Swine influenza virus (SIV) is a disease we have faced for many years. Wide temperature swings in the spring and fall are traditionally times for most problems. But, we also see chronic infections.

SIV is easily transmitted in the air. Continuous production systems have the most problems.

SIV usually affects grow-finish pigs. It can also impact sow herds, causing sows to go off feed and run fevers, resulting in breeding problems. Farrowing rates and the size of litters decline after an outbreak.

New Strain Challenge

Two years ago, we began dealing with the new H3N2 strain of SIV. Most of the infected herds had no previous exposure or immunity so the impact was quite dramatic. Sow death losses increased, overall performance decreased.

Today that strain of the virus is quite endemic in sow herds and grow-finishers and it is difficult to distinguish from the more common H1N1 strain. Strain identification is vital to setting the best farm control strategy.

Porcine Reproductive and Respiratory Syndrome (PRRS) has taught us to stabilize the breeding herd to control PRRS throughout the system.

The same is true for SIV. The immunity level and exposure level of replacement gilts greatly influences the stability of SIV in the breeding herd. If SIV is not stable in the breeding herd, the virus is shed to the weaned pigs, resulting in positive pigs entering the nursery or finisher.

Case Study No. 1

An 800-sow, farrow-to-finish farm has had SIV for several years. Serological profiling indicates that titers are present for both the H1N1 and H3N2 strains. The farm purchases all of its replacement gilts as iso-wean gilts from a single source. Serological monitoring of this source indicates that these pigs carry both strains of SIV.

It is our goal to immunize these iso-wean gilts or expose them to the virus so they have immunity prior to going into the breeding herd. We have isolated the H3N2 strain from this farm and are using that as an autogenous H3N2 vaccination. We are also using a commercial H1N1 vaccine.

After 12 months of this program, we have less off-feed sows and clinical SIV problems in the sow herd. However, sow titers continue to be high. We have also started semi-annual sow vaccination with the two different SIV strains.

Respiratory problems in grow-finish have decreased. However, the herd is still positive for PRRS and Mycoplasmal pneumonia. We occasionally see pigs die from a respiratory disease complex.

Our control protocol has not eliminated the problem. But we feel we have stabilized the herd and are close to reaching acceptable production levels.

Case Study No. 2

This farm is a 1,500-sow, farrow-to-finish operation that utilizes three-site production. Pigs were experiencing a respiratory problem 12 to 16 weeks after placement in the finishing barn. Serological profiling indicated the presence of PRRS and both strains of SIV. We worked to stabilize the PRRS within the herd and disregarded the SIV.

Through a series of nasal swabs of nursery pigs, we isolated H1N1 and H3N2 strains of SIV. We then formulated an autogenous vaccine from these isolates and vaccinated the sow herds on a semi-annual schedule and vaccinated the nursery pigs with the first dose at weaning and the second dose three weeks later. There was dramatic improvement in the finishing pigs. Serological profiles showed pigs were still positive for both SIV strains.

Steps to Avoid SIV

Both strains of SIV are affecting today's pig production. It is likely there will be new strains introduced in the future. Good biosecurity is not always adequate to prevent the introduction of SIV. The virus spreads very easily through the air and is not routinely tested for by a lot of genetic suppliers.

Likewise, there are few SIV-negative sow herds. As veterinarians, our goal is to institute programs to reduce the effects of SIV. We feel it is important to know levels of both strains of virus in your breeding herd and grow-finish. Visit with your genetic supplier to understand SIV status of replacement stock. To understand how SIV is affecting your herd:

  1. Perform adequate diagnostics to learn the extent of SIV infection;

  2. Know the health status of your replacement gilt supplier, and

  3. Identify the specific SIV strain you are dealing with to ensure your vaccine program includes that strain.

Work with your veterinarian to understand and control SIV in your herd.