Getting Down Into The Weeds of AAPV-Induced Congenital Tremor, By Jordan Buchan from South West Ontario Veterinary Service

Congenital tremor (CT) or “Shaky Pig” disease caused by atypical porcine pestivirus (APPV) is seen in most pig producing areas of the world. Atypical Porcine Pestivirus had not been identified as a cause of CT but the availability of next generation gene sequencing helped to answer that decades long riddle. It should be noted that CT can also be caused by infection in utero with classical swine fever virus, genetic factors in British Landrace and Saddleback breeds and trichlorfon-intoxications . Classical Swine Fever (CSF)  (another member of the Pestivirus family) can cause CT CSF is a very important reportable transboundary disease. These Norwegian researchers wanted to get down into the weeds on the specifics of clinical signs for APPV-induced CT. The objective was to characterize the progression of clinical signs of APPV-induced CT. 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 and general and neurological parameters were described.

The researchers found the following:

• Tremor severity within CT litters could range from “grave severity” to no tremor.
• Tremor persisted throughout the suckling period for 100%, to weaner age for 60 % and to slaughter age for 40 % of initially affected pigs .
• Tremor persistence was unrelated to the initial degree of tremor (P = 0.9).
• Tremors were consistent with intention tremor where the pigs did not have a tremor as they slept but would start to have tremors when they awoke.
• Tremors could initially affect the entire body but most commonly the extent of tremors diminished to a few smaller body regions as the pig aged.
• Tremor frequency increased  and tremor amplitude decreased as the affected pig aged.
• Tremor was associated with hypermetria (P = 0.0018) and a broad stance (P = 0.0198) during the suckling period. ( Hypermetria is a condition of cerebellar brain dysfunction in which voluntary muscular movements tend to result in the movement of bodily parts beyond the intended goal. )
• Tremor associated with APPV did not appear to be expressed as “splay leg”.
• Tremor characterized as “severe” 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).