Acute Encephalitis, Polyarthritis, and Myocarditis Associated with West Nile Virus Infection in a Dog

Abstract

A 13-year-old spayed female Golden Retriever-Irish setter mix weighing 28.6 kg was presented with a 3-day history of inappetence and lethargy at the Veterinary Medical Teaching Hospital (VMTH) of the University of California, Davis in September, 2005. Two days prior to presentation, a physical examination by the referring veterinarian revealed tachycardia (96 beats/min) and pyrexia (103.1uF [39.5uC]). The results of routine CBC, blood chemistry tests, and urinalysis at that time did not reveal any clinically important abnormalities. The dog was treated with amoxicillin (20 mg/kg PO q12h) and enrofloxacin (10 mg/kg PO q12h) but did not show any improvement. On examination at the VMTH, the dog was depressed, 5% dehydrated, pyrexic (106.0uF [41.1uC]), tachycardic (140 beats/min), and tachypneic (92 breaths/min). Abnormalities of cardiac rhythm were not detected. Additional abnormalities detected on physical examination included bilateral enophthalmos, mild serous ocular discharge and conjunctivitis, moderate atrophy of the temporalis, quadriceps, and gastrocnemius muscles, and mild cranial abdominal discomfort on palpation. Examination of the ocular fundus did not reveal any abnormality. Abnormalities detected on neurological examination included decreased conscious propriocep-tive reactions in all four limbs and pain upon manipulation of the neck. The results of routine CBC and blood chemistry tests disclosed only a mild normocytic, normochromic, nonregenerative anemia (hematocrit of 37.5%; reference range, 40-50%). Cultures for aerobic and anaerobic bacteria of 5 sequentially collected blood samples were negative. Serological analyses of the blood samples for Ehrlichia canis, Anaplasma phagocytophilum, and Borre-lia burgdorferi were also negative. Abdominal ultra-sound disclosed mild mesenteric lymphadenopathy and moderate sublumbar lymphadenopathy. The dog was treated with lactated Ringer's solution a (3 mL/kg/h IV) with potassium chloride supplementa-tion a (20 mEq/L), amoxicillin b (22 mg/kg PO q8h), enrofloxacin c (10 mg/kg PO q24h), and doxycycline d (5 mg/kg PO q12h). Physical examination on day 2 revealed persistent pyrexia (105.6uF [40.9uC]), tachycar-dia (108 beats/min), and a stiff gait, but there was no evidence of joint pain or swelling on palpation. Cytologic analysis of synovial fluids collected from the carpal and tibiotarsal joints by arthrocentesis revealed mild suppurative and mononuclear inflammation. Tho-racic, abdominal, spinal, and joint radiographs did not reveal any abnormalities. On day 3, the dog became tetraparetic, and was unable to stand for longer than a few seconds. Pyrexia (104.5uF [40.3uC]) persisted, and treatment with dexa-methasone sodium phosphate e (0.2 mg/kg IV once) and hydromorphone f (0.05 mg/kg IV once) was instituted, in addition to the previously noted treatments. Neurologic examination revealed mental dullness, decreased conscious proprioceptive reactions in all four limbs, and normal segmental reflexes. Further evaluation for neurologic disease, including imaging of the brain, cerebrospinal fluid analysis, or both, was offered, but declined by the owner because of financial limitations. On day 4, the dog was normothermic and sternal recumbency was noted. Prednisone (1 mg/kg PO q12h) g and metronidazole (10 mg/kg PO q8h) h were added to the treatment regime. Despite this treatment, the clinical status of the dog progressively worsened, and by day 5 she was laterally recumbent and obtunded. The owner elected for euthanasia based on the poor prognosis. Macroscopic lesions noted at postmortem examination included severe acute pancreatitis with multifocal to coalescing fat necrosis, moderate pleural and peritoneal serosanguineous effusion, and a raised plaque on the buccal mucosa. Aerobic and anaerobic cultures of the liver, spleen, lung, and joint fluid yielded no clinically important organisms. Tissue samples were fixed in 10% buffered formalin and embedded in paraffin, and serial histologic sections were cut at 4 or 6 mm thickness for routine hematoxylin and eosin staining. Microscopic lesions were present within the brain, spinal cord, heart, pancreas, oral mucosa, and synovium. There was mild multifocal gliosis and perivascular to random lympho-plasmacytic and neutrophilic polioencephalomyelitis. The cervical spinal cord was the most severely affected and contained multiple degenerate neurons (Fig 1A). There was evidence of severe lymphocytic and neutro-philic myocarditis and vasculitis with focally extensive hemorrhage and myonecrosis, which was randomly distributed throughout the myocardium as well as subjacent to the atrioventricular valves (Fig 2A). Severe acute multifocal necrotizing perivascular and random neutrophilic pancreatitis and steatitis were detected