Managing swine influenza has become more complicated due to new viral subtypes emerging, according to veterinarians and scientists.

For many years, only one subtype, known as H1N1, was almost always the cause of swine influenza virus in the United States. In 1998, a new strain, known as H3N2, surfaced.

Of the samples submitted to the National Veterinary Services Laboratory 31 percent were H3N2 and 67 percent were H1N1. In 2000, another SIV strain, H1N2, was reported in the U.S. swine population. It accounts for 2 percent of samples submitted to NVSL for typing.

Because swine influenza viruses can cause significant illness and economic loss, veterinarians and producers need to obtain an accurate diagnosis, and make use of the best vaccines, treatment and management strategies to control the disease, say veterinarians.

Terri Wasmoen, DVM, senior director of biological research for Schering-Plough Animal Health, says that to ensure the best results, any vaccine that producers use to combat SIV must contain the viral subtype causing disease in a herd.

Vaccinations need to be timed carefully, which requires blood testing for the presence of maternal antibodies. Piglets can have maternal antibodies against SIV from sows, which can interfere with vaccine effectiveness. She says, vaccinations need to be given after the antibody levels drop.

Co-administration of other vaccines also might interfere with SIV vaccination effectiveness.

Wasmoen emphasizes that it’s important to confirm that the SIV vaccine used induces antibody response to all the SIV strains present in a herd. To maintain high antibody levels, repeated vaccination is commonly used.