NEW YORK – A team from Portugal, the UK, and elsewhere has tapped into a mpox virus (MPXV) collection in Portugal to get a better look at the viral transmission patterns present there during an outbreak in 2022.
"Presently, a large multi-country mpox outbreak is ongoing worldwide," co-senior and corresponding author João Paulo Gomes, an infectious diseases researcher affiliated with Portugal's National Institute of Health Doutor Ricardo Jorge and Lusófona University, and his colleagues wrote in Nature Medicine on Monday.
"The outbreak has disproportionately affected men who have sex with men (MSM), and MSM with mpox frequently had skin lesions in the anogenital area, suggesting the amplification of transmission through sexual networks," the authors added.
Although the international mpox outbreak was traced back to Nigeria with genomic data assessed in the past, the current study focused on MPXV transmission, using genomic, clinical, laboratory, and epidemiological data from Portugal, where the virus is being monitored through a National Epidemiological Surveillance System.
To untangle the history and transmission dynamics found in Portugal in 2022, the researchers brought together viral genome sequences representing 495 PCR-confirmed mpox cases found there between early May and mid-September of 2022, representing more than half of the 951 mpox identified in the country that year.
"As one of the countries that reported the first cases and, similar to the United Kingdom and Spain, one of the most affected countries during the early stages of the 2022 outbreak, it is very likely that Portugal's epidemics played an important role in the early and widespread dissemination of MPXV worldwide," the authors noted.
Almost all the sequenced isolates came from infected individuals under the age of 50 years old, with the majority sampled from under-40-year-olds who identified as male. Nearly 43 percent of infected individuals who reported their HIV status had tested positive for that virus in the past, the researchers noted, and nearly 97 percent of participants who self-reported their sexual orientation were MSM.
The new sequence data made it possible to pick up viral sublineages that tended to turn up most frequently in infected individuals in Portugal, while untangling relationships between the broader collection of mpox sublineages present there in 2022 and those described in other parts of the world during the outbreak.
Past studies have shown that mpox outbreak strains tend to belong to a B.1 lineage in a subclade dubbed hMPXV1 within a broader IIb clade, previously known as the West African clade, the team noted, and studies so far have linked clade IIb viruses to lower lethality rates and more muted symptoms than viruses in clade I, formerly known as the Congo Basin clade.
With the new sequence data, the researchers placed all but one of the isolates from Portugal into the B.1 lineage. They also flagged viral sublineages that appeared to support the notion that sublineages that went on to spread internationally showed early emergence and spread in Portugal.
When it came to transmission patterns, meanwhile, the researchers saw signs of viral spread through both sexual connections and "superspreader" gatherings at venues where sexual contacts occurred, consistent with past suggestions that some saunas may have contributed to early mpox spread.
"We cannot directly point to saunas as the main trigger for the extensive dissemination of MPXV, as it is not possible to ascertain whether these locations were the actual settings of transmission for all of these cases," the authors cautioned. "However, our study clearly supports the important role of such potential superspreader events in outbreak dissemination, as these cases were frequently integrated into large subclusters … and were commonly found across subclusters with international sequences."