Tremor tales: A cohort study of general and neurological signs in pigs with atypical porcine pestivirus-induced congenital tremor

Congenital tremor (CT) caused by atypical porcine pestivirus (APPV) is a widespread disease in the swine industry. It is characterized by tremors in newborn piglets, but tremor description and association to other clinical signs are not well documented. This study's objectives were to characterize general and neurological clinical signs of APPV-induced CT and describe the progression and associations between the different signs. A cohort study was conducted including 37 pigs from litters with APPV-confirmed CT and 27 control pigs from healthy litters. All pigs were examined five times from birth to slaughter, including general and neurological parameters, and detailed tremor characterization. All levels of tremor, from grave severity to no tremor, were seen within litters. Tremor persisted throughout the suckling period for all, to weaner age for 60 % and to slaughter age for 40 %, unrelated to the initial degree of tremor (P = 0.9). Tremors were consistent with intention tremor and typically went from affecting the whole body to smaller regions as the pig aged, while frequency increased, and amplitude decreased. Tremor was associated with hypermetria (P = 0.0018) and a broad stance (P = 0.0198) during the suckling period. No other neurological signs, or splay leg, were observed. Severe tremor inhibited voluntary movement and was associated with reduced general condition (P = 0.0017), lower body condition score (P = 0.0044), more carpal lesions (P = 0.0163) and arthritis (P = 0.0198). Intention tremor and hypermetria corresponds to cerebellar diseases, although other typical signs of this were absent. Both the tremor observed, and the associated clinical manifestations appear to have severe animal welfare implications.