Abstract

plagued pig populations worldwide causing severe economical impacts. In order to establish effective strategies for prevention of PRRS, infection patterns on the herd level are primarily evaluated. In the present study, therefore, serological and virological analyses were conducted in 20 pig farms suffering from PRRS. Seroprevalence levels in each farm were grouped into 3 patterns: SN (Stable sow groups/Not infected piglet groups, SI (Stable sow groups and Infected piglet groups), and UI (Unstable sow groups and Infected piglet groups). The rates of each serological pattern were 15% (n=3), 10 % (n=2), and 75 % (n=15), respectively. In addition, the pattern analysis was extended to viro-logical monitoring on the same farms that further included suckling pig groups. As a result, the in-fection pattern was classified into 4 categories: SNI (Stable sow groups/Not infected suckler groups/Infected piglet groups), SII (Stable sow groups/Infected suckler groups/Infected piglet groups), UNI (Unstable sow groups/Not infected suckler groups/Infected piglet groups), and UII (Unstable sow groups/Infected suckler groups/Infected piglet groups). The rates of each viropreva-lence were estimated at 50 % (n=10), 30 % (n=6), 10 % (n=2), and 10 % (n=2), respectively. PRRSV viro-prevalence results of suckling pig groups revealed that 8 farms were considered virus positive. In 2 farms among these farms, PRRSV appeared to be transmitted vertically to suckling piglets from their