibody titers greater than or equal to 40 for swine-origin IAVs, according to Choi and colleagues. One employee, a butcher, had fourfold titer increases in both hemagglutination inhibition and microneutralization assay antibody titers to swine H1N2 and A/Mexico/4108/2009 influenza A viruses. This employee neither received the seasonal influenza vaccine during the surveillance period nor reported any influenza-like illness, the investigators wrote. Results of swine and environmental surveillance showed that influenza A viruses were cultured in 72 of 84 swine lungs, in 30 of 45 air samples from the animal holding area, and on five of 21 pen railings.

Results of whole genome sequencing on 122 influenza A isolates from the swine and the environment indicated there were multiple strains and subtype codetections involved.

“We report that multiple IAV strains and subtypes were cocirculating, identified new viral reassortants and provided evidence indicating interspecies transmission of IAV from swine to persons,” Choi and colleagues wrote.– by Colleen Owens

Disclosure: The researchers report no relevant financial disclosures.