Detection and isolation of Influenza A virus subtype H1N1 from a small backyard swine herd in Colorado.

Influenza A virus subtype H1N1 A(H1N1)pdm09 was first confirmed in pigs in the United States in October 2009. In November 2010, lungs and intestines from 2 York piglets from a small, privately owned herd were submitted to the Colorado State University Veterinary Diagnostic Laboratory. The submitting veterinarian reported rapid weight loss and signs of pneumonia in the piglets. Gross lesions included caudoventral pneumonia in both piglets, and histologic lesions in the lungs showed characteristics consistent with influenza virus and bacterial infection. Ribonucleic acid extracted from fresh lung homogenates from both piglets was positive for influenza A(H1N1)pdm09 by a real-time reverse transcription polymerase chain reaction. Virus was isolated from lung homogenates from both piglets in Madin-Darby canine kidney cells, as well as in 10-day-old specific pathogen-free embryonated chicken eggs. Sequence analysis showed 98% homology with 2009 H1N1 human isolates from across the United States and 98% homology against two 2009 and 2010 swine isolates from Nebraska and Minnesota. The current report documents the possible transmission of pandemic influenza A(H1N1)2009 virus [A(H1N1)pdm09] from a human being to a small, privately owned backyard swine herd. The owner was employed as a pharmacist, making occupational exposure to the pandemic influenza A(H1N1)pdm09 a possibility.