First reported human SHAV-EU1 infection causes fatal encephalitis in France

New Shamonda virus clades, SHAV-EU1 and SHAV-EU2, emerged in Europe in summer 2026, primarily affecting cattle. This report describes the first identified human SHAV-EU1 infection, in a French patient with a severely weakened immune system. The patient developed fatal encephalitis in September 2026, one month after allogeneic stem cell transplantation.

Metatranscriptomic analysis detected SHAV-EU1 in cerebrospinal fluid, with the finding confirmed by RT-PCR. Central nervous system biopsies showed high viral loads. Investigations also detected the virus in serum, respiratory and stool samples at least two months before encephalitis onset.

The report documents severe disease in one highly immunocompromised patient and does not establish the frequency of human infection, transmission routes or risk to other populations. The findings come from a single case and do not support conclusions about treatment or prevention. The authors’ report highlights the detection of a newly emerged animal-associated virus in a human case, but provides no guidance on routine testing or clinical management.