Mpox (also known as monkeypox)

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Causative agent

Mpox (also known as monkeypox) is a zoonosis caused by monkeypox virus. First discovered in 1958 in monkeys kept for research, hence the virus was named ‘monkeypox virus’.

Human infection of monkeypox was given its name since 1970 when the first case was reported in the Democratic Republic of Congo (then known as Zaire). From that time, most of the reported monkeypox outbreaks have occurred in Central and West Africa, and some outbreaks outside Africa were found to be related to the imported animals or travelers from Africa. Since May 2022, there has been a multi-country outbreak of monkeypox reported from many countries in widely disparate geographical areas globally.

On 28 November 2022, WHO recommended “mpox” as a synonym of the disease of “monkeypox” in English. Mpox becomes a preferred term in English, replacing monkeypox, after a transition period of one year.

Clinical features

The symptoms are similar to those of smallpox, but in milder forms. The first few days after infection with mpox are characterised by fever, intense headache, myalgia and lymphadenopathy. Severe swollen lymph nodes before the appearance of rash could be a distinctive feature of mpox. Lesions in mouth and body appear about 1 to 3 days after onset of fever. The lesions progress from maculopapules to vesicles, pustules and followed by crusts within a period of 10 days to two weeks and the lesions typically progress simultaneously at all parts of the body.

Taking reference from the global mpox outbreak in 2022, patients may present with atypical symptoms like unexplained genital, ano-genital or oral lesion(s) (for example, ulcers, nodules) or proctitis in sexually active adults.

Mpox is usually a self-limited disease with symptoms lasting from 14 to 21 days. The case fatality in previous outbreaks has been between 1% and 10%.

Mode of transmission

Infection could occur when a person comes into contact with the virus from infected animals, infected humans or contaminated materials. Humans could get infected from various wild animals, such as some species of primates, rodents and squirrels, etc., through bite or scratch, or direct contact with their body fluids. Human-to-human transmission is also possible through respiratory droplets during prolonged face-to-face contact or direct contact with body fluids.

Incubation period

The incubation period is usually from 6 to 13 days, with a range from 5 to 21 days.

Management

In principle, treatment of mpox includes the control of symptoms, management of complications and the prevention of long-term sequelae. Secondary bacterial infections should be treated as indicated. An antiviral agent known as tecovirimat that was licensed by the European Medicines Agency for mpox in 2022, but it is not yet widely available.

Prevention

The Government has procured a third generation vaccine called "JYNNEOS" by making reference to the earlier recommendations of the Scientific Committee on Vaccine Preventable Diseases and the Scientific Committee on Emerging and Zoonotic Diseases as pre-exposure and post-exposure vaccination. The vaccine has arrived in Hong Kong in September 2022 to be used in the Mpox Vaccination Programme. "JYNNEOS" has been licensed by the U.S. Food and Drug Administration (FDA) for the protection of mpox in 2019.

To reduce the risk of infection, members of the public travelling to places affected by monkeypox virus should:

• Avoid close, skin-to-skin contact with sick people or people with a rash that looks like mpox;
• Avoid contact with objects and materials that a person with mpox has used, such as eating utensils or cups, bedding, towels, or clothing;
• Avoid contact with sick or dead animals;
• Implement appropriate infection control precautions when taking care of ill people or handling animals, such as wearing protective clothing and equipment including gloves and surgical masks;
• Maintain hand hygiene. Clean hands with liquid soap and water when they are visibly soiled or likely contaminated with blood and body fluid. When hands are not visibly soiled, they could be cleaned with 70-80% alcohol-based handrub;
• Thoroughly cook all animal products before eating; and
• Seek medical advice promptly for any suspicious symptoms.