Smallpox was a highly contagious and often deadly viral infection caused by the variola virus. It caused widespread illness and death for thousands of years, leaving a lasting visual impact on survivors. Understanding its distinctive rash was once crucial for diagnosis and containment.
Identifying Smallpox: The Distinctive Rash
The smallpox rash had a characteristic appearance, setting it apart from other skin conditions. Lesions were deep-seated, firm, and felt like peas under the skin. They were round and uniform in size, showing the same stage of development in any body area. The rash often appeared first in the mouth and on the face, then spread to extremities like the arms, legs, palms, and soles, before moving to the trunk.
Individual lesions progressed through distinct stages. They appeared as flat, red spots (macules), then developed into raised bumps (papules). These evolved into fluid-filled blisters (vesicles) over four to five days.
Within one to two days, vesicles developed a central indentation and transformed into firm, pus-filled pustules. These tense, deep-seated pustules eventually formed crusts and scabs. Scabs fell off around 14 days after the rash first appeared, leaving deep, pitted scars known as pockmarks.
How Smallpox Progressed
Smallpox began with an incubation period, typically lasting 10 to 14 days (range 7-19 days). During this time, an infected person showed no symptoms and was not contagious. A prodromal phase followed, lasting two to four days, characterized by sudden flu-like symptoms. These included high fever, severe headache, backache, and sometimes vomiting.
The eruptive stage began as the fever subsided, with the rash appearing first in the mouth and on the tongue as small red spots that quickly turned into sores. As these oral sores broke open, a skin rash emerged, starting on the face and extremities, then spreading to the trunk within 24 hours in a centrifugal pattern. As the rash progressed through its stages—from macules to papules, then to vesicles and pustules—the fever could return and remain high until scabs formed. The entire process of rash development, from initial appearance to scabs falling off, took three to four weeks.
Smallpox’s Global Eradication
Smallpox cases are now rare because the disease has been globally eradicated. The World Health Organization (WHO) launched a global eradication program in 1959, intensifying efforts in 1967. This effort relied on widespread vaccination campaigns and diligent surveillance.
Vaccination played a key role. The smallpox vaccine, developed by Edward Jenner in 1796, was the first successful vaccine against a contagious disease. Surveillance and containment strategies were also applied; public health workers identified cases, isolated patients, and monitored their contacts. The last known natural case of smallpox occurred in Somalia in 1977. In 1980, the WHO officially declared smallpox eradicated worldwide, making it the only human infectious disease to achieve this distinction.
Smallpox vs. Similar-Looking Conditions
Smallpox shares symptoms like fever and rash with other conditions, which can lead to confusion. Chickenpox (varicella) is one such disease, but their rashes differ. Smallpox lesions are deep-seated, firm, and progress uniformly through their stages across the body. In contrast, chickenpox lesions are more superficial, itchy, and can appear in different stages (macules, papules, vesicles, and scabs) simultaneously on the same body area.
Another distinct condition, mpox (formerly monkeypox), is caused by a virus related to smallpox. While mpox can also cause a rash and flu-like symptoms, its lesions evolve at the same rate, similar to smallpox. However, mpox symptoms are milder than smallpox, and mpox patients often have swollen lymph nodes. Unlike smallpox, which is no longer found naturally, mpox is a circulating disease.