Tissue distribution and genetic typing of porcine circoviruses in pigs with naturally occurring congenital tremors

Congenital tremors (CT) type A2 is associated with porcine circovirus (PCV) and deficient and abnormal myelin. The aim of this study was to determine the tissue distribution and genetic type of PCV in 12-day-old pigs with nat urally occurring CT type A2 using in situ hybridization, polymerase chain r eaction (PCR), and indirect fluorescent antibody tests on frozen tissue sec tions. CT-affected and clinically normal pigs were selected from 4 farms in the midwestern USA that were undergoing outbreaks of CT type A2. All CT an d most normal pigs were infected with PCV PCV was widely distributed in tis sues of infected pigs and was most common in tissues of the central nervous system and liver. In all infected pigs, there were more PCV-infected cells in brain and spinal cord than in nonneural tissues. CT pigs had many more PCV-infected cells in the brain and spinal cord than did clinically normal pigs because of a more diffuse distribution and a larger proportion of infe cted cells. The cells most commonly infected with PCV in brain and spinal c ord were large neurons. In nonneural tissues, macrophages were the most fre quent cell type infected. PCR analysis demonstrated only PCV type 2 and not PCV type 1 in all PCV infected pigs on all 4 farms.