Seven cutaneous mast cell tumors were identified in 6 geriatric California sea lions (Zalophus californianus). All tumors were within the dermis and grossly appeared as single, or in one case two, less than 1-cm-diameter, well-circumscribed, raised nodules. The majority (6/7) of the neoplasms occurred near mucocutaneous junctions (eyelid, lip, or anus). The mast cell tumors were composed of round cells arranged in sheets with poorly granulated cytoplasm or an absence of cytoplasmic granules in routine hematoxylin and eosin-stained sections. Cytology (n = 1) showed adequate staining of mast cell granules with Diff-Quik and Wright-Giemsa stains. Immunohistochemistry for cKIT revealed cytoplasmic to membranous immunoreactivity in all tumors. Giemsa staining for metachromatic granules was inconsistent. No local recurrence or metastasis has been observed in the 5 living individuals with follow-up periods ranging from 6 to 42 months. Given these findings, similar poorly granulated mast cell tumors in geriatric California sea lions are suspected to have biologically benign behavior.

Mycobacteria (Mycobacteriaceae family) comprise five genera (Mycobacterium, Mycolicibacterium, Mycolicibacter, Mycolicibacillus, and Mycobacteroides), which include relevant animal and human pathogens. Histology is a rapid method for preemptively diagnosing mycobacteriosis, contributing to surveillance, control, and eradication. A constraint on histology is the limited sensitivity and specificity of acid-fast stains, as the number of detectable bacilli in formalin-fixed paraffin-embedded (FFPE) tissue varies and other microorganisms are acid-fast positive. Immunohistochemistry has low specificity and is cross-reactive with other bacteria. We developed an RNAscope probe-based in situ hybridization (ISH) assay, targeting a conserved sequence of 16S rRNA gene of Mycobacteriaceae, and tested it on archived FFPE tissues from 22 mammals, birds, amphibians, and fish, collected between 1999 and 2024, infected with 23 species of mycobacteria of veterinary importance, and tissue from 7 animals infected with other bacteria. Mycobacterium spp. (n = 17), Mycobacteroides spp. (n = 2), Mycolicibacter spp. (n = 1), and Mycolicibacterium spp. (n = 3) confirmed infected tissues were tested, and results were compared with 2 acid-fast stains, Ziehl-Neelsen and Fite-Faraco, and Mycobacterium spp. PCR from FFPE tissues. Hybridization signals were detected in all FFPE tissues, archived for up to 25 years, with confirmed Mycobacterium spp. (17/17; 100%), Mycobacteroides spp. (2/2), Mycolicibacter spp. (1/1), and Mycolicibacterium spp. (3/3), including cases with few or no acid-fast bacilli. Available FFPE tissues were positive by PCR (15/15, 100%). Hybridization signal was not identified in other bacterial infections. This ISH assay is a rapid screening and specific diagnostic tool for mycobacteria in FFPE tissues.

The vacuole formation (VF) rat is an autosomal recessive myelin mutant characterized by generalized tremor, hypomyelination, and periaxonal VF of the central nervous system. We previously identified a nonsense mutation in the DOP1 leucine zipper-like protein A (Dop1a, also known as Dopey1) gene located on rat chromosome 8. In this study, we investigated the kinetics of oligodendrocyte progenitor cells (OPCs) and oligodendrocytes by assessing the expression patterns of transcription factors that are involved in oligodendrocyte development. The number of small, round oligodendrocytes lacking distinct cellular processes, immunolabeled with anti-adenomatous polyposis coli (APC, clone CC1) antibody, was increased in the spinal cords of the VF rats, suggesting a disrupted maturation of oligodendrocytes. In addition, the terminal differentiation and maturation of OPCs into myelinating mature oligodendrocytes may be impaired and compensatory myelination largely could fail in the VF rat. Our findings also demonstrated that the DOP1A protein is expressed in OPCs as well as mature oligodendrocytes. Finally, the intracellular trafficking of myelin basic protein (Mbp) mRNAs may be disrupted in oligodendrocytes of the VF rats. Our data suggested that DOP1A dysfunction causes impaired differentiation and maturation of oligodendrocyte-lineage cells, resulting in hypomyelination and an impaired compensatory myelination.

Aliarcobacter butzleri is a Campylobacter-like bacteria associated with watery diarrhea in humans and is infrequently reported in nonhuman primate (NHP) populations. While clinical and microscopic features in humans are indistinguishable from Campylobacter spp. infection, descriptions of A. butzleri-associated colitis in NHP are lacking. Here, we describe the clinical and pathological features of diarrhea and colitis associated with A. butzleri in rhesus macaques using a retrospective approach. Over a 3-year period, A. butzleri was isolated from 10 macaques with diarrhea. Five of the 10 were submitted for necropsy and had features of chronic enterocolitis, consistent with existing literature. However, 40% (2/5) of the cases were characterized by ulcerative colitis, which has not previously been described as a feature of A. butzleri colitis. A. butzleri should be considered a differential diagnosis in cases of diarrhea and enterocolitis in captive rhesus macaques.

Handheld confocal laser endomicroscopy (CLE) enables an instantaneous assessment of the cellular morphology of different tumor types and margin assessment ex vivo. Here, we describe the correlation between CLE images and histology and the feasibility of incorporating this technology in assessing surgical biopsy specimens. A CLE microscope (Optiscan, ViewnVivo) acquired high-definition confocal images of surgical biopsy cases and a single autopsy case (15 canine, 1 feline, and 1 equine cases). Following minimal training on the imaging modality, 14 participants (6 anatomic pathologists and 8 anatomic pathology residents) were asked to assess 17 cases with and without signalment and clinical history. The CLE captured detailed cellular morphology and tissue microarchitecture in various surgical biopsy and select autopsy specimens. Averaging the diagnostic accuracy with and without clinical history, study participants were able to distinguish abnormal tissue in 15/17 cases, neoplasia from inflammation in 12/17 cases, and the cellular morphology of neoplasia in 8/13 cases. Across all questionnaires, there was a statistically significant improvement in the diagnostic accuracy when clinical history was provided (P-value: 3.07E-07 to .005, paired t-test). CLE enables the capture of the high-resolution microarchitecture of tissue and can be readily correlated to histology images. We demonstrated that with little training, anatomic pathologists could evaluate surgical biopsy specimens that can provide a rapid preliminary diagnosis and margin assessment.

In 2022, piggeries in southeastern Australia experienced an increase in reproductive losses and occasional neurologic disease in neonates with up to 100% mortality in some litters. Molecular testing identified a genotype IV Japanese encephalitis virus (JEV) as the etiological agent, detected for the first time in Australia. Necropsy of 235 JEV-positive domestic piglets, mostly stillbirths with 30% mummified, revealed hydranencephaly-porencephaly impacting the dorsal cerebrum as the most common lesion. Microscopically, this was characterized by varying degrees of parenchymal collapse as a result of liquefactive necrosis, hypoplasia, and dysplasia, with nonsuppurative inflammation and mineralization. In the most severe cases, hydranencephaly reduced the cerebral parenchyma to a thin membrane enclosing dilated lateral ventricles. Histologically, the affected neuroparenchyma was largely devoid of mature neurons, axons, myelin, and oligodendrocytes. What remained was mostly a dense population of IBA-1-positive histiocytes and few CD3-positive T-lymphocytes, interspersed within a dense network of GFAP-positive astrocytic processes. Immunohistochemistry for flaviviral antigen showed colocalization of viral antigen-positive neurons and necrotic foci. In less severe cases, cerebral necrosis occurred in well-demarcated, locally extensive regions or isolated gyri, sometimes with a vascular distribution, resulting in porencephaly. In addition, vascular calcification was noted, although with unknown significance and pathogenesis. Arthrogryposis, scoliosis, and kyphosis were observed in a small subset of the cases, which had myelodysplasia. Myelodysplastic changes varied and included central canal duplication, dysplastic gray matter, and bifurcation of the ventral medial sulcus. Multifocal necrosis and inflammation were also observed in the spinal cord, although the extent was typically limited.

Between June 2020 and January 2022, 10 cases of shell rot with unknown etiology were investigated in Chinese stripe-necked turtles (Mauremys sinensis) from aquaculture farms in southern Taiwan. Histology revealed gram-positive filamentous bacteria within the dermis of the limbs and the shell bone, with all cases exhibiting shell ulceration. One unusual case also showed hepatic necrosis, with consistent bacteria isolated from the liver. Full-length 16S rRNA gene sequencing of our isolates demonstrated 99.7% similarity to the Austwickia chelonae type strain and complete identity to A. chelonae L16-18, previously isolated from Chinese crocodile lizards. To our knowledge, this represents the first report of natural infection with A. chelonae in M. sinensis. The findings suggest that A. chelonae infections may originate as cutaneous lesions, and in severe cases, the disease can progress to hematogenous spread to internal viscera, such as the liver.