A clinical case of congenital tremors in piglets without evidence of PCV-1 and PCV-2

Congenital tremor (CT) is a disease of newborn pigs characterized by spontaneous clonic contractions of one or more groups of voluntary muscles. Besides suspected or confirmed etiologies of CT such as classical swine fever virus, pseudorabies virus, Japanese encephalomyelitis virus, hereditary disorders in Landrace or Saddleback pigs, organophosphorus poisoning etc., porcine circovirus (PCV) has been described as a potential cause of CT. The type AII seems to be the most common form of CT. Although a potential association between PCV1 or PCV2 and CT-AII has been observed, about 50% CT cases described up till now are caused by unknown reasons.
In a PCV-seropositive 108-sow, farrow-to-finish Belgian pig farm breeding hyperprolific Landrace, 42 litters with shaking piglet(s) were reported since June 2006. On March 2012, piglets born from four sows of a 27 sow batch demonstrated CT. After exclusion of main etiologies of CT from these CT-affected piglets, it was hypothesized that PCV1 or PCV2 could be the reason. Necropsies (n=8) and histopathology (n=3) were performed and no evidence of macroscopic or microscopic lesions were seen in cerebrum, cerebellum and spinal cord. Pre-suckled and post-suckled (after 3 days of colostrum uptake) serum samples were also collected from 9 piglets to determine PCV1- and PCV2-specific Ab titres by an immuno-peroxidase monolayer assay (IPMA). No PCV-specific Ab titres were observed in pre-suckled serum samples (≤40), whereas IPMA Ab titres of ≥640 were observed in post-suckled serum samples. Both PCV1 and PCV2 could not be isolated (<101.7 TCID50/g tissue) from 4 tested piglets (in heart, brain and lungs). The present results do not support the hypothesis that PCV1 or PCV2 are linked to CT in newborn piglets.