Differentiated Contact Tracing for Emerging Zoonotic Hantavirus and Ebolavirus Infections: Lessons from the 2026 Andes Virus (MV Hondius) and Bundibugyo Virus Outbreaks

In May 2026, two outbreaks occurred at once: an Andes virus outbreak aboard the MV Hondius expedition cruise ship (13 cases (12 laboratory-confirmed and 1 probable), 3 deaths, and more than 600 contacts traced across 32 countries and territories; passengers and crew from 23 countries; data as of 22 June 2026) and a Bundibugyo virus disease (BDBV) outbreak in Central Africa (more than 1000 laboratory-confirmed cases and more than 250 confirmed deaths in the Democratic Republic of the Congo and Uganda; data as of 22 June 2026). The two pathogens diverge sharply in their transmission epidemiology. Aboard the MV Hondius, person-to-person transmission was sustained across three generations from a single index case, and one asymptomatic, PCR-positive contact later developed symptoms, indicating pre-symptomatic ANDV RNA detection, although the extent to which this corresponds to infectiousness and onward transmission remains uncertain. BDBV, on current evidence, has not been documented to sustain pre-symptomatic transmission as a major driver of its outbreaks, which allows for contact tracing of different timing and intensity. This Perspective draws together the epidemiological data from the MV Hondius outbreak, the endemic-region experience (Chile's 2021-2025 secondary attack rate of 5.7%; Argentina's 1996 El Bolsón and 2018 Epuyén outbreaks), the molecular pathogenesis, the diagnostic platforms, the therapeutic pipeline (favipiravir, tocilizumab, Icatibant) and the vaccine strategies (USAMRIID DNA vaccine, phase 1 completed). We set the contact-tracing and active-surveillance protocols applied to ANDV against the less stringent protocols that may suffice for BDBV.