As our production methods have changed, so has the clinical picture of swine influenza virus (SIV). Larger groups of single site, confined pigs have changed the disease dynamics.
The acute syndrome usually associated with SIV has evolved to a more chronic and slower-progressing picture. Recovery isn't as quick as the virus takes longer to move through a group of pigs.
SIV has become a key piece of the Porcine Respiratory Disease Complex (PRDC), affected by factors ranging from the pigs' environment to viral activity in the source sow herd.
The two major strains identified in pigs are the original H subscript 1N subscript 1 and H subscript 3N subscript 2 (1998).
Given the nature of the flu virus, it may only be a matter of time before another variant emerges as a significant problem.
Case Study No. 1 We were called to a 1,500-sow, farrow-to-wean farm that brings 40-lb. replacement gilts directly into the gestation barn for acclimation. Purchased as weaned pigs from a multiplier farm, they are raised to 40-50 lb. off-site.
The gilts are introduced into the breeding farm every 10 weeks. One time, 10 days after a new group of gilts was introduced, two died suddenly and 20% went off feed.
Postmortems of the dead pigs indicated wet and heavy lungs, pointing to a viral infection. Some younger parity gestating sows also went off feed.
Two days later, there were sporadic abortions in the gestation barn. These ranged from 45 to 90 days of gestation. Aborted sows went off feed but were back on feed in one to two days. There was also a higher return rate in the breeding groups.
Lab work on the lungs from a replacement gilt confirmed the H subscript 3N subscript 2 strain of SIV. Serological evaluation of aborted sows indicated a very high titer for H subscript 3N subscript 2 strain. The sows were serologically negative for H subscript 1N subscript 1 but had low titers to porcine reproductive and respiratory syndrome (PRRS) virus; leptospirosis and parvovirus titers were within normal limits.
The SIV apparently came in with the new gilts, or else the new gilts were infected after they came into the barn. It is impossible to determine exactly the source of the virus.
However, we also feel the abortions and off-feed sows can be attributed to SIV, based on the history of the gilts with active SIV and the high blood titers to the H subscript 3N subscript 2 strain.
This farm has chosen to vaccinate the sow herd semi-annually with a dual strain SIV product. The goal of whole-herd vaccination is to stabilize the herd, reduce virus in pigs at weaning and lessen interruptions in production during new gilt introductions.
Case Study No. 2 A second case involved a 1,300-sow, farrow-to-finish farm with all-in, all-out (AIAO) nurseries and finisher barns but not sites.
The farm had not experienced any cough until August. It spread slowly throughout all the sites and completely exposed a three-barn site in two weeks. Death loss remained unchanged, and there were very few treatments, despite the noticeable cough in all the pigs.
A serological profile was done on one site; 10 samples were pulled from each barn. The oldest pigs were coughing but younger pigs weren't. Serology indicated the youngest pigs were negative for PRRS, Mycoplasmal pneumonia and the H subscript 1N subscript 1 and H subscript 3N subscript 2 SIV strains.
The oldest pigs were negative for PRRS, mycoplasma and H subscript 3N subscript 2 but were positive for the H subscript 1N subscript 1 strain. This work-up was done in August; there weren't any clinical losses.
However, this fall the level of cough and clinical signs of pneumonia have increased. Death loss has crept up from 1-2% to 3-4%. Postmortem work-ups of these pigs suggest bacteria and SIV.
We have decided to vaccinate for SIV in the nursery two weeks postweaning and booster four weeks later as they exit the nursery. The goal is to minimize losses.
Summary With SIV, conduct an accurate diagnostic work-up to sort out the key pathogens involved. The extent of clinical SIV depends on barn environment, the level of challenge and the other disease agents present.
Vaccination is a tool. Use only after making every effort to ensure all other stresses have been minimized. AIAO site management can help.
If you feel you have influenza problems in your operation, consider these four things:
- Work with your veterinarian on an accurate diagnosis;
- Follow good management procedures that include managing the environment as well as reducing secondary infections;
- Formulate a prevention plan that fits your operation and pig flow; and
- Practice good biosecurity to prevent your farm from becoming re-infected.