Poxvirus Infections
Poxvirus infections are caused by viruses of the family Poxviridae (subfamily Chordopoxvirinae). They are the largest double-stranded DNA viruses known to infect humans, with a complex brick-shaped or oval structure. What sets poxviruses apart biologically from most other DNA viruses is that they replicate and assemble entirely in the cytoplasm of the host cell, without relying on the transcription machinery in the nucleus. This is possible because the poxvirus genome encodes all the enzymes it needs to make its own RNA and DNA.
In dermatology, the Poxviridae family includes two medically important genera: Molluscipoxvirus, represented by molluscum contagiosum virus (MCV), which causes very common, benign dimpled bumps; and Orthopoxvirus, which includes mpox virus (MPXV) and smallpox virus (variola virus). In addition, members of the genus Parapoxvirus (such as orf virus and pseudocowpox virus) cause nodular skin lesions passed from animals to people. These viruses typically drive strong thickening of the epidermis (acanthosis) and produce characteristic inclusion bodies in the cytoplasm of infected cells.
At Haute-Derma, managing poxvirus skin lesions combines dermoscopy, precise removal of individual lesions and minimally invasive treatment. Whether we are dealing with scattered molluscum bumps in a child or a pustular mpox rash, our doctors aim to clear the infection completely and limit cross-infection, while using advanced skin-repair treatments to prevent secondary bacterial infection, pitted scars and dark marks.
How Poxviruses Cause Disease and Replicate in the Cytoplasm
Cytoplasmic Replication and Inclusion Bodies
- Entry and uncoating: The virus particle attaches to epidermal cells via glycosaminoglycan receptors, fuses with the cell membrane and releases its core into the cytoplasm.
- Synthesis in the cytoplasm: The virus uses its own RNA polymerase to transcribe its early genes. Replication takes place in specialized cytoplasmic zones known as viral factories.
- Inclusion body formation: Masses of virus particles and structural proteins build up in the cytoplasm of spinous cells, forming large, characteristic inclusion bodies – Henderson-Paterson bodies in molluscum contagiosum and Guarnieri bodies in orthopoxvirus infections.
Epidermal Changes and Cell Proliferation
- Poxviruses release growth factors (such as epidermal growth factor-like proteins) that keep spinous-layer cells dividing, thickening the epidermis and lengthening the rete ridges down into the dermis.
- Spinous cells at the center of the lesion swell and degenerate, forming a soft core packed with live virus particles. This is what gives the lesion its dimpled (umbilicated) appearance.
Clinical Features of Each Type
Molluscum Contagiosum (MCV):
- Who gets it: Common in preschool children, sexually active adolescents and people with weakened immunity.
- Skin lesions: Small dome-shaped bumps 2–5 mm across, smooth and shiny, pale pink or skin-colored, with a clear central dimple (umbilication).
- The molluscum core: Gentle pressure or curettage releases an ivory-white, cheesy core full of virus particles. The bumps are painless but may itch slightly.
Mpox (MPXV):
- Systemic phase: High fever of 38.5–40.0°C, severe headache, muscle aches and enlarged lymph nodes (lymphadenopathy) in the neck, armpits or groin – an important feature that helps distinguish mpox from chickenpox.
- How the rash evolves: Lesions progress in sync through each stage: flat red spots, then bumps, blisters, umbilicated pustules and finally crusts.
- Location: Very painful and burning, concentrated on the face, palms, soles, genitals and around the anus.
Orf and Pseudocowpox (Parapoxvirus):
- Caught from sheep, goats or cattle by people who farm, slaughter or care for animals.
- A single lesion on the hand or forearm that starts as a red bump, becomes a target-like (targetoid) nodule with a deep red center and white ring surrounded by a red halo, and finally forms a coarse crust.
Telling Bumpy and Blistering Rashes Apart
| Molluscum Contagiosum (MCV) | Mpox | Herpes Simplex (HSV) |
|---|---|---|
| Dome-shaped bumps with a central dimple | Umbilicated pustules that all evolve at the same pace | Clusters of small blisters on red skin |
| No fever or tiredness at all | High fever, muscle aches, clearly swollen lymph nodes | Possible mild fever during the first episode |
| Usually painless, occasional mild itch | Intense burning pain, marked itching | Tingling, stinging, burning pain |
| Sticky white core (molluscum body) | Positive MPXV PCR, Guarnieri bodies | Positive Tzanck smear, positive HSV PCR |
How Poxvirus Infections Are Diagnosed at Haute-Derma
Clinical Examination and Dermoscopy:
- Lesions are examined with a dermatoscope to identify the central dimple.
- Molluscum on dermoscopy: an opaque white or yellow-gray center (the inclusion bodies) surrounded by a ring of vessels (crown pattern) or scattered dotted vessels around the base of the bump.
Direct Cytology: The molluscum core is gently extracted with fine forceps, pressed onto a glass slide and stained with Giemsa or Gram stain. Under the light microscope, large oval Henderson-Paterson bodies (molluscum bodies) are seen inside or outside the cells.
Molecular Testing (Real-Time PCR): Used for pustules suspected to be mpox, and for giant or unusually widespread molluscum in people with weakened immunity.
How Poxvirus Infections Are Managed and Treated at Haute-Derma
Treating Molluscum Contagiosum
- In-office removal (our first choice at Haute-Derma):
- The area is numbed with EMLA 5% cream for 30–45 minutes.
- Each core is removed with a dedicated curette, or lifted out whole with sterile fine forceps. This clears the lesions immediately and has a low recurrence rate.
- Liquid nitrogen cryotherapy: a freeze–thaw cycle of 5–10 seconds for each bump.
- Topical treatments:
- Trichloroacetic acid (TCA 25–30%) or cantharidin 0.7% applied precisely to the center of each bump.
- Imiquimod 5% cream or retinoids (adapalene 0.1%, tretinoin 0.05%) applied in the evening to trigger a local immune response that makes the lesions regress.
Managing Mpox and Systemic Poxvirus Infections
- Supportive care and pain relief:
- The patient is isolated in a well-ventilated room to protect the community.
- Acetaminophen (paracetamol, 10–15 mg/kg every 4–6 hours) for fever and pain; tramadol if anogenital pain is severe.
- Preventing secondary infection and restoring the skin:
- Ruptured pustules are cleaned twice daily with octenidine dihydrochloride or nano-silver solution.
- Once the lesions have fully crusted and dried, a moisturizer with ceramides, vitamin B5 and niacinamide helps rebuild the skin barrier.
- Low-energy fractional CO₂ laser or long-pulsed Nd:YAG 1064 nm laser stimulates collagen remodeling to smooth out pitted scars after recovery.
