Congenital tremors in piglets infected with atypical porcine pestivirus

Amanda Mansz

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2023;27(4):14.

Two sucking piglets from a farrow-to-finish operation were submitted to the AHL for postmortem following a one-month history of an increased prevalence of piglets developing full body shaking/tremoring and splayleg within the first week of age.  Approximately 70-80% of litters were affected, with some litters having 2-3 animals affected, and others involving all littermates.  Affected piglets were farrowed from both gilts and multi-parity sows.  The majority of the piglets survived with eventual resolution of clinical symptoms.  There were no other obvious health concerns (e.g., scours, coughing, wasting) involving these piglets, and no sows were affected.

Prior to postmortem, piglets were bright and alert, but aggressively shaking/tremoring (link to video posted below).  Postmortem findings revealed the piglets were in good body condition, and there were no visible gross lesions in the brain, spinal cord, or any other organ system.  Microscopic changes were very subtle and consisted solely of patchy subtle cerebral and cerebellar neuronal degeneration, and mild multifocal white matter vacuolation in the brain and spinal cord.  Sections of brain were sent to the Iowa State Veterinary Diagnostic Laboratory, and were PCR positive for the detection of atypical porcine pestivirus (APPV).

APPV was first identified in the United States in 2015 and has a global distribution; however, its clinical relevance is poorly understood.  APPV has been associated with congenital tremors (CT) in newborn pigs.  Clinical signs include muscle spasms, posterior paresis and splayleg.  Litters from gilts are most commonly affected.  There are no gross lesions associated with infection, and hypomyelination or demyelination of the brain and spinal cord can sometimes be seen microscopically.  Experimental infection of gilts/sows with APPV during gestation can result in transplacental (vertical) transmission with development of CT in offspring.  Horizontal transmission can also occur, but infection seems to be transient, and piglets do not develop clinical signs.  In litters infected with APPV, morbidity is highly variable and ranges from 0–100%.  There is no treatment for APPV infection; therefore, strategies for control often include acclimatization of replacement gilts to ensure APPV exposure before breeding, testing of semen for APPV RNA before insemination, and feedback on farms with clinical CT cases. 

Link for the video: https://www.youtube.com/shorts/iBw-udZ54FI

References

1. Hause BM, et al.  Discovery of a novel putative atypical porcine pestivirus in pigs in the USA. J Gen Virol. 2015;96:2994–98.

2. Buckley AC, Falkenberg SM, Palmer MV, et al.  Distribution and persistence of atypical porcine pestivirus in experimentally inoculated pigs. J Vet Diagn Invest. 2021;33(5):952-955.

3. de Groof A, et al.  Atypical porcine pestivirus: a possible cause of congenital tremor type A-II in newborn piglets. Viruses. 2016;8:271.