Response to PRRSV and PCV2b is Affected by Vaccination and WUR Genotype in Nursery Pigs

Abstract Text: Genetic marker WUR10000125 (WUR) on chromosome 4 has been associated with response to Porcine Reproductive and Respiratory Syndrome (PRRS) virus (PRRSV) in growing pigs, but little is known about its association in a co-infection disease model. The objective of this study was to assess the effects of marker WUR and vaccination on nursery pigs co-infected with PRRSV and Porcine Circovirus type-2b (PCV2b). At 28 days prior to infection, 206 commercial Yorkshire*Landrace weaned pigs, preselected to be AA or AB at WUR, were randomly allocated to one of two rooms and pigs in one room were treated with a modified live PRRSV vaccine. At 0 days post-infection (dpi), all piglets were co-infected with PRRSV and PCV2b, and euthanized at 42 dpi. Weekly body weights were used to calculate weight gain (WG) from 0-21 dpi (WG0_21) and 21-42 dpi (WG21_42). Viral load (VL) was calculated as area under the curve of log-transformed viremia for PRRSV (PRRSV_VL) and PCV2b (PCV_VL). WG and VL traits were analyzed in a model with fixed effects of vaccination (vaccinated/not), WUR genotype (AA/AB), WUR*vaccination, and pre-infection weight (covariate), and random effects of pen, sire, and dam. Analysis of VL included pre-infection viremia of the trait analyzed as a covariate. Weekly viremia (PRRSV/PCV) was analyzed using repeated measurements, with the same effects as used for WG, along with dpi and interactions, and viremia of the other virus as covariate in order to assess the relationship between the two viral infections. Vaccination had opposite significant (P<0.05) effects on WG0_21 and WG21_42, with vaccinated animals having greater growth than non-vaccinated for WG0_21 but lower growth for WG21_42. Vaccination and WUR had significant effects (P<0.05) on PRRSV_VL and PCV_VL. Vaccination resulted in lower PRRSV_VL, but greater PCV_VL. The effect of WUR was consistent across viruses, with AB animals having lower PRRS_VL and PCV_VL. PCV2b viremia had a significant effect (P<0.05) on PRRSV viremia at 21, 28, and 35 dpi, whereas PRRSV viremia lowered (P<0.05) PCV2b viremia on 28, 35, and 42 dpi, indicating lagged relationship between these two viruses. This study indicates that the WUR AB genotype also results in lower PRRS_VL with co-infection, as well as in lower PCV_VL. Vaccination against PRRS had contrasting results, and the positive relationship between PRRSV and PCV2b viremia indicates that PCV2b may attenuate the effects of PRRS in nursery pigs. Acknowledgements: USDA NIFA 2013-38420-20496 and 2013-68004-20362, PIC/Genus, Choice Genetics, and PigGen Canada.

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Disease