The World Health Organization (WHO) has issued a new Public Health Emergency of International Concern (PHEIC) for mpox due to rapid spread in the Democratic Republic of the Congo (DRC) and neighboring countries. This mpox PHEIC comes just a year after the previous mpox emergency expired, and while they both concern mpox, the current PHEIC has some notable differences.
Historically there have been two major clades of monkeypox virus: clade I and clade II (mpox is the preferred synonym for the disease, the virus causing mpox is still called monkeypox virus). Clade I is endemic in Central Africa, primarily circulating in the Congo Basin including the DRC, and has been associated with about 10 percent mortality. Clade II is endemic in West Africa, most common in Nigeria, and is associated with lower mortality than clade I. Both clades of monkeypox virus have persisted as zoonoses with somewhat limited person-to-person spread, primarily causing isolated outbreaks in close communities, households, and hospital/clinical settings.
The largest mpox outbreak outside of Africa prior to 2022 occurred in the United States in 2003. This outbreak was linked to the importation of Gambian pouched rats from Ghana. The rats transmitted monkeypox virus to prairie dogs in an animal facility, and after the prairie dogs were sold as pets, 79 cases of mpox were reported, resulting in 19 hospitalizations with no deaths. The majority of patients reported exposure to the prairie dogs and no cases were directly attributed to person-to-person transmission. While the genetic makeup of the virus causing the past outbreak is unknown, Ghana is located in West Africa and this outbreak was likely caused by clade II monkeypox virus.
However, in 2022, sustained person-to-person transmission of a new variant of clade II (known as clade IIb) began circulating around the world. A few important observations were made early in the outbreak. Many patients were men who have sex with men (MSM) and they usually had just one or two lesions in their anogenital region (as opposed to the more typical centrifugal distribution of lesions over the body). These findings suggested a new route and/or ease of transmission for monkeypox virus. Monkeypox virus can be spread in biologic fluids and viral DNA has been previously detected in semen. However, sexual partners may also directly contact the lesions on an infected individual or contaminated clothing and bedding. It is unclear whether the virus is spread via sexual intercourse (which could be prevented with barrier protection), close intimate contact, or both.
The global outbreak of clade IIb mpox was associated with a lower mortality rate – 229 deaths have been reported among over 100,000 cases – which is consistent with the lower mortality of clade II mpox. When the incidence of new cases dropped in early 2023, the WHO allowed the PHEIC to expire. It’s important to note that clade IIb continues to circulate globally, but at a lower rate than observed in 2022.
Over the past two years, the incidence of mpox reported throughout the DRC and neighboring countries has been increasing at rates that have not been observed before. Genetic sequencing identified the first outbreak of sexually transmitted clade I monkeypox, caused by a variant now known as clade Ib. While not all cases can be assessed via genetic analysis, the increasing cases of clade I mpox among sexual networks is concerning due to the association of increased severity and higher mortality with clade I mpox. If clade Ib mpox is as transmissible as clade IIb mpox, there may be more deaths due to the disease, prompting the new emergency status from the WHO.
When announcing the PHEIC, WHO Director-General Dr. Tedros Adhanom Ghebreyesus stated, “The emergence of a new clade of mpox, its rapid spread in eastern DRC, and the reporting of cases in several neighboring countries are very worrying. On top of outbreaks of other mpox clades in DRC and other countries in Africa, it’s clear that a coordinated international response is needed to stop these outbreaks and save lives.”
The WHO has released funds from the WHO Contingency Fund for Emergencies to scale up surveillance, preparedness and response activities. The WHO is also coordinating with countries and partners for access to vaccines, therapeutics, and diagnostics.
In clinical practice, mpox should be considered in persons with undiagnosed sexually transmitted infection, particularly for those with at-risk behaviors or with recent travel to DRC or surrounding countries. Public health authorities are encouraged to make vaccines available to any at-risk communities. Considerable disparities exist in vaccine availability, healthcare access, and public education, making this mpox outbreak challenging to control.
