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 The Virus

MPXV is an orthopoxvirus closely related to variola virus (VARV), a human virus that caused smallpox and was eradicated in 1980. MPXV is a zoonotic virus present in a natural animal reservoir in rodents in Africa, including squirrels, Gambian rats, and dormice, and can be transmitted to monkeys and humans. Two clades of MPXV have been identified.



Clade I (Central Africa or Congo Basin) is associated with a high mortality rate (~10–15 percent) and long chains of human-to-human transmission. By contrast, clade IIa (West Africa) is associated with a low mortality rate (~one percent) and is less transmissible between humans. The MPXV isolate-causing infections outside Africa are related to clade IIa and were designated as clade IIb. The MPXV genome consists of a double-stranded DNA molecule of ~200,000 base pairs encoding 190 proteins.