Despite the swine industry's continued push to achieve greater efficiencies using multiple-site production systems, disease challenges seem to prevail. One ongoing challenge that has definitely managed to change with the times is swine influenza virus (SIV).
SIV, much like its human counterpart the past several years, apparently has developed a somewhat unique ability to mutate very rapidly.
In my practice, it seems as though I isolate one strain subtype on a producer's farm, and a mutant subtype pops up that may or may not be antigenically different. An antigen is a protein, toxin or enzyme that is capable of stimulating an immune response. This activity makes controlling the virus very difficult.
Case Study No. 1
I was called out to a 1,000-head finisher site with primary complaints of pigs off feed, coughing and very lethargic. The double-curtain-sided, slotted floor barn with a 10-ft.-deep manure pit is operated on an all-in, all-out (AIAO) basis. The barn was being filled from two sow herds.
The pigs weighed approximately 160 lb. and exhibited a dry, hacking cough. The producer had lost two pigs during the night and necropsy revealed secondary Streptococcus suis as the main cause of death.
The problem started a week earlier when a curtain cable broke and the barn temperature had dropped to below 55 °F.
The pigs were placed on water medication to stop death loss.
Diagnostics were conducted on lung samples, serum samples and nasal swabs from acutely sick pigs.
As a result, the sow herds were vaccinated with a commercial SIV vaccine and a killed, autogenous porcine reproductive and respiratory syndrome (PRRS) vaccine prior to farrowing.
SIV was isolated from the lung tissue and an autogenous vaccine was developed to vaccinate sows prior to farrowing. The entire breeding herd was double vaccinated with a new SIV vaccine three weeks apart. Incoming gilts were also double vaccinated three weeks apart during the isolation/acclimation period.
The finisher death loss stopped and the cough subsided after 7-10 days. When the finisher was emptied, it was cleaned and disinfected. The finisher was refilled and has not suffered another SIV outbreak.
Case Study No. 2
The second case study involves a multiple-site system where the sow herd is separate from the rest of the production. However, the nursery and finishing operations are all on one site. The nursery is operated on a continuous-flow basis with six rooms of pigs. The finishers are operated AIAO, by building.
The sow herd is vaccinated with a killed PRRS vaccine, along with the routine vaccinations for reproductive problems.
The sow herd broke with abortions and high fevers, and sows were off-feed. The outbreak was sporadic throughout the herd, but primarily occurred during late gestation.
Fetuses were submitted, along with nasal swabs and serum samples. Before the diagnostic test results were fully completed, the nursery and finishers broke with a severe cough. Death loss was minimal.
Necropsy of pigs from the nursery and finisher revealed Strep suis and a few Haemophilus parasuis organisms as secondary invaders. Water medication and individual pig treatments minimized death loss.
Lab tests of the sows revealed normal vaccine titers, but unstable SIV titers. Convalescent serum samples have been submitted. Virus isolation for PRRS and SIV were negative. The herd has since quieted down.
Case Study No. 3
This is the most difficult case of all since it involves a single-site system. This is a 600-sow herd that is positive for PRRS and SIV. The sows are vaccinated before farrowing with killed products, but the nursery and finishers receive no vaccinations.
The sow herd has been stabilized for some time now, but the nursery and finisher broke with a severe cough. The combined death loss in the nursery and finisher was 8%. Death loss was mostly due to Strep suis and Haemophilus parasuis. Water medication stopped death loss, but several pigs turned into culls. A few pigs died of gastric ulcers from being off feed.
Diagnostics revealed a different subtype of SIV. The isolate was added to the sow herd vaccine protocol.
An accurate diagnosis of swine influenza is difficult, at best, and the overall control of the virus is even more difficult.
Stabilization of the sow herd is the key to control. Unfortunately, vaccination does not always guarantee protection since the number of variant subtypes continues to increase.
Area spread and the realization that there is an interdependence between systems helps us establish databases within sow herds.