PCV2 Associated CNS Disease
Congenital tremors in pigs are associated with demyelination of brain and spinal cord. The most common form in North America is transmissible and classified as type A2. This form is characterized by clonic contractions of skeletal muscles of varying severity that decrease with time and usually resolves by 4 weeks of age. Hines and Lukert (1994) were the first to report on a potential association between PCV and congenital tremors. Four PCV seronegative sows were experimentally infected with PCV obtained from a piglet with congenital tremor. The sows didn’t develop any clinical signs, but all of the piglets had congenital tremors of varying degrees. Stevenson et al. (2001) demonstrated PCV2-antigen (IFA) and nucleic acids (ISH and PCR) intralesional in affected neonatal pigs from four different farms in the Midwestern US.
In contrast to this, Kennedy et al. (2003) investigated central nervous system and nonneural tissue of 40 pigs affected by congenital tremor from Spain, the United Kingdom, Ireland, and Sweden by IHC, ISH, and PCR (Spanish cases only). PCV1 or PCV2 nucleic acids or antigen were not found in any of the pigs (Kennedy et al., 2003).
Hines RK, Lukert PD: Porcine circovirus as a cause of congenital tremors in newborn pigs. In: Proc Am Assoc Swine Pract. Chicago, Illinois. 25:344-345, 1994
Kennedy S, Segalés J, Rovira A, Scholes S, Domingo M, Moffett D, Meehan B, O'Neill R, McNeilly F, Allan G: Absence of evidence of porcine circovirus infection in piglets with congenital tremors. J Vet Diagn Invest. 15:151-156, 2003
Stevenson GW, Kiupel M, Mittal SK, Choi J, Latimer KS, Kanitz CL: Tissue distribution and genetic typing of porcine circoviruses in pigs with naturally occurring congenital tremors. J Vet Diagn Invest. 13:57-62, 2001