Smallpox and monkeypox are members of the poxvirus family, which does not include chickenpox, despite the shared surname and uncomfortable, itchy lesions (1). Monkeypox and smallpox are both part of the genus Orthopoxvirus in the family Poxviridae. Both viruses cause similar symptoms (2). An infected individual first experiences fever and headaches, followed by swollen lymph nodes, and finally, painful, pustules all over the body. The hallmark pustules can persist for three weeks before they scab and heal, although they often leave behind long-lasting scars.
Distinguishing monkeypox from smallpox can be tricky, but monkeypox is generally milder, and swollen lymph nodes are less common in smallpox (3). Luckily, smallpox was eradicated in 1980 thanks to the smallpox vaccine, so if these symptoms arise, they are almost surely caused by the monkeypox virus.
Members of the Poxviridae family of viruses are brick-shaped with a structure akin to mitochondria (4). They have a thick outer shell composed of an inner membrane and outer membrane decorated with projections that protect their genomic DNA from the unfriendly immune cells floating around the body.
The projections — shaped like pawn pieces in a chess set — interact with receptors on the surface of cells and release their genetic material and viral enzymes into the cell, initiating viral replication (5). Eventually, viral-induced cell lysis occurs and spreads the virus to neighboring cells.
Scientists reported the first case of monkeypox in humans in 1970. Like countless other viruses, monkeypox is a zoonotic virus, meaning that it originated in animals before jumping to humans. In the past, people caught monkeypox from animals such as prairie dogs. Many recent cases occurred in men who have sex with men, but that doesn’t mean that the virus is sexually transmitted. Monkeypox spreads from close contact, including via clothes and linens (6). Viral particles are found in the throat, which can lead to airborne transmission via respiratory droplets.
Health officials are considering giving close contacts of people diagnosed with monkeypox a smallpox vaccine as a preventative measure since the vaccine dampens the virus’ side effects and shortens its course. Diagnosing, treating, and vaccinating against Poxviridae has a long history, dating all the way back to 1500 BCE.