H3N1 Identified in Swine in Two States

The U.S. Department of Agriculture IAV-S surveillance program has identified several H3N1s in U.S. swine in at least two states since December 2013. Although this is not the first time H3N1s have been detected in swine in the United States, it is a rare occurrence and needs further examination.

More importantly, two of these H3N1s carry a novel human seasonal HA gene from contemporary human viruses and are distinct from our current swine H3 viruses.

A review of Genbank data indicates there may be more human-like H3 genes (in either H3N1 or H3N2) circulating in U.S. swine subtypes than what the USDA surveillance data has captured. Potential spread of H3N1 or H3N2 that carries the human-like H3 could have significant impact in swine herds due to poor herd immunity as well as potential public health ramifications. Preliminary findings by the USDA-ARS from testing of one of these H3N1 isolates with the human-like H3 gene in swine indicate the virus is fully virulent, causing typical influenza disease.

We are sharing this information to alert producers, veterinarians, and National Animal Health Laboratory Network labs of this occurrence. The surveillance program for IAV-S in swine was established to:

  • Monitor the genetic evolution of endemic IAV-S to better understand endemic and emerging influenza virus ecology,
  • Make IAV-S isolates and associated epidemiologic data available for research and analysis, and
  • Select proper isolates for the development of relevant diagnostic reagents, updating diagnostic assays, and vaccine seed stock products in swine.

The identification of this new human-like H3 in swine subtypes is a key example of how IAV-S surveillance can benefit swine health.

It is anticipated that additional information about swine subtypes carrying the human-like H3 will be captured through the surveillance system to assist in determining how wide-spread the virus is and whether additional actions may be needed by veterinarians, producers and vaccine manufacturers. 

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