Mpox was named after lab monkeys, though monkeys probably are not its source
Scientists first identified the virus in 1958 after pox-like outbreaks in research monkey colonies, so it was called monkeypox. Yet the likeliest natural hosts are small African mammals such as the fire-footed rope squirrel. A close cousin of smallpox, mpox is usually mild, but one strain is far deadlier than the other.
The virus belongs to the genus Orthopoxvirus, alongside the agents of smallpox, cowpox and vaccinia. Humans first caught it on record in 1970, in Basankusu in what is now the Democratic Republic of the Congo, and it is endemic in Central and Western Africa. Outbreaks have grown more frequent and severe since then, possibly because routine smallpox vaccination stopped and population immunity has faded.
Illness usually starts about a week after infection, though the gap can range from one day to four weeks. Fever, muscle aches and a sore throat give way to swollen lymph nodes and a rash of small spots that swell into bumps, fill with fluid, burst and scab, a cycle of roughly ten days. Some people get one sore, others hundreds, and some none at all. Symptoms last two to four weeks, longer in people with weakened immunity, and complications include pneumonia, sepsis, encephalitis and blindness after corneal infection. The virus passes through contact with infected skin or body fluids, including sex, and people stay contagious until every lesion has healed.
Two main branches exist. Clade I is considered more severe than clade II, and past outbreaks carried death rates estimated between 1% and 10%. The 2022 to 2023 global outbreak, driven by clade IIb, killed around 0.16% of those infected, mostly people already immunocompromised, whereas the clade I epidemic in Congo stood at 4.9% in April 2024. Part of that gap may reflect missed mild cases where health care is thin, as well as real differences in virulence. A new variant, clade Ib, emerged in Congo in 2023, and in August 2024 the WHO declared it a public health emergency of international concern.
No vaccine was built specifically for mpox, but smallpox vaccines work against it, and the antiviral tecovirimat is used although its benefit is unproven. In November 2022 the WHO adopted the name mpox, partly to curb racist and stigmatising remarks about the old one.
Source: Mpox
