Mpox is a viral infection that causes a distinctive rash of fluid-filled blisters, along with fever and body aches. The illness typically lasts two to four weeks. Formerly called monkeypox, the disease is caused by a virus in the same family as smallpox, though it is generally less severe. The World Health Organization declared a public health emergency of international concern in August 2024 after a new strain began spreading in central Africa and beyond.
The Virus Behind the Disease
The mpox virus (MPXV) is a large, brick-shaped DNA virus belonging to the Orthopoxvirus genus, the same group that includes the smallpox virus and the vaccinia virus used in smallpox vaccines. Each viral particle measures roughly 200 to 250 nanometers across and is wrapped in a ridged outer membrane made of fat and protein. Unlike many common viruses that carry RNA, mpox carries double-stranded DNA, which makes it relatively stable and slower to mutate.
Three recognized clades (genetic branches) of the virus circulate in different parts of the world, and they differ significantly in how dangerous they are:
- Clade I originates in the Congo Basin region of central Africa and carries the highest risk, with mortality reaching up to 10%. It spreads primarily from animals to humans.
- Clade IIa is found in West Africa, has a mortality rate below 1%, and also spreads mainly through animal contact.
- Clade IIb is the strain behind the global outbreak that began in May 2022. It is closely related to Clade IIa, carries a similarly low mortality in people with healthy immune systems, and is notable for spreading extensively from person to person rather than from animals.
A newer sublineage called Clade Ib triggered the 2024 emergency declaration. It emerged in the Democratic Republic of the Congo, spread to neighboring countries, and reached areas that had never reported mpox before.
How Mpox Spreads
Mpox moves between people primarily through close physical contact. Skin-to-skin touching, sexual contact, kissing, and even prolonged face-to-face conversation can transmit the virus, because infectious particles can be released from skin lesions, saliva, and respiratory droplets. Household members of an infected person are at particular risk.
You can also pick up the virus from contaminated objects. Clothing, bed linens, and towels that have touched an infected person’s rash can carry viable virus. Healthcare workers face exposure through needlestick injuries, and community settings like tattoo parlors pose a risk if equipment or surfaces are contaminated. In a 2021 case study from Dallas, Texas, researchers detected live mpox virus on household surfaces a full 15 days after the infected person had left the home. Related poxviruses can survive even longer in cool, dry, UV-protected environments, potentially remaining viable for months.
Animal-to-human transmission happens through bites, scratches, or handling infected animals during hunting, skinning, or cooking. Pregnant individuals can pass the virus to their baby during pregnancy or birth.
Symptoms and How the Rash Progresses
After exposure, the incubation period runs roughly one to two weeks, with a range of 3 to 17 days. Early symptoms often include fever, headache, muscle aches, swollen lymph nodes, and exhaustion. The hallmark rash usually appears within a few days of these initial symptoms.
The rash follows a predictable sequence of stages. Lesions sometimes first appear on the tongue and inside the mouth, then spread to the face, arms, legs, palms, and soles. Each lesion moves through four visible phases:
- Macules (days 1–2): Flat, discolored spots on the skin.
- Papules (days 1–2): The spots become raised bumps.
- Vesicles (days 1–2): Bumps fill with clear fluid.
- Pustules (days 5–7): Fluid turns opaque and the lesions become firm, round, and deeply seated with a dimple in the center.
After the pustule stage, lesions crust over and form scabs that persist for about one to two weeks before falling off. A person remains contagious until all scabs have naturally separated and fresh skin has formed underneath. The entire illness from first symptoms to the last scab typically spans two to four weeks.
Who Faces the Greatest Risk
Most healthy adults recover from mpox without medical intervention, especially from Clade IIb infections. Severe disease is more likely in people with weakened immune systems, including those with poorly controlled HIV, organ transplant recipients, and anyone on immunosuppressive medications. Young children, pregnant or breastfeeding individuals, and people with certain skin conditions (eczema, psoriasis, burns, active shingles, or a condition called Darier disease) are also at higher risk for the virus spreading widely across the body.
Serious complications can include lesions covering 25% or more of the body, secondary bacterial infections of open sores, airway compromise when lesions develop in the throat, and rare but dangerous inflammation of the heart or brain.
Testing and Diagnosis
The gold-standard test for mpox is a real-time PCR test that detects the virus’s DNA. Samples are collected by swabbing the fluid or surface of a skin lesion. Lesion crusts and the tissue from a blister roof also work. Blood alone is not a reliable specimen because the phase when the virus circulates in the bloodstream may have already passed by the time the rash appears. A negative blood test cannot rule out infection.
If you develop an unexplained rash with fluid-filled blisters, especially alongside fever and swollen lymph nodes, getting tested promptly matters for both your care and preventing spread to others.
Treatment Options
For most people, mpox management focuses on relieving symptoms: controlling pain, keeping lesions clean, and staying hydrated. The antiviral tecovirimat, originally developed for smallpox, is available in certain situations. In the United States, the CDC provides access to it for people at high risk of severe disease, including those with compromised immune systems, pregnant or breastfeeding individuals, children under 18, and anyone presenting with widespread or life-threatening lesions.
Clinical trial results have been mixed. Two randomized studies found that while tecovirimat was safe, it did not significantly speed up the time it took for lesions to resolve compared to a placebo. Its use remains targeted to people most likely to develop dangerous complications rather than as a routine prescription for every case.
Vaccination
The JYNNEOS vaccine (also marketed as Imvanex or Imvamune outside the U.S.) is the primary vaccine used against mpox. It is given as two doses, injected under the skin four weeks apart. Data from a large U.S. study showed 75% effectiveness after one dose and 86% after two. A 2023 study from the United Kingdom estimated 80% effectiveness following the full two-dose series.
Vaccination is most effective as pre-exposure protection for people at elevated risk, or as post-exposure prevention given within days of a known contact. Because the mpox virus is related to smallpox, older smallpox vaccines also provide some cross-protection, which is why people vaccinated against smallpox before routine vaccination ended in the 1970s and 1980s may have partial immunity.
Protecting Yourself
Avoiding direct skin contact with anyone who has an active mpox rash is the most effective way to prevent infection. If someone in your household is infected, wear gloves when handling their laundry or bedding, disinfect shared surfaces regularly, and avoid sharing towels, clothing, or utensils. The virus is susceptible to common EPA-registered disinfectants, but its ability to survive on surfaces for weeks means routine cleaning matters.
In areas where mpox circulates in animal populations, avoid handling wild animals, especially rodents and primates, and cook all meat thoroughly before eating. If you’re in a group that qualifies for vaccination, completing the full two-dose series well before any potential exposure gives you the strongest protection.