A new strain of swine influenza virus (SIV) has hit herds in North Carolina, Iowa and Minnesota. The strain, H3N2, has previously been identified in European herds. It is only the second known strain of SIV in the U.S., the other being H1N1, still the dominant strain of SIV.

First Case In North Carolina The first case of H3N2 was isolated by Gene Erickson, DVM, of the North Carolina Microbiology Testing Laboratory.

That first case involved a 2,000-sow herd that had been in production about one year, comments Erickson. They had been using a half dose of SIV vaccine on just the 40% of the herd's new gilts that came from North Carolina. The other 60% of gilts, originating from out of state, were not vaccinated for SIV before shipment or at the time the herd was assembled. All sows and gilts, regardless of background, were given a half dose of SIV vaccine pre-farrowing. (Schering-Plough Animal Health has the only SIV vaccine on the market.)

First farrowing was normal. But during the second farrowing, in late August '98, the farm veterinarian called to report some unusual problems. Sows were very sick with temperatures up to 106 degrees F; some were dying. The veterinarian told Erickson the outbreak looked a lot like SIV, but said he was confounded by the fact that he had been vaccinating and there were still problems. He acknowledged he hadn't used the full dose of vaccine, as is recommended by the company, because he was afraid of reactivity problems in the breeding herd and was also trying to cut costs. Label directions for the Schering vaccine call for two doses three weeks apart (pigs or sows) and a booster dose for sows.

According to Erickson the outbreak of H3N2 SIV was the hardest on those gilts that had never been vaccinated for SIV.

The disease swept through that entire herd in less than a week, relates Erickson. In the end, a total of 27 sows aborted and 56 sows died. Most sows that had been bred 30 days earlier, returned to heat.

Iowa, Minnesota Experience So far, says Bruce Janke of Iowa State University's diagnostic laboratory, four isolates of the new H3N2 SIV have been identified. Two cases were from Iowa; two were from southern Minnesota.

The first outbreak occurred in a 400-head, off-site nursery in Iowa. In a few days, a nearby farm containing sows in a farrowing unit and nursery pigs on the same site became ill. From 40-80% of sows were affected.

A second Iowa case involved a 3,200-sow operation in which flu-like conditions affected about 200 sows and nursing pigs. Again, there were a few abortions but no sow deaths, he reports. Replacement gilts had been vaccinated for SIV twice on entrance into the breeding herd. Virus was isolated from sows and 14- to 19-day-old pigs.

In the two cases of SIV from Minnesota, sows experienced typical flu-like symptoms. One of the two cases had flu problems in the nursery and finisher on and off all fall, before the outbreak occurred in sows in the other herd, relates Janke.

According to Rick Sibbel, Schering-Plough veterinarian, the company has applied for federal license for an H3N2 strain SIV vaccine. Eventually, plans are to develop a bivalent vaccine that contains both SIV strains.