JPC SYSTEMIC PATHOLOGY

SPECIAL SENSES SYSTEM

April 2024

S-V04

 

Signalment (JPC #4141684): Female juvenile green sea turtle

 

HISTORY: This turtle presented with a mass on the cornea and multiple additional masses on the skin. Initial surgery was performed to remove the masses. However, the corneal mass regrew, and the eye was enucleated and submitted for histology.

 

HISTOPATHOLOGIC DESCRIPTION: Eye, parasaggital section: Expanding the corneal and scleral epithelium and stroma is a multilobulated, pedunculated, well-demarcated, unencapsulated neoplasm composed of two populations of cells; in the first population, epithelial cells progress from a hyperplastic stratum basale to a hypertrophic stratum spinosum (acanthosis) and forming deep, anastomosing rete ridges overlying thick, bland aggregates of fibroblasts and collagen on a dense fibrovascular stroma. Anisocytosis and anisokaryosis are moderate, and there are 9 mitotic figures per 2.37 mm². The second population extends from the corneal stroma and is composed of fibroblasts in haphazard streams and bundles. Fibroblasts have indistinct cell borders, a moderate amount of eosinophilic, fibrillar cytoplasm, and an oval nucleus with finely stippled chromatin and up to two prominent, magenta nucleoli. Neoplastic cells have distinct cell borders, moderate amounts of finely granular eosinophilic cytoplasm, and an oval vesiculate nucleus with a 3-5 µm diameter, homogenous, eosinophilic intranuclear viral inclusion. The fibroblasts and corneal stroma are admixed with aggregates of lymphocytes, plasma cells, fewer macrophages (keratitis), numerous melanocytes and melanin laden macrophages (hyperpigmentation), and small caliber blood vessels (neovascularization). Within the superficial corneal stroma, there is amorphous eosinophilic material admixed with necrotic heterophils, cellular and karyorrhectic debris (lytic necrosis). Multifocally, inflammatory cells surround anisotropic material - either suture material (suture granuloma), or yellow-golden, 3 µm thick, oval, approximately 20 x 30 µm, trematode eggs with a central miracidium. The cornea multifocally displays orthokeratotic hyperkeratosis or ulceration and replacement by a serocellular crust. The iris is adhered to the cornea (anterior synechia). The lens has abundant melanin adhered to the anterior capsule. There are few lymphocytes, plasma cells, and rare heterophils within the ciliary body and iris (uveitis). There are few previously described trematode eggs within the choroid.

 

MORPHOLOGIC DIAGNOSIS: 

1. Eye, cornea: Viral fibropapilloma, green sea turtle, chelonid.
2. Eye: Trematode eggs, few.

 

ETIOLOGIC DIAGNOSIS: Herpesviral papilloma

 

CAUSE: Chelonid herpesvirus 5 (ChHV-5)

 

CONDITION: Fibropapillomatosis of sea turtles

 

GENERAL DISCUSSION:

ChHV-5:

• Double stranded DNA virus (dsDNA), Alphaherpesvirus (Scutavirus genus) -> Alphaherpesvirinae contains all herpesviruses that infect non-avian reptiles
• ChHV-5 causes benign cutaneous fibropapillomas and internal sarcomas of marine turtles
• Neoplasia other than fibropapillomatosis is rare in sea turtles (Diaz-Delgado, J Comp Pathol, 2019)
• Primarily affects green sea turtles, but documented in every species of sea turtle
• ChHV-5 has been documented in healthy animals, suggesting fibropapillomatosis is a multifactorial disease
• Suspected horizontal transmission; superspreaders implicated in propagating the virus in naïve populations
• Stressors that may predispose juveniles to infection: recent migration, adapting to new environments, social dynamics when encountering new populations, parasitism (especially with spirorchiid trematode ova), elevated water temperatures, increased local human activity, and toxic algal blooms

 

PATHOGENESIS:

• Viral attachment occurs when virion glycoprotein spikes bind host cell receptors, the viral envelope fuses with host cell plasma membrane, the nucleocapsid enters the cytoplasm, and then the DNA-protein complex is released and enters the nucleus and halts host cell macromolecule production; following viral replication, virions bud through host cell plasma membrane to gain envelope 
• Capsid protein VP26 is common component of many herpesviruses, which remains in the cytoplasm when no viral replication is occurring; VP26 translocates to nucleus during viral replication
• Demonstrated F-VP26 in the nucleus of cells with intranuclear viral inclusions confirms active viral replication takes place in these cells
• Transmission is sporadic, and not necessarily correlated with cells with intranuclear viral inclusions

 

TYPICAL CLINICAL FINDINGS:

• Cutaneous fibropapillomas; despite being benign, vision, breathing, or feeding may be compromised depending on location of lesions
• May interfere with normal swimming locomotion

 

TYPICAL GROSS FINDINGS:

• Tumors may be flat and plaque-like lesions, to raised and exophytic, gray to black, verrucous masses, possibly greater than 30 cm in diameter
• Typically arise from the skin around the eyes, mouth, and limbs, but are reported on the cornea, and the surfaces of the carapace and plastron
• Internal lesions develop late in the disease and are usually well-demarcated, firm, white, smooth, fibrous to fibromyxomatous nodules on various internal organs

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

ChHV-5:

• Early bland fibroblast proliferation, followed by epidermal hyperplasia
• Exophytic nodules composed of papilliferous, hyperkeratotic projections
• Acanthosis, basal cell necrosis, clefting at the dermo-epidermal junction
• Possible subepidermal clefts, spongiosis, and epidermal inclusion cysts with inflammation
• Prominent interdigitating rete ridges extend to deep dermis
• Eosinophilic intranuclear viral inclusions are rare and transient
• Internal tumors (oral cavity, glottis, lungs, kidney, heart, liver, spleen, GI tract) arise late in disease progression
• Internal lesions have highly variable morphologies
  • Linear, interlacing, whorling patterns, or any combination
  • Compact stroma, honeycomb appearance, or myxoid appearance

Spirorchiid trematodes:

 

ULTRASTRUCTURAL FINDINGS:

• Single, linear dsDNA packaged in protein capsid, ~125 nm in diameter
• Variable envelope size, leading virions to range from ~200-300 nm in diameter
• Capsids aggregate near the nucleus and associate with keratin filaments

 

ADDITIONAL DIAGNOSTIC TESTS:

• Myxoid morphology internal lesions have been Alcianophilic
• Epithelial component of fibropapilloma is AE1/AE3 cytokeratin immunopositive
• In situ hybridization has demonstrated ChHV-5 in tumor cells
• PCR has been performed successfully on formalin fixed parrafin-embedded tissue (Diaz-Delgado, J Comp Pathol, 2019)

 

DIFFERENTIAL DIAGNOSIS:

 

COMPARATIVE PATHOLOGY:

Chelonid herpesvirus-5 in other (not green sea turtle) species:

Other Chelonid herpesviruses:

• Chelonid herpesvirus 1 (Gray patch disease): Epidermal necrosis, papules, hyperkeratosis of head, neck, flippers in green sea turtle hatchlings
• Chelonid herpesvirus 6 (Lung, eye, tracheal disease virus [LETV]): Ocular, pharyngeal, and tracheal necrosis, pneumonia in juvenile green sea turtles

Other virally induced papillomas/skin neoplasms:

• Eastern box turtles: Terrapene herpesvirus 2 (TerHV-2) is associated with fibropapillomas (Andersson, J Vet Diagn Invest, 2021)
• Freshwater and marine fish: 
  1. Lymphocystis disease virus (Iridoviridae) (LDV, I-V15) induces variably sized raised, white to tan masses on the skin, oral mucous membranes, and gills; dermal fibroblasts are extremely cytomegalic and hypertrophied
  2. Carp pox (Cyprinid herpesvirus 1) raised, waxy skin lesions with intranuclear inclusions in carp/koi.
• Lagomorphs: Domestic rabbits (Oryctolagus), cottontails (Sylvilagus), hares/jack-rabbits (Lepus): 
  1. Cottontail rabbit papilloma virus “Shope papilloma virus” (Papillomaviridae); primarily in Sylvilagus, firm warts may resemble horns on the head, neck, pinna, eyes, can progress in Sylvilagus and Oryctolagus to squamous cell carcinoma 
  2. Rabbit fibroma virus “Shope fibroma virus” (Poxviridae); in Sylvilagus and Oryctolagus induces cutaneous fibromas (I-V09); eosinophilic cytoplasmic viral inclusions are common in both epithelial cells and fibroblasts
  3. Myxomatosis (Poxviridae); Sylvilagus are carriers, Oryctolagus are clinically ill with myxomatous lesions on the face, base of ears, and anogenital skin; eosinophilic cytoplasmic viral inclusions are in epithelial cells only 
• Gray squirrels: Squirrel fibroma virus (Poxviridae) causes lesions similar to Shope fibromas in rabbits
• Bovine: Bovine papillomavirus, primarily-1 and -2 causes fibropapillomas in cattle, horses, and cats
• Cervids: Cutaneous fibromas (I-V02) caused by fibroma viruses (Papillomaviridae); intranuclear viral inclusions are inconsistent
• Equid: Equine papillomavirus, primarily -2 is associated with penile papillomas and squamous cell carcinomas

 

REFERENCES:

1. Andersson, KE, Adamovicz L, Mumm LE, et al. Detection of a novel herpesvirus associated with squamous cell carcinoma in a free-ranging Blanding's turtle. J Vet Diag Invest. 2021;33(2):348-351.
2. Diaz-Delgado J, Gomes-Borges JC, Silveira AM, et al. Primary multicentric pulmonary low-grade fibromyxoid sarcoma and Chelonid alphaherpesvirus 5 detection in a leatherback sea turtle (Dermochelys coriacea). J Comp Pathol. 2019;168:1-7.
3. MacLachlan NJ, Dubovi EJ, eds. Herpesvirales. In: Fenner's Veterinary Virology, 5^th Ed. San Diego, CA:Elsevier. 2017:208.
4. Rodriguez CE, Duque AMH, Steinberg J, Woodburn DB. Chelonia. In: Terio KA, McAloose D, St. Leger J, eds, Pathology of Wildlife and Zoo Animals. San Diego, CA:Elsevier. 2018:837-840.

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