The infection occurred in all four breeding units at a commercial operation with 2,600 sows, and in two associated grow to finish operations located several hundred kilometers away from the breeding facility. These associated grow to finish operations received batches of pigs at varying intervals from the farrow to weaning operation. There are currently no reports of this new virus anywhere else in the world. As of October 1998, the infection was still circulating in the farrow to weaning operation and in one grow to finish operation. Most pigs become infected at 12 to 16 weeks of age, after colostral immunity wanes.
Infection is no longer present in the other grow to finish operation.
Eradication of infection in this operation is thought to be due to herd immunity achieved when no shipments of 8 week old pigs were received at the operation for a period of 10 weeks. Eradication plans for the other two premises are being developed. Quarantine measures are in effect. Pigs are only allowed to move off the affected premises directly to slaughter. All of the affected premises are quite geographically isolated from other commercial swine operations.