Health officials in Spain have documented what appears to be the first case of human-to-human transmission of mpox clade 1b outside of endemic regions in Africa without any known travel link.

The report, published in the International Journal of Infectious Diseases, describes a 49-year-old man who presented to a Madrid clinic in October 10, 2025, with a single genital ulcer and swollen, painful lymph nodes in his groin area. 

The patient, who had previously received two doses of the Imvanex smallpox/mpox vaccine (known as Jynneos in the United States), had not traveled abroad. He reported sexual contact with two local partners, neither of whom had traveled to endemic regions. 

Polymerase chain reaction (PCR) testing of the lesion confirmed an infection with mpox clade 1b, a highly transmissible strain that emerged during an outbreak in the Democratic Republic of the Congo in 2023. In August 2024, the World Health Organization (WHO) declared mpox a Public Health Emergency of International Concern (PHEIC) because of the risk of international spread. 

Previous cases in Europe tied to endemic regions

After Spanish authorities reported the case, investigations in Europe and the United States identified additional cases not associated with travel to endemic regions. The WHO lifted the PHEIC designation in September 2025 after cases declined in affected countries, but the newly identified infection highlights the need to be alert to possible human-to-human transmission in non-endemic regions.

Several countries in Africa have sustained human-to-human transmission of mpox clade 1b. The first case reported outside of Africa was in a Swedish national who traveled to an endemic African region. Cases have been detected in countries outside of Africa since then, though almost all have been in people who recently traveled to endemic African countries or who had contact with others who had traveled to those regions. 

To help prevent mpox spread and ensure an effective publish health response, the authors recommend control measures when a case is detected, clade-specific testing in all confirmed cases, vaccination of individuals at higher risk of exposure (particularly men who have sex with men), and coordination with scientific societies and community organizations.

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