The Usutu virus (USUV) is a mosquito-borne zoonotic flavivirus. Despite its continuous circulation in Europe, knowledge on the pathology, cellular and tissue tropism and pathogenetic potential of different circulating viral lineages is still fragmentary. Here, macroscopic and microscopic evaluations are performed in association with the study of cell and tissue tropism and comparison of lesion severity of two circulating virus lineages (Europe 3; Africa 3) in 160 Eurasian blackbirds (Turdus merula) in the Netherlands. Results confirm hepatosplenomegaly, coagulative necrosis and lymphoplasmacytic inflammation as major patterns of lesions and, for the first time, vasculitis as a novel virus-associated lesion. A USUV and Plasmodium spp. co-infection was commonly identified. The virus was associated with lesions by immunohistochemistry and was reported most commonly in endothelial cells and blood circulating and tissue mononucleated cells, suggesting them as a major route of entry and spread. A tropism for mononuclear phagocytes cells was further supported by viral labeling in multinucleated giant cells. The involvement of ganglionic neurons and epithelial cells of the gastrointestinal tract suggests a possible role of oral transmission, while the involvement of feather follicle shafts and bulbs suggests their use as a diagnostic sample for live bird testing. Finally, results suggest similar pathogenicity for the two circulating lineages.

Fifty-one meningiomas obtained from 28 dogs and 23 cats were selected for this study to investigate the immunohistochemical expression of matrix metalloproteinase (MMP)-2 and MMP-9 and to compare it to the reverse transcriptase subunit of human-telomerase, progesterone receptor expression, and the proliferative index of the tumors, expressed by Ki67 and proliferating cellular nuclear antigen. Paraffin-embedded tumor tissue was obtained from biopsy samples (28 cases) and at necropsy (23 cases). The most common histotype was malignant in dogs (12/28) and transitional in cats (12/23). Slides immunolabelled for MMPs showed a diffuse cytoplasmic pattern. Twenty-one cases (19 dogs and 2 cats) did not express MMP-2, while only 2 cases were completely negative for MMP-9. The highest values of MMP-2 and MMP-9 were observed in a psammomatous and meningothelial tumor, respectively. On statistical analysis, MMP-2 expression did not show a significant correlation with MMP-9. Moreover, both MMP expressions failed to show significant variance among histologic patterns of the tumor and correlation with the proliferative index. MMP immunolabeling showed an inconstant correlation with progesterone receptor expression. No significant correlation was found between MMP and reverse transcriptase subunit of human-telomerase expression. In feline meningiomas, the MMP-2 value was significantly higher than in canine tumors and the MMP-9 value tended to be low for meningiomas with a follow-up duration from the 23 ^rd month to the 44 ^th month. In cats, the longer the time from surgery, the lower the proliferative index seemed to be. In dogs, we failed to find a correlation between MMP expression and the follow-up duration.

A cerebral granular cell tumor is described in a 6-year-old, shorthaired, female cat. The tumor was observed above the corpus callosum and completely infiltrating the third ventricle. Histologic examination revealed that the tumor was characterized by large cells containing densely packed intracytoplasmic granules and expressed psammoma body-like patterns and cholesterinic degeneration. immunohistochemical analysis revealed granular neoplastic cells that were diffusely and strongly vimentin-positive, while they did not express cytokeratins, lysozyme, and synaptophysin. Based on morphologic and immunohistochemical findings, the tumor under study was considered to be of meningeal origin arising directly from the meninges or from meningeal elements scattered in the tela choroidea of the third ventricle roof.

Choroid plexus tumors (CPTs) are reported with an increasing incidence in dogs, and they call for a reexamination of histologic features and criteria of classification corresponding to their biological behavior. In this study, the human World Health Organization classification was applied to 16 canine CPTs, and the expression of molecules involved in neoplastic cell adhesion (E-cadherin, N-cadherin), invasion (doublecortin), and proliferation (Ki-67) was investigated. Mitotic index was found to be the main criterion for grading CPTs. Cell density and multilayering of papillae were also statistically associated with histologic grade. Intraventricular spread and parenchymal invasion was observed for tumors showing histologic benign features. E-cadherin was expressed in all CPT grades, independent of tumor invasion. N-cadherin immunolabeling was more expressed in grade I than high-grade CPTs, whereas doublecortin expression was not detected in CPTs. An increasing proliferative activity was observed in relation with histologic grade.