JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2237801): Adult female king snake
HISTORY: This is one of six snakes in a private collection of over 250 snakes that developed vomiting and runny yellow feces over a period of 6 months. Three snakes died.
HISTOPATHOLOGIC DESCRIPTION: Lung: Diffusely faveolar septa are markedly expanded up to 100 microns by edema, fibrin, congestion, and low numbers of macrophages, lymphocytes and heterophils. Multifocally pneumocytes lining faveolar lumina are lined by plump cuboidal epithelial cells that are hyperplastic (type II pneumocyte hyperplasia). Rare pneumocytes are necrotic characterized by hypereosinophilic cytoplasm and pyknosis or karyorrhexis, or pneumocytes form 30 um diameter syncytial cells with up to 10 nuclei. Pneumocytes and syncytial cells contain variably sized and shaped 3-5 micron eosinophilic intracytoplasmic viral inclusion bodies. Multifocally, faveolar lumina are variably occluded by many degenerate heterophils, occasional macrophages, and sloughed epithelial cells admixed with abundant cellular and karyorrhectic debris (necrosis). The respiratory epithelium lining the septal apices and central lumen is diffusely hyperplastic, piling up to 7 cell layers thick. Epithelial cells are often swollen and vacuolated (degenerate) and contain similar intracytoplasmic inclusions. The pleura is diffusely expanded up to 1 mm by edema, congested vessels, low numbers of lymphocytes, plasma cells, macrophages, and heterophils.
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, interstitial, proliferative and lymphohistiocytic, diffuse, moderate, with type II pneumocyte hyperplasia, syncytial cells, and intracytoplasmic eosinophilic inclusion bodies, etiology consistent with Ferlavirus, King Snake (Lampropeltis spp.), reptile.
ETIOLOGIC DIAGNOSIS: Ferlaviral pneumonia
SYNONYMS: Ophidian (snake) paramyxovirus (OPMV), Viper pneumonitis virus, Fer-de-lance virus
- Single-stranded enveloped pleomorphic RNA virus, Family Paramyxoviridae; genus Ferlavirus
- Nomenclature of ophidian paramyxovirus no longer used because of the discovery of “Sunshine virus”, a novel neurorespiratory disease of snakes, also a paramyxovirus but not a ferlavirus
- Respiratory system, central nervous system, and pancreatic disease in snakes
- Most commonly detected in snakes, but also been described in lizards and tortoises
- Older snakes appear to be more susceptible
- Secondary infections with Pseudomonas, Aeromonas, Salmonella, Morganella and Providencia species are common
- Inhalation of contaminated respiratory secretions > virions bind and fuse to respiratory epithelium via two glycoproteins located on their envelopes:
- Hemagglutinin-neuraminidase (HN) protein - Hemagglutinin is an attachment protein and neuraminidase mediates virion release by cleaving receptor attachments
- Fusion (F) protein - Mediates fusion of the viral envelope with the cellular membrane, assists in viral attachment, and mediates syncytia formation
- Virions enter epithelial cells > transcription of viral progeny > infected cells undergo virus-induced lysis > desquamate from the mucosa > secondary bacterial infection
- Syncytia allow for spread without virus release, even in the presence of antibodies
TYPICAL CLINICAL FINDINGS:
- Nasal discharge
- Caseous debris in oral cavity
- Gaping of the mouth with abundant clear mucus
- Prostration and loss of muscle tone (appearing “stretched out”), head tremors
- +/- Dilated pupils
- Often expulsion of brownish to bloody fluid from the glottis or regurgitation of previously eaten prey
- May die within 24 hrs of initial signs; often found dead
TYPICAL GROSS FINDINGS:
- Respiratory tract is the primary target of Paramyxovirus in snakes.
- Acute suppurative pneumonia with bronchoepithelial proliferation
- Lungs are thickened, edematous, and congested
- Diffuse pulmonary hemorrhage or multifocal to diffuse accumulations of mucoid or caseous necrotic exudate within the airways and trachea
- Blood may be found in the coelomic cavity or mouth
- Terminally, many snakes expel a caseopurulent material (due to secondary bacterial infection) from the glottis which may fill the nasal passages, cover the oral mucosa, and may be partially swallowed into the upper esophagus
- Pancreatic hyperplasia and necrosis, and encephalitis also reported
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Proliferative interstitial pneumonia with syncytia with vacuolation of epithelial cells lining faveoli
- Eosinophilic intracytoplasmic inclusion bodies
- Syncytial cells and intracytoplasmic inclusions are inconsistent findings
- Pathologic changes are progressive and are most severe in the cranial portions of the lung and progress caudally
- Degeneration, necrosis, hypertrophy and hyperplasia of the epithelium lining the air capillaries, bronchioles, and often the trachea
- An exudate composed of desquamated epithelial cells, cellular debris, heterophils and erythrocytes often fills the alveoli
- Pulmonary interstitium expanded by variable numbers of lymphocytes, macrophages, heterophils and edema
- Common sequela is secondary bacterial infections (usually gram-negative) that spreads to the liver, kidneys, and the female reproductive system
- Pancreatic ductular hyperplasia and acinar necrosis with heterophilic and lymphocytic infiltrates
- Diffuse hepatic necrosis or multifocal pyogranulomatous inflammation with eosinophilic intracytoplasmic inclusions
- Nervous system
- Demyelination in brainstem and upper spinal cord
- Multifocal gliosis and minimal perivascular cuffing in brain
- Aggregates of 12-18 nm ribonucleic-like tubular particles (“herringbone” nucleocapsid material)
- Budding virions from epithelial cell plasma membrane
ADDITIONAL DIAGNOSTIC TESTS:
- RT-PCR, hemagglutination inhibition (HI), immunohistochemistry, electron microscopy, virus isolation, immunofluorescence
- Aspiration pneumonia
- Pasteurella multocida, hemolytica, P. testudinis – pyogranulomatous interstitial pneumonia
- Pseudomonas and Aeromonas
- Edwardsiella tarda, Klebsiella and Proteus
- Staphylococcus aureus and hemolytic Streptococcus
- Escherichia coli
- Mycobacterium – in acute cases, suppurative pneumonia; in chronic cases, granulomatous pneumonia
- Severe lungworm (Rhabdias) infestation
- Severe pentastome infestation
- Adenovirus – Large, basophilic intranuclear inclusion bodies
- Boid Inclusion Body Disease (Arenavirus) – Eosinophilic intracytoplasmic inclusion bodies with lack of associated inflammation
- Sunshine virus – Also forms syncytial cells in lungs, but brain lesions more prominent
- Parainfluenza -1 (Sendai virus) – Humans, monkeys, guinea pigs, rabbits, mice, rats, swine
- Parainfluenza -2 (Simian virus 5) – Humans, monkeys, dogs; plays a role in kennel cough syndrome of dogs
- Parainfluenza -3 – Humans, cattle, sheep, goats, water buffaloes, deer, horses, swine, dogs, cats, monkeys, apes, guinea pigs, and rats; part of shipping fever complex in cattle
- Newcastle Disease (Paramyxovirus 1) – Respiratory, CNS, and GI
- Avian paramyxoviruses (types 2-9) – Pathogenicity varies with infected species and virus strain
- Paramyxovirus – Caiman lizards, spiny tailed iguanas; proliferative pneumonia, syncytia, eosinophilic intracytoplasmic inclusions
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