Swine influenza virus (SIV) used to be just a mild, seasonal problem. Basically it struck finishing hogs in the fall and spring. They'd develop a barking, raspy cough which would resolve itself in a week or two.
But in recent years, SIV has become more subtle, striking pigs of any age with a milder cough but more serious respiratory problems, complicated by PRRS (Porcine Reproductive and Respiratory Syndrome) and mycoplasmal pneumonia. The result is a chronic condition that cuts into performance and can result in deaths.
A Disease On The Rise Veterinary pathologists have documented the growth of SIV cases.
"The diagnosis of SIV probably has doubled and perhaps even tripled over the last five years at our lab," reports Douglas Hoefling, DVM, chief veterinarian, Animal Disease Laboratory, Illinois Department of Agriculture.
According to Hoefling the biggest change is the age of animals affected by SIV. "We used to see flu in the finisher period. Now we're seeing it earlier - in the nursery, during the grower period and, occasionally, in the farrowing house in pigs before they are weaned," he says.
Bruce Janke, diagnostic pathologist, Iowa State University Veterinary Diagnostic Laboratory adds: "I think there has been a real increase in influenza among nursery pigs. In the past, influenza was more likely to appear in older pigs."
With its broader scope, this new form of SIV can strike a herd more often, causing rapid onset of fever, a milder cough and labored breathing.
But Janke thinks sometimes there is more infection than can be visibly observed from the pen. While evaluating many cases of swine respiratory disease, he has seen numerous lung samples with damage characteristic of that caused by SIV.
"Many of the lesions are chronic and in the repair stage. These pigs may not have a history of acute respiratory disease and the virus may no longer be present, but the lesions suggest that SIV infection likely occurred earlier."
The most recent serologic surveys indicate that 80-90% of swine herds in the Upper Midwest are infected with SIV.
Reasons For Increase Kossuth Veterinary Clinic swine practitioner Dale Mechler of Algona, IA, says there are several reasons why SIV has become a year 'round problem. Chief on his list is the industry's move to segmentation.
"Before we were continuous flow and if your herd was positive, everybody was kind of positive for SIV. Now, we have segmented the industry out so much that you've got a naive set of nursery pigs. We move those pigs and then we've got a large population of naive pigs in the finisher. Consequently, when they break, they break relatively hard," he says.
The rise in SIV cases could also be partly due to increased diagnosis. "We're looking for it more and we are recognizing it a bit easier," says Hoefling. In Mechler's case, he's looking for it more as part of the mix of respiratory pathogens he knows are in his clients' comingled, contract nursery pigs. To keep abreast of the disease complex problems, he routinely conducts sow herd serological profiles.
What he often finds are SIV infections precipitated by mycoplasmal pneumonia, not PRRS (Porcine Reproductive and Respiratory Syndrome). Many of the herds will have antibody titers for PRRS, but it's mycoplasma and SIV that are doing most of the damage in nurseries in his practice area of north central Iowa.
Mechler also believes in performing routine serological profiles of nursery pigs as insurance. Select a statistical sample of 10-30 head at random, apply eartags for identification and blood test. Continue blood testing the same group of pigs every month through finishing. If there are particular problems cropping up in finishing, set up a serological profile. Also, consider regularly posting finisher pigs that are typical of the affected population.
Treatment To control the respiratory disease complex, sow herds need to have stable immune status. Start by proper isolation and acclimation of breeding stock, advises Christopher Olsen, DVM, University of Wisconsin SIV researcher. Next conduct a serological test of the sow herd. If serology shows a significant level of active antibody titers due to SIV, vaccination offers a solid treatment approach, says Kirk Clark, DVM, Purdue University.
"Among the practitioners I've talked to, vaccination for SIV is the way to go," he says. "By vaccinating sows, they are less likely to contract disease and shed virus, piglets will have more passive antibody to SIV, and there's a better chance of controlling disease. It might even be possible to prevent outbreaks of other respiratory diseases by controlling SIV."
Rick Sibbel, DVM, technical services veterinarian with Schering-Plough Animal Health, maker of the only SIV vaccine, says generally only sows are vaccinated if pigs breaking with SIV are less than 8 weeks of age. Maternal antibodies provide protection for pigs through this age.
In pigs with signs of SIV beyond 8 weeks of age, implement a pig vaccination program, says Sibbel.
Mechler follows a sow vaccination program exclusively, administering it 2-4 weeks pre-farrowing. In his experience, maternal antibodies provide protection out to early finishing age (55 lb.). When sows are vaccinated just before farrowing, he stresses the sow herd must be stable, especially to PRRS. Also ensure the vaccine is at room temperature.