Congenital tremors (CT; myoclonia congenita ) is a sporadic but globally distributed disease of neonatal pigs characterized by action-related repetitive myoclonus. The first reports of the disease date back nearly one hundred years, yet most contemporary cases of CT are clinically ascribed to an unidentified virus.
The aims of this project were twofold: 1) to identify potential pathogen(s) using next generation sequencing in cases of CT, and 2) to develop an innovative inoculation model to reproduce CT.
Next generation sequencing was performed on tissues from two field cases of CT. A novel agent was detected. For the second aim, seven individually identified crossbred sows were randomly assigned to one of three separately-housed groups: 1) sham-inoculated at 45 days gestation (n=1) and 62 days gestation (n=1), 2) pestivirus-inoculated at 45 days gestations (n=2), and 3) pestivirus-inoculated at 62 days gestation (n=3). Sows were anesthetized and the uterus exteriorized. A handheld linear array ultrasound was used to visualize each fetus and to inject each fetal vesicle with 0.25mL of either PBS (sham) or pestivirus-laden serum. Sows were also inoculated simultaneously by intravenous and intranasal routes per protocol. Sows farrowed normally. Video of each uniquely-identified piglet was taken at 0, 24 and 48 hours post-farrowing. Tremor severity was evaluated blindly by four investigators whereby each piglet received an averaged tremor severity score. Piglets were humanely euthanized and necropsied at 48 hours postfarrowing.
A novel virus most closely related to a Chinese bat pestivirus at the time and now more closely related to a recently published novel porcine pestivirus was discovered from field cases of CT. Pestivirus RNA was detected by PCR in multiple tissues from piglets with CT but not in unaffected piglets from three separate farm investigations. Neonatal piglets from groups inoculated with pestivirus at both 45 and 62 days gestation were affected with CT, with prevalence within affected litters ranging from 57 to 100%. Tremor severity varied from mild to severe. Pestivirus RNA was consistently detected by PCR in numerous tissues at necropsy including serum, whole blood, cerebrum, cerebellum, brainstem, spinal cord, mesenteric lymph node, and tracheobronchial lymph node. Congenital tremors were not observed in control piglets and pestivirus RNA was not detected by PCR.
This is the first report to 1) identify a novel porcine pestivirus associated with CT and 2) successfully reproduce CT following inoculation of fetuses in utero.
Development of congenital tremors following novel Pestivirus inoculation. L. Arruda, Paulo Arruda, Drew R. Magstadt, Kent J. Schwartz, Tyler Dohlman, Jennifer A. Schleining, Abby Patterson, and Joseph Victoria. IPVS, 2016.