By Catherine Wu, Communications Assistant

In May, a hantavirus outbreak aboard the MV Hondius cruise ship prompted epidemiologists Dr. Jason Andrews, MD, Stanford professor in the Division of Infectious Diseases and Geographic Medicine and Global Health Faculty Fellow, and Dr. Isaac Bogoch, MD, MSc, University of Toronto professor in the Department of Medicine, to revisit the past to study Andes virus, the only type of hantavirus known to spread between people, rather than just from rodents to people. Hantaviruses are rare in people but have a high fatality rate.

In a new comment in the Lancet Microbe, the researchers shared findings from their recent analysis of contact network records from the two most extensively documented Andes outbreaks to date: a 1996 cluster in El Bolsón, Argentina, with 18 cases, and a 2018-19 outbreak in Epuyén, Argentina, with 34 cases. By characterizing the transmission dynamics of the virus during these two events, Andrews and Bogoch hoped to guide future public health responses to Andes virus outbreaks. 

Andrews and Bogoch’s analysis revealed that the virus doesn’t spread evenly from person to person. Instead, a small number of highly contagious individuals — just the top 20% — were responsible for 81% of all new infections. In addition to who is spreading the virus, the researchers also looked into when it is most contagious. They found that a quarter of transmission happens before the onset of severe febrile illness — including high fever, headache, and muscle pain — that is characteristic of the illness and can occur 20 days after infection. This timing creates a major challenge for controlling outbreaks in crowded settings, like cruise ships, where symptom screening alone won’t catch all infectious patients. By the time an individual starts feeling feverish enough to seek help, they may have already infected others.

Andrews and Bogoch’s findings also pointed to the virus’s limited transmissibility. In their computer simulations, 7 out of 10 individual cases resulted in the virus dying off on its own before any secondary infections. 

“These findings suggest large-scale outbreaks are unlikely if we have an agile public health response, though the risk of localized superspreading events remains real, especially in high-density, crowded environments,” Andrews said in a recent LinkedIn post.