14.2 Poxviruses & Human Papillomavirus Manifestations

14.2 Poxviruses & Human Papillomavirus Manifestations

Overview and Biology of Cutaneous Poxviruses

The Poxviridae are among the largest and most complex animal viruses known. They are enveloped, brick-shaped or oval double-stranded DNA viruses (130–375 kilobase pairs). A critical, distinguishing biological characteristic tested on specialist examinations is that poxviruses replicate entirely within the cytoplasm of host keratinocytes, operating independently of host nuclear transcription machinery by encoding their own viral DNA-dependent RNA polymerase and capping enzymes.

Three genera of Poxviridae cause primary cutaneous disease in humans:

1. Molluscipoxvirus: Molluscum contagiosum virus (MCV types 1 to 4; exclusively human host).
2. Parapoxvirus: Zoonotic parapoxviruses producing self-limiting cutaneous nodules: Orf virus (from sheep and goats) and Pseudocowpox virus (milker's nodules, from dairy cattle).
3. Orthopoxvirus: Mpox virus (monkeypox), Cowpox virus, and historical Variola virus (smallpox).

Molluscum Contagiosum

Virology & Epidemiology

• Etiology: Molluscum Contagiosum Virus (MCV), a double-stranded DNA molluscipoxvirus. Subdivided into four genomic types (MCV-1 to MCV-4). MCV-1 is responsible for over 90% of infections in immunocompetent children; MCV-2 is disproportionately recovered from sexually active adults and immunocompromised patients.
• Transmission: Direct skin-to-skin contact, sexual intercourse, auto-inoculation (scratching), and contaminated fomites (shared bath towels, gymnasium equipment, swimming pools).

Clinical Morphology & Anatomical Distribution

• Primary Lesion: Firm, smooth, dome-shaped, discrete, pearly-white, flesh-colored, or translucent papules (1–5 mm in diameter) featuring a pathognomonic central punctate dell or umbilication. Lateral manual compression of a mature lesion extrudes a white, curd-like, pasty core known as the molluscum body (consisting of millions of virions packed inside degenerated keratinocytes).
• Pediatric Presentation: Typically localized to the trunk, axillae, antecubital and popliteal fossae, and face. Perilesional eczematous dermatitis ("molluscum dermatitis") develops in ~10% to 30% of atopic children, representing a localized cell-mediated immune reaction.
• Adult Presentation: Predominantly anogenital: lower abdominal wall, pubic area, inner thighs, vulva, penile shaft, and perineum (considered a sexually transmitted infection [STI]).
• Immunocompromised Host Presentation: In patients with advanced HIV infection (CD4 count <100–200 cells/µL) or iatrogenic T-cell immunosuppression, molluscum presents with giant (>1 cm), confluent, disfiguring, verrucous, or ecthymatous lesions heavily clustered across the face, beard region, and neck. These can mimic cryptococcosis, histoplasmosis, or penicilliosis.

Histopathology

Biopsy demonstrates a sharply demarcated, cup-shaped, inverted lobular epidermal hyperplasia expanding down into the upper dermis. Keratinocytes in the spinous and granular layers enlarge markedly and become filled with enormous, homogeneous, oval, intracytoplasmic inclusion bodies termed Henderson-Paterson bodies (molluscum bodies). These bodies start as small, eosinophilic cytoplasmic structures in the lower stratum spinosum and gradually transition into basophilic, amorphous masses that displace and compress the host keratinocyte nucleus to the cell periphery.

Natural History & European Management Guidelines

• Watchful Waiting (First-Line in Children): In immunocompetent pediatric patients, molluscum contagiosum is a benign, self-limiting condition. The median duration of an episode is 6 to 18 months. Development of erythema, swelling, and suppuration around lesions (the "BOTE" sign: Beginning Of The End) signals host cell-mediated immune recognition and imminent spontaneous resolution—it should not be mistaken for secondary bacterial infection requiring antibiotics.
• Active Procedural & Topical Options:
  • Physical / Destructive: Gentle curettage with a sharp curette under topical local anesthesia (EMLA); light cryotherapy with liquid nitrogen (5–10 second freeze); or manual enucleation with forceps.
  • Chemical Keratolysis: Topical potassium hydroxide (KOH) 5% or 10% aqueous solution applied daily at home until localized erythema appears; or topical cantharidin 0.7% solution applied in the clinic, left for 2 to 4 hours before washing off (blister beetle toxin causing acantholysis).
  • Immunomodulatory: Topical imiquimod 5% cream applied 3 nights per week.
• HIV-Associated Disease: Restoration of host cell-mediated immunity via Antiretroviral Therapy (ART) is the primary, definitive treatment for extensive facial molluscum in HIV.

Parapoxviruses: Orf & Milker's Nodules

1. Orf (Contagious Ecthyma)

• Etiology & Transmission: Caused by the Orf virus, a Parapoxvirus endemic in sheep and goats. Inoculation occurs via direct transcutaneous contact with infected animals, oral scabs, wool, or contaminated butchering shears through microtrauma on the hands or fingers.
• The Six Predictable Clinical Stages (over ~6 weeks):
  1. Stage 1 (Maculopapular): Erythematous, elevated, dark red macule or papule at the inoculation site.
  2. Stage 2 (Targetoid): Characteristic nodule displaying a three-zone targetoid architecture: a red, weeping center surrounded by a pale, necrotic white ring and an outer red erythematous halo.
  3. Stage 3 (Acute / Weeping): Exudative, boggy nodule with central ulceration and weeping.
  4. Stage 4 (Regenerative): Dry crust develops over the nodule with multiple tiny black dots.
  5. Stage 5 (Papillomatous): Exophytic, verrucous, vegetating nodule that strongly resembles a pyogenic granuloma or amelanotic melanoma.
  6. Stage 6 (Regressive): Spontaneous flattening, crust shedding, and complete healing without significant scarring.
• Management: Orf is entirely self-limiting in immunocompetent patients. Conservative local antiseptic wound care and dry dressings are standard. Surgical excision is avoided. In immunosuppressed patients with giant, non-healing, proliferative lesions, topical imiquimod 5% or topical/intralesional cidofovir has demonstrated curative efficacy.

2. Milker's Nodules (Pseudocowpox / Paravaccinia)

• Etiology: Caused by Pseudocowpox virus (Parapoxvirus). Transmitted by direct milking contact with the infected teats of dairy cattle. Clinically presents as 1 to 4 painless, blue-red or purplish, firm nodules on the fingers or hands, resolving spontaneously through stages similar to Orf over 4 to 6 weeks.

Mpox (Monkeypox)

Virology & 2022–2024 Global Outbreak Dynamics

• Etiology: Mpox virus, an enveloped double-stranded DNA virus belonging to the genus Orthopoxvirus. Subdivided into two distinct genetic clades:
  • Clade I (Congo Basin Clade): Endemic in Central Africa; historically associated with severe systemic disease and higher case-fatality rates (up to 10%). Subclade Ib emerged with enhanced human-to-human transmission.
  • Clade II (West African Clade): Historically milder disease (case-fatality <1%). Clade IIb drove the unprecedented 2022–2024 global multicountry outbreak.
• Transmission Dynamics: Unlike classical zoonotic transmission from African rodents, the global Clade IIb outbreak spread predominantly through close, intimate physical and sexual contact (frequently within dense sexual networks among men who have sex with men [MSM]), direct skin-to-skin contact with active lesions, body fluids, respiratory droplets during prolonged face-to-face interaction, and contaminated fomites (bedding, sex toys).

Clinical Presentation

• Systemic Prodrome: Abrupt fever, chills, intense cephalalgia, myalgias, back pain, and asthenia.
• Pathognomonic Physical Sign: Prominent, tender lymphadenopathy involving the submandibular, anterior/posterior cervical, axillary, and especially inguinal lymph node chains. Tender lymphadenopathy is present in >80% of mpox cases and reliably distinguishes mpox from chickenpox (VZV) and smallpox.
• Cutaneous Morphology: Firm, deep-seated, well-circumscribed, umbilicated lesions that progress synchronously through defined morphological stages within a specific anatomical area: $\text{Macule} \longrightarrow \text{Papule} \longrightarrow \text{Vesicle} \longrightarrow \text{Deep-Seated Umbilicated Pustule} \longrightarrow \text{Crust}$
• Anogenital & Mucosal Predilection: In the sexual transmission setting, lesions are densely concentrated in the anogenital region (perianal ulcers, labial, penile, and scrotal lesions) and oropharynx.
• High-Morbidity Complications:
  • Severe, excruciatingly painful proctitis presenting with rectal tenesmus, bloody purulent rectal discharge, and secondary acute urinary retention.
  • Severe necrotic tonsillitis / pharyngitis compromising airway patency.
  • Ocular Mpox: Inoculation into the conjunctiva causing severe conjunctivitis, keratitis, corneal ulceration, and permanent vision loss.
  • Secondary invasive S. aureus or S. pyogenes soft-tissue sepsis.

Diagnostic Confirmation & European Management

• Diagnostic Gold Standard: Real-time PCR performed on viral swabs taken directly from the base of unroofed vesicles or vigorous swabs of ulcerated lesion exudates.
• Specific Antiviral Pharmacotherapy:
  • Tecovirimat (TPOXX): Potent oral/IV inhibitor of the Orthopoxvirus VP37 envelope protein, preventing the formation of egress-competent enveloped virions. Indicated for severe disease, immunocompromised patients (advanced HIV with CD4 <200), extensive anogenital ulcerations, ocular involvement, and pediatric cases.
• Immunization & Prophylaxis:
  • MVA-BN (Modified Vaccinia Ankara - Bavarian Nordic; commercialized as Imvanex in Europe, Jynneos in the USA): A 3rd-generation, non-replicating, live-attenuated smallpox/mpox vaccine with an exceptional safety profile.
  • Administered as a 2-dose subcutaneous schedule (0 and 28 days).
  • Indicated as Pre-Exposure Prophylaxis (PrEP) for individuals at high behavioral risk of exposure (MSM with multiple partners, sex workers, laboratory staff handling Orthopoxviruses) and as Post-Exposure Prophylaxis (PEP) administered ideally within 4 days (up to 14 days) following high-risk exposure.

Human Papillomavirus (HPV) Virology & Molecular Oncogenesis

Genomic Organization & Life Cycle

Human Papillomaviruses (HPVs) are non-enveloped, double-stranded circular DNA viruses (~8000 base pairs) belonging to the family Papillomaviridae. Over 200 distinct genotypes have been cataloged, classified phylogenetically into genera: Alpha-papillomaviruses (mucosal genital and cutaneous lesions) and Beta-papillomaviruses (cutaneous lesions in epidermodysplasia verruciformis and organ transplant recipients).

HPVs specifically infect dividing basal keratinocytes exposed through microscopic trauma. The viral life cycle is strictly tied to the differentiation gradient of the host epithelium:

• Early Genes (E1 to E7): Expressed in the basal and suprabasal layers to coordinate viral DNA replication (E1, E2) and cell cycle entry (E6, E7).
• Late Genes (L1 and L2): Encode the major (L1) and minor (L2) structural capsid proteins, which are expressed only in the upper, terminally differentiating layers (upper stratum spinosum and stratum granulosum), where complete virions assemble and are shed through natural epithelial desquamation.

Molecular Mechanics of E6 and E7 Oncoproteins

In high-risk oncogenic HPV types (predominantly HPV 16 and 18), the viral genome frequently integrates into the host chromosome, disrupting the viral E2 repressor gene. Unchecked over-expression of E6 and E7 oncoproteins drives cellular transformation through two canonical mechanisms:

+--------------------------------------------------------------------------+
|               MOLECULAR MECHANISMS OF HPV ONCOGENESIS                     |
+--------------------------------------------------------------------------+
| HIGH-RISK E6 ONCOPROTEIN:                                                |
| Binds host E6AP (Ubiquitin Ligase) -> Forms E6/E6AP complex -> Degrades   |
| p53 TUMOR SUPPRESSOR via proteasome -> Blocks p53-dependent apoptosis    |
| and eliminates G1/S checkpoint arrest -> Activates hTERT (immortality).  |
|                                                                          |
| HIGH-RISK E7 ONCOPROTEIN:                                                |
| Binds with high affinity to active hypophosphorylated RETINOBLASTOMA (pRb)|
| -> Displaces and releases E2F TRANSCRIPTION FACTOR -> E2F transactivates |
| S-phase genes (Cyclin E/A) -> Forces unscheduled host DNA replication.   |
+--------------------------------------------------------------------------+

Cutaneous Non-Oncogenic HPV Manifestations

1. Verruca Vulgaris (Common Warts)

• Etiology: Predominantly HPV 2, 4, 7, and 1.
• Morphology: Firm, exophytic, hyperkeratotic, verrucous papules and plaques with a rough, fissured, papillomatous ("vegetating") surface. Most commonly located on the dorsum of hands, fingers, periungual areas, knees, and elbows.
• Pathognomonic Dermoscopic & Clinical Sign: Paring the hyperkeratotic surface reveals multiple tiny punctate black dots, representing thrombosed, dilated dermal capillary loops within elongated dermal papillae.
• Clinical Variants:
  • Filiform warts: Slender, elongated, finger-like projections commonly arising on the eyelids, perioral, and facial skin.
  • Butcher's warts: Large, cauliflower-like verrucous plaques on the hands of meat, fish, and poultry handlers; strongly linked to HPV 7.
  • Koebner phenomenon: Warts can appear in a linear distribution along scratch marks or surgical scars.

2. Verruca Plantaris (Plantar Warts)

• Etiology: Deep, painful endophytic warts (Myrmecia) are caused by HPV 1; superficial, painless, coalescent plaque-like warts (Mosaic warts) are caused by HPV 2.
• Clinical Morphology: Endophytic, thick, hyperkeratotic plaques embedded deeply into the weight-bearing surfaces of the soles (metatarsal heads, heels).
• Diagnostic Distinction: Plantar Wart vs Corn / Callus (Clavus):

3. Verruca Plana (Flat Warts)

• Etiology: HPV 3, 10, 28, and 41.
• Morphology: Smooth, flat-topped, slightly elevated, flesh-colored, pink, or light brown papules (1–4 mm). Characteristically occur in large numbers on the face, forehead, chin, dorsal hands, and shins. Display prominent linear Koebnerization triggered by scratching or shaving.

Treatment Modalities for Cutaneous Warts

• Topical Keratolysis (First-Line Home Therapy): Salicylic acid (15% to 40%) in collodion or plaster base. Applied daily following gentle paring and hydration with warm water for 8 to 12 weeks. Stimulates epidermal shedding and induces localized mild inflammation.
• Cryotherapy: Liquid nitrogen applied via open spray or cotton-tipped applicator (two freeze-thaw cycles of 10–15 seconds each) repeated every 2 to 3 weeks. Induces ice-crystal cellular lysis and necrosis of infected keratinocytes.
• Second-Line / Refractory Options: Topical 5-fluorouracil (5-FU) cream (often combined with salicylic acid); intralesional bleomycin injections (induces acute microvascular thrombosis and DNA scission; causes painful blackened eschar); pulsed dye laser (PDL, targeting dermal capillaries); and topical cantharidin.

Anogenital HPV & Mucosal Pathologies

1. Condylomata Acuminata (Anogenital Warts)

• Etiology: Over 90% of benign anogenital warts are caused by "low-risk" non-oncogenic HPV types 6 and 11.
• Morphology: Soft, moist, fleshy, pink, whitish, or hyperpigmented exophytic papules with a cauliflower-like, sessile, or pedunculated architecture. Located on the moist mucosal and cutaneous surfaces of the external genitalia (penile foreskin, coronal sulcus, shaft, frenulum, vulva, labia, introitus), perineum, perianal skin, and anal canal.

European Guideline Management (IUSTI / EADV Guidelines)

+--------------------------------------------------------------------------+
|                ANOGENITAL WARTS: THERAPEUTIC REGIMENS                    |
+--------------------------------------------------------------------------+
| PATIENT-APPLIED REGIMENS:                                                |
| - Podophyllotoxin 0.5% sol / 0.15% cream: Antimitotic (tubulin poison).  |
|   Bid x 3 consecutive days/week, up to 4-5 wks. CONTRAINDICATED in PREG. |
| - Imiquimod 5% cream: TLR-7 agonist (IFN-a, IL-12). 3x/wk at bedtime     |
|   wash off 6-10 hrs, up to 16 wks. Lowest recurrence rate (immune memory)|
| - Sinecatechins 10%/15% ointment: Green tea extract. Tid up to 16 wks.   |
|                                                                          |
| CLINICIAN-APPLIED REGIMENS:                                              |
| - Cryotherapy (liquid nitrogen): Weekly/biweekly. SAFE in PREGNANCY.     |
| - Trichloroacetic Acid (TCA 80-90%): Caustic chemical. SAFE in PREG.     |
| - Surgical Excision / Electrosurgery / CO2 Laser: For extensive/bulky.   |
+--------------------------------------------------------------------------+

High-Risk Oncogenic HPV & Premalignant / Malignant Lesions

1. High-Risk Genotypes & Anogenital Neoplasia

"High-risk" oncogenic mucosal HPVs (HPV 16 and 18, followed by types 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68) are the primary drivers of cervical intraepithelial neoplasia (CIN) and cervical carcinoma, anal intraepithelial neoplasia (AIN) and anal squamous cell carcinoma (SCC), vulvar intraepithelial neoplasia (uVIN), penile intraepithelial neoplasia (PeIN), and oropharyngeal SCC (especially tonsillar and base of tongue).

2. Bowenoid Papulosis

• Etiology: Driven by high-risk mucosal types, overwhelmingly HPV 16.
• Demographics: Young, sexually active adults (20–40 years of age).
• Clinical Presentation: Multiple discrete, smooth, flat-topped, velvety, reddish-brown, violaceous, or hyperpigmented papules and small plaques distributed over the penile shaft, prepuce, vulva, perineum, or perianal folds. Clinically resembles flat warts, seborrhoeic keratoses, or lichen planus.
• Histopathology: Paradoxically aggressive appearance demonstrating intraepidermal squamous cell carcinoma in situ (Bowen disease architecture): complete loss of epidermal maturation, full-thickness cellular atypia, pleomorphic "windblown" hyperchromatic nuclei, dyskeratotic cells, and abundant atypical mitotic figures.
• Clinical Course & Management: In immunocompetent patients, Bowenoid papulosis behaves clinically as an indolent process with low risk of invasive transformation (<1–2%), though lesions can persist or recur. In immunocompromised patients, the risk of progression to invasive SCC is markedly elevated. Standard management includes local conservative ablation (cryotherapy, laser, imiquimod 5% cream). Partner advice: Because the lesion carries high-risk HPV 16, sexual partners should be encouraged to attend cervical or anogenital screening as appropriate.

3. Giant Condyloma of Buschke-Löwenstein

• Etiology: Caused by low-risk HPV 6 and 11 (rarely high-risk types).
• Pathology & Behavior: A massive, slowly growing, exophytic, cauliflower-like, foul-smelling, destructive tumor of the perianal, vulvar, or penile region. Histopathologically, it represents a well-differentiated, low-grade verrucous carcinoma.
• Distinguishing Clinical Behavior: It is characterized by extensive, aggressive local infiltration into the deep dermis, subcutaneous adipose tissue, corpus cavernosum, and rectum, forming chronic fistulae and sinuses. It does not metastasize to regional lymph nodes. Definitive treatment requires wide local surgical excision with clear margins.

Epidermodysplasia Verruciformis (EV)

Molecular Genetics & Pathogenesis

Epidermodysplasia Verruciformis (EV / Lewandowsky-Lutz dysplasia) is a rare genodermatosis inherited in an autosomal recessive manner.

• Mutations: Loss-of-function homozygous mutations in either the EVER1 (TMC6) or EVER2 (TMC8) gene located on chromosome 17q25.
• Mechanism: The EVER1 and EVER2 genes encode integral membrane proteins localized to the endoplasmic reticulum that form a complex with zinc transporter proteins (ZnT-1). Deficiency of the EVER/ZnT-1 complex disrupts intracellular zinc homeostasis within keratinocytes, selectively crippling host cell-mediated cytotoxic T-cell immunity against ubiquitous beta-papillomaviruses (HPV 5 and 8, as well as types 9, 12, 14, 17, 20, 47).

Clinical Presentation

• Onset: Begins in early childhood (ages 3 to 10 years).
• Morphological Spectrum:
  1. Widespread flat, smooth, verruca plana-like macules and papules on the dorsal hands, feet, face, and neck.
  2. Broad, slightly scaly, reddish-brown, pink, or hypopigmented macules and confluent patches on the trunk, neck, and limbs resembling pityriasis versicolor.

Malignant Transformation to Cutaneous SCC

• Incidence: In 30% to 50% of patients with EV, cutaneous lesions undergo malignant transformation into invasive cutaneous squamous cell carcinomas (cSCC) and premalignant actinic keratosis-like lesions, typically in the 3rd to 4th decades of life.
• Anatomical Site: Malignant conversion occurs almost exclusively on sun-exposed anatomical sites (forehead, nose, zygomatic arches, ears, dorsum of hands).
• Oncogenic Synergy: Oncogenesis requires the critical synergistic interaction between solar ultraviolet radiation (UV-B) and the beta-HPV oncoproteins (E6 and E7) of HPV 5 and 8. Unlike alpha-HPV E6, beta-HPV 5/8 E6 does not target p53 for degradation; instead, beta-HPV E6 inhibits UV-induced apoptosis and impairs the repair of UV-induced DNA photoproducts (such as cyclobutane pyrimidine dimers) by promoting the degradation of the pro-apoptotic protein Bak and inhibiting homologous recombination repair. Unrepaired UV mutational signatures accumulate, driving progression to invasive cSCC.

Clinical Management Protocol

• Rigorous Lifelong Photoprotection: Strict avoidance of sun exposure, broad-spectrum high-factor sunscreens, UV-protective clothing.
• Total-Body Skin Surveillance: Regular dermatological examinations every 3 to 6 months for life.
• Early Surgical Intervention: Conservative surgical excision or Mohs micrographic surgery for all premalignant and invasive squamous cell carcinomas.
• Chemoprevention: Oral systemic retinoids (Acitretin 0.5–1.0 mg/kg/day) to slow down wart proliferation and retard neoplastic progression.

Prophylactic HPV Vaccines

Available Vaccine Formulations

Prophylactic HPV vaccines are non-infectious, subunit recombinant vaccines consisting of virus-like particles (VLPs) assembled from the recombinant L1 major capsid protein expressed in yeast or baculovirus systems. They elicit high titers of neutralizing IgG antibodies that transudate into mucosal and cutaneous secretions, blocking initial viral attachment to the basal lamina.

European Administration Guidelines

• Target Population: Routine universal vaccination of both girls and boys prior to sexual debut (recommended at ages 9 to 14 years).
• Two-Dose Schedule (Ages 9 to 14 years): Administered at 0 and 6 to 12 months.
• Three-Dose Schedule (Age ≥ 15 years or Immunocompromised): Administered at 0, 1 to 2, and 6 months. All HIV-infected or immunocompromised individuals must receive the 3-dose schedule regardless of age.
• Important Clinical Rule: The vaccines are strictly prophylactic, not therapeutic. They do not accelerate clearance of pre-existing HPV infections or pre-existing clinical lesions.