JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
December 2021
D-V30

 

Signalment (JPC #2548995):  Red-tailed boa constrictor (Boa constrictor constrictor).

 

HISTORY:  This 3-year-old animal was in a collection of over 40 exotic snakes of various species.  It had a 5-month history of lethargy, intermittent anorexia, weight loss, and fetid loose feces.  It was dehydrated and had petechiation of its oral mucosa and ventral scutes.

 

HISTOPATHOLOGIC DESCRIPTION:  Intestine: Multifocally 75% of the mucosal epithelial cells, lymphocytes within gut-associated lymphoid tissue (GALT), and rarely ganglion cells of the myenteric plexus contain one to multiple, 3-10 µm, intracytoplasmic, brightly eosinophilic inclusion bodies.  Extending from the superficial mucosal epithelium into the submucosa are multifocal, large (up to 3mm) areas of ulceration with loss of mucosal architecture and replacement by eosinophilic cellular and karyorrhectic debris, fibrin, edema, scattered mixed 1-2um to 1x3um bacterial colonies, and large numbers of macrophages, fewer multinucleated giant cells, and heterophils, often centered on fungal hyphae.  Fungal hyphae are 5-20 µm wide, non-septate, with 2um thick, non-parallel walls and irregular, non-dichotomous branching.  Hyphae often infiltrate the submucosal vessel walls, where they are admixed with necrotic debris, edema, and few inflammatory cells which expand the tunica media and efface the tunica intima (necrotizing vasculitis).  Multifocally scattered vessels contain fibrin thrombi with enmeshed fungal hyphae.  

 

MORPHOLOGIC DIAGNOSIS:  

1. Intestine, enterocytes; lymphocytes; and ganglion cells:  Eosinophilic intracytoplasmic inclusion bodies, numerous, Red-tailed boa constrictor (Boa constrictor constrictor), ophidian.

2. Intestine: Enteritis, ulcerative and granulomatous, subacute, multifocal, severe, with necrotizing vasculitis, fibrin thrombi, and fungal hyphae, etiology consistent with Mucorales (order) fungi (formerly Zygomyces sp.).

 

CONDITIONS:  Inclusion body disease (IBD) of boid snakes and mucormycosis (formerly zygomycosis)

 

ETIOLOGY:  Arenavirus; secondary infection with a mucormycete

 

ETIOLOGIC DIAGNOSES:  Arenaviral and zygomycotic enteritis

 

SYNONYMS: Boid inclusion body disease

 

GENERAL DISCUSSION:

• Disease caused by Reptarenavirus (or reptile-associated Arenavirus) that naturally infects boa constrictors (Boa constrictor) and Corrallus annulatus (ringed tree boa, annulated tree boa, norther annulated tree boa) with worldwide distribution in captive populations
  • Virions: pleomorphic, two segments of single-stranded RNA denoted as large (L) and small (S)
• Transmissible, progressively fatal disease almost exclusively in captive boids (boas and pythons)
• Disease characterized by formation of intracytoplasmic inclusions in peripheral blood (lymphocytes, and rarely thrombocytes, basophils, and granulocytes), in lymphocytes within lymphoid aggregates in the esophagus (esophageal tonsils), myeloid precursors in bone marrow, and virtually all tissues, especially within neurons in central nervous system, liver, stomach, esophageal tonsils, and pancreas
  • Inclusion bodies are composed of a 68KDa protein (reptarenavirus nucleoprotein, also termed inclusion body disease protein) and do not contain virus particles
• Snakes may have a concurrent neoplasm (e.g. cutaneous sarcoma, leukemia/lymphoid; one report of peripheral odontogenic fibromyxoma [Hellebuyck, V Vet Diagn Invest. 2015])
• Strict 6 month to 1 year quarantine of new boas to prevent spread; no mixing of pythons and boas
• Other non-Boidae species have been diagnosed with similar histologic findings to this disease
• Mortality often associated with secondary infections (bacterial, fungal)

 

PATHOGENESIS:  

• Numerous routes of transmission proposed:
  • Possible vector: Snake mite Ophionyssus natricis (common in epizootics)
  • Direct contact, intrauterine &/or venereal transmission
• Incubation period unknown

 

TYPICAL CLINICAL FINDINGS:

• No treatment; invariably fatal; euthanasia recommended if diagnosed
• Clinical signs and progression of disease differ between boas and pythons
• In boas:
  • Chronic regurgitation and CNS abnormalities are the most common
  • Progressive debilitation, anorexia, weight loss
  • Head tremors, disorientation, incoordination, paresis, stargazing, torticollis; can progress to flaccid paralysis
  • Secondary bacterial infections (ulcerative stomatitis, pneumonia)
• In pythons:
  • Typically no regurgitation but are anorexic
  • Earlier, more severe, rapidly progressing CNS signs with death in weeks

 

TYPICAL GROSS FINDINGS:

• Atrophy and fibrosis of spleen and pancreas
• May see pneumonia, ulcerative stomatitis, nodular lesions in stomach & esophagus

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Cytoplasmic inclusions are the most striking, distinctive diagnostic feature of IBD:1-4 µm diameter, variably-sized, eosinophilic (H&E), intracytoplasmic inclusion bodies in epithelial cells of multiple organs (biopsy & histopathology preferred tissues to sample are liver, stomach, esophageal tonsils), commonly observed with or without associated inflammation
  • Hepatocytes and renal tubular epithelial cells most commonly affected
  • Inclusions are often limited to the central nervous system in those snakes (particularly pythons) with a rapid progression of neurological disease
  • Inclusions can be seen in more systems (enteric, respiratory, and renal epithelial cells, hepatocytes, pancreatic acinar cells, and mononuclear cells) in chronic disease which is reported in boa constrictors
  • Intraneuronal inclusions in brain (neurons and glial cells) and spinal cord with nonsuppurative meningoencephalitis, neuronal degeneration, gliosis, and demyelinization
  • Intralymphocytic inclusions
• Pancreatic exocrine atrophy
• Renal granulomas
• Hepatocyte vacuolation and hydropic degeneration
• Lymphoid depletion
• Rare concurrent sarcomas, lymphoid neoplasia reported
• Secondary bacterial, fungal, and protozoal infections are common

 

ULTRASTRUCTURE:

• Inclusions: Nonviral, non-membrane bound protein being deposited by surrounding radio-dense polyribosomes

 

ADDITIONAL DIAGNOSTIC TESTS:

• Peripheral blood smears: inclusions visible (pale blue on Romanowsky-type stains), pushes leukocyte nucleus to side causing “crescent-shape” appearance

 

DIFFERENTIAL DIAGNOSIS:  

• Ophidian paramyxovirus: Proliferative pneumonia with syncytia & eosinophilic intracytoplasmic inclusion bodies resembling those of morbillivirus in size & shape
  • Commonly reported in captive viperids and crotalids, but susceptibility spans colubrids, elapids, boids
• Sunshine virus (reclassified from paramyxovirus into its own viral family): snakes exhibit neurologic signs and inappetance; lesions include white matter spongiosis and gliosis
• Secondary bacterial and fungal diseases are frequently blamed for IBD lesions

 

COMPARATIVE PATHOLOGY:

Other selected Arenaviridae; all in genus Mammarenavirus:

• Lymphocytic choriomeningitis
  • Mice (N-V18): Lymphocytic choriomeningitis; clinical signs are rare; causes vasculitis, glomerulonephritis, lymphocytic inflammation in the brain, liver, adrenal gland, kidney, lung
  • Marmosets and tamarins (D-V27): transmitted through ingestion or contact with infected mice; causes enlarged liver and spleen, jaundice, possible coagulopathy, hemorrhage within muscle, pericardial and pleural effusion; microscopically, multifocal hepatic necrosis with neutrophilic and lymphocytic inflammation
  • Other primates (including humans): transmitted through ingestion or contact with infected mice; causes transient typically nonfatal meningoencephalitis
• Lassa virus: cause of viral hemorrhagic fever in humans in West Africa (must be differentiated from Ebola); studied in guinea pigs (Bell, Vet Pathol. 2017)
• Machupo virus: cause of Bolivian hemorrhagic fever in humans; studied in guinea pigs (Bell, Vet Pathol. 2016)

 

REFERENCES:

1. Bell TM, Bunton TE, Shaia CI, et al. Pathogenesis of Bolivian Hemorrhagic Fever in Guinea Pigs. Vet Pathol. 2016;53(1):190-199.
2. Bell TM, Shaia CI, Bearss JJ, et al. Temporal Progression of Lesions in Guinea Pigs Infected With Lassa Virus [published correction appears in Vet Pathol. 2018;55(2):355]. Vet Pathol. 2017;54(3):549-562.
3. Hellebuyck T, Pasmans F, Ducatelle R, Saey V, Martel A. Detection of arenavirus in a peripheral odontogenic fibromyxoma in a red tail boa (Boa constrictor constrictor) with inclusion body disease. J Vet Diagn Invest. 2015;27(2):245-248.
4. Jacobson ER. Viruses & viral diseases of reptiles. In: Jacobson ER, ed. Infectious disease and pathology of reptiles. Boca Raton, Florida: CRC Press; 2007:410-411, 450, 452, 457.
5. Jacobson ER, Samuelson DA. Identifying reptile pathogens using electron microscopy. In: Jacobson ER, ed. Infectious disease and pathology of reptiles. Boca Raton, Florida: CRC Press; 2007:339-340.
6. Jacobson E, Oros J, Tucker S, et al. Partial characterization of retroviruses from boid snakes with inclusion body disease. Am J Vet Res. 2001; 62:217-224.
7. Lock BA, Wellehan J. Ophidia (snakes). In: Miller RE, Fowler ME, eds. Zoo and Wild Animal Medicine. Vol. 8. Philadelphia, PA: Elsevier-Saunders; 2015:70.
8. MacLachlan NJ, Dubovi EJ. Fenner’s Veterinary Virology. 5th ed. London, UK: Academic Press; 2017: 434.
9. Origgi FC, Pare JA. Isolation of pathogens. In: Jacobson ER, ed. Infectious disease and pathology of reptiles. Boca Raton, Florida: CRC Press; 2007:678.
10. Ossibof RJ. Serpentes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 908-909, 911.
11. Raymond J, Garner M, Nordhausen R, Jacobson E. A disease resembling inclusion body disease of boid snakes in captive palm vipers (Bothriechis marchi). J Vet Diagn Invest. 2001;13:82-86.
12. Schumaker J, Jacobson ER, Homer BL, Gaskin JM. Inclusion body disease in boid snakes. J Zoo and Wildlife Med. 1994;25:511-24.
13. Strik NI, Alleman AR, Harr KE. Circulating inflammatory cells. In: Jacobson ER, ed. Infectious disease and pathology of reptiles. Boca Raton, Florida: CRC Press; 2007:185, 212, 213. 
14. Vancraeynest D, Pasmans F, Martel A, et al. Inclusion body disease in snakes: a review and description of three cases in boa constrictors in Belgium. Vet Rec. 2006;158:757-761.
15. Wozniak E, McBride J, DeNardo D, et al. Isolation and characterization of an antigenically distinct 68kd protein from nonviral intracytoplasmic inclusions in boa constrictors chronically infected with the inclusion body disease virus (IBDV:Retroviridae). Vet Pathol. 2000;37:449-459.

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