JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-V01

 

Signalment (JPC #4044167): Tissue from a one-year-old male greyhound

 

HISTORY: Two week history of breathing difficulty, inappetence, and lethargy.  

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Affecting approximately 95% of the lung,  the alveoli and to a lesser extent bronchi and bronchioles are filled with an exudate composed of many foamy macrophages, viable and degenerate neutrophils, fewer lymphocytes, hemosiderin laden macrophages, hemorrhage, eosinophilic beaded to fibrillar material (fibrin), and pale eosinophilic homogenous fluid (edema). Alveolar septa are either necrotic, characterized by loss of cellular architecture and replacement with eosinophilic cellular and karyorrhectic debris (lytic necrosis), or are expanded up to three times normal by macrophages, fewer lymphocytes and plasma cells, and edema, and often lined by cuboidal epithelium (type II pneumocyte hyperplasia). Alveolar epithelial cells are often multinucleated with up to 10 nuclei (viral syncytia) and frequently contain 2-5µm eosinophilic intracytoplasmic and/or intranuclear viral inclusion bodies, or are shrunken and angular with hypereosinophilic cytoplasm and a pyknotic nucleus (necrotic), and often sloughed into the alveolar lumina. Subepithelial connective tissue of bronchi and bronchioles is expanded by low numbers of lymphocytes, plasma cells, macrophages, increased clear space and ectatic lymphatic vessels (edema). Bronchial and bronchiolar glands are frequently ectatic, filled with a similar exudate, lined by attenuated epithelium that rarely contains similar intracytoplasmic and intranuclear inclusion bodies. Bronchial and bronchiolar epithelium is multifocally hyperplastic with cells piling up to five layers thick, forming folds that extend into the lumina. Multifocally, the subpleural connective tissue contains few neutrophils, lymphocytes, and plasma cells, and the overlying mesothelium is diffusely reactive. 

 

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, bronchointerstitial, histiocytic and neutrophilic, diffuse, severe, with pyogranulomatous bronchopneumonia, hemorrhage, necrosis, viral syncytia, and intranuclear and intracytoplasmic viral inclusion bodies, Greyhound, canine.

 

ETIOLOGIC DIAGNOSIS: Morbilliviral pneumonia 

 

CAUSE: Canine Morbillivirus 

 

SYNONYM: Canine distemper; Canine distemper virus (CDV)

 

GENERAL DISCUSSION:  

• Important, ubiquitous in a wide range of terrestrial carnivores including canids, mustelids, procyonids (raccoons), as well as pinnipeds; ferrets particularly susceptible
• Morbillivirus genus in the Paramyxoviridae family, closely related to Rinderpest, peste de petit ruminants, measles, and phocine distemper virus (PDV)
• Irregularly shaped, lipoprotein enveloped, large RNA virus 150-250 nm in diameter with negative-sense, single-strand RNA
• Common secondary pathogens include: Bordetella, adenovirus, Bartonella, Pneumocystis, Toxoplasma, Clostridium piliforme, Sarcocystis, Encephalitozoon, Cryptosporidium, E. coli, Listeria monocytogenes (Weyna et al., J Vet Diagn Invest, 2022)
• CDV is rarely diagnosed in European dogs; there are sparse reports in healthy dogs or dogs with canine infectious respiratory disease complex (CIRDC) (Day et al., J Comp Pathol 2020)

 

PATHOGENESIS:

• Envelope studded with hemagglutinin glycoproteins that mediate attachment to host and fusion glycoproteins that allow penetration and fusion of infected host cells with uninfected cells
• Natural transmission is usually by inhalation, and the virus is shed in all excretions (especially respiratory) during the systemic phase of infection
• Shed in respiratory and oral secretions > inhalation > infects macrophages or lymphocytes of upper respiratory tract or lungs > conveyed to local lymph nodes and tonsils within 24 hours > virus replication in local lymphoid tissues > cell-associated and cell-free viremia 2 days post-infection (PI) > spread to all lymphoreticular tissues and blood lymphocytes one week PI > lymphocytolysis and leukopenia > immunosupression > dissemination to respiratory, GI, urinary, and central nervous systems via leukocyte trafficking and cell-free viremia; skin, endocrine, and exocrine glands also affected 
• In lungs, primary target cells are ciliated and non-ciliated mucosal epithelial cells > cells lyse > inhibit mucociliary clearance > predisposes to secondary infections
• Disease severity depends on immune status of host, titer of antibodies to envelope glycoprotein, age of host, and virus strain:

• Adequate humoral and cellular immunity à clear infection by 14 days
• Intermediate immunity à infection of mucosal epithelium and brain
• Poor immunity à systemic infection of epithelial tissuesà respiratory, enteric, CNS disease and shedding

• Pantropic virus; entry receptor on immune cells is CD 150 (SLAM); epithelial receptor is PVRL4 (nectin-4) (Garcia et. al, Vet Pathol, 2022)
• Fusion glycoproteins (viral F protein) facilitate penetration into cell, cell-to-cell spreading, and formation of syncytia
• Viral attachment is mediated by hemagglutinin glycoproteins (viral H protein)

 

TYPICAL CLINICAL FINDINGS:

• Systemic disease affecting respiratory, gastrointestinal, and nervous systems
• Puppies with biphasic fever, depression, anorexia, serous to mucopurulent oculonasal discharge, pharyngitis, coughing, vomiting, diarrhea (targets intestinal cryptal epithelium), hyperkeratosis of foot pads and nose, enamel hypoplasia, abortion
• Neurologic signs: Seizures, myoclonus, ataxia, paraparesis or paraplegia
• Virally-induced immunosuppression
• Thrombocytopenia (due to virus-antibody complexes on platelet membranes and direct viral infection of megakaryocytes)

 

TYPICAL GROSS FINDINGS:  

• Respiratory:

• Serous, catarrhal, or mucopurulent exudate covers nasopharynx
• Edematous lungs
• Bronchointerstitial pneumonia, with red to tan, generalized, patchy, rubbery lesions beneath pleura and at lung margins

• Lymphoid: Inapparent, atrophied, or swollen lymphoid organs
• Integument (I-V12): Hyperkeratosis of the nose and footpad (“hardpad disease”), pustular dermatitis
• Digestive: Diarrhea, congestion of small intestine, with thin walls and shortened villi (atrophy); enamel hypoplasia
• Nervous: Often inapparent gross lesions
• Ocular: Mucopurulent conjunctivitis
• Cardiovascular: Pale streaks in heart

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Nonspecific in mild cases
• Generally, eosinophilic intracytoplasmic and intranuclear viral inclusion bodies are most obvious in brain (astrocytes, neurons) and epithelial tissues (particularly urinary bladder and renal pelvis in acute disease; U-V07)
  1. Nervous tissue typically contains intranuclear inclusions
  2. All other tissues often contain intracytoplasmic inclusions

• Respiratory (lesions common):

• Bronchointerstitial pneumonia, with scant suppurative exudate in the bronchiole lumina 
• Inclusion bodies most obvious in cytoplasm of bronchial and bronchiolar epithelial cells; inclusions most prominent 10-14 days PI
• Alveolar epithelial viral syncytial cells
• Type II pneumocyte hyperplasia, +/- viral inclusions

• Hematopoietic: Lymphoid depletion in spleen, lymph nodes, thymus, GALT, BALT; thymic atrophy common in puppies

• Urinary: intracytoplasmic and rarely intranuclear inclusion bodies in swollen transitional epithelial cells of bladder and renal pelvis 
• CNS (N-V12):  

• Virus first appears within perivascular astrocytes and macrophages, with early infection of choroid plexus epithelium; CSF often contains large amounts of virus
• White matter: Demyelination in white matter tracts; most severe in cerebellum, rostral medullary velum, optic tracts, spinal cord, and around fourth ventricle
  • Lateral funiculi of the lumbosacral spinal cord most often affected (demyelination, astrocytosis, microgliosis) (Areco et al., J Comp Path 2021)
  • Astrocytes usually contain nuclear inclusions, with rare astrocyte-derived syncytia
  • Surviving animals may have sclerotic astrocytic foci with myelin loss
• Gray matter: Lesions occur less often, within cerebellum, brainstem, spinal cord, cerebral cortex
  • In early lesions, neurons may contain nuclear or cytoplasmic inclusions; affected neurons undergo necrosis, with non-suppurative perivascular inflammation that infiltrates the neuropil
  • Mild nonsuppurative meningitis
• Old dog encephalitis: Rare variant of canine distemper infection, likely caused by infection with a replication-defective virus; chronic progressive neurologic disease with perivascular lymphoplasmacytic inflammation, and intranuclear inclusions in astrocytes and neurons
• Canine distemper infection has been associated with modified live CDV vaccines, and most often manifests as neurologic disease

• Dental: Necrosis and cystic degeneration of ameloblastic epithelium leads to defective enamel (enamel hypoplasia)
• Eye: Optic neuritis, conjunctivitis, keratitis, and retinitis; intranuclear inclusions in ganglion cells and glia; with chronicity, progression to neuronal loss, retinal scarring, proliferative retinal pigmented epithelium 
• Skin: Cutaneous lesions most often affect the footpad and nose, and less often haired-skin; nuclear and cytoplasmic inclusion bodies and syncytial cells occasionally found in the epidermis
• Heart: Myocardial necrosis and mineralization 
• Bone: With experimental infection, persistence of primary spongiosa and osteoclast necrosis
• Other: Inclusion bodies, mononuclear inflammation, and degenerative changes in gastric, cholangiolar, hepatic, pancreatic ductular, epididymal, and testicular epithelium, thymic atrophy

 

ADDITIONAL DIAGNOSTIC TESTS:

• Cytology: +/- viral inclusions in erythrocytes, leukocytes, and platelets on peripheral blood smears; one or two discrete, eosinophilic, round to oval bodies in the cytoplasm; CSF tap yields lymphocytic pleocytosis +/- inclusions
• IHC, immunofluorescence, in situ hybridization, PCR (Young et. al, J Vet Diagn Invest, 2021)
• Immunoperoxidase technique: CDV antigen readily demonstrated in infected cells

 

DIFFERENTIAL DIAGNOSIS:   

Intracytoplasmic inclusions in dogs:

Intranuclear Inclusions in bronchiolar or airway epithelium:

• Canine adenovirus-2 (CAV-2) (P-V21): Large, amphophilic intranuclear inclusions in alveolar macrophages and neutrophils; intracytoplasmic inclusions and syncytial cells are not a feature; necrotizing bronchiolitis; often a co-infection with CDV
• Canine herpesvirus-1 (CHV-1)(U-V03): In acute disease, rare eosinophilic intranuclear inclusions, often within nasal mucosa; necrotizing rhinotracheitis and occasionally bronchopneumonia, especially in neonatal puppies (4-6w)
• Canine parvovirus-1 (canine minute virus): Sporadic cause of respiratory disease; mild enteritis, myocarditis in young puppies; intranuclear inclusions within villus epithelium

Other canine viral pneumonias: 

• Canine parainfluenza virus (CPIV; family Paramyxoviridae genus Rubulavirus): Most often seen as co-infection with Bordatella, though can serve as primary pathogen; tracheobronchitis and bronchiolitis, with mixed inflammation and epithelial vacuolation
• Canine respiratory coronavirus (CRCoV; genus Betacoronavirus): Mild upper respiratory tract disease with minor lung lesions; virus infects ciliated and goblet cells in the trachea, bronchi, and bronchioles
• Influenza A virus

• H3N8: Self-limiting upper respiratory tract infection, with tracheobronchial epithelial cell necrosis and uniquely causes a similar lesion in bronchial glands; less often causes bronchiolar erosion or hyperplasia, with neutrophilic luminal exudate

Canine bacterial pneumonia:  

 

COMPARATIVE PATHOLOGY: 

Other morbilliviruses in domestic and lab animal species:

• Rinderpest virus (D-V28): Erosions, ulcerations, and hemorrhagic lesions affecting oral cavity, and rarely the rumen and reticulum, in domestic cattle, buffalo, and yaks
• Peste des petits ruminants virus (goat plague, ovine rinderpest, stomatitis-pneumoenteritis complex)(P-V04): Pseudomembranous oral lesions, necrotizing tonsillitis, fibrinonecrotic tracheitis, bronchointerstitial pneumonia, fibrinohemorrhagic enteritis; intracytoplasmic and intranuclear eosinophilic viral inclusions, viral syncytia
• Measles virus (Rubeola) (P-V02): Highly contagious disease in captive NHPs
  • Old World primates: Bronchointerstitial pneumonia, Koplik’s spots (small, white foci rimmed by a raised red border within oral mucosa near opening of Stensen ducts) are considered pathognomonic but are inconsistent, lymphoid depletion
  • New World primates: Necrotizing enterocolitis, periorbital edema

Other paramyxoviruses (non-morbilliviruses) in domestic and lab animal species:

• Equine paramyxovirus (Hendra virus; genus Henipavirus)(P-V26): Sporadic cause of acute interstitial pneumonia
• Porcine paramyxovirus (Nipah virus; genus Henipavirus): Closely related to equine paramyxovirus; necrotizing vasculitis affecting arterioles, venules, and capillaries of lung, brain, renal glomeruli, and lymphoid organs; also moderate lymphoplasmcytic bronchointerstitial pneumonia and mild necrotizing bronchiolitis; occasionally eosinophilic intracytoplasmic and intranuclear inclusions in neurons and syncytial endothelial cells

Canine distemper virus in zoo and exotic species:

• Collared peccaries: Encephalitis; lesions restricted to brain, with intracytoplasmic eosinophilic inclusions in neurons
• Canidae, ursidae, and aliuridae
  • Acute lesions in non-domestic canids, as well as the few reports in free ranging ursids, are similar to those seen in domestic dogs
  • Arctic foxes: CDV associated with lipid pneumonia
  • Gray foxes: Mortality near 100%
    • Fennec fox: Case report of vaccine induced CDV and canine adenovirus-2 coinfection following vaccination with a multivalent modified live virus vaccine containing CDV and canine adenovirus-2 (Tamukai et al., J Vet Diagn Invest 2020)
    • CDV with concurrent Clostridium piliforme infection diagnosed in 2 dogs and a gray fox kit (Jacobson et al., J Vet Diagn Invest 2022)
    • Associated with concurrent clinical Sarcocystis sp. Infection in a gray fox (Neupane et. al, J Vet Diagn Invest 2023)
  • Gray wolf: Case report of severe systemic CDV infection, with evidence of canine parvovirus-2 infection in the spleen, following vaccination with a multivalent vaccine that included CDV, and canine parvovirus (Stilwell, J Vet Diagn Invest 2019)
  • Red pandas: Reports of vaccine-induced CDV infections, with lesions similar to those seen with natural infection
• Felidae: CDV is a significant concern, with lesions similar to those in other carnivores; infection of wild felids associated with unvaccinated wild dogs 
• Mesocarnivores (fishers, foxes, mink, skunk, raccoon): New England mesocarnivores are affected by a distinct clade of CDV; lesions most often noted in the lung followed by the urothelium, biliary tract, GI tract and brain (Nedle et. al, J Vet Diagn Invest, 2019)
• Mustelids: CDV, and another morbillivirus similar to phocine distemper virus, reported
  • Black-footed ferrets: Increased sensitivity
  • Striped skunks: Relatively resistant
• Procyonidae, viverridae, hyenidae, herpestidae, eypleridae, and prionodontidae: 
  • CDV reported in most listed groups; most common microscopic findings are bronchointerstitial pneumonia and generalized lymphoid depletion
  • Farmed civets: Nonsuppurative polioencephalitis has been reported in Thailand
• Xenartha, erinacoemorpha, some afrotheria, and phloidota:
  • Giant anteater: Reported in a single family group; findings similar to CDV infection in canids
  • Sloths: Natural CDV reported in 5 adult Linnaeus’s 2-toed sloths; lesions included widespread and random hepatic necrosis, lymphoid depletion, and bronchointerstitial pneumonia; absence of gross or microscopic lesions in the brain, though CDV antigen was present within meningeal vessels, choroid plexus, and ependyma (Watson et al., Vet Pathol 2020)

Other morbilliviruses in zoo and exotic species:

• Pinnipeds (fur seal, sea lion, true seal, walrus): PDV common, with similar findings to CDV in carnivores, including viral-induced immunosuppression and concurrent infections
• Cetaceans (whales, dolphins, porpoises):  
  • Cetacean morbilliviruses (CeMV; P-V03) include at least 6 strains (porpoise morbillivirus, dolphin morbillivirus, pilot whale morbillivirus, beaked whale morbillivirus)
  • Most cause pneumonia and encephalitis, with secondary infections
  • Generally, the lymph node cortex is best location to identify syncytial inclusions; gold standard for diagnosis is virus isolation utilizing VERO or SLAM cells
  • An atypical CeMV has been documented in stranded cetaceans with signs indicating chronicity including:  Profound lymphoid depletion and fatal secondary infections, with a and lack of respiratory and nervous lesions; morbillivirus detected in lymphoid tissues, but not lungs or brain
  • Brain lesions have been the sole lesion in some cetaceans that survive systemic infection

                                    

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