Temporal distribution of porcine circovirus 2 genogroups recovered from postweaning multisystemic wasting syndrome affected and nonaffected farms in Ireland and Northern Ireland

Porcine circovirus type 2 (PCV2) is now recognized as the essential infectious component of porcine postweaning multisystemic wasting syndrome (PMWS). PMWS was first recognized in high-status, specific pathogen-free pigs in Canada in 1991 and is now an economically important disease that affects the swine industry around the world. Recently, reports of genomic studies on PCV2 viruses indicated that 2 distinctive genogroups of PCV2 exist.4,10 This report involves the results of a study on the distribution of predominant PCV2 genogroups recovered from samples taken from PMWS-affected and PMWS-nonaffected farms on the island of Ireland over a 9-year period and the results of a study on PCV2 genogroup recovery from fecal samples taken from a farm in Northern Ireland from 2003 to 2005 that was first diagnosed as PMWS positive in August 2005. The results indicate that, although at least 2 distinct genogroups of PCV2 have been circulating on pig farms on the island of Ireland, there does not appear to be a direct relationship between infection with these different genogroups of PCV2 and the development of PMWS.

Primary demyelination in experimental canine distemper virus induced encephalomyelitis in gnotobiotic dogs. Sequential immunologic and morphologic findings

Experimental infection of gnotobiotic Beagle dogs at 21 days of age with neurovirulent R252 strain of canine distemper virus (R252-CDV) resulted in a non-suppurative encephalomyelitis. Segmental internodal primary demyelination was found in almost 90% of the dogs from 27 days post inoculation (DPI). Ultrastructurally demyelination was initiated by the insertion of CDV-infected astrocytic processes at nodes of Ranvier with subsequent cleavage of well-preserved myelin from the axolemma. CDV-infected macrophages were consistently involved in myelin phagocytosis. Some remyelination of denuded axons occurred after 35 DPI. Persistent productive infection of the choroid plexus and ependyma in the fourth ventricle was consistently associated with subependymal foci of demyelination.

Primary demyelination occurred without detectable CDV-specific virus-neutralizing (CDV-VN) antibody in either serum or cerebrospinal fluid (CSF). There were no immunoglobulin deposits or inflammatory cells within the lesions. These findings indicate that both direct CDV antibody-dependent and CDV antibody-dependent cell-mediated immune mechanisms of cytolysis or myelin destruction are not involved in the genesis of initial primary demyelination. The sequential morphologic and serologic findings in this model of demyelinating encephalomyelitis indicate that direct virus-induced injury has a major role in both the initiation and early progression of primary demyelination.

Experimental canine distemper encephalomyelitis in neonatal gnotobiotic dogs. A sequential ultrastructural study

The ultrastructural morphogenesis of neuronal degeneration and necrosis and patterns of associated myelin and axonal degeneration were studied in gnotobiotic dogs neonatally infected with neurovirulent R252 strain of canine distemper virus (CDV-R252). Distemper virus-infected neurons underwent a distinct sequence of ultrastructural changes culminating in direct viral-induced necrosis beginning after 21 days post inoculation (DPI). Viral-induced neuronal cytolysis occurs apparently independently of anti-viral immune mechanisms of immunologic destruction. Viral nucleocapsid aggregates in postsynaptic axosomatic and axodendritic complexes and in structurally intact axons provided morphologic evidence for viral-induced functional modulation of synaptic transmission and possible trans-synaptic interneuronal viral spread. There were secondary degenerative axonal and myelin changes, particularly in heavily myelinated tracts. There was no evidence of primary demyelination. Active phagocytosis of degenerating axons and myelin debris in foci of virus-associated necrosis was apparently restricted to CDV-containing macrophages. Demonstration of a productive CDV infection of choroid plexus epithelium 10 DPI and thereafter was identified as an intracranial source of free infectious virus.