Monkeypox (Mpox)
Table of Contents
- Overview
- Epidemiology and Clades
- Virology and Pathophysiology
- Transmission
- Clinical Presentation
- Rash Progression and Differential Diagnosis
- Diagnosis
- Treatment: Tecovirimat and Supportive Care
- Vaccines: JYNNEOS and Smallpox Cross-Protection
- Prevention
- Prognosis and Complications
- Recent Research
- References
- Featured Videos
Overview
Monkeypox — officially renamed mpox by the World Health Organization in November 2022 to reduce stigma and avoid misleading geographic and species associations — is a viral disease caused by the monkeypox virus (MPXV). The virus retains its scientific name despite the disease rename.
MPXV belongs to the genus Orthopoxvirus, family Poxviridae. It is a large double-stranded DNA virus with a genome of approximately 200 kilobases, placing it in the same genus as the variola virus (smallpox), vaccinia (used in smallpox vaccines), and cowpox. Like all poxviruses, MPXV replicates entirely within the cytoplasm of host cells — a distinctive feature compared with most DNA viruses that replicate in the nucleus.
The virus was first discovered in 1958 in research monkeys at the Statens Serum Institut in Copenhagen, Denmark, which gave rise to the historical name "monkeypox." However, monkeys are not the primary reservoir. The true reservoir is believed to be small African rodents, including rope squirrels (Funisciurus spp.), Gambian pouched rats (Cricetomys gambianus), dormice, and African squirrels. "Monkeypox" is therefore a historical misnomer that the mpox renaming sought to address.
The first confirmed human case was identified in 1970 in the Democratic Republic of Congo (then Zaire), in a 9-year-old child. For decades, human cases were sporadic and confined to Central and West Africa.
There are two major clades (genetic lineages) of MPXV:
- Clade I (formerly called Congo Basin or Central African clade): higher case fatality rate of approximately 1–10%; associated with more severe disease; endemic to DRC and neighboring Central African countries.
- Clade II (formerly called West African clade): lower case fatality rate of approximately 0.1–3.6%; responsible for the 2022 global outbreak (specifically Clade IIb).
The 2022 global outbreak was caused by Clade IIb and spread predominantly through sexual networks, particularly among men who have sex with men (MSM), across more than 110 non-endemic countries. The WHO declared a Public Health Emergency of International Concern (PHEIC) in July 2022, lifted it in May 2023, and then re-declared a PHEIC in August 2024 due to a Clade I surge in the DRC and East Africa.
A historically important protective feature: smallpox vaccination, discontinued globally after eradication was certified in 1980, provides approximately 85% cross-protection against mpox. The post-eradication cohort (born after ~1980) has grown and now represents a large immunologically naive population susceptible to mpox.
Epidemiology and Clades
Mpox has been endemic in the Democratic Republic of Congo for decades, with the DRC accounting for roughly 90% of historical human cases worldwide. The Congo Basin region and parts of West Africa (notably Nigeria) are the primary endemic zones. In recent years, the DRC has reported more than 15,000 suspected cases annually, with Clade I case fatality rates ranging from 1% to 10% — substantially higher in children, malnourished individuals, and those with HIV.
The 2022 global outbreak (Clade IIb) was a watershed event. Over 87,000 confirmed cases were reported across more than 110 non-endemic countries, representing the first instance of sustained human-to-human transmission outside the African continent. The United States recorded more than 30,000 cases, the largest count among non-endemic countries, with a case fatality rate well below 0.1% in the immunocompetent population. The outbreak was concentrated in sexual networks, with MSM (gay, bisexual, and other men who have sex with men) accounting for approximately 98% of cases in US and European surveillance.
Key epidemiological features of the 2022 outbreak:
- Predominantly MSM sexual networks with multiple or anonymous partners
- Sex workers disproportionately affected
- Household close contacts of cases at elevated risk
- Casual contacts (workplaces, public transit, brief encounters) at very low risk
- Median age of cases: mid-30s; predominantly male
The 2024 DRC/East Africa outbreak (Clade Ib) introduced a new dimension of concern. Clade Ib is a newly described sub-clade demonstrating enhanced person-to-person transmissibility beyond sexual contact, including household and community spread in eastern DRC. This prompted WHO to declare a second PHEIC in August 2024, as the outbreak spread to Burundi, Rwanda, Uganda, and Kenya. The higher intrinsic transmissibility of Clade Ib raised pandemic risk concerns not associated with the 2022 Clade IIb event.
HIV coinfection significantly worsens outcomes. Persons with HIV, particularly those with CD4 counts below 200 cells/µL, experience more severe and prolonged disease, atypical presentations with extensive ulcerating lesions, higher rates of hospitalization, and increased mortality. Optimization of antiretroviral therapy is a key component of mpox management in HIV-positive individuals.
Children in endemic DRC bear a disproportionate Clade I burden. Proximity to animal reservoirs through bushmeat handling, hunting, and forest exposure, combined with high rates of malnutrition and limited healthcare access, contribute to pediatric case fatality rates reaching 10% in some DRC series. By contrast, children were largely spared in the 2022 Clade IIb outbreak.
Virology and Pathophysiology
MPXV is a large double-stranded DNA virus with a genome of approximately 200 kilobases. Like all poxviruses, it replicates entirely within the cytoplasm of host cells, encoding its own transcription machinery and carrying out DNA replication independent of the host nucleus. The virion has a complex brick-shaped or ovoid morphology measuring approximately 200–300 nanometers.
Four distinct viral forms are produced during the replication cycle, each with different roles in pathogenesis:
- Intracellular mature virion (IMV): the primary infectious form; responsible for initial cell entry and most cell-to-cell spread within tissues.
- Intracellular enveloped virion (IEV): wrapped in additional membranes during transport to the cell surface.
- Cell-associated enveloped virion (CEV): on the outer cell surface; mediates direct cell-to-cell spread and actin-tail propulsion.
- Extracellular enveloped virion (EEV): released into the extracellular environment; responsible for systemic dissemination and long-range spread within the host.
The pathophysiological sequence after infection proceeds in stages:
- Entry via mucous membranes (respiratory, oral, genital), broken skin, or animal bites/scratches
- Initial replication at the entry site (may produce a primary lesion)
- Spread to regional lymph nodes → pronounced lymphadenopathy (a hallmark distinguishing mpox from smallpox)
- Primary viremia: virus enters the bloodstream → seeding of the reticuloendothelial system (liver, spleen, lymph nodes)
- Secondary viremia: massive viral replication in reticuloendothelial organs → widespread blood-borne dissemination
- Skin seeding: virus reaches dermal capillaries → infects keratinocytes → characteristic rash eruption
The incubation period is typically 5–21 days (most commonly 7–14 days). The extent to which infected but pre-symptomatic individuals shed infectious virus remains an active area of research; asymptomatic transmission has been documented but is not thought to be the primary driver of spread.
Skin lesion formation: viral infection of keratinocytes triggers rapidly progressing dermal inflammation, driving the characteristic papule-to-vesicle-to-pustule-to-umbilicated-to-scab progression. Umbilication (a central dimple or depression in the lesion) results from central necrosis of the infected epidermis and is a pathognomonic poxvirus feature.
Key virulence and immune evasion mechanisms include:
- Viral IL-18 binding protein: sequesters host IL-18, dampening NK cell and T-cell responses
- Complement inhibitors: viral proteins that block complement activation at the lesion surface
- Interferon antagonists: multiple viral proteins that interfere with type I and type II interferon signaling
- Apoptosis inhibitors: prevent premature death of infected cells, prolonging viral replication
- Immunomodulatory cytokine homologs: viral mimics of host cytokines and receptors that manipulate immune signaling
A distinctive feature distinguishing mpox from smallpox clinically is the pronounced lymphadenopathy that accompanies mpox. This reflects significant viral replication in lymph nodes and a more robust local lymph-node response compared with smallpox, and it appears early — often in the prodrome before rash onset.
Transmission
MPXV transmission occurs through multiple routes, with the relative importance of each route varying by context (endemic zoonotic exposure vs. outbreak sexual network transmission).
Zoonotic (Animal-to-Human) Transmission
In endemic African settings, the primary mode of acquisition is exposure to infected animals. This includes bites and scratches from infected rodents, direct contact with animal blood, body fluids, or lesions, and handling or consuming undercooked bushmeat. Children in DRC are exposed through play near forest edges, trapping small animals, and sharing living spaces with potential reservoir species.
Human-to-Human Transmission
Human-to-human transmission requires close, direct physical contact. The main mechanisms are:
- Direct skin-to-skin contact with rash lesions, scabs, or body fluids of an infected person — the dominant route in the 2022 outbreak
- Mucous membrane contact with oral, genital, or anal lesions during intimate or sexual activity
- Respiratory droplets from coughing or talking: large droplets (not aerosols); requires prolonged face-to-face contact (typically >3 hours in a confined space); mpox is NOT airborne in the way measles or SARS-CoV-2 are
- Fomites: contaminated bedding, clothing, towels, and surfaces; virus can survive on dry surfaces for days to weeks in experimental conditions
Sexual Transmission Nuance
MPXV is not classified as a classical sexually transmitted infection — the virus is not present in genital secretions in the way gonorrhea or HIV are. However, sexual activity involving skin-to-skin contact with genital, anal, or oral lesions is an extremely efficient transmission route because of the high viral load in lesions and the intimacy of contact. Virus has been detected in seminal fluid, but whether seminal fluid itself is infectious independent of direct lesion contact remains unproven.
Duration of Contagiousness
An infected person is contagious from the onset of prodromal symptoms until all lesions have fully resolved — all scabs have fallen off and new skin has formed underneath. This typically takes 3–4 weeks. Early lesion stages (vesicular and pustular) have the highest viral loads and greatest transmission risk.
Healthcare Settings
Standard precautions plus contact and droplet precautions are required for mpox patients in healthcare settings. Airborne precautions (N95 respirators) are added for aerosol-generating procedures such as intubation, bronchoscopy, or wound irrigation. Full PPE (gown, gloves, eye protection, N95) is required during direct patient care.
Import and Travel Risk
The 2003 US Midwest outbreak — the first outside Africa — occurred when prairie dogs became infected from imported Gambian pouched rats sold as exotic pets, then transmitted to human owners. International travel from endemic regions, importation of infected animals, and global sexual networks can all carry virus across borders rapidly.
Clinical Presentation
Classic mpox follows a characteristic biphasic pattern: a prodromal phase followed by a rash phase. However, the 2022 outbreak introduced atypical presentations that broadened the clinical picture.
Prodrome (Days 1–4)
The prodrome typically lasts 1–4 days and consists of:
- Fever: 38–40°C (100.4–104°F), often abrupt onset
- Severe headache: often described as intense and incapacitating
- Intense myalgia: classically described as "back-breaking" pain; myalgia can be so severe that patients have difficulty ambulating
- Profound fatigue and chills
- Deep inguinal lymphadenopathy: the pathognomonic distinguishing feature of mpox (see below)
Lymphadenopathy: The Pathognomonic Feature
Prominent lymph node enlargement — particularly inguinal, femoral, axillary, and cervical nodes — is the key clinical feature that differentiates mpox from both smallpox and chickenpox. Lymphadenopathy appears early, often during the prodrome before rash onset, is frequently painful and tender on palpation, and can be dramatic (nodes palpable as large firm masses). Neither smallpox nor chickenpox produces the degree of lymphadenopathy seen in mpox.
Rash Phase (Days 5–21+)
Rash typically begins 1–5 days after prodrome onset. In classic mpox:
- Centrifugal distribution: starts on the face, then spreads centrifugally to the trunk, arms, legs, palms, and soles. This pattern — face and extremities involved, including palms/soles — distinguishes mpox from chickenpox (centripetal, trunk-predominant, palms/soles spared).
- Mucous membranes are frequently involved: oropharynx (enanthem), conjunctivae (ocular mpox), and genital/anal mucosa
- Lesion count: traditionally in the hundreds to thousands in severe endemic Clade I disease
Atypical 2022 Outbreak Presentations
The 2022 Clade IIb outbreak among MSM frequently presented atypically:
- Rash often appeared first in the genital or anal region, at or near the site of inoculation
- Rash may precede systemic prodromal symptoms (reversed sequence)
- Many cases had only 1–5 lesions total rather than the hundreds seen in textbook descriptions
- Fewer or absent systemic prodromal symptoms in many patients
- Proctitis: severe rectal pain, tenesmus, and discharge in those with rectal inoculation — one of the most painful and debilitating features
- Penile edema and balanoposthitis from penile/preputial lesions
- Pharyngitis with severe odynophagia from oropharyngeal inoculation
Ocular Mpox
Ocular involvement is rare but serious. Poxviral keratitis can result in corneal scarring and permanent visual impairment or blindness. Conjunctivitis, blepharitis, and periorbital lesions may also occur. Patients should be evaluated by ophthalmology if ocular symptoms develop.
Rash Progression and Differential Diagnosis
Understanding mpox lesion morphology and progression is essential for clinical recognition and appropriate differential diagnosis.
Classic Poxviral Lesion Progression
Mpox lesions follow a predictable morphological sequence over 2–4 weeks:
- Macule: flat, discolored skin spots (2–5 mm); earliest lesions
- Papule: firm, raised lesions; well-circumscribed, hard to the touch; more indurated than chickenpox papules
- Vesicle: fluid-filled, clear or cloudy; tense
- Pustule: cloudy, pus-filled; deep-seated; umbilicated (central dimple due to central epidermal necrosis) — pathognomonic of poxvirus
- Crust/Scab: lesions dry out and form firm crusts; shedding of scabs releases viral particles (contagious)
- Healing: scabs fall off leaving pink or hyperpigmented scars; depigmented pock-mark scars are common long-term sequelae, especially on the face
The Most Important Clinical Distinguishing Feature
All mpox lesions progress through the same stage simultaneously. At any given moment, all lesions on a patient's body are in the same morphological stage — all macules, all papules, all pustules, or all scabs at the same time. This synchronicity directly contrasts with chickenpox, where lesions appear in successive crops over days, so at any moment a patient has lesions in multiple different stages simultaneously — fresh red macules next to fluid vesicles next to dried scabs.
This single feature — same-stage vs. multi-stage lesions — is the most reliable clinical bedside differentiator between mpox and varicella (chickenpox).
Lesion Depth
Mpox pustules are deep-seated and indurated — they feel hard and "buried" under the skin surface. Chickenpox vesicles are more superficial, delicate, and easily ruptured. This depth difference is palpable on examination.
Palms and Soles Involvement
Mpox characteristically involves the palms and soles, which is also a feature of secondary syphilis. Chickenpox rarely affects palms and soles. This is a clinically useful pattern recognition clue, particularly in the 2022 outbreak context where syphilis coinfection was common.
Umbilication
The central dimple (umbilication) of mpox pustules is shared with molluscum contagiosum, but molluscum lesions are much smaller (2–5 mm vs. mpox 5–15 mm), lack the inflammatory base, and do not ulcerate or crust in the same way.
Differential Diagnosis Summary
- Chickenpox (varicella): multi-stage lesions simultaneously; centripetal (trunk-first); palms/soles spared; no deep lymphadenopathy; superficial vesicles; milder prodrome
- Smallpox (eradicated): centrifugal (like mpox); more severe systemic illness; no significant lymphadenopathy; higher mortality; eradicated since 1977
- Secondary syphilis: maculopapular rash on palms/soles; painless; serological testing distinguishes; no lymphadenopathy of mpox scale
- Herpes simplex virus: grouped vesicles on erythematous base; dermatomal/anatomic distribution; recurrent; PCR distinguishes
- Herpes zoster (shingles): dermatomal unilateral distribution; older/immunocompromised; grouped vesicles
- Molluscum contagiosum: smaller umbilicated papules; slower progression; no systemic illness; no fever or lymphadenopathy
- Drug hypersensitivity reactions: often diffuse, non-staged, associated with medication exposure; no lymphadenopathy
Diagnosis
Accurate and prompt diagnosis is essential to initiate isolation, treatment, contact tracing, and post-exposure vaccination. Clinical suspicion based on rash morphology and exposure history should prompt testing.
Gold Standard: PCR
Real-time PCR (RT-PCR) of a lesion swab is the diagnostic gold standard. To obtain an adequate sample: vigorously swab both the base and the roof/surface of an open lesion (this is often painful for the patient but necessary for adequate viral DNA yield). Dry swabs or swabs in viral transport media (VTM) are acceptable.
Two PCR assay levels are available:
- Orthopoxvirus PCR: a generic assay that detects DNA shared across all Orthopoxviruses (mpox, cowpox, vaccinia). A positive result confirms an orthopoxvirus but does not specify which.
- MPXV-specific PCR: confirms monkeypox virus specifically. Available at CDC and reference laboratories.
- Clade differentiation: requires whole-genome sequencing or clade-specific PCR assays; important for epidemiological tracking (Clade I vs. IIb vs. Ib).
Sample Types (in order of preference)
- Vesicle fluid (aspirated directly) or swab of unroofed vesicle base — highest viral load
- Swab of pustule base after unroofing
- Dried crusts/scabs (can be placed in dry tube)
- Oropharyngeal swab (for pharyngitis or systemic illness without skin lesions)
- Rectal swab (for rectal disease/proctitis)
- Blood (during acute viremia; less sensitive for PCR diagnosis)
Histopathology
Skin biopsy can demonstrate characteristic poxviral cytopathic changes including Guarnieri bodies (granular intracytoplasmic inclusions representing viral replication factories). This finding is not mpox-specific (present in all poxvirus infections) and histopathology is not routinely used for clinical diagnosis, but can be informative in unusual presentations.
Electron Microscopy
Transmission electron microscopy can demonstrate the characteristic brick-shaped poxvirus morphology. This modality is available only at specialized reference laboratories and is rarely needed for clinical management.
Serology
Serological assays measuring anti-orthopoxvirus antibodies are available but have limited clinical utility for acute diagnosis because: (1) antibodies take 1–2 weeks to develop after symptom onset; (2) cross-reactivity with other orthopoxviruses (including vaccination with ACAM2000 or JYNNEOS) makes interpretation difficult. Serology is primarily used for epidemiological seroprevalence studies.
Who to Test
Any person presenting with new unexplained rash or mucocutaneous lesions consistent with mpox should be tested, particularly those with: recent sexual contact with new or multiple partners; travel to endemic regions; known exposure to a confirmed mpox case; or skin lesions in the context of HIV infection or other immunocompromising condition.
Treatment: Tecovirimat and Supportive Care
Management of mpox combines antiviral therapy (for eligible patients), wound care, pain management, and treatment of complications. Most immunocompetent adults with mild disease recover fully with supportive care alone.
Tecovirimat (TPOXX)
Tecovirimat (brand name TPOXX in the US; ST-246) is an antiviral drug FDA-approved for smallpox treatment. For mpox, it has been used under an expanded access Investigational New Drug (IND) protocol (the STOMP trial and related access programs).
Mechanism of action: Tecovirimat specifically inhibits VP37, a viral protein required for wrapping of intracellular mature virions into extracellular enveloped virions. By blocking this step, tecovirimat prevents the formation and release of the extracellular enveloped virion (EEV) form — the form responsible for systemic dissemination and long-range spread within the host. Without EEV formation, the virus is largely contained to its initial replication site.
STOMP Trial Results
The STOMP trial (Study of Tecovirimat for Human Monkeypox) was the first large randomized controlled trial of tecovirimat for mpox, enrolling participants during the 2022 outbreak. Results published in 2024 showed that tecovirimat did not significantly reduce time to lesion resolution compared with placebo in immunocompetent adults with 2022-outbreak Clade IIb mpox. The trial's findings were surprising to many clinicians who had observed apparent clinical benefit during the outbreak.
However, subgroup and secondary analyses suggested potential benefit in specific populations:
- Immunocompromised patients (particularly HIV+ with low CD4 counts)
- Severe disease requiring hospitalization
- Patients with extensive lesions (>100 lesions)
- Rectal disease and severe proctitis
Current Treatment Indications
Per CDC and IDSA guidance (as of 2023–2024), tecovirimat is recommended for:
- Immunocompromised patients, especially HIV+ with CD4 <200 cells/µL
- Severe disease requiring hospitalization
- Ocular mpox (keratitis risk)
- Rectal disease causing severe proctitis, rectal prolapse, or inability to defecate
- Penile/genital disease with necrosis risk
- Pediatric cases
- Pregnant or breastfeeding individuals
Dosing
Standard adult dosing: 600 mg orally twice daily with a high-fat meal (food significantly increases bioavailability) for 14 days. An intravenous formulation is available for severe cases where oral administration is not feasible.
Alternative Antivirals
- Cidofovir: a nucleotide analog with broad antiviral activity including poxviruses; limited by significant nephrotoxicity (requires hydration and probenecid co-administration); reserved for tecovirimat treatment failure.
- Brincidofovir (CMX001): lipid-conjugated prodrug of cidofovir with improved bioavailability and potentially lower nephrotoxicity; in vitro activity against poxviruses; limited clinical mpox data.
Vaccinia Immune Globulin Intravenous (VIGIV)
VIGIV contains high-titer antibodies against vaccinia (and cross-reactive with mpox). It is used for severe or progressive mpox disease, particularly in immunocompromised patients who fail antiviral therapy. Supply is limited (maintained in the Strategic National Stockpile).
Supportive Care
- Pain management: lesion pain — especially rectal, penile, and oropharyngeal — can be severe. NSAIDs, acetaminophen, and opioids (for severe cases) are used. Topical lidocaine for rectal/genital lesions.
- Antihistamines: for pruritus (itching of lesions)
- Wound care: keep lesions clean and dry; avoid rupturing pustules; antiseptic washes to prevent secondary bacterial superinfection (Staphylococcus aureus, Group A Streptococcus)
- Antibiotics: only if secondary bacterial infection develops — not prophylactically
- Hydration and nutrition: important especially in children and patients with oropharyngeal involvement affecting oral intake
- Isolation: infected persons should remain isolated at home until all lesions have fully resolved and new skin has formed
Vaccines: JYNNEOS and Smallpox Cross-Protection
Vaccination is the most effective preventive intervention for mpox. Two vaccines are available in the United States, with very different risk profiles.
JYNNEOS (Modified Vaccinia Ankara)
JYNNEOS (also marketed as Imvamune in Canada and Imvanex in Europe) contains the Modified Vaccinia Ankara (MVA) strain — a live attenuated, non-replicating vaccinia virus. Because it cannot replicate in human cells, JYNNEOS is safe for immunocompromised individuals, including HIV-positive persons, unlike the older replication-competent ACAM2000 vaccine.
JYNNEOS is FDA-approved for monkeypox and smallpox in adults 18 years of age and older who are at risk of infection.
Dosing Routes and Schedule
- Standard subcutaneous (SC) route: 0.5 mL injected subcutaneously; two doses 28 days apart
- Dose-sparing intradermal (ID) route: 0.1 mL injected intradermally; same 28-day schedule; FDA authorized under emergency use during 2022 outbreak to effectively multiply available doses fivefold
Both routes produce similar immunogenicity. Full protection requires the second dose; detectable immunity begins approximately 2 weeks after dose 2.
Efficacy
Observational effectiveness data from the 2022 outbreak showed approximately 76–85% effectiveness against mpox infection after 2 doses. Single-dose effectiveness was approximately 36–75% (variable across studies). The vaccine appears more effective at preventing disease acquisition than at reducing lesion severity once infected, though some benefit in severity reduction was also observed.
Post-Exposure Vaccination (Ring Vaccination)
JYNNEOS can be used as post-exposure prophylaxis:
- Within 4 days of exposure: 2 doses given as rapidly as possible; can prevent disease
- 4–14 days after exposure: 2 doses; may reduce severity but unlikely to prevent all disease
- After 14 days: too late for post-exposure benefit; proceed with monitoring and supportive care
ACAM2000 (Older Replication-Competent Vaccine)
ACAM2000 is a live, replication-competent vaccinia virus — the successor to the Dryvax vaccine used during the smallpox eradication campaign. It provides approximately 85% cross-protection against mpox and is available in the Strategic National Stockpile for military personnel and laboratory workers with high occupational risk.
ACAM2000 carries significant adverse event risks:
- Progressive vaccinia (life-threatening uncontrolled vaccine virus replication in immunocompromised individuals)
- Myopericarditis (estimated 1 per 175 vaccinees)
- Eczema vaccinatum (severe generalized vaccinia in patients with atopic dermatitis)
- Accidental inoculation at other body sites
For this reason, ACAM2000 is contraindicated in immunocompromised individuals, pregnant women, and persons with atopic dermatitis or eczema. JYNNEOS is the preferred vaccine for general population use.
Historical Smallpox Vaccine Cross-Protection
Individuals vaccinated against smallpox before the program ended (~1980) retain approximately 85% reduced risk of mpox, even decades later. Studies of 2022 outbreak cases showed those with smallpox vaccination scars (indicating prior vaccination) had markedly lower rates of severe disease. This waning but persistent cross-immunity has shaped the age distribution of mpox susceptibility globally, with post-1980 birth cohorts bearing disproportionate risk.
Vaccination Strategy
- Pre-exposure prophylaxis (PrEP): recommended for MSM with multiple or anonymous sexual partners, sex workers, persons whose sexual partners have mpox, laboratory workers handling orthopoxviruses, and healthcare workers with frequent mpox exposure
- Post-exposure: ring vaccination of close contacts within 4 days of last exposure
- Endemic DRC/pediatric strategy: WHO and Africa CDC prioritizing childhood vaccination campaigns for Clade I endemic areas
Prevention
Mpox prevention combines individual behavioral measures, vaccination, and public health responses including case identification and contact tracing.
Avoiding Animal Exposure (Endemic Regions)
- Avoid contact with sick or dead animals, especially small rodents and primates in Central and West Africa
- Do not handle bushmeat, animal carcasses, or consume undercooked wild game from endemic regions
- Wear gloves and protective clothing when caring for sick animals
- Do not keep exotic rodents from endemic regions as pets
Reducing Human-to-Human Transmission During Outbreaks
- Avoid close skin-to-skin contact with persons who have a rash, lesions, or scabs consistent with mpox
- Reduce the number of sexual partners and be aware of partners' health status during active outbreaks
- Use condoms during sex: while condoms reduce risk, they do not eliminate it — lesions on skin not covered by a condom can still transmit
- Delay sex until fully recovered if you have mpox (until all lesions have resolved)
- Discuss mpox symptoms with sexual partners before engaging in intimate contact
Vaccination
Eligible high-risk individuals should receive the JYNNEOS vaccine (2-dose series, 4 weeks apart). See the Vaccines section for eligibility criteria. Vaccination is the most effective preventive measure.
Healthcare Settings
Standard infection control requires:
- Standard precautions always (hand hygiene, PPE for contact with body fluids)
- Contact precautions: gown and gloves for all patient contact
- Droplet precautions: surgical mask within 6 feet of patient; private room preferred
- Airborne precautions: N95 respirator for aerosol-generating procedures (intubation, bronchoscopy, wound irrigation)
- Eye protection (face shield or goggles): for direct patient care
Case Isolation
Infected persons should isolate at home until all lesions have resolved and new skin has fully formed — typically 3–4 weeks. During isolation: avoid sharing bedding, towels, or clothing with household members; wash contaminated items separately at high temperature; cover lesions with bandages when sharing spaces.
Contact Tracing and Post-Exposure Vaccination
Public health authorities should be notified of confirmed cases promptly. Close contacts (defined as persons with prolonged direct skin contact, sexual contact, or household cohabitation with an infectious case) should be identified, monitored for symptoms, and offered post-exposure JYNNEOS vaccination within 4 days of last exposure.
Environmental Decontamination
MPXV can survive on dry surfaces (experimental data: days to weeks under favorable conditions). Standard hospital-grade disinfectants effective against non-enveloped viruses (EPA List Q for poxviruses) are adequate. Porous materials (bedding, clothing, upholstered furniture) should be washed or steam-cleaned. Healthcare rooms should be terminally cleaned after patient discharge before re-use.
Prognosis and Complications
Prognosis varies substantially by clade, immune status, age, and access to care.
Prognosis in Immunocompetent Adults (2022 Clade IIb Outbreak)
For most immunocompetent adults in the 2022 Clade IIb outbreak, mpox was a self-limiting illness with full recovery expected within 2–4 weeks. The case fatality rate was well below 0.1% in North America and Europe. The main burdens were pain (often severe, especially from rectal or genital lesions), enforced isolation, and psychological distress.
Endemic DRC Clade I Disease
Clade I disease has a case fatality rate of 1–10% in endemic settings. Mortality is concentrated in:
- Children under 15 (nutritional deficiency, healthcare access barriers)
- Malnourished individuals (immune compromise, poor wound healing)
- HIV-positive persons with low CD4 counts
- Persons in resource-limited settings without access to supportive care
Complications
- Secondary bacterial skin infections: the most common complication; Staphylococcus aureus and Group A Streptococcus superinfect open lesions; can progress to cellulitis, abscess, or septicemia
- Severe proctitis: rectal pain, bleeding, tenesmus, and in extreme cases, rectal prolapse; one of the most disabling complications of the 2022 outbreak
- Penile necrosis: rare but reported; genital lesions with secondary infection and ischemia can cause permanent penile tissue damage
- Keratitis and corneal scarring: ocular mpox can permanently impair vision; early ophthalmology referral is critical
- Encephalitis: rare; more common in immunocompromised; can be life-threatening
- Bronchopneumonia: poxviral pneumonia from primary respiratory seeding or secondary bacterial pneumonia
- Septicemia: from secondary bacterial infection in extensive skin disease
- Scarring: depigmented pock-mark scars, especially on the face, are common long-term sequelae; can be disfiguring
HIV-Positive Patients with Advanced Immunosuppression
Perhaps the highest-risk group in high-income countries. HIV-positive patients with CD4 counts below 200 cells/µL can develop prolonged, extensively ulcerating lesions that fail to heal, high-grade fever and systemic toxicity, poor response to tecovirimat without concurrent antiretroviral therapy optimization, and fatality rates substantially above the general population. Optimizing antiretroviral therapy to suppress HIV viral load and improve CD4 count is a critical parallel intervention.
Mental Health Impact
The 2022 outbreak was associated with significant psychological morbidity. Stigma (association with sexual behavior and specific communities), prolonged enforced isolation, severe pain, uncertainty about prognosis, and sexual health anxiety contributed to high rates of depression and anxiety among affected individuals. Mental health support should be integrated into mpox care pathways.
Recent Research
The 2022 global outbreak and the 2024 DRC/East Africa re-emergence have substantially accelerated mpox research across virology, therapeutics, vaccine science, and epidemiology.
STOMP Trial (Tecovirimat)
The STOMP (Study of Tecovirimat for Human Monkeypox) randomized controlled trial was conducted across multiple US sites during the 2022 outbreak. Its 2024 results — showing no significant benefit of tecovirimat over placebo in immunocompetent adults — were a pivotal finding that shifted thinking about antiviral indications. The trial has renewed focus on identifying which patient subgroups derive the greatest benefit, with immunocompromised individuals and severe disease remaining key targets for antiviral therapy.
Clade Ib Emergence and Pandemic Risk
The identification of Clade Ib in eastern DRC in 2024, with evidence of enhanced person-to-person transmissibility beyond sexual networks, raised significant concern about pandemic potential. Unlike Clade IIb (which remained largely contained to sexual networks), Clade Ib appears capable of sustained household and community spread. WHO's second PHEIC declaration and emergency vaccine mobilization for eastern DRC reflect the urgency of this development.
mRNA Vaccine Development
Moderna's mRNA-1769, a combined mpox and smallpox mRNA vaccine, entered Phase 1 clinical trials. If successful, mRNA technology would offer advantages over MVA-based JYNNEOS including faster manufacturing scale-up and potentially greater flexibility in responding to new orthopoxvirus threats.
Genomic Epidemiology and APOBEC3 Hypermutation
Whole-genome sequencing of 2022 outbreak MPXV isolates revealed an extraordinary number of mutations concentrated in a characteristic APOBEC3 signature — a pattern produced when the cellular APOBEC3 antiviral defense enzymes mutate viral DNA. This hypermutation signature indicates the virus had been undergoing sustained human-to-human transmission for an extended period before the recognized outbreak, and represents viral adaptation to the human host. The 2022 outbreak was traced genomically to a single ancestral introduction that spread through global sexual networks.
Immune Correlates of Protection
Studies of survivors from the 2022 outbreak are characterizing which antibody specificities and T-cell responses best correlate with protection against reinfection. These data will inform rational next-generation vaccine design targeting the most protective epitopes.
Pediatric Burden and Childhood Vaccination in DRC
WHO and Africa CDC have identified closing the childhood vaccination gap in DRC as the highest-priority intervention for reducing Clade I mortality. Research is ongoing to characterize the safety and optimal dosing of JYNNEOS in children under 18, for whom the vaccine is not yet FDA-approved.
References
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Research Papers
The following PubMed topic searches retrieve current peer-reviewed literature on Monkeypox (Mpox).
- Mpox monkeypox pathogenesis review
- Monkeypox 2022 outbreak epidemiology
- Mpox tecovirimat treatment STOMP trial
- JYNNEOS vaccine mpox effectiveness
- Mpox HIV immunocompromised clinical
- Mpox MSM sexual transmission network
- Monkeypox Clade I DRC Congo outbreak
- Orthopoxvirus smallpox cross immunity
- Mpox rash differential diagnosis
- Mpox proctitis anorectal manifestation
- Monkeypox genomics APOBEC3 evolution
- Mpox PCR diagnosis lesion swab
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