JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-V07

 

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 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 necrotic 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-like virus 

 

ETIOLOGIC DIAGNOSIS: Molluscipoxviral dermatitis

 

CONDITION: Molluscum contagiosum

 

 

GENERAL

• Molluscum contagiosum (MC) is a mildly contagious, self‑limiting, cutaneous infection caused by a molluscipoxvirus (linear double stranded DNA)
  1. Family: Poxviridae, Subfamily: Chordopoxvirinae, Genera: Molluscipoxvirus (Molluscum contagiosum virus (MCV))
  2. See table below for other genera of poxviruses
• Molluscipoxvirus is most commonly reported in humans, reports in veterinary literature include predominantly horses
• Current literature supports that the virus that infects humans is closely related to but distinct from the virus found in equines and other animals (Fox R et al, Vet Rec. 2012, Ehmann R et al, J Gen Virol. 2021), sharing 90% sequence similarity to the closely related human molluscipoxvirus and there may be limited zoonotic potential
  1. Current literature may refer to the virus as “molluscum contagiosum-like virus” or “molluscipoxvirus-like infection” and in horses, equine molluscum contagiosum-like virus (EMCLV)
  2. It is uncertain if MC in chimpanzees is due to a human or chimpanzee-specific virus
• Found worldwide but more common in the tropics

 

PATHOGENESIS

• Transmission is via direct contact with skin lesions or fomites or through sexual contact
• Presence of a DNA sequence encoding a conserved domain of epidermal growth factor (EGF) may explain the proliferative nature of the lesions; a similar sequence has been described in some orthopoxviruses

 

TYPICAL GROSS FINDINGS

• Multiple 2‑8 mm, circular, smooth or roughened surface, gray to white papules
• Most common on the neck, chest, shoulders, limbs, and inguinal region and may remain localized to one body region (e.g. muzzle, prepuce, or scrotum) or they may become widespread  
• Papules may become umbilicated with a central pore and bleed, have a central white to brown crust, horn projection, or caseous plug or waxy exudate from the surface
• Lesions may remain for months to years without regression

 

TYPICAL LIGHT MICROSCOPIC FINDINGS

• Well-demarcated foci of epidermal and follicular hyperplasia forming pear- or flask-shaped lobules with a central pore that extend into the superficial dermis
• Keratinocytes are shed through the central pore, which enlarges to a central crater, are markedly hypertrophic or swollen 
  1. Keratinocytes within the hyperplastic stratum spinosum contain ‘molluscum bodies’: pathognomonic large eosinophilic, intracytoplasmic viral inclusion bodies that peripheralize the nuclei 
  2. As keratinocytes move toward the surface, molluscum bodies enlarge and become more basophilic (molluscum bodies in stratum corneum are often deeply basophilic)
• In the dermis subjacent to epithelial lesions, there is usually no dermal reaction

 

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
• PCR

 

DIFFERENTIAL DIAGNOSIS

• 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 MVC, which are larger and more prominent
• Equine
  1. Clinically similar to two other orthopoxvirus infections that bear resemblance to MC, but differ in having generalized and larger lesions:
     • Uasin Gishu (UGDV): Can be grown in culture unlike MCV
     • Equine viral papular dermatitis (horsepox virus) – very rare
  2. Equine coital exanthema: Cause by the equine herpesvirus-3 (EHV-3) virus, spread through sexual contact or indirect contact; limited to genitals, molluscum bodies not present

 

COMPARATIVE PATHOLOGY

• MCV infection most common in humans; in veterinary, predominately horses. Rare  reports in macropods (kangaroos and quokkas), chimpanzees, donkeys, and anecdotal reports in dogs
• Horses and donkeys:
  1. Numerous multifocal to coalescing cauliflower-like nodules or plaques; commonly affects glabrous skin; usually non-pruritic and non-painful
• 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

 

Animal poxviruses in subfamily Chordopoxvirinae

Orthopoxvirus	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
Parapoxvirus	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
Avipoxvirus	Fowlpox virus (I-V05) Pigeonpox virus
Capripoxvirus	Sheeppox virus (P-V24) Goatpox virus Lumpy skin disease virus NOTE: These may all be strains of a single virus
Leporipoxvirus	Myxoma virus (I-V10) Rabbit fibroma virus (Shope fibroma virus, I-V09A)
Suipoxvirus	Swinepox virus
Molluscipoxvirus	Molluscum contagiosum virus
Yatapoxvirus	Tanapox virus Yaba monkey tumor virus (I-V08)

*Adapted from Wachtman et al, 2012 and Maudlin EA et al, 2016

 

REFERENCES

1. Ehmann R, Brandes K, et al. Molecular and genomic characterization of a novel equine molluscum contagiosum-like virus. J Gen Virol. 2021 Mar;102(3):001357. 
2. Fox R, Thiemann A, et al. Molluscum contagiosum in two donkeys. Vet Rec. 2012;170:649-651. 
3. Lowenstine, LJ, McManamon, R, Terio, KA. Apes. In: Terio, KA, McAloose, D, St. Leger, J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:383.
4. Maudlin EA, Peters-Kennedy J.  Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6^th ed. Philadelphia, PA: Elsevier Saunders; 2016: 616,621-22. 
5. Wachtman L and Mansfield K. Viral Diseases of Nonhuman Primates. In: Abee CR, Mansfield K, Tardif S, Morris T, ed. Nonhuman Primates in Biomedical Research. Volume 2: Diseases. 2nd ed. Oxford, UK: Elsevier Inc; 2012:3, 7. 
6. Welle MW, Linder KE. The Integument. In: Zachary JF, McGavin MD, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier Mosby; 2022: 1162.

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