By combining epidemiological investigations (who was infected and how) with whole-genome sequencing of the virus, researchers showed that all confirmed cases belonged to the same viral group (Clade IIb, lineage C.1). This means the outbreak most likely started from one introduction of the virus, followed by local transmission between people.

The study found that transmission mainly occurred through close and intimate contact within connected social networks. No cases reported recent international travel or contact with animals, suggesting the outbreak was driven by local spread rather than repeated introductions from abroad.

This work shows how genomic epidemiology helps health authorities understand how viruses spread and supports more targeted public health responses. It also shows how regional viral strains can spread into new countries, emphasizing the need for ongoing surveillance and strong laboratory capacity. The study was carried out in collaboration with the Cambodian Ministry of Health and the Institute of Tropical Medicine.