MPOX (Monkeypox) Disease

PATHCHAT Edition No. 90
Published: July 2024
Please contact your local Ampath pathologist for more information.

Author:

• Dr. Terry Marshall

Virology and Epidemiology

✅ What is Monkeypox (MPOX)?

• MPOX is caused by the Monkeypox virus (MPXV), a member of the Poxviridae family, genus Orthopoxvirus.
• It is a zoonotic virus, primarily circulating in animals but capable of human-to-human transmission.
• Human infections were historically rare, but outbreaks have become more common, including in South Africa in 2024.

✅ Monkeypox Virus Characteristics

• Large (~300 nm), brick-shaped, enveloped virus.
• Contains double-stranded DNA and a viral DNA-RNA polymerase.
• Infects host cells via complex interactions with mammalian cell surface molecules.

✅ Genetic Clades of MPXV

1. Clade I (Congo Basin Clade):
   • More severe disease.
   • Higher transmission rates, primarily through household settings.
   • Predominantly affects children (70% of cases in the DRC).
2. Clade II (West African Clade):
   • Divided into subclades IIa and IIb.
   • Clade IIb caused the global 2022 outbreak.
   • More frequently associated with sexual transmission.

📌 Monkeypox outbreaks have shifted from primarily animal-human transmission to sustained human-human spread in recent years.

Transmission

✅ Person-to-Person Transmission

• Prolonged close contact (e.g., skin-to-skin, kissing, sexual contact).
• Respiratory droplets (less common).

✅ Zoonotic Transmission

• Direct contact with infected animals through:
  • Bites and scratches.
  • Handling bush meat.
  • Butchering infected animals.
  • Ingestion of undercooked contaminated meat.
• Rodents are the primary reservoir, while primates are incidental hosts.

✅ Other Possible Routes

• Contact with contaminated materials (e.g., bedding, clothing).
• Large droplet transmission (uncommon but possible).

✅ Infectious Period

• Virus transmission starts up to four days before symptoms appear and continues until all lesions heal (scabs have fallen off, revealing healthy skin).

📌 Prolonged isolation and contact tracing are crucial for controlling monkeypox outbreaks.

Clinical Features of MPOX

✅ Typical MPOX Symptoms

• Incubation period: 3–17 days (monitor exposed individuals for 21 days).
• Prodromal symptoms (may include):
  • Fever.
  • Cough.
  • Sore throat.
  • Headache.
  • Malaise.
  • Lymphadenopathy.

✅ Progression of MPOX Rash

1. Macules (first 2 days).
2. Papules (days 3–4).
3. Vesicles (days 5–6).
4. Pustules (5–7 days):
   • Firm, rounded, opaque.
   • Depressed center (umbilicated).
   • Eventually forms scabs.
5. Scabs (up to 2 weeks):
   • Once scabs fall off, the patient is no longer infectious.

✅ Atypical MPOX Presentations (Since 2022)

• Variability in rash appearance:
  • May be localized instead of widespread.
  • Genital, peri-anal, rectal, or oral lesions.
  • Palms and soles may be unaffected.
  • May present as a single lesion.
  • Lesions may be at different developmental stages (similar to varicella-zoster virus).
• Marked rectal pain and bleeding.
• Neurological, respiratory, and ocular complications.
• HIV & MPOX Co-Infection:
  • Severe disease in patients with CD4 <200 cells/mm³.
  • Necrotizing or hemorrhagic lesions, lung involvement, sepsis in CD4 <100 cells/mm³.

📌 Clinicians should be aware of atypical MPOX presentations, particularly in immunocompromised patients.

Diagnosis and Management of MPOX

✅ Diagnostic Steps

1. Isolate the patient.
2. Wear PPE (gloves, gown, eye protection, N95/KN95 mask).
3. Collect a sample for MPXV PCR:
   • Use a dry swab to unroof a lesion and collect fluid.
   • Swab the lesion base with the same swab.
   • Scabs can also be submitted.
4. Triple-package the sample for transport.
5. Complete and submit the NICD case reporting form.
6. PCR testing is performed at Ampath’s Molecular Biology Laboratory in Centurion.
7. Positive samples are sent to the NICD for sequencing (without delaying PCR results).

✅ Reporting and Contact Tracing

• Notify the case via the Notifiable Medical Conditions (NMC) App.
• Inform the provincial Communicable Disease Control Centre (CDCC) for contact tracing.
• Alert hospital infection control teams (if applicable).

📌 Early case detection and strict isolation are essential to preventing further transmission.

Home Isolation and Supportive Care

✅ Home Isolation Guidelines

• Avoid sexual contact and close skin-to-skin contact.
• Remain in isolation until fully recovered.
• Leave home only for essential medical care.
• Do not share utensils, bedding, towels, toothbrushes, or razors.

✅ Medical Management

• Supportive care for mild cases.
• Pain management as needed.
• Monitor for complications (e.g., ocular or neurological involvement).

📌 Most MPOX cases are self-limiting, but severe cases require hospitalization and possible antiviral treatment.

Antiviral Treatment Options

✅ Severe MPOX Cases May Require Antivirals

• Indications for antivirals:
  • Immunocompromised patients.
  • Extensive lesions (>100).
  • Severe complications (e.g., ocular, CNS involvement, myocarditis).

✅ Available Antiviral Options

1. Tecovirimat (TPOXX) 600 mg BID for 14 days
   • Most effective option.
   • Available in South Africa via Section 21 application.
2. Brincidofovir (Tembexa)
   • Prodrug of cidofovir.
   • May be used in combination with Tecovirimat in severe cases.
3. Cidofovir (Vistide)
   • Limited human data, but effective in vitro and animal models.
   • Consider in severe disease when other options are unavailable.

📌 Antivirals should be reserved for high-risk patients with complicated or severe MPOX.

Vaccination for MPOX

✅ Jynneos Vaccine (Live, Non-Replicating Smallpox/MPOX Vaccine)

• Used for:
  • Post-exposure prophylaxis (PEP): Must be given within 4 days of exposure.
  • Pre-exposure prophylaxis (PrEP): Two doses, 28 days apart, for high-risk individuals.
• Not yet available in South Africa, but efforts are underway to secure access.

📌 Vaccination could play a crucial role in reducing MPOX transmission and severity.