Case of PRRS in pig holding - epidemiological and economical analysis

In June 1998, 12 gilts were purchased at a new, small (annual production 25 0 piglets) farm. The animals were free from PRRSV antibodies. After one mon th of quarantine the gilts were placed in two separate pens A and B. The fi rst female was bred in mid-August and the last one at the beginning of Octo ber. In order to ensure the empty rooms at the nursery house were occupied, in mid-November the farmer purchased 120, 8-week old weaners from an epide milogically unrecognised herd. Unfortunately, the weaners were immediately introduced onto the farm. One-week later antibodies to PRRSV were accidenta lly detected in this group of pigs. Because the pig holding was under the c ontrol of the Institute, there was an opportunity to monitor the eventual s preading of PRRSV from weaners to gilts. In order to do this, blood samples was taken from all gilts, 2, 4, 6 and 10 weeks after the weaners had been introduced onto the farm. Four weeks afte r purchasing the weaners, antibodies were detected in 3 out of 6 gilts from pen A and 2 weeks later PRRSV antibodies were found in a further 2 females . The last gilt from this pen was sero-converted 10 weeks after the weaners had been introduced. In pen B, PRRSV sero-conversion was detected in the f irst 2 gilts 6 weeks after the weaners introduction, and 2 other gilts were sero-converted 4 weeks later. One gilt from this pen did not have antibodi es at the end of the observation period. The consequences of PRRSV spreading among pregnant gilts were observed duri ng the furrowing period. Ten out of twelve females delivered dead or mummif ied piglets. Three litters were normal and in these cases the gilts had bee n infected during the 8-9 weeks of pregnancy. The economical consequences o f introducing weaners infected with PRRSV into the newly established herd w ere very serious: the average number of piglets born alive per gilt was 6.8 . The average number of piglets weaned was 6.2 and fatteners sold per sow w ere 5.7.