The Myth of Fibroid Degeneration in the Canine Intervertebral Disc: A Histopathological Comparison of Intervertebral Disc Degeneration in Chondrodystrophic and Nonchondrodystrophic Dogs.

Since the seminal work by Hans-Jörgen Hansen in 1952, it has been assumed that intervertebral disc (IVD) degeneration in chondrodystrophic (CD) dogs involves chondroid metaplasia of the nucleus pulposus, whereas in nonchondrodystrophic (NCD) dogs, fibrous metaplasia occurs. However, more recent studies suggest that IVD degeneration in NCD and CD dogs is more similar than originally thought. Therefore, the aim of this study was to compare the histopathology of IVD degeneration in CD and NCD dogs. IVDs with various grades of degeneration (Thompson grade I-III, n = 7 per grade) from both CD and NCD dogs were used (14 CD and 18 NCD dogs, 42 IVDs in total). Sections were scored according to a histological scoring scheme for canine IVD degeneration, including evaluation of the presence of fibrocyte-like cells in the nucleus pulposus. In CD dogs, the macroscopically non-degenerated nucleus pulposus contained mainly chondrocyte-like cells, whereas the non-degenerated nucleus pulposus of NCD dogs mainly contained notochordal cells. The histopathological changes in degenerated discs were similar in CD and NCD dogs and resembled chondroid metaplasia. Fibrocytes were not seen in the nucleus pulposus, indicating that fibrous degeneration of the IVD was not present in any of the evaluated grades of degeneration. In conclusion, intervertebral disc degeneration was characterized by chondroid metaplasia of the nucleus pulposus in both NCD and CD dogs. These results revoke the generally accepted concept that NCD and CD dogs suffer from a different type of IVD degeneration, in veterinary literature often referred to as chondroid or fibroid degeneration, and we suggest that chondroid metaplasia should be used to describe the tissue changes in the IVD in both breed types.

Multiple introductions of salmonid alphavirus from a wild reservoir have caused independent and self-sustainable epizootics in aquaculture.

Salmonid alphavirus (SAV) causes infections in farmed Atlantic salmon and rainbow trout in Europe. Genetic diversity exists among SAV strains from farmed fish and six subtypes have been proposed based on genetic distance. Here, we used six full-genome sequences and 71 partial sequences of the structural ORF to estimate the evolutionary rate of SAV. The rate, 2.13×10(-4) nt substitutions per site per year, was further used to date evolutionary events in a Bayesian phylogenetic framework. The comparison of these dates with known historical events suggested that all six subtypes diverged prior to the twentieth century, earlier than the first attempts to introduce and farm rainbow trout in Europe. The subtypes must therefore have existed in a wild reservoir, as yet unidentified. The strains of each subtype, with the exception of subtype 2, have a common ancestor that existed after the 1970s - the start of modern farming of Atlantic salmon. These ancestors are likely to represent the independent introductions to farmed fish populations from the wild reservoir. The subtypes have developed subsequently into self-sustainable epizootics. The most parsimonious phylogeographic reconstruction suggested that the location of the wild reservoir is in or around the North Sea. After the initial introductions to aquaculture, further transmission of SAV was likely related to the industry infrastructure. This was exemplified by the finding of genetically identical subtype 2 and 3 strains separated by large geographical distances, as well as genetically distinct co-circulating lineages within the same geographical area.