Swine influenza is an RNA virus, which makes it prone to constant change in one of two ways. The virus either undergoes antigenic drift — natural mutations — or antigenic shift, which occurs when segments from two different viruses come together to form a new genome, Gauger explained.

Both processes contribute significantly to the antigenic diversity seen in the field and make swine flu harder to control. Each of the two major subtypes of swine flu — H1 and H3 — have different genetic “clades” or groups. It’s important to know which clade is circulating on a farm so the best decisions can be made regarding vaccination, he said, noting that more veterinarians are obtaining genetic sequencing of flu viruses.

Even though there are genetic differences in the swine flu strains circulating, they tend to present similarly with coughing and respiratory distress — but there are some differences, depending on various factors. For instance, endemic infections tend to come on slowly and manifest primarily in the nursery, while new viruses — or new clades — might cause clinically more severe cases.

Gauger also told Pig Health Today about two interactive websites that will help veterinarians diagnose and manage swine flu. One is ISU FLUture, from Iowa State University, and the other is Disease Bioportal, from the University of California–Davis.