Mpox

Overview

Mpox is a viral disease that is caused by two distinct clades of the monkeypox virus (MPXV), known as Clade I and II. Most common symptoms of the disease are rash and fever. Serious complications or death can occur in medically vulnerable individuals.

Disease epidemiology

Prior to 2022, mpox was primarily reported in parts of Central (clade I) and West Africa (clade II) where it is endemic. Almost all mpox cases occurring outside of Africa were linked to international travel to endemic regions or through imported animals.

2022 – 2023 global outbreak of MPXV clade IIb: In May 2022, cases of mpox caused by MPXV clade IIb were reported concurrently in multiple countries outside of Africa, which were not historically known to be endemic to mpox, including in Singapore. On 23 July 2022, the World Health Organization (WHO) declared the ongoing outbreak of mpox to be a Public Health Emergency of International Concern (PHEIC) due to its global spread. The PHEIC status was subsequently lifted on 10 May 2023 following a global decline in mpox cases and deaths. Nonetheless, mpox continues to be transmitted at low levels globally.

2023 – 2024 outbreak in Africa: In 2023, the Democratic Republic of the Congo (DRC) reported a significant increase in mpox cases and deaths. Unlike the global outbreak associated with MPXV clade IIb, the virus circulating in the DRC is of the endemic clade I, which has thus far only been detected within the African continent. From July 2024, several countries in the region, including those where historically mpox clade I was not endemic, have also reported mpox cases and outbreaks.

On 14 August 2024, the WHO declared that the mpox outbreak in the DRC and the growing number of countries in Africa constitutes a PHEIC. This follows the Africa Centres for Disease Control and Prevention’s declaration of a Public Health Emergency of Continental Security on 13 August 2024. While there is cross-border spread of mpox clade I in parts of Central and East Africa, the clade I outbreak has thus far largely remained within the African continent.

Get the latest updates on the mpox situation from the World Health Organization (WHO) website.

List of affected countries

Get more information from the regions and countries that have reported mpox clade I and II cases from WHO here.

Local situation update

Please refer to the Weekly Infectious Diseases Bulletin for the number of confirmed mpox cases in Singapore.

To date, all mpox infections detected in Singapore were the milder clade IIb infections.

Pathogen(s)

MPXV is a member of the Orthopoxvirus genus in the Poxviridae family. There are two genetic clades: clade I and clade II.

Transmission

Mpox can spread through physical contact with infected individuals, skin lesions and body fluids, contaminated materials and environments, or exposure to respiratory secretions. The virus can also spread from animals to humans, such as through bites or scratches from an infected animal, bush meat preparation, or direct contact with the blood, body fluids, or skin or mucosal lesions of infected animals.

In the global outbreak of MPXV clade IIb, the main mode of transmission is via close physical or prolonged contact, such as face to face and skin to skin contact, including sexual contact. Many cases were identified in individuals who reported intimate contact (including sexual contact) with infected people. Cases were also reported where infection was attributed to household transmission. Regardless of sexual orientation, persons engaging in high-risk sexual behaviours, such as having multiple or casual sexual partners are most at risk of infection in the context of the current outbreak.

Food (other than bushmeat) has never been identified as being associated with human cases of mpox. Currently, there is also no evidence that food or food packaging is a likely source or route of transmission of the virus. As such, the risk of mpox transmission through food is low. Please refer to the Singapore Food Agency (SFA) website for more information.

Incubation period: Typically 6 to 16 days; up to 21 days.

Infectious period: From onset of symptoms until after all lesions have healed and scabs on the skin have fallen off and a fresh layer of intact skin has formed underneath.

Clinical features

Clade I infections have historically been characterised by more severe disease than clade II infections. Based on currently available data, individuals who are at higher risk of severe illness include young children, pregnant women or immunocompromised individuals.

Symptoms for both clades may include:

• Skin rash often starting from the face before becoming generalized including involvement of palms and soles. However, presentation in the global outbreak of clade II involved only a few or single localised lesions, especially in the genital and groin areas, which do not spread further.

• Fever

• Headache

• Backache

• Swollen lymph nodes

• Muscle ache

• General feeling of exhaustion or profound weakness

For clade II, infected persons will develop a maculopapular rash within 1 to 3 days after the onset of fever, often starting from the face before becoming generalised (centrifugal distribution), including involvement of palms and soles in up to 75% of cases. The lesions progress to become vesicles and then pustules, before crusting in approximately 10 days. After which, the resultant scabs spontaneously fall off. The disease is typically self-limiting, with symptoms usually resolving spontaneously within 14 to 21 days.

In the 2022 outbreak, infected individuals were observed to present with clinical disease that was atypical when compared to clade I mpox. That was widely variable in terms of the order of onset of fever versus rash, and the extent of dissemination of rash. The disease caused by clade II mpox in the 2022 outbreak had been milder than in ‘classic’ mpox, likely due to the causative virus being of different subtype (known as ‘clade’). About 72% of cases reported prodromal systemic symptoms (e.g. fever, fatigue, muscle aches). Anal and genital lesions were commonly reported, and lesions may initially appear quite non-specific.

Atypical features include:

• Only a few or even just a single lesion, lesions which begin in the genital or perineal/perianal area and do not spread further.

• Lesions appearing at different (asynchronous) stages of development.

• Appearance of lesions before the onset of fever, malaise, and other constitutional symptoms.

• Symptoms may masquerade as other sexually transmitted infections (STIs), and mpox may occur concurrently with other STIs. Patients remain infectious from the onset of fever until the vesicles/lesions have scabbed over and have separated, with normal skin underneath (re-epithelialisation).

Risk factors

Risk factors include:

• Relevant travel history to countries endemic of mpox

• Contact with infected animals

• Preparation or consumption of bush meat

• Close contact with confirmed cases (including sexual contact)

• Having multiple sex partners

Diagnosis

Mpox infection is diagnosed when MPXV is detected in samples (e.g. vesicles swabs, throat swabs or blood (less preferred) through PCR.

Treatment and management

Treatment is typically symptomatic. Mpox is typically a self-limiting illness, and most patients usually recover within two to four weeks, although serious illness and complications may occur especially in vulnerable persons (e.g. young children, pregnant women, or immunocompromised individuals). Usually, no specific antiviral treatment is required for majority of cases, and clinical management is supportive. In severe cases, the use of tecovirimat may be considered on discussion with an infectious disease specialist.

Suspect and confirmed mpox cases should be isolated, preferably in a negative pressure isolation room, if admitted. Healthcare workers caring for these cases should practice strict hand hygiene and don personal protective equipment including disposable gowns, gloves, N95 masks or equivalent, as well as eye protection.

The MVA-BN (JYNNEOS), a third-generation smallpox vaccine, is currently available as Post Exposure Prophylaxis (PEP) for persons who have been identified to be close contacts of confirmed mpox cases. While JYNNEOS is estimated to provide over 80% protection against mpox, current data remains limited in concluding the level and duration of protection conferred by vaccination, and persons are advised to continue adhering to the recommended precautions against the disease.

Precaution, prevention, and control

Prevention measures include:

• Observing and practising good personal hygiene at all times

• Washing hands regularly with soap, especially before handling food or eating, after going to the toilet, or when hands are dirty from coughing or sneezing

• Using an alcohol-based hand sanitiser that contains at least 60% alcohol if water is not available

• Avoiding contact with persons who are unwell (e.g., those with rash or other lesions) 

• Avoiding sharing common items that may be contaminated with bodily fluids

• Practising safe sex, including avoiding high-risk sexual activities such as having multiple sex partners or engaging in casual sex

• Avoiding close contact with persons who have a rash that looks like mpox, particularly in social events such as parties and clubs

• Avoiding feeding or touching animals, especially stray or wild animals, and the consumption of bush meat when travelling

Travellers from countries affected by mpox should monitor for symptoms for 21 days upon their return from these countries. Please refer to Health Advice for Travellers for precautionary measures to be taken when travelling.

The MVA-BN (JYNNEOS) vaccine is available as pre-exposure prophylaxis (PrEP) for persons identified to be at higher risk of being infected with mpox based on epidemiological factors in the 2022 outbreak.

Aligning with international recommendations, mass population-wide vaccination is currently not recommended as a preventive strategy for mpox, as the risk to the general public remains low with disease transmission predominantly via close physical or prolonged contact.

Notification

Mpox is a notifiable disease under the Infectious Diseases Act.

• Who should notify:

  • Medical practitioners

  • Laboratories

• When to notify:

  • On clinical suspicion or laboratory confirmation

• How to notify:

  • Please refer to the Infectious Disease Notification for more information.

• Notification timeline:

  • MPXV clade Ia/IIa: Immediately

  • MPXV clade Ib/IIb: As soon as possible

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the number of mpox cases in Singapore.

For more information on mpox, please refer to the WHO and Centers for Disease Control and Prevention (CDC) website.

Please refer to the SFA website for more information on the risk of mpox transmission through food.

For general travel advisory, please refer to Health Advice for Travellers.