New Andes virus isolate haplotype obtained during prospective close contacts follow-up of an Hantavirus cardiopulmonary syndrome fatal case, Chile

Andes virus (ANDV) is a zoonotic orthohantavirus that causes hantavirus cardiopulmonary syndrome. Transmission occurs mainly through contact with infected rodent excreta and, less frequently, between humans. Viral isolation from human samples is rare; in Chile, only one strain (CHI-7913, 2002) has been reported. The limited number of isolates reflects the challenge of obtaining samples during early viremia before antibodies appear, and maintaining long-term production of infectious particles in culture. We investigated an asymptomatic case from a family cluster, sampled during early infection. The absence of anti-ANDV antibodies in sera was confirmed by ELISA. Blood fractions were used to infect Vero E6 cells for six weeks, with infectivity monitored by RT-qPCR and Immunofluorescence. We obtained a replication-stable isolate from the buffy-coat fraction, achieving high viral loads at early passages. Whole-genome sequencing revealed a novel haplotype with mutations that reverted during non-human cell culture adaptation. This isolate, designated CHI-Hu13724, represents a new human-derived ANDV strain first reported in over two decades in Chile. It provides a valuable tool to study viral replication, infectivity, and pathogenicity.