Mpox clade Ib transmitted in a healthcare setting outside Africa

Mpox is a viral disease usually transmitted from animals to humans and symptoms include fever and skin rashes.  In 2023, a new variant of monkeypox virus (MPXV), called clade Ib, emerged in Kamituga in the Democratic Republic of the Congo.

In their rapid communication published in Eurosurveillance, McLoughlin et al. describe, to their knowledge, the first reported transmission of MPXV clade Ib in a healthcare setting outside of the African continent. In total, four epidemiologically linked mpox cases were identified in an outbreak in Ireland during August and October 2025. One person in this mpox cluster was a healthcare worker who treated an mpox patient in hospital before mpox was considered as a differential diagnosis.

The hospitalized patient had no travel history and initial clinical presentation did not include skin lesion counts or respiratory symptoms typically expected with mpox. This complicated early recognition of the disease. Once mpox was included as a differential diagnosis, infection prevention and control measures included isolation under airborne/contact/droplet precautions and identification of contacts in the community to offer vaccination.

Whole genome sequencing analysis confirmed MPXV clade Ib for the three cases with available sequences which were genetically identical, confirming an epidemiological link between these cases. The genomic results also showed mutations consistent with human-to-human as opposed to zoonotic transmission from animals.

Needed: high level of clinical suspicion of mpox

Based on the travel history (from Pakistan via Eastern Mediterranean Region) of the initial case, the authors note that "this cluster highlights the ongoing possibility of mpox transmission from travel-associated cases and emphasises the need for a high level of clinical suspicion of mpox in cases with relevant clinical symptoms associated with travel to countries where mpox is currently circulating."

In the same Eurosurveillance issue, Bugeme et al. describe a shift from sexual to predominantly non-sexual transmission in their surveillance study on community transmission of mpox clade Ib in the eastern part of the Democratic Republic of the Congo (DRC) during 2024. They hypothesise that overcrowded housing likely accelerated the spread during this mpox outbreak which primarily affected children and adolescents below the age of 15 years and showed limited reported sexual transmission.

Anyone who presented with a rash or skin lesions during the study period was considered a suspected mpox case and eligible for the analysis by the authors.

Between June and October 2024, 973 suspected mpox cases were recorded at the mpox treatment centre in Uvira (DRC), half of them were females. The majority of mpox cases was found among children and adolescents, with 68% (n = 620) aged <15 years and 35% (n = 344) younger than 5 years of age.

The proportion of cases aged < 15 years increased as the outbreak progressed until mid-July 2024 and severe to very severe clinical presentation of mpox with more than 100 lesions was observed in 22% (n = 191/858) of suspected cases.

Bugeme et al. found that two-thirds of patients (68%) reported exposures primarily within their own households, and among these, the majority (67%) involved exposure to multiple suspected mpox cases. Reported exposure within a healthcare facility was relatively low in comparison (14 of 439 respondents).

The authors conclude that "several factors likely contributed to the high incidence of MPXV clade Ib among children: (i) cryptic transmission; (ii) prior smallpox immunity in older individuals; and (iii) age-related differences in MPXV susceptibility, exacerbated by child malnutrition." Based on this, they advocate for speeding up the development of mpox vaccines for children and supporting prevention efforts in homes and communities.