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.
Figure 2: Outline of mpvx clades. Note that a 2017 mpox outbreak in Nigeria had a fatality rate of 9 percent, according to CDC experts who briefed Majority Committee Staff. Years later, this mpox was classified as a clade IIb strain. However, other clade II outbreaks had low lethality rates.
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.[1]
- ↑ Fok-Moon Lum et al., Monkeypox: Disease Epidemiology, Host Immunity and Clinical Interventions, 22 Nature Rev. Immunology 597, 597–613 (2022), https://doi.org/10.1038/s41577-022-00775-4.
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