Progress after one year of a pseudorabies eradication program for large swine herds.

Six large farrow-to-finish swine herds quarantined for pseudorabies in Illinois participated in the USDA-initiated Large Herd Cleanup Study. These herds were monitored for antibodies to pseudorabies virus (PRV) for 1 year after the initiation of an intensive eradication program. Herd size ranged between 425 and 1,500 females of breeding age. Gene-deleted modified-live virus vaccines were used on all farms, with 3 of the 6 herds receiving a vaccine with a deletion of the gene for glycoprotein-I and the other 3 herds receiving a vaccine with a deletion of the gene for glycoprotein-X. The breeding herd and growing pigs were vaccinated on each farm. Each herd produced its own replacement gilts. In addition, management changes emphasizing all-in, all-out pig flow were initiated. One year after initiation of the vaccination program, sera for the measurement of PRV antibodies were obtained from sows and heavy finishing pigs (> 70 kg) from each of the farms. Prevalence of PRV antibodies attributable to wild-type virus infection ranged from 7 to 63% (median, 33%) for sows and from 0 to 42% (median, 4%) for finishers, as determined by the appropriate vaccine differential test. For each sow herd, there was a large decrease in the PRV seroprevalence rate after 1 year of the program (range, -21 to -68%; median, -42%). Examination of PRV prevalence rates by parity indicated decreased seroprevalences in the lower parities (< 2) in 3 of the herds, suggesting that vaccination reduced the spread of PRV.(ABSTRACT TRUNCATED AT 250 WORDS)