Mpox, formerly known as Monkeypox, is a viral disease caused by the Mpox virus, a member of the Orthopoxvirus genus, the same family of viruses that includes smallpox. The most visible symptom is a distinct rash. Understanding the disease involves recognizing the initial systemic signs that precede the rash, the characteristics of the lesions, and how they change over time.
The Initial Systemic Symptoms
Mpox infection often begins with a prodromal phase, characterized by generalized, flu-like symptoms that appear before any skin lesions. This period typically lasts for one to four days. The most common systemic symptoms include fever, headache, muscle aches, and profound exhaustion.
A distinguishing feature of the prodrome is lymphadenopathy, or the swelling of lymph nodes. These nodes may be localized in the neck, armpits, or groin area, and they can be tender to the touch. While historically the rash followed these symptoms, recent outbreaks show the rash can sometimes appear first, or the prodromal symptoms may be mild or entirely absent.
This initial phase represents the body’s reaction to the virus multiplying after an incubation period, which can range from three to seventeen days. Recognizing this pre-rash stage is important, as a person may be contagious even before visible skin lesions develop. Symptoms like sore throat, cough, and chills also commonly accompany this early systemic reaction.
Characteristics and Distribution of the Rash
The Mpox rash is the definitive visual sign of the illness, often beginning with flat, discolored spots known as macules. These spots rapidly progress into raised, solid bumps called papules. The lesions are described as deep-seated, meaning they feel firm and rubbery, extending into the deeper layers of the skin.
A specific feature of these lesions is umbilication, where a small depression forms in the center of the bump, making them look like a small crater. The lesions are well-circumscribed, meaning they have clearly defined borders, and they can be intensely painful until healing begins. Some patients may develop only a single lesion, while others may have hundreds spread across the body.
The rash distribution can vary, but it frequently appears on the face, palms, and soles of the feet. The lesions also commonly affect the mucous membranes, appearing inside the mouth or in the genital and perianal areas, which can cause significant pain and discomfort. The rash may be confined to localized areas, especially the site of viral entry, or it may spread across the body.
The Stages of Lesion Development
The lesions undergo a sequential transformation from their initial appearance to the final stage of healing. After the initial papules form, they transition into vesicles, which are small blisters filled with clear fluid. This vesicular stage typically lasts for a couple of days before the fluid becomes opaque and yellowish, transforming them into pustules.
The pustules represent a mature stage of the lesion, are sharply raised, and remain firm for about five to seven days. A key diagnostic characteristic is that most lesions in a specific area tend to be in the same stage of development simultaneously, known as synchronous evolution. This synchronous progression helps distinguish Mpox from other viral rashes, like chickenpox, where lesions often appear in multiple stages at once.
The final phase involves the pustules drying out, forming a hard crust or scab. These scabs fall off over one to two weeks, which marks the end of the infectious period, and a fresh layer of skin forms underneath. The healing process can take up to four weeks from the start of symptoms, and the lesions may leave behind pitted scars or areas of altered skin pigmentation.