JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 1856170): 2.5-year-old female grey kangaroo (Macropus fuliginosus)
HISTORY: Two cutaneous masses, one on the right distal tibia and one on the left forelimb digit, were excised.
HISTOPATHOLOGIC DESCRIPTION: Haired skin: There is a focally extensive area of marked follicular epithelial and to a lesser extent epidermal hyperplasia characterized by a thickened stratum spinosum (acanthosis) that markedly compresses the interfollicular superficial dermis. Keratinocytes within the stratum spinosum frequently exhibit ballooning degeneration with pale, swollen cytoplasm and often contain a single, 15 - 20 µm, amphophilic to basophilic, irregularly shaped, intracytoplasmic viral inclusion body (molluscum body) that is surrounded by a clear halo and peripherally displaces the nucleus. There is moderate epidermal and follicular orthokeratotic and parakeratotic hyperkeratosis; the stratum corneum also contains remnant molluscum bodies. There are multifocal erosions overlain by a serocellular crust composed of viable and degenerate neutrophils, fibrin, erythrocytes, and high numbers of expelled molluscum bodies. The subjacent dermis is infiltrated by dense, nodular aggregates of moderate numbers of lymphocytes, plasma cells, macrophages, and fewer viable and degenerate neutrophils.
MORPHOLOGIC DIAGNOSIS: Haired skin: Hyperplasia, epidermal and follicular, marked, with parakeratotic and orthokeratotic hyperkeratosis, lymphoplasmacytic and histiocytic dermatitis, and numerous intracytoplasmic viral inclusion bodies (molluscum bodies), grey kangaroo (Macropus fuliginosus), marsupial
ETIOLOGY: Molluscum contagiosum virus
ETIOLOGIC DIAGNOSIS: Molluscipoxviral dermatitis
CONDITION: Molluscum contagiosum
· Mildly contagious, self‑limiting, cutaneous infection primarily of humans caused by a molluscipoxvirus (linear double stranded DNA)
· Transmission via direct skin-to-skin contact and through infected fomites
· May be anthropozoonosis (infectious disease in which the etiologic agent is carried by humans and transferred to other animals)
· Immunocompromised animals are more susceptible
· Clinical, histological, and ultrastructural similarity of lesions have been reported in birds, (chickens, sparrows, and pigeons) chimpanzees, horses, donkeys, South American sea lions, macropod marsupials
· World-wide distribution
· Transmitted through direct contact with skin lesions and fomites, or through sexual contact in humans
· Presence of a DNA sequence encoding a conserved domain of epidermal growth factor may explain the proliferative nature of the lesions; a similar sequence has been described in some orthopoxviruses
· Molluscum contagiosum viral protein binds to FADD using a death effector domain-mediated interaction that results in interference with apoptotic signaling pathways and protects cells from Fas- and TNFR-induced apoptosis
TYPICAL GROSS FINDINGS:
· Multiple, 1 ‑ 8 mm, circular, smooth or roughened surface, gray to white papules
· Umbilicated with a central pore; often a caseous plug or waxy exudate
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Well-demarcated foci of epidermal hyperplasia and hypertrophy forming pear or flask shaped lobules in the superficial dermis
· Markedly hypertrophic or swollen, brightly eosinophilic, dyskeratotic individual centrally enlarged keratinocytes
· Contain pathognomonic large intracytoplasmic viral inclusion bodies ‘molluscum bodies’ that peripheralize the nuclei
· Electron dense, intranuclear particles that spare the nucleolus in keratinocytes of the stratum spinosum immediately superficial to the basal cells
· Intracytoplasmic, large clusters of oval to brick-shaped pox virions within keratinocytes
· Individual mature virions measure 300 x 200 x 100 nm and contain a biconcave nucleoid and two lateral bodies
· As keratinocytes move toward the surface, molluscum body enlarges
· In the dermis subjacent to epithelial lesions, fibroblasts have bizarre nuclei, and virus or inflammatory cells are absent
ADDITIONAL DIAGNOSTIC TESTS:
· Cytology: Sebum-like material expressed from the lesions and stained with Wright’s stain may contain keratinocytes with large, basophilic cytoplasmic inclusion bodies
· Viral Papillomas: Swollen, degenerate keratinocytes in viral papillomas may contain condensed eosinophilic cytoplasmic aggregates of keratin due to the cytopathic effects of the virus; these differ from the characteristic molluscum bodies with molluscipoxvirus which are larger and more prominent
· Chimpanzees: Multifocal to coalescing, circular, gray to white papules with smooth or roughened surface and depressed centers on the palms and soles of feet, face, eyelids, and inguinal area
· Horses and donkeys: Numerous multifocal to coalescing cauliflower like nodules or plaques; commonly affects glabrous skin; usually non pruritic and non painful
· Clinically similar to two other orthopoxviral infections that bear resemblance to molluscum contagiosum, but differ in having generalized and larger lesions:
· Uasin Gishu (UGDV): can be grown in culture unlike molluscum contagiosum
· Equine viral papular dermatitis (horsepox virus)
Animal poxviruses in subfamily Chordopoxvirinae5
· Cowpox virus
· Vaccinia virus (buffalopox virus, rabbitpox virus)
· Horsepox virus
· Camelpox virus
· Ectromelia virus (mousepox virus) (I-V06)
· Monkeypox virus
Unassigned member of the genus:
· Uasin Gishu disease virus
· Orf virus (contagious pustular dermatitis virus, contagious ecthyma virus) (I-V11, D-V22)
· Pseudocowpox virus (milker's nodule virus)
· Bovine papular stomatitis virus (D-V21)
· Parapox virus of red deer
Unassigned members in the genus:
· Auzduk disease virus (camel contagious ecthyma virus)\
· chamois contagious ecthyma virus
· sealpox virus
· Fowlpox virus (I-V05)
· Pigeonpox virus
· Sheeppox virus (P-V24)
· Goatpox virus
· Lumpy skin disease virus
· Myxoma virus (I-V10)
· Rabbit fibroma virus (Shope fibroma virus, I-V09A)
· Swinepox virus
· Molluscum contagiosum virus
· Tanapox virus
· Yaba monkey tumor virus (I-V08)
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