Submitted to: World Veterinary Congress
Publication Type: Proceedings
Publication Acceptance Date: May 18, 1995
Publication Date: N/A
Technical Abstract: Porcine reproductive and respiratory syndrome (PRRS) is a new viral disease of swine which has had a significant impact on swine production throughout the world. Clinical signs of a PRRS epizootic are late-term maternal reproductive failure (abortions, early farrowings, infertility, stillborn and weak piglets) and a flu-like respiratory disease which has a high morbidity for all ages of swine. Little information is available concerning the formation and duration of protective immunity and the possibility of one strain forming cross protection for other strains. The objective of this study was to test the ability of a North American strain (NADC-8) of PRRSV to induce protective immunity in pregnant gilts subsequently challenged with either the same or an antigenically distinct European strain (Lelystad) of PRRSV. Forty gilts free of PRRSV antibody were divided into 5 groups of 8: group 1 = noninfected control group; groups 2 and 4 = positive controls for each virus strain; groups 3 and 5 were immunized with the NADC-8 strain at the time of breeding [0 day of gestation (DG)] and subsequently challenged at about 90 DG with either the homologous (NADC-8) or heterologous (Lelystad) strain, respectively. Gilts were necropsied at 111 DG and tested for protective immunity based on 2 criteria: 1) the presence of challenge virus in the gilt's alveolar macrophages; and 2) the presence of fetal infection in the gilt's litter. Results from groups 2 and 3 indicate a homologous protection was induced with PRRSV; groups 2 and 4 suggest the NADC-8 strain is more virulent for fetuses than the Lelystad strain; group 5 suggests that a limited heterologous protection may exist.