Persistent atypical porcine pestivirus (APPV) infection in gilts

Authors: Buckley, Alexandra; ARRUDA, BAILEY - Iowa State University; Falkenberg, Shollie; Miller, Laura; Lager, Kelly

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/6/2019
Publication Date: 11/27/2019
Citation: Buckley, A.C., Arruda, B., Falkenberg, S.M., Miller, L.C., Lager, K.M. 2019. Persistent atypical porcine pestivirus (APPV) infection in gilts. Meeting Abstract. p. 35.

Interpretive Summary:

Technical Abstract: Introduction: Atypical porcine pestivirus (APPV) is a recently discovered virus that can be sporadically detected in swine. It has been associated with Type AII (viral related) congenital tremors (CT) in newborn pigs and APPV was shown to cause CT by direct inoculation of fetal amniotic vesicles with APPV-positive serum. Much is still unknown about the pathogenesis and epidemiology of this virus, especially the long-term consequences of CT in gilts. This report characterizes: 1) the duration of viremia and antibody response in gilts born APPV positive, 2) the transmission potential of APPV, and 3) if persistently infected gilts produce APPV and CT positive piglets. Materials and Methods: Nine gilts were selected from a commercial grow/finish barn in Iowa based on originating from a CT litter at birth and the persistent presence of APPV in serum throughout the finishing phase. These gilts were obtained from the commercial farm at market weight and transported to the National Animal Disease Center for further study. Gilts were bled monthly and oral fluids were collected prior to breeding and during gestation. The gilts were synced and bred via artificial insemination with APPV negative semen. One gilt was necropsied for tissue collection to evaluate viral distribution at the time of breeding. Throughout breeding and gestation gilts were allowed fence-line contact with three separate groups of naïve contact pigs to study transmission potential. Contact pigs were allowed nose-to-nose contact for approximately 1 month and then removed. Blood, oral, and rectal swabs were collected at weekly intervals for the month during the transmission period as well as for approximately 1 month after the contact period and removal. Post farrowing piglets will be observed daily for approximately the first week and assigned a tremor severity score. Piglets will be bled and swabbed at farrowing and at weekly intervals until necropsy. At necropsy, tissues will be collected from both the gilts and piglets. Rectal swabs, oral swabs, oral fluids and serum will be tested for APPV RNA by PCR and the antibody response determined by ELISA. Tissue will be tested for APPV RNA by in situ hybridization. Results: Viremia was detected at multiple time points for five months after birth. While viremia was not consistently detected at each sample time point, oral fluids and oral swabs were consistently positive for APPV by PCR testing. Transmission of the virus was successful as determined by the contact pigs testing positive for APPV. One contact initially tested positive for APPV at 25 days post contact (dpc), while the second did not consistently sample positive in serum and swabs until 53 dpc. Two months after the first set of contact pigs, a boar was placed in contact with the gilts (8 months) and also tested PCR positive for APPV. When the gilts are 11 months old and nearing the end of gestation the third group of contact pigs will be housed beside gilts. ELISA results for gilts and contact pigs are pending. Piglet results are pending as gilts are due to farrow in October of 2019. Conclusion: Piglets born APPV positive with and without CT continue to test positive by PCR for APPV for an extended period of time. These animals have been demonstrated to transmit virus to naïve contact animals. Furthermore, the virus can be found in a wide variety of tissues and sample types. Understanding infection dynamics of APPV and applicable sample types for monitoring infection following exposure can aide control measures for this virus in addition to reducing Type AII CT due to APPV.