Mpox

Mpox (, EM-poks; originally known as monkeypox) is an infectious viral disease that can occur in humans and other animals. Symptoms include a rash that forms blisters and then crusts over, as well as fever and swollen lymph nodes. The illness is usually mild, and most infected individuals recover within a few weeks without treatment. The time from exposure to the onset of symptoms ranges from three to seventeen days, and symptoms typically last from two to four weeks. However, cases may be severe, especially in children, pregnant women, or people with suppressed immune systems.

The disease is caused by the monkeypox virus, a zoonotic virus in the genus Orthopoxvirus. The variola virus, which causes smallpox, is also in this genus. Human-to-human transmission can occur through direct contact with infected skin or body fluids, including sexual contact. People remain infectious from the onset of symptoms until all the lesions have scabbed and healed. The virus may spread from infected animals through handling infected meat or via bites or scratches. Diagnosis can be confirmed by polymerase chain reaction (PCR) testing a lesion for the virus's DNA.

Vaccination is recommended for those at high risk of infection. No vaccine has been developed specifically against mpox, but smallpox vaccines have been found to be effective. There is no specific treatment for the disease, so the aim of treatment is to manage the symptoms and prevent complications. Antiviral drugs such as tecovirimat can be used to treat mpox, although their effectiveness has not been proven.

Mpox is endemic in Central and Western Africa, where several species of mammals are suspected to act as a natural reservoir of the virus. The first human cases were diagnosed in 1970 in Basankusu, Democratic Republic of the Congo. Since then, the frequency and severity of outbreaks have significantly increased, possibly as a result of waning immunity since the cessation of routine smallpox vaccination. A global outbreak of clade II in 2022–2023 marked the first incidence of widespread community transmission outside of Africa. In July 2022, the World Health Organization (WHO) declared the outbreak a public health emergency of international concern (PHEIC). The WHO reverted this status in May 2023, as the outbreak came under control, citing a combination of vaccination and public health information as successful control measures.

An outbreak of new variant of clade I mpox (known as clade Ib) was detected in the Democratic Republic of the Congo during 2023. As of August 2024, it had spread to several African countries, raising concerns that it may have adapted to more sustained human transmission. In August 2024, the WHO declared the outbreak a public health emergency of international concern.

Nomenclature

In 1958, the pathogen that caused mpox was discovered following two incidents where monkey colonies were infected with a pox-like illness for research purposes. It was originally dubbed "monkeypox", but the exact origin of the disease is not known. It is believed that transmission from African rodents and non-human primates, including monkeys, is possible.

Beginning during the 2022 outbreak, public health experts and researchers, particularly in Africa, had urged the World Health Organization (WHO) to rename the disease. There had been racist comments on social media associating the disease's name with African populations. Stigmatizing remarks had also wrongly identified mpox as a "gay disease," as gay men, bisexuals, and men who have sex with men are among the most affected globally. This stigma is thought to deter individuals from seeking diagnosis, vaccination, and treatment, reminiscent of the early days of the HIV/AIDS pandemic in the 1980s. Additionally, misinformation has incited violence against monkeys in certain regions, wrongly held accountable for transmitting monkeypox.

The WHO put forth its approval for the new name Mpox, which was gradually adopted as the preferred term in the International Classification of Diseases (ICD) after December 2023. The name change retains a connection to poxviruses while making it easier to spell in various languages. The subtypes of mpox virus were also renamed; the clade formerly known as "Congo Basin (Central African)" was renamed clade I, and the clade formerly known as "West African" was renamed clade II. For the purpose of preserving access to historical records to facilitate research, the term monkeypox and old subtypes names will remain in the ICD database as searchable terms.

In September 2025, the United States Centers for Disease Control and Prevention (CDC) returned to using the name monkeypox, citing the monkeypox virus causes the disease.

Signs and symptoms

Initial symptoms of mpox infection are fever, muscle pains, and sore throat, followed by an itchy or painful rash, headache, swollen lymph nodes, and fatigue. Not everyone will exhibit the complete range of symptoms.

People with mpox usually become symptomatic about a week after infection. However the incubation period can vary in a range between one day and four weeks.

The rash comprises numerous small lesions, which may appear on the palms, soles, face, mouth, throat, genitals, or anus. They begin as small flat spots, before developing into small bumps, which then fill with fluid, eventually bursting and scabbing over, typically lasting around ten days. In rare cases, lesions may become necrotic, requiring debridement and taking longer to heal.

Some people may manifest only a single sore from the disease, while others may have hundreds. An individual can be infected with Orthopoxvirus monkeypox without showing any symptoms. Symptoms typically last for two to four weeks but may persist longer in people with weakened immune systems.

Complications

Complications include secondary infections, pneumonia, sepsis, encephalitis, and loss of vision following corneal infection. Persons with weakened immune systems, whether due to medication, medical conditions, or HIV, are more likely to develop severe cases of the disease. If infection occurs during pregnancy, this may lead to stillbirth or other complications.

Outcome

Provided there are no complications, sequelae are rare; after healing, the scabs may leave pale marks before becoming darker scars.

Deaths

Historically, the case fatality rate (CFR) of past outbreaks was estimated at between 1% and 10%, with clade I considered to be more severe than clade II.

The case fatality rate of the 2022–2023 global outbreak caused by clade IIb was very low, estimated at 0.16%, with the majority of deaths in individuals who were already immunocompromized. In contrast, as of April 2024, the outbreak of clade I in Democratic Republic of the Congo has a CFR of 4.9%.

The difference between these estimates is attributed to:

• differences in the virulence of clade I versus clade II.
• under-reporting of mild or asymptomatic cases in the endemic areas of Africa, which generally have poor healthcare infrastructure.
• evolution of the virus to cause milder disease in humans.
• better general health, and better health care, in the populations most affected by the 2022–2023 global outbreak.

In other animals

It is thought that small mammals provide a reservoir for the virus in endemic areas. Spread among animals occurs via the fecal–oral route and through the nose, through wounds and eating infected meat. The disease has also been reported in a wide range of other animals, including monkeys, anteaters, hedgehogs, prairie dogs, squirrels, and shrews. Signs and symptoms in animals are not well researched and further studies are in progress.

There have been instances of animal infection outside of endemic Africa; during the 2003 US outbreak, prairie dogs (Cynomys ludovicianus) became infected and presented with fever, cough, sore eyes, poor feeding and rash. There has also been an instance of a domestic dog (Canis familiaris) which became infected displaying lesions and ulceration.

Cause

Mpox in both humans and animals is caused by infection with Orthopoxvirus monkeypox – a double-stranded DNA virus in the genus Orthopoxvirus, family Poxviridae, making it closely related to the smallpox, cowpox, and vaccinia viruses.

The two major subtypes of virus are clade I and clade II. In April 2024, after detection of a new variant, clade I was split into subclades designated Ia and Ib. Clade II is similarly divided into subclades: clade IIa and clade IIb.

Clade I is estimated to cause more severe disease and higher mortality than clade II.

The virus is considered to be endemic in tropical rainforest regions of Central and West Africa. In addition to monkeys, the virus has been identified in Gambian pouched rats (Cricetomys gambianus), dormice (Graphiurus spp.) and African squirrels (Heliosciurus, and Funisciurus). The use of these animals as food may be an important source of transmission to humans.