Hantavirus: Andes virus is unlikely to cause large outbreaks, but case isolation remains essential

Due to its characteristics, the Andes virus (ANDV) —the hantavirus strain responsible for the outbreak reported on a cruise ship in recent weeks—is unlikely to cause large outbreaks, even if a case is introduced into a population that remains entirely susceptible. This is the conclusion of a study based on mathematical modeling that has just been published in Eurosurveillance ( link to the paper).

The study, conducted by researchers from the Center for Health Emergencies at Fondazione Bruno Kessler and the Italian national institute of health (Istituo Superiore di Sanità, ISS), simulated the potential spread of the virus following the introduction of a single case into a generic population, developing different scenarios based on the percentage of cases effectively isolated. “According to the results of the analyses,” the authors write in the conclusions, “four months after symptom onset in the index case, the outbreak would be unlikely to exceed 50 cases, with a high probability of transmission dying out, especially if more than half of the cases were effectively isolated from the outset.”

The authors explain that effective case isolation is made possible by the characteristics of the virus. Available data indicate that infections are generally symptomatic and severe, while the long incubation period and the extended interval between symptom onset in a primary case and a secondary case give public health authorities more time to trace contacts before they become contagious. However, the authors note that the analyses are based on epidemiological parameters estimated from a single outbreak, which represents one of the study’s main limitations, as those conditions may not be fully comparable to different contexts or to an epidemiological situation such as the current one.

“The results of the analysis,” the article concludes, “confirm the assessment by international authorities that the risk of widespread transmission in the general population is low or very low. Although the findings suggest a scenario involving a limited number of cases even after several months of unmitigated transmission, the high fatality rate associated with the virus requires the adoption of the strongest possible precautions to limit the spread of infection. The results also underscore that timely diagnosis and case isolation are key measures for stopping transmission within communities.”

The publication’s first authors are Valentina Marziano and Alfredo De Bellis, with Stefano Merler as senior author, and contributions from the entire FBK Center for Health Emergencies research team: Carla Molina Grané, Francesco Menegale, Lorenzo Luchini, Mattia Manica, Giorgio Guzzetta, and Piero Poletti, together with colleagues from ISS.