Mpox, formerly known as Monkeypox, is a viral disease caused by the Mpox virus (MPXV), a species of the Orthopoxvirus genus, which belongs to the larger Poxviridae family. The illness has garnered global attention due to its recent spread beyond regions where it is historically found. While outbreaks were once sporadic, the disease has seen a sustained increase in incidence and geographic expansion over the past few years. Mpox typically causes a painful rash, fever, and other systemic symptoms, though most people recover fully within a few weeks.
Viral Classification and Origin
The Mpox virus is a large, enveloped double-stranded DNA virus, placing it within the Orthopoxvirus genus, alongside the variola virus that causes smallpox. This classification means the smallpox vaccine offers protection against Mpox infection. The virus is genetically categorized into two main clades: Clade I, historically found in Central Africa and associated with more severe illness, and Clade II, found in West Africa.
The 2022 global outbreak was caused by a lineage within the Clade II group, specifically Clade IIb, which tends to cause less severe disease. The virus was first identified in captive monkeys in Denmark in 1958, leading to its original name. The first reported human case occurred in 1970 in the Democratic Republic of the Congo. Mpox is considered a zoonosis, meaning it primarily circulates in animals, with small African rodents like squirrels and rats being the most likely hosts.
How the Infection Spreads
Human-to-human transmission of Mpox primarily occurs through close, sustained physical contact with an infectious person. The most common route involves direct skin-to-skin contact, often during intimate or sexual activities, where the virus is transmitted from skin lesions or mucosal surfaces. Contact with infectious bodily fluids, such as saliva, respiratory secretions, or fluids from lesions around the genitals, anus, or mouth, can also facilitate spread. The virus enters the body through broken skin, the respiratory tract, or mucous membranes like the eyes, nose, or mouth.
Transmission can also happen via contaminated materials, known as fomites, which include clothing, bedding, or towels used by an infected person. Respiratory transmission via large droplets is considered a minor route and typically requires prolonged, face-to-face contact with an infected individual. This is not considered airborne transmission over long distances, but rather the result of being physically close to someone who is talking or breathing.
Animal-to-human transmission, or zoonotic spillover, occurs when a person is bitten or scratched by an infected animal or through contact with its bodily fluids or lesions. This initial transmission event introduces the virus into the human population. Subsequent spread is maintained through the close contact routes described above.
Identifying the Signs of Mpox
Symptoms of Mpox typically begin within 3 to 21 days after exposure to the virus, with an average incubation period of about one to two weeks. The illness often starts with systemic symptoms that resemble the flu, lasting for one to four days. These initial signs include the sudden onset of fever, intense headache, muscle aches, and profound exhaustion. A distinguishing feature is the swelling of the lymph nodes (lymphadenopathy), which may occur in the neck, armpits, or groin.
The characteristic skin rash usually appears one to four days after the onset of these systemic symptoms, although in some recent cases, the rash has been the first or only symptom. The lesions can be painful or itchy and may appear anywhere on the body, including the face, hands, feet, and mucosal surfaces like the mouth or genitals. The rash progresses through distinct phases:
- Beginning as flat, discolored areas (macules).
- Becoming raised, firm spots (papules).
- Evolving into small, fluid-filled blisters (vesicles).
- Turning into pustules filled with yellowish fluid.
- Eventually crusting over and forming scabs.
The entire progression of the rash can last between two and four weeks. An infected person is considered contagious from the onset of the first symptom until all lesions have fully healed, the scabs have fallen off, and a fresh layer of intact skin has formed beneath.
Prevention and Post-Exposure Care
Prevention strategies for Mpox involve both proactive measures and reactive medical interventions. For individuals at high risk of exposure, a two-dose vaccine regimen is available as pre-exposure prophylaxis (PrEP). The preferred vaccine, JYNNEOS, is a live, non-replicating virus vaccine approved for the prevention of both smallpox and Mpox. It is administered as a series of two subcutaneous doses given four weeks apart.
If a person has been exposed to the virus, the same JYNNEOS vaccine can be used as post-exposure prophylaxis (PEP). Vaccination should occur as quickly as possible following exposure, ideally within four days, to offer the best chance of preventing the illness entirely. If administered between four and fourteen days after exposure, the vaccine may still help reduce the severity of the symptoms. General preventive practices involve avoiding close physical contact with anyone who has an active rash and practicing good hand hygiene.
Individuals who develop the disease must follow strict isolation procedures to prevent further community spread. Isolation should be maintained until all symptoms have resolved and a new layer of skin has replaced every lesion. For severe cases or for individuals who are at high risk of severe illness, such as those with weakened immune systems, antiviral treatments like Tecovirimat (TPOXX) may be used. TPOXX is available through specific expanded access programs under physician guidance.