New Strains of Swine Flu are Elusive

An Elusive PathogenControlling new strains of swine influenza virus can be a difficult task.

September 19, 2011

4 Min Read
New Strains of Swine Flu are Elusive

After spending a weekend with my son hunting prairie dogs in Kansas, I couldn’t help but ponder the analogy between the prairie dog population we were trying to reduce and the elusive swine influenza virus (SIV) we are trying to control.

Hunting prairie dogs at the end of the normal season can be a difficult task, just as can be controlling new swine flu strains.

Case Study No. 1

A 300-sow, single-site, farrow-to-finish operation had been recently repopulated with gilts negative for porcine reproductive and respiratory syndrome (PRRS), Mycoplasma pneumonia, Actinobacillus pleuropneumonia (APP) and SIV. The well-managed, isolated unit has no other pigs within 10-12 miles.

With empty finishing space during the startup phase, we decided to bring in 50-lb. grower pigs from a farm in the same genetic pyramid. The other unit was negative for PRRS, mycoplasma, and APP. SIV type H1N1 had been diagnosed in the grower pig herd earlier, although there had been no clinical signs at that unit for over 60 days.

These feeder pigs developed a dry, hacking cough within two weeks after introduction to the 300-sow site; 10% went off feed for 2-3 days. Symptoms suggested mycoplasma. Soon after, death loss was noted in mature breeding animals. Necropsy lesions and diagnostic results yielded Haemophilus parasuis (HPS) and SIV. Multiple therapies included water medications and injectable products given to the entire population. The incoming feeder pigs were free of clinical signs.

While the HPS was quickly controlled, the hacking cough continued in some pigs for two weeks. A commercial flu vaccine is now used on incoming pigs and on sows pre-farrowing, eliminating clinical signs.

Case Study No. 2

A 2,500-sow, weaner pig producer called complaining that a row of gilts were completely off feed and very lethargic. The gilts were introduced within the last two weeks; 60-70% were non-responsive, were completely off feed, and had temperatures of 103.5° to 105.5° F. Several gilts had purple snouts, ears and underlines and refused to get up.

Two gilts were humanely euthanized for postmortem. On examination, the lungs appeared good. There was less than 3% lung consolidation indicative of pneumonia. The lungs were excessively heavy and when sliced, large volumes of foamy fluid exuded from the incision. Samples were confirmed as SIV at the diagnostic lab.

Our investigation uncovered that this set of gilts had received only one dose of commercial flu vaccine during the offsite isolation/acclimation period. All prior gilt entries had received two doses of vaccine. None of the older gilts or sows exhibited clinical signs. This reminded staff of the importance of following protocols and procedures.

Ultimately, no other gilts died, although multiple injections were given to reduce fever and control secondary bacteria. Aspirin was also administered in the water. This set of gilts had higher death loss and cull rates than other group and never achieved the reproductive efficiencies of their contemporaries, which had received two doses of flu vaccine.

Since implementing two doses of commercial swine flu vaccine to incoming gilts, outbreaks have ceased.

Case Study No. 3

Weaned pigs at a 1,200-sow site with a connecting hotel-style nursery were suffering from a chronic respiratory syndrome 10-14 days postweaning, which lasted for 2-3 weeks. Multiple necropsies and diagnostics yielded a variety of infective agents including Streptococcus suis, HPS, mycoplasma, bordetella, pasteurella and SIV. The sow herd showed no clinical signs of SIV, and both gilts and sows were vaccinated. Multiple therapies tried in the nursery to control the secondary bacterial agents have met with sporadic success.

The site has been unable to depopulate the nursery and. therefore, SIV continues to sporadically cycle through each set of pigs. To date, we have had no long-term success in warding off SIV in this continuous-flow nursery and will continue to put band-aids on the secondary agents.


Like prairie dogs, SIV can be a very pesky and elusive agent to hunt. This virus has been able to change over time and continues to wreak havoc among many swine systems.

Work closely with your herd veterinarian to ensure proper diagnostics have been performed and accurate results achieved, as there are multiple respiratory agents that can create similar signs. Good luck prairie dog and SIV hunting!

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