Veterinary Pathology

Apoptosis can be defined as a carefully regulated process, characterized by specific morphologic and biochemical features. It is initiated by both physiologic and pathologic stimuli, and its full expression requires a signaling cascade in which caspase activation plays a central role. Knockout mice lacking key genes encoding proteins constituting the core apoptotic cascade have helped us to establish the functional hierarchy of the mechanisms controlling apoptosis in animal development and, to a lesser extent, in disease. Induced mutant mice have also revealed the intimate crosstalk between apoptotic and other homeostatic pathways and have defined distinct temporal and tissue-specific roles of individual apoptotic effectors. Eliminating genes controlling caspase-dependent apoptosis can convert an apoptotic phenotype to a necrotic one, both in vitro and in vivo. This suggests that necrosis and apoptosis represent morphologic expressions of a shared biochemical network through both caspase-dependent mechanisms as well as non-caspase-dependent effectors such as cathepsin B and apoptosis-inducing factor. The cell death program, whether by apoptosis or necrosis, is mediated through an integrated cascade, which can be accessed at multiple sites, and propagated through numerous branch points. An understanding of the physiologic conditions that influence these decisions is required to adequately prevent, or induce, cell death.

Cyclooxygenase (COX) enzymes catalyze the synthesis of prostaglandins and exist as two isoforms, COX-1 and COX-2. COX-2 is a potent inducible mediator of inflammation. COX-2 is also upregulated in several human tumors and in canine squamous cell, renal cell, and transitional cell carcinomas, prostatic adenocarcinoma, and intestinal neoplasia. The purpose of this study was to determine whether COX-2 is expressed in various feline tumors. Results of this study may help determine whether COX-2 is a potential target for therapeutic and preventive strategies in cats. Immunohistochemical studies were performed on paraffin-embedded tissues using the amplified streptavidin-biotin-horseradish peroxidase system. COX-2 was found in 7 of 19 (37%) feline transitional cell carcinomas and in 2 of 21 (9%) feline oral squamous cell carcinomas. No COX-2 immunoreactivity was detected in cutaneous squamous cell carcinomas (6), adenocarcinomas (nine mammary, eight pulmonary, seven intestinal), lymphomas (six nasal, six intestinal), or 10 vaccine-associated sarcomas. The widespread absence of COX-2 expression in most feline neoplasms might suggest that COX-2 inhibitors would have a low potential as anticancer agents.

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones involved in electrolyte and fluid homeostasis. Our laboratory has investigated the use of ANP and BNP as diagnostic markers of cardiac disease in cats. We hypothesize that the cardiac distribution of ANP and BNP increases in cats with hypertrophic cardiomyopathy (HCM). Accordingly, we evaluated the immunohistochemical distribution of ANP and BNP in hearts of four cats with naturally occurring HCM relative to five healthy controls. Indirect immunoperoxidase was performed with polyclonal immunoglobulin G against feline ANP (1–28) and proBNP (43–56). In control cats, ANP and BNP immunoreactivity was restricted to the atria. Staining for both peptides was most intense adjacent to the endocardial surface. Auricles stained more diffusely than atria for both peptides. The interstitial capillaries and nerve fibers within the heart were positive only for BNP. Atrial immunoreactivity for ANP and BNP was more diffuse and had a less distinctly layered pattern in HCM than in control cats. Ventricular cardiomyocytes of HCM cats were negative for ANP but stained lightly and diffusely for BNP. The capillaries and nerve fibers remained positive for BNP. We conclude that in cats with HCM, the cardiac distribution of ANP and BNP is more diffuse in the atria and that novel expression of BNP in the ventricular cardiomyocytes occurs.

A 9-month-old male German Shepherd dog was referred for evaluation of progressive exercise intolerance. Clinical examination revealed a stiff, stilted gait and marked atrophy and hypotonia of skeletal muscle. The dog had raised creatine kinase (181 U/liter), lactate dehydrogenase (510 U/liter), and aspartate aminotransferase (123.6 U/liter) levels, suggesting a muscle disease. Histochemical evaluation of muscle biopsies revealed the presence of subsarcolemmal oxidative activity, reduced nicotinamide adenine dinucleotide, and succinate dehydrogenase, and the absence of cytochrome oxidase activity. Ragged red fibers were demonstrated with Gomori trichrome stain. Ultrastructural examination of the muscle confirmed the presence of subsarcolemmal accumulations of mitochondria and morphologically atypical mitochondria.

This study examines apoptosis and viral neuropathogenesis in a murine model infected with vesicular stomatitis virus (VSV). VSV induces apoptotic cell death in cultured cell lines, raising the possibility that apoptosis of infected neurons and other target cells may contribute to disease and mortality. To determine whether or not VSV induces apoptosis in neural tissues, mice were inoculated intranasally with VSV. At 24, 48, 72, 96, and 120 hours postinfection, brain tissues were assayed for the presence of viral RNA by in situ hybridization and viral antigen by immunohistochemistry. Apoptosis was identified by in situ terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling and electron microscopy. Viral replication and lesions were observed predominantly in central nervous system neurons. Apoptotic cell death was restricted to the same regions of the brain in which infected cells and tissue injury were identified. Results suggest that VSV-induced apoptosis is a mechanism causing cell death, tissue injury, and mortality in VSV-infected mice.

The objective of this study was to determine whether vaccination with bacterins commonly used in the USA, when administered at a time typical of US protocol, enhances porcine circovirus type 2 (PCV2) replication and the incidence and severity of clinical signs and lesions characteristic of postweaning multisystemic wasting syndrome (PMWS) in conventional pigs. Sixty-one pigs free of PCV2 were randomly assigned to four groups. Groups 1 (n = 15) and 2 (n = 15) pigs served as sham-inoculated negative controls. Groups 3 (n = 14) and 4 (n = 17) pigs were inoculated intralymphoid with PCV2 field isolate ISU-40895. Pigs in groups 2 and 4 were vaccinated with Actinobacillus pleuropneumoniae (APP) and Mycoplasma hyopneumoniae (M. hyopneumoniae) bacterins 21 days before and again 1 day before inoculation with PCV2. Mild transient respiratory disease and diarrhea were observed from 13 to 34 days postinoculation (DPI) in pigs in groups 3 and 4. Half the pigs from each group were necropsied at 22 and 34 DPI, respectively. Moderately enlarged, tan-colored lymph nodes were observed in the majority of pigs in groups 3 and 4. There was a significantly (P < 0.05) longer length of viremia (2.14 ± 0.26 versus 4.44 ± 0.23 weeks), a higher copy number of the PCV2 genome in serum, a wider range of tissue distribution of PCV2 antigen, and an increased severity of lymphoid depletion in pigs vaccinated with commercial APP and M. hyopneumoniae vaccines and inoculated with PCV2 compared with PCV2-inoculated unvaccinated pigs. Swine producers and veterinarians may need to consider changes in vaccination protocols in herds with recurrent PCV2-associated PMWS.

A clinical, morphologic, ultrastructural, and genetic study was performed on five rough-coated dachshund semisiblings with osteogenesis imperfecta (OI). Clinical signs consisted of pain, spontaneous bone and teeth fractures, joint hyperlaxity, and reduced bone density on radiography. Primary teeth were extremely thin-walled and brittle. The hallmark of the disease was a severe osteopenia characterized by impairment of lamellar bone formation in the long bones, skull, and vertebral column. No deformity or dwarfism was present. The columns of chondrocytes and primary trabeculae in the epiphyses and metaphyses were histologically normal. An abrupt failure of secondary spongiosa and lamellar bone formation was evident in the medullary and cortical zones in all animals. The few existing trabeculae consisted of woven bone. There was no increase in the number and size of osteoclasts or lacunae. In the teeth, the dentine layers were thin and lacked a tubular pattern. Ultrastructurally, osteoid apposition on bone surfaces was reduced, and small numbers of large cytoplasmic vacuoles were present in a few osteoblasts. Molecular analyses of the collagen type I-encoding genes COL1A1 and COL1A2 revealed several nucleotide differences compared with the published canine sequences but were not significant for OI. Therefore, OI in these Dachshund litters was characterized by a severe, generalized osteopenia and dentinopenia. This pattern of reduced bone formation is suggestive of defective production of collagen type I.

Five young adult pet marmosets (Callithrix spp.) were presented with weight loss (5/5); fecal retention (3/5); diarrhea (2/5); impaired locomotion (3/5); anemia (4/4); hypoproteinemia or hypoalbuminemia (3/4); elevations of creatine phosphokinase, lactic dehydrogenase, and alanine aminotransferase (3/4); and renal failure with hypercholesterolemia (2/4). All anemic marmosets had low serum vitamin E levels. The anemia responded to vitamin E and selenium therapy in two marmosets. One of the five marmosets died before presentation, and two others died despite therapy. The two marmosets necropsied had degenerative myopathy, pyogranulomatous pansteatitis, and increased erythrophagocytosis and hemosiderosis. The striated muscle and adipose tissue of both marmosets were negative for coxsackievirus ribonucleic acid by in situ hybridization. These findings suggest that vitamin E deficiency may be involved in the development of anemia, myopathy, and steatitis in callitrichids; however, in some marmosets, underlying diseases such as chronic colitis may have influenced the development of anemia and impaired vitamin E status.

Characteristic ganglion-like cell proliferation observed in the skin of Djungarian hamsters was investigated using 24 male and 24 female hamsters, 1–6 months of age, to examine the anatomic location of these ganglion-like cells and their morphologic features. One abdominal skin tumor composed of these cells and resembling proliferative fasciitis in humans was also examined. Skin ganglion-like cells were rarely observed in young animals but increased in number and extent with age, especially in males. These cells were frequently seen in the ventral and medial regions of the trunk and legs rather than in the dorsal and lateral regions. Light microscopic examination of these ganglion-like cells revealed abundant vesicular basophilic cytoplasm with delicate intracytoplasmic silver stain-positive fibrils. Ultrastructurally, these cells contained abundant rough endoplasmic reticulum and Golgi complexes with dilated cisternae; intracellular collagen fibrils were present within these cisternae. Heat shock protein 47, β-tubulin, and androgen receptor were expressed in these cells. The morphologic features of cells of one tumor resembling human proliferative fasciitis were identical to those observed in ganglion-like cells. The results of the present study suggest that these ganglion-like cells are derived from intrinsic undifferentiated mesenchymal cells in the dermis or subcutaneous adipose tissue and that any tumor-like lesion they form should be regarded as an abnormal proliferative lesion of skin ganglion-like cells rather than as proliferative fasciitis or fibroma.

We describe a case of a dog with hepatosplenic lymphoma, a disease characterized by infiltration of the liver, spleen, and bone marrow with γδ T cells, absence of peripheral lymphadenopathy, and an aggressive clinical course. Physical examination findings, hematologic and biochemical abnormalities, and clinical course of the disease in this patient were similar to those in humans. Immunophenotyping of liver and spleen aspirates supported an antemortem diagnosis of T-cell lymphoma consistent with hepatosplenic lymphoma. The diagnosis was confirmed postmortem by a combination of routine histopathology, showing a consistent pattern of organ involvement, and immunohistochemistry showing the infiltrating neoplastic lymphocytes to be T cells expressing the γδ T-cell receptor. To our knowledge, this is the first reported case of hepatosplenic lymphoma in a dog.

Subclinical gastritis was observed in 10 of 10 baboons (Papio spp.) from a toxicity study in a research facility. The lesions were similar in xenobiotic-treated and control animals, suggesting a spontaneous rather than chemical-induced disease. Histologic examination revealed lymphoplasmacytic gastritis in the antral mucosa. The fundic mucosa contained minor, scattered aggregates of lymphocytes and plasma cells. A Warthin-Starry silver stain and ultrastructural examination revealed numerous spiral-shaped bacteria morphologically resembling Helicobacter pylori in antral glands and numerous spiral-shaped bacteria morphologically consistent with H. heilmannii-like organisms in fundic glands. Polymerase chain reaction assay of paraffin-embedded antral and fundic tissue using primers for the urease gene and 16S ribosomal ribonucleic acid gene amplified deoxyribonucleic acid fragments with a high degree of sequence homology for H. pylori and H. heilmannii. This is the first report of gastritis associated with Helicobacter-like organisms in baboons.

A tumor located in the optic nerve extended through the optic chiasm, involving the hypophysis and the hypothalamic area in a 3.5-year-old male Boxer dog. It showed a biphasic pattern in which numerous highly fibrillated, well-differentiated pilocytic areas were intermingled with pleomorphic, microcystic tumor tissue. Immunohistochemical analysis of the tumor revealed that most of the neoplastic cells were immunore-active for S-100 protein, with less intensity for glial fibrillary acidic protein (GFAP) and vimentin. A diagnosis of anaplastic astrocytoma was made on the basis of the histopathologic findings and immunohistochemical results. Moreover, there were similarities with the malignant variant of pilocytic astrocytoma described in human adults as an optic chiasmatic-hypothalamic glioma.

Polyarteritis nodosa (PAN) is an idiopathic necrotizing vasculitis affecting small- to medium-sized arteries. The disease is well recognized in humans, and PAN-like syndromes have been described in a number of other species. This report describes a case of PAN in a 6-year-old male cynomolgus macaque. The animal had necrotizing arteritis affecting vessels in the kidney, small intestine, colon, heart, spleen, mesentery, urinary bladder, and pancreas. The lesions were segmental in distribution and of varying severity and stage of development. A transmural mixed inflammatory cell infiltrate was present, often accompanied by fibrinoid necrosis of the tunica media and loss of the internal elastic lamina. Immunohistochemical staining showed that many of the infiltrating cells were T lymphocytes and histiocytes, suggesting a cell-mediated component to the pathogenesis.

The proliferation of footpad keratinocytes of canine distemper virus (CDV)—infected dogs was investigated. Footpads of 19 dogs inoculated experimentally with a virulent distemper strain (A75/17) and of two noninoculated control dogs were collected at necropsy. Dogs were divided into four groups according to results of the postmortem examination: dogs with severe distemper (group 1), dogs with mild distemper (group 2), inoculated dogs without distemper (group 3) and noninoculated dogs (group 4). There was no distinct difference of epidermal thickness among the four groups. Infection of the footpad epidermis with CDV was demonstrated using immunohistochemistry for viral nucleoprotein and in situ hybridization for nucleoprotein messenger ribonucleic acid (mRNA). Only group 1 dogs had viral antigen and mRNA in the footpad epidermis with the same distribution. Footpad epidermis of group 1 dogs had more mitotic figures in the basal layer, and significantly more basal keratinocytes were positive for the proliferation markers Ki-67 and proliferating cell nuclear antigen. Double-staining for Ki-67 and viral nucleoprotein identified rare double-labeled basal keratinocytes. These findings suggest that the presence of CDV particles in the footpad epidermis is associated with keratinocyte proliferation.

Left ventricular (LV) outflow tract-right atrial (RA) communication associated with bacterial endocarditis is described in a 6-year-old intact male Great Pyrenees dog with a 4- to 5-day history of fever, lethargy, weight loss, severe regenerative anemia, and asplenia. Typical vegetative mural endocardial lesions were observed grossly. Histologic evaluation revealed small gram-negative coccobacilli that were consistent with Bordetella avium-like organisms. These bacteria were associated with severe endocardial inflammation characterized by neutrophilic infiltration, extensive necrosis of endocardium, and fibrin deposition. LV-RA shunt (Gerbode defect) is a rare cardiac defect in humans that can be either congenital or, more rarely, secondary to septic endocarditis, valve replacement procedures, or thoracic trauma. B. avium-like organisms causing septicemia and endocarditis in immunocompromised and asplenic human patients have been described. To our knowledge, no previous descriptions of Gerbode defect associated with bacterial endocarditis in domestic animals have been reported in veterinary literature.

A female 8-month-old Simmental calf was presented with a history of a gradually enlarging mass in the ventral abdominal skin since 4 months of age. The mass was well circumscribed, lightly pigmented, and rough surfaced with many fine fissures and was attached to the skin by a relatively broad pedicle. On cut section, there was a border between the reddish-black stroma and overlying epithelium, including hemorrhagic foci of variable sizes. Histologically, the tumor was papillomatous with angiokeratomatous features and irregular hyperplasia with epidermal rete ridges and dilated vascular channels filled with blood in the superficial dermis. In the epidermis, orthokeratotic hyperkeratosis, variably sized keratohyalin granules, and many koilocytes, some of which had papillomavirus (PV) genus-specific structural antigen-positive nuclei, were also observed. Cells lining the dilated vascular spaces were positive for vimentin and alpha-smooth muscle actin but negative for factor VIII-related antigen, desmin, and PV. The lesion was regarded as an angiokeratomatous papilloma and was similar to other angiomatous lesions.

The placenta from a 300-day-gestational age, female, Arabian equine fetus was examined. Multifocal to coalescing, 0.5- to 4-cm-diameter, white, smooth nodules covered 50% of the placenta. Microscopic evaluation of the nodules revealed undifferentiated germ cells and a haphazard arrangement of immature, mesenchymal stroma, cartilage, squamous cornifying epithelium, scattered ducts and secretory acini lined by cuboidal to columnar epithelium, and mineralized foci. No umbilicus, arrangement about an axial skeleton, or organized polarity of structures was present. The lesion was diagnosed as a placental teratoma, a lesion not reported in species other than man.