Pathology in Practice

Sally E. Henderson Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Elizabeth S. Clark Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Paul C. Stromberg Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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M. Judith Radin Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Maxey L. Wellman Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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History

A 10-week-old 1.6-kg (3.5-lb) sexually intact male mixed-breed dog was evaluated because of progressive nasal discharge and chemosis, sudden onset of seizures, respiratory distress, and lethargy. The puppy had been purchased from a local pet store 1 week prior.

Clinical Findings

On physical examination, the puppy was dull and unresponsive, tachycardic, and tachypneic. The puppy was 7% to 10% dehydrated and had pale mucous membranes, severe chemosis with marked scleral injection, and diffuse corneal edema in both eyes (Figure 1). Harsh bronchovesicular lung sounds were auscultated in all thoracic quadrants. Moderate abdominal distension was present. A full neurologic examination could not be performed. However, the puppy had motor activity in all 4 limbs, and palpebral reflexes were intact. During examination, the puppy had 2 seizure episodes of 60 to 90 seconds’ duration each. Thoracic radiography revealed a diffuse interstitial and alveolar pattern in the right middle lung lobe, consistent with aspiration pneumonia. Hematologic and serum biochemical analyses revealed abnormalities (Table 1).

Figure 1—
Figure 1—

Photograph of a 10-week-old male mixed-breed puppy with respiratory distress and acute onset seizures. Notice the marked chemosis.

Citation: Journal of the American Veterinary Medical Association 247, 12; 10.2460/javma.247.12.1375

Table 1—

Hematologic and serum biochemical abnormalities detected at the initial evaluation of a 10-week-old male mixed-breed puppy with respiratory distress and acute onset seizures.

Hematologic abnormalitiesBiochemical abnormalities
VariableValueReference rangeVariableValueReference range
Hct (%)1737–56Creatinine (mg/dL)0.00.6–1.6
Hemoglobin (g/dL)5.912.1–18.8Phosphorus (mg/dL)2.83.2–8.1
RBC count (X 1012 RBCs/L)3.04.8–8.1Calcium (mg/dL)5.99.3–11.6
Mean corpuscular volume (fL)6367–79Sodium (mEq/L)135143–153
Mean corpuscular hemoglobin concentration (g/dL)31.032.5–34.8Chloride (mEq/L)101.2109–120
RBC distribution width (%)16.911.5–14.6Potassium (mEq/L)3.54.2–5.4
Absolute reticulocyte count3.6< 60Osmolality calculated (mOsm/kg)267285–304
Platelet count (X 109 platelets/L)65108–433Alkaline phosphatase (U/L)19515–120
Total leukocyte count (X 109 cells/L)17.54.1–15.4Corticosteroid-induced alkaline phosphatase (U/L)210–6
Neutrophil count (X 109 cells/L)12.43.0–10.4Creatine kinase (U/L)46150–400
Band neutrophil count (X 109 cells/L)0.40–0.1Total protein (g/dL)3.95.1–7.1
Lymphocyte count (X 109 cells/L)0.71.0–4.6Albumin (g/dL)2.22.9–4.2
   Globulin (g/dL)1.72.2–2.9

Additional hematologic findings included mild toxic change in neutrophils and moderate anisocytosis. Values of other clinicopathologic variables were within reference ranges.

A blood smear and a conjunctival scraping were submitted for cytologic evaluation. One day after initial evaluation, repeated hematologic analyses revealed a low-normal leukocyte count (6.7 × 109 leukocytes/L; reference range, 4.1 × 109 leukocytes/L to 15.4 × 109 leukocytes/L). The puppy's condition continued to decline, and it was euthanized 2 days after initial evaluation by means of an IV injection of euthanasia solution. A complete necropsy was performed.

Formulate differential diagnoses from the history, clinical findings, and Figure 1 and Table 1—then turn the page →

Cytologic and Histopathologic Findings

Evaluation of the blood smear revealed single to multiple, variably sized, amorphous eosinophilic inclusions in occasional neutrophils, lymphocytes, and monocytes only in slides stained with a commercial quick stain,a but not in those stained with a differential Wright-Giemsa–like stainb (Figure 2). These inclusions were interpreted as canine distemper virus (CDV) inclusions.

Figure 2—
Figure 2—

Photomicrographs of peripheral blood smears from the puppy in Figure 1. A—Multiple variably sized amorphous eosinophilic inclusions are present in a neutrophil (arrows). Commercial quick stain; bar = 10 μm. B—In a lymphocyte, a clear inclusion is evident (arrow). Wright-Giemsa–like stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 247, 12; 10.2460/javma.247.12.1375

Microscopic examination of the conjunctival scraping revealed moderate to marked cellularity. Most cells were hyperplastic squamous epithelial cells. Occasional epithelial cells contained 1 to several round, oval, or irregularly shaped eosinophilic cytoplasmic inclusions of various sizes, interpreted as CDV inclusions (Figure 3).

Figure 3—
Figure 3—

Photomicrograph of conjunctival scraping from the puppy in Figure 1. Several epithelial cells contain 1 to several round, oval, or irregularly shaped eosinophilic cytoplasmic inclusions of various sizes (arrows). Commercial quick stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 247, 12; 10.2460/javma.247.12.1375

Histologic assessment of various tissue samples revealed panlymphocytolysis of the spleen, lymph nodes, thymus, and tonsils. There was evidence of widespread septicemia, vasculitis, and a spectrum of individual cell death, including pyknosis and karyorrhexis, in the samples of brain, pituitary gland, spinal cord, tongue, lungs, liver, kidneys, and conjunctiva. Large 1- to 3-μm intracytoplasmic and intranuclear eosinophilic viral inclusions consistent with CDV were identified in urinary bladder epithelium, lymphoid organs (tonsillar epithelium, vascular endothelial cells, and histiocytes), and the CNS (vascular endothelial cells, neurons, astrocytes, and ependymal cells). There was a predominance of progranulocytes and metamyelocytes in the bone marrow, but the myeloid-to-erythroid ratio was within expected limits. Megakaryocyte count appeared mildly low. No viral inclusions were identified in the bone marrow. Results of a quantitative real-time reverse transcription PCR assay performed on samples of urine, conjunctiva, and whole blood confirmed CDV infection.

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: marked widespread epithelial and lymphoid necrosis with vasculitis and intralesional intracytoplasmic and intranuclear inclusions consistent with canine Morbillivirus infection.

Case summary: CDV infection in a 10-week-old mixed-breed puppy.

Comments

Canine distemper is a systemic infection of unvaccinated or improperly vaccinated domestic dogs caused by a Morbillivirus of the family Paramyxoviridae.1,2 Canine distemper virus is an enveloped, nonsegmented, singlestranded, negative-sense RNA virus that is highly contagious to a variety of carnivores, including dogs, ferrets, wild dogs, foxes, jackals, coyotes, hyenas, lions, tigers, leopards, cheetahs, seals, sea lions, and dolphins.1

Canine distemper virus is transmitted to susceptible dogs by inhalation of airborne virus or through aerosol droplets, primarily oronasal secretions.1,3 Clinical signs and duration and severity of disease are variable. Affected dogs may completely recover, become persistently infected, or die, depending on age and immune status.2,4 A 50% mortality rate has been suggested.3 The incubation period ranges from 1 to 4 weeks, and viremia is divided into 2 stages. The first viremic stage occurs within the first 24 hours after exposure, during which the virus is disseminated by respiratory tissue macrophages, monocytes, and B and T lymphocytes from the lymphoid tissues of the respiratory tract.1,3 Over the next 4 to 6 days, the virus replicates in the spleen, thymus, lymph nodes, bone marrow, mucosa-associated lymphatic tissue, and macrophages of the lamina propria of the gastrointestinal tract.1 Lymphopenia is often present 3 to 6 days after infection. Initial clinical signs are mild and vague and include lethargy, dehydration, anorexia, and weight loss.2 Biphasic fever is common at 7 to 8 days following infection and recurs 4 to 5 days later.2 Hematologic and biochemical abnormalities are often nonspecific and may reflect dehydration, inflammation, or viral effects on the bone marrow and gastrointestinal epithelium.5 The dog of the present report had marked microcytic, hypochromic nonregenerative anemia attributable to anemia of inflammatory disease and bone marrow destruction. Hypoalbuminemia, hypoglobulinemia, and electrolyte loss were likely related to anorexia and viralassociated compromise of the gastrointestinal epithelial layer. As detected in this dog, marked hypocalcemia has been reported for CDV-infected dogs, likely secondary to parathyroid gland inactivity, degeneration, and viral infection.6

The second viremic phase occurs 8 to 10 days after infection when the virus disseminates by hematogenous pathways and through CSF to epithelioid tissues and the CNS. This leads to infection of multiple tissues, including the respiratory tract, gastrointestinal tract, urinary tract, endocrine cells, lymphocytes, CNS, endothelial cells, epithelial cells, and neuroectodermal cells.1 Cytoplasmic and intranuclear inclusion bodies consisting of virus antigen can frequently be found in various organs and tissues.3 Clinical signs depend on affected tissues and include anorexia, serous nasal and ocular discharge, conjunctivitis, large pustules on the abdomen and thighs, hyperkeratosis of the digital pads, inflammation of the bronchi and larynx, and variable gastrointestinal and respiratory tract signs.1,3

Neurologic signs may be seen in addition to the catarrhal changes associated with the acute systemic form of CDV infection. However, as a result of viral persistence in the CNS, neurologic signs also can develop in the absence of other signs or 1 to 3 weeks after recovery from gastrointestinal and respiratory tract signs.1,2 Neurologic signs include myoclonus, ataxia, blindness, circling, nystagmus, conscious proprioception deficits, paresis, paraplegia, vocalization, tremor, seizures, and coma.1,3 Dogs that develop neurologic signs usually die. Occasionally, dogs recover but often have lifelong residual signs, such as persistent myoclonus.3

Canine distemper virus infection is characterized by severe leukopenia and the inability of lymphocytes to proliferate, leading to immunosuppression.1 Lymphopenia occurs secondary to stress and acute viral infection.7 The dog of the present report had leukocytosis attributed to inflammation secondary to the respiratory infection, but 1 day after initial evaluation, the dog had a low normal leukocyte count. Histologic evaluation of the bone marrow revealed a normal myeloid-to-erythroid ratio with a predominance of metamyelocytes and progranulocytes. This may have reflected the early release of more mature myeloid cells. Additionally, the marrow was characterized by an inadequate megakaryocytic response to the peripheral thrombocytopenia, as has been reported for dogs experimentally inoculated with CDV.8

An intact humoral and cell-mediated immune response is necessary for elimination of CDV.3 Anti-CDV IgM produced during the first 2 weeks of infection contributes either to viral persistence or to viral elimination and recovery when a vigorous humoral response occurs, characterized by highly specific anti–viral nucleoprotein antibodies followed by virus envelope protein–specific antibodies.1,3 A strong T-cell–mediated, CDV-specific immune response leads to virus elimination.2 The lack of an effective humoral response is associated with an acute, often fatal clinical course.3 Weak humoral and cell-mediated responses lead to systemic intracellular spread of virus to epithelial cells of gastrointestinal and urinary tracts, skin, endocrine organs, and CNS.2

Because of a lack of effective antiviral drugs, supportive care is the only treatment option for infected animals. Secondary bacterial infections are common and often contribute to death.1 For the dog of the present report, respiratory tract infection likely was the initial route of infection. Despite aggressive supportive therapy, respiratory distress secondary to pneumonia and depressed mentation persisted.

Diagnosis of CDV infection is challenging because of the number of diseases with similar clinical signs, including parvovirus, coronavirus, and bacterial infections; canine respiratory disease complex; and other causes for neurologic signs (trauma or toxin). It is also difficult to distinguish naturally acquired disease from the immune response following vaccination. Current antemortem diagnostic tests include immunofluorescence assay, serologic evaluation, cell culture, quantitative real-time reverse transcription PCR assay, and the observation of viral inclusions during cytologic or histologic evaluation.2 Inclusions are seen predominately during the acute phase of infection after dissemination of the virus to organs and tissues and are often present before severe clinical signs develop.3,8 Therefore, the observation of inclusions in cells on peripheral blood smears is infrequent; however, the presence of inclusion bodies in circulating neutrophils for up to 6 weeks following the onset of clinical signs has been documented.6 In blood smears and conjunctival scrapings from the dog of the present report, viral inclusions were prominent on slides stained with a commercial quick stain,a but not on those stained with a differential Wright-Giemsa–like stain.b Cytoplasmic inclusions appear dark magenta with commercial quick stain or similar stains,9 whereas they are clear or pale blue with Romanowsky-type stains.4 If CDV infection is a differential diagnosis, use of commercial quick staina or similar stains is recommended to more easily identify viral inclusions in appropriate specimens.

a.

Hema 3, Fisher Scientific Co LLC, Kalamazoo, Mich.

b.

Astral Diagnostics Inc, West Deptford, NJ.

References

  • 1. Carvalho OV, Botelho CV, Ferreira CGT, et al. Immunopathogenic and neurologic mechanisms of canine distemper virus. Adv Virol [serial online]. 2012; 2012: 163860. Available at: www.hindawi.com/journals/av/2012/163860/. Accessed Nov 1, 2013.

    • Search Google Scholar
    • Export Citation
  • 2. Kapil S, Yeary TJ. Canine distemper spillover in domestic dogs from urban wildlife. Vet Clin North Am Small Anim Pract 2011; 41: 10691086.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3. Beineke A, Puff C, Seehusen F, et al. Pathogenesis and immunopathology of systemic and nervous canine distemper. Vet Immunol Immunopathol 2009; 127: 118.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Raskin RE. Hematologic disorders. In: Schaer M, ed. Clinical medicine of the dog and cat. 2nd ed. London: Mansing Publishing Ltd, 2010; 227288.

    • Search Google Scholar
    • Export Citation
  • 5. Shell LG. Canine distemper. Compend Contin Educ Pract Vet 1990; 12: 173179.

  • 6. Weisbrode SE, Krakowka S. Canine distemper virus-associated hypocalcemia. Am J Vet Res 1979; 40: 147149.

  • 7. Brockus CW. Erythrocytes. In: Latimer KS, ed. Duncan & Prasse's veterinary laboratory medicine: clinical pathology. 5th ed. West Sussex, England: Wiley-Blackwell, 2011; 344.

    • Search Google Scholar
    • Export Citation
  • 8. Axthelm MK, Krakowka S. Canine distemper virus-induced thrombocytopenia. Am J Vet Res 1987; 48: 12691275.

  • 9. Atkins KA, Powers CN. The cytopathology of infectious diseases. Adv Anat Pathol 2002; 9: 5264.

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