Mpox

Mpox (formerly monkeypox) is caused by an Orthopoxvirus. A clade II outbreak from 2022 continues to cause cases in Australia, almost exclusively in men who have sex with men, transmitted through sexual and other close contact. A separate, more severe clade I outbreak in Africa has had very few Australian cases and no sustained local transmission to date.

Vaccination (JYNNEOS / MVA-BN)

JYNNEOS (MVA-BN, a non-replicating vaccinia vaccine) is the preferred vaccine for both primary vaccination and post-exposure prophylaxis. State-funded and free for eligible groups; given through sexual health clinics and some GPs and pharmacies — check local supply.

Eligible (recommended):

• GBMSM, including transgender and gender-diverse people
• Sex workers
• People with HIV or other immunosuppression, if at risk of exposure
• Anyone else in the sexual networks of GBMSM
• Travellers to a clade I region who may have sexual risk activities (new partner, sex-on-premises venue, sex work, large events) — regardless of orientation
• Laboratory workers handling orthopoxviruses
• May be considered for healthcare workers at risk of exposure to mpox patients

PEP: medium- or high-risk contacts (as classified by the public health unit) — as soon as possible, within 14 days of exposure. Within 4 days it can prevent disease; between 4 and 14 days it mainly attenuates it.

Schedule: 2 × 0.5 mL subcutaneously, 28 days apart (a minimum interval — a late dose 2 is simply given). PEP is a single SC dose, with dose 2 at 28 days if exposure risk is ongoing. No booster is recommended after 2 doses, even if immunocompromised. Can be co-administered with other vaccines.

Time to protection: most effective 2 weeks after dose 2, at about 80%; lower in the immunocompromised (~70%). One dose gives partial protection only. Vaccinated patients can still get mpox, usually milder.

Side effects: common and mild. Local: injection-site pain, redness, swelling, induration. Systemic: myalgia, headache, fatigue, nausea, chills. Local reactions are worse with the intradermal route and in atopic dermatitis. Serious events are very rare — over 1 million doses in 2022 with no major safety concerns.

Contraindications: anaphylaxis to a previous dose or component only. Grown in chicken embryo cells — refer severe egg/chicken allergy to an allergist or specialist immunisation clinic first. Safe in pregnancy and breastfeeding on limited data; safe in HIV.

Clinical presentation

Painful lesions on skin and mucosal surfaces, evolving macule → papule → vesicle → pustule → crusted scab over about 3 weeks (can be longer). Proctitis, anal pain and/or bleeding are common presenting features. Prodromal symptoms — fever, lymphadenopathy, headache, myalgia, arthralgia, back pain — typically last up to 5 days and can precede or accompany the rash. Asymptomatic infection is rare.

Complications:

• Secondary bacterial cellulitis — common
• Severe lesion pain, sometimes needing hospital management for anorectal pain — uncommon
• Dehydration from vomiting, diarrhoea or oral lesions limiting intake — uncommon
• Sepsis — less common
• Pneumonia, encephalitis, keratitis with permanent vision loss — rare

Complications are more common in people who are immunocompromised, particularly HIV with a CD4 count under 200 cells/µL.

Diagnosis

On clinical suspicion, phone the local public health unit immediately for advice on exclusion/restriction before the patient leaves the clinic — this is a notifiable condition and testing/isolation logistics need public health input from the outset, not after results return. Contact the laboratory first to confirm mpox NAAT availability.

• Lesion fluid (NAAT of a dry swab) is the preferred specimen — ideally collected from a de-roofed vesicle or pustule.
• Lesion tissue/crust or skin biopsy (dry container) if no fluid-filled lesion is available.
• Anorectal swab for patients with anal symptoms who can’t tolerate anoscopy — not for asymptomatic testing.
• Use dry swab transport tubes where possible; wear gown, gloves, surgical mask and eye protection; avoid contact with contaminated material (e.g. bedding).

Testing is only for symptomatic patients — asymptomatic screening or testing of asymptomatic contacts isn’t recommended, since asymptomatic carriage appears rare. Swab suspected lesions for HSV, syphilis and LGV PCR too, since these are important differentials, and do a full HIV/STI screen at presentation given common co-infection. Consider swabbing for microscopy/culture/sensitivity as secondary bacterial cellulitis is common.

Management

Most cases are mild and self-limiting, needing supportive care only: analgesia, antibiotics for secondary cellulitis, and stool softeners for anal lesions. Topical lignocaine can help lesion pain in troublesome sites like the oropharynx and anorectum; good lesion wound care reduces cellulitis risk.

Discuss with an infectious diseases or sexual health specialist for severe disease or complications (sepsis, encephalitis, eye involvement, secondary cellulitis, dehydration, pneumonia), or anyone at risk of severe disease (immunocompromise, children, pregnancy, breastfeeding).

Antiviral (tecovirimat) and vaccinia immunoglobulin are held in the National Medical Stockpile in limited quantities and are not first-line. Tecovirimat’s in-vitro rationale has not been confirmed by randomised trials, though it may still be considered for selected high-risk patients on specialist advice.

If hospital admission is needed, discuss with the receiving infectious diseases team before transport so biocontainment can be arranged.

Isolation and transmission

Cases are infectious until scabs have fallen off and a fresh skin layer has formed; anal symptoms (pain/bleeding) must have fully resolved too. Mpox viral DNA persists in semen for some weeks after recovery, though no confirmed transmissions via semen have been reported — patients may wish to use condoms for a period after recovery as a precaution for partners who aren’t vaccinated or previously infected. Pets can be infected and may need temporary re-housing during a patient’s isolation.

Occupational transmission risk to healthcare workers is minimal if standard precautions and PPE are followed. Seek public health unit assistance early for contact tracing.