A 5-week-old, male entire Husky cross puppy presented to the University of Saskatchewan’s, Veterinary Medical Centre (VMC) emergency service with a one-day history of abnormal neurological behaviour that included circling, ataxia, vocalization and an obtund mentation. On presentation the puppy had an inappropriate mentation, menace was absent bilaterally, normal pupillary light response was noted, a gag reflex was present and no other cranial nerve deficits were noted. The puppy was circling to the left and had an ataxic gait. There were no other significant neurological findings. Neuroanatomical localization was suggestive of multifocal central nervous system lesions within the forebrain and brainstem. The local humane society had received the dam and her 8 puppies from Northern Saskatchewan; the mother was vaccinated on arrival to the shelter. The puppies were subsequently vaccinated seven days later with a modified live vaccine (Nobivac 1 DAPPC, Merck Animal Health) after all puppies tested negative for canine parvovirus with an enzyme-linked immunosorbent assay (SNAP Parvo test, IDEXX Laboratories, Markham, ON). All the other puppies and the dam were asymptomatic with the exception of one litter mate who presented to the VMC one day prior to the puppy reported on here with a 3-day history of lethargy, increased respiratory effort and bilateral serous nasal discharge. An upper respiratory tract infection was suspected. Amoxicillin (Apotex Inc.; Toronto; ON) 22 mg/kg PO q12 for 10 days was prescribed and the puppy was discharged with instructions to be immediately weaned from the mother and isolated from the other puppies. No neurological abnormalities were noted in this or in any of the other littermates at any time point. This puppy was placed in isolation on arrival based on a suspicion of an underlying infectious disease, including possible canine distemper. Consent was obtained from the local humane society to perform diagnostics and provide supportive care. Normosol R (Hospira, Montreal, QC) fluids were given intravenously at 4 ml/kg/hr. and analgesia was provided with hydromorphone (Sandoz Inc., Boucherville, QC) 0.05 mg/kg IV q4. An emergency panel revealed a packed cell volume of 22% (26.5–35.5), total protein of 5.8 g/dl (3.7–4.8), Azotstick® (Siemens Healthcare Diagnostics Inc., Tarrytown, NY) blood urea nitrogen of 5-15 mg/dl (13.1–46.2) and blood glucose of 10.3 mmol/l (6.7–8.9). A complete blood count was also submitted to Prairie Diagnostic Services Inc. (PDS), which revealed a moderate regenerative anaemia; red blood cell count (RBC) 3.25 × 1012/L (5.8–8.5) and haematocrit (HCT) 0.22 L/L (0.39–0.56). A moderate left shift with toxic change indicative of acute inflammation was also noted; white blood cell count (WBC) 10.7 × 109/L (4.9–15.4), segmented neutrophils 8.0 × 109/L (3.0–10.0) and bands 1.0 × 109/L (0.0–0.1). Bloodwork results included age specific reference ranges relevant for this patient []. Initial differential diagnoses for the neurologic signs included canine distemper, bacterial meningitis, protozoal meningitis (e.g., toxoplasmosis), and less likely a possible unusual manifestation of rabies. Symptomatic treatment with broad spectrum antibiotics was initiated and included Metronidazole (Baxter, Mississauga, ON) 25 mg/kg IV q12, Piperacillin (SteriMax Inc., Oakville, ON) 40 mg/kg IV slowly over 30 min q6, and the intent to administer Clindamycin (Intervet, Kirkland, QC) 12.5 mg/kg PO q12. Clindamycin was unable to be administered as the puppy quickly lost his gag reflex as his mentation progressively deteriorated within the first 4 h following presentation. The puppy was losing and regaining consciousness every minute and became non-responsive to external stimuli. After further discussion with the local humane society it was decided for welfare reasons and a suspected poor prognosis to euthanize the puppy. The puppy was euthanized with intravenous Pentobarbital (Bimeda-MTC, Cambridge, ON) 2 ml/4.5 kg; death was confirmed by cardiac auscultation. No additional anaesthetic agent was required due to the puppy’s obtund mentation. The puppy was euthanized 18 h after clinical signs were first noted. A necropsy was performed at Prairie Diagnostic Services (PDS), Saskatoon, Saskatchewan the following day. The puppy was in good body condition. Significant gross findings were oedematous, mottled pink to pale red lungs, and a diffusely enlarged, pale brown liver. No oedema of the gall bladder was noted. Histopathology was performed on major organs including brain (cerebrum, thalamus, cerebellum, pons, medulla), lungs, heart, liver, spleen, eyes, bone marrow, kidneys, lymph nodes, and small intestines. Areas of hyper-cellularity in the brain centered on vessels and accompanied by acute haemorrhage were observed particularly in the corona radiata, caudate nucleus, thalamus, pons and leptomeninges. Vessels were surrounded and infiltrated by macrophages and this was associated with oedema, small amount of fibrin, necrotic inflammatory cells and haemorrhage in the Virchow-Robbin space and the adjacent neuropil. A few macrophages displayed erythrophagia. Endothelial cells were hypertrophied and often contained a large basophilic intranuclear inclusion body. Hepatocytes were diffusely, mildly vacuolated and there was rare individual cell necrosis. Hepatocyte nuclei also frequently contained large basophilic inclusion bodies. Pulmonary alveoli were filled with oedema fluid, a small amount of fibrin, red blood cells and the alveolar walls were multifocally infiltrated by macrophages. Rarely endothelial cells of interalveolar capillaries contained intranuclear inclusion bodies. Endothelial cells containing these intranuclear inclusion bodies were also commonly seen in vessels of multiple organs including in the kidneys, bone marrow, lymph nodes, liver and retina. Signs of vascular injury and haemorrhage were variably present. The main final histologic diagnoses were meningoencephalitis with vasculitis and hepatic necrosis suspected to be from a viral infection based on the presence of the intranuclear inclusion bodies. The etiological differential diagnoses were Canid Alphaherpesvirus 1 (CaHV-1), Canine Adenovirus type 1 (CAdV) and canine distemper virus (CDV) infections. Given the puppy was older than 3 weeks of age, Canine herpes virus infection was considered less likely. Immunohistochemistry for Adenovirus, CDV and Rabies were performed on brain tissue. Results were positive for Adenovirus, and negative for CDV and Rabies. CDV was, however, detected by reverse transcription PCR (IDEXX Laboratories) in a sample of whole blood collected prior to euthanasia. The immunohistochemical staining for both CAdV and CDV was performed on brain tissues at PDS on an automated staining platform (Autostainer Plus, Dako Canada Inc., Mississauga, ON). Heat-induced epitope retrieval was performed, and the primary antibodies (goat anti-CAdV, Virostat, Portland, ME and mouse anti-CDV (clone DV2–12), Custom Monoclonals International, West Sacramento, CA) were used at a 1:4000 dilution. An avidin/biotin blocking reagent (Vector Labs; Burlingame, CA) was applied before the CAdV antibody. Binding of the CAdV antibody was detected using rabbit anti-goat immunoglobulins (Vector Labs; Burlingame, CA) and an avidin-biotin immunoperoxidase complex reagent (Vector Labs; Burlingame, CA), and binding of the CDV antibody was detected using an HRP-labelled polymer detection reagent (EnVision+ System - HRP Labelled Polymer, Dako Canada Inc., Mississauga, ON). The staining was visualized using 3,3′-diaminobenzidine tetrahydrochloride (DAB) (Dako Canada Inc., Mississauga, ON) as the chromogen. CDV antigens were not detected. However, numerous cells with strong cytoplasmic and nuclear staining for CAdV antigens were observed within the endothelial cells, confirming infectious canine hepatitis Further immunohistochemistry staining was also performed at the University of Minnesota Veterinary Diagnostic Laboratory to perform specific staining to differentiate between CAdV-1 and CAdV-2. Results indicated few endothelial cells had positive immunoreactivity for CAdV-1. IHC staining for CAdV-2 was negative. Follow-up of the litter revealed that none of the 7 other puppies developed neurological signs and the puppy with respiratory signs made a full recovery on antibiotics. The mother and puppies were kept for surveillance at the humane society for 2 months before being adopted out. Recheck of all puppies 5 months later revealed all puppies were doing well, with no current health concerns.