Mpox is a zoonosis, meaning that both humans and animals can be infected with it

Mpox is caused by a virus, MPXV, which is related to smallpox virus. There are two main groups of MPXV, clade I and clade II. Regardless of the clade, the disease is less severe than smallpox.

Mpox can be transmitted to humans from infected animals and spread from person to person. The period from being infected to developing symptoms (the incubation period) is on average 6-13 days, but can be shorter or as long as 21 days. You can only infect others when you develop symptoms yourself. Infection between people occurs through close contact, including sexual contact. Infection can also occur indirectly through material with the virus on it, such as bedding, etc. Finally, it has been seen that infected pregnant women can also pass the infection on to their unborn children.

The disease has been known in Africa for many years, with the first human case being detected in 1970 in the Democratic Republic of Congo (DRC).

From 2022, a subclade (IIb) of clade II spread to large parts of the world outside Africa, including Europe and Denmark, primarily among men who have sex with men. The course of the disease has generally been mild. It has been possible to contain the spread, including through vaccination of risk groups and guidance on how to prevent infection. In Denmark, there have been sporadic cases of mpox, all of the IIb subclade.

However, the situation is different in Africa. Since 2022, there has been a significant increase in the number of mpox cases in the DRC. In contrast to the global outbreak with the IIb subclade in 2022, the outbreak in central Africa has had a predominance of children < 15 years of age among those infected, and the cases have, based on preliminary information, a more severe clinical presentation, including a higher mortality rate. It is assumed that infection occurs through close person-to-person contact, including, but not limited to, sexual contact.

In September 2023, a new subclade of clade I, called Ib, was identified among infected people in eastern DRC. This variant spread to neighboring countries, including Burundi, Kenya, Rwanda, and Uganda. As clade 1 had been suspected of causing more severe disease and having a broader pattern of infection than clade 2, the WHO declared the outbreak in central Africa a 'Public Health Emergency of International Concern' (PHEIC) on August 14, 2024. Such a declaration allows some additional tools to be used for international control of the disease. However, it turned out, also based on experience with subclade 1b outside Africa, that this variant did not cause as severe disease as feared, which is why the WHO lifted the mpox outbreak as a PHEIC in September 2025.

Worldwide, as of February 2026, almost 180,000 confirmed or suspected cases of mpox have been registered in the world. In the past year, travel-related cases of mpox clade I have been detected in countries outside Africa, including in Europe, and in recent months, also non-travel-related cases. All cases of this clade in these countries have been mild, and it is still mainly men who have sex with men (MSM) who are infected outside Africa. In April 2026, the first mpox clade Ib case was detected in Denmark.

Symptoms

Mpox often presents with general symptoms such as fever, chills, headache, muscle aches and fatigue. Swollen lymph nodes are also often seen. Within 1 to 3 days after the onset of symptoms, the patient may develop a rash with blisters, possibly only around or on the genitals or around the anus, and which may be limited to this area. In some of those infected with subclade IIb, proctitis (inflammation of the anus) has also been seen as the only symptom, without any visible blisters. Proctitis can be extremely painful. During previous outbreaks (most often in Africa), the symptom picture has been somewhat different, with a rash and blisters that often begin on the face and then spread to other parts of the body. Regardless of the location of the blisters, they dry out and eventually form crusts. The typical size of the elements is 0.5 to 1 cm.

Differential diagnosis may include chickenpox, syphilis, herpes and molluscum contagiosum, where there is a risk of confusion. If samples have been taken for one of these diseases in adult men on the basis of blisters and the samples have come out negative, testing for mpox may be considered, just as testing for symptomatic rectal chlamydia in men may be considered.

The disease is usually of mild to moderate severity, lasts about 2-4 weeks and resolves on its own for most people.

Cause

Mpox is a zoonosis that can be transmitted to humans from infected animals and can spread from person to person.

Transmission routes

Mpox is transmitted through close contact, including sexual contact, and by sharing clothing or bedding with people who are sick with mpox. Infected pregnant women have been seen to have transmitted the infection to their unborn children.