Fatal Encephalitis Diagnosed in France Following Europe-Wide Cattle Infections
An immunocompromised patient in France has died from multi-organ failure and neuro-invasive disease caused by the Shamonda-Europe 1 virus, marking the first documented human infection of this emerging orthobunyavirus, according to a peer-reviewed report published in Eurosurveillance. The patient, who lived in a rural area of the French Rhône-Alpes region and had a medical history of T-cell prolymphocytic leukaemia, developed acute cortical blindness and confusion on September 23, 2026, according to a report published in Eurosurveillance.
The case follows an investigation into an unidentified bovine disease that triggered fevers, diarrhea, and substantial milk drops in dairy cattle across Europe earlier in the year. Germany’s Friedrich Loeffler Institut (FLI) announced on August 3, 2026, that its investigation discovered high levels of a novel orthobunyavirus of the Simbu serogroup in affected livestock, noting at the time that these viruses were not generally considered significant zoonotic risks to humans.
Medical Timeline and Clinical Progression
The patient was diagnosed with T-cell prolymphocytic leukaemia in November 2025 and received first-line treatment with alemtuzumab between December 2025 and February 2026. This was followed by an allogeneic haematopoietic stem cell transplantation on an unspecified prior date from an HLA-matched related donor, using a conditioning regimen of thiotepa, fludarabine, and busulfan.
The patient was hospitalised continuously in Lyon starting on August 18, 2026. Viral course investigations revealed that the pathogen was present in the patient’s blood for several weeks, with the earliest tested sample returning positive on July 2. Given that clinical signs in European dairy cattle were documented as early as June 2026, researchers estimate the patient contracted the virus between mid-June and July 1, 2026. On June 19, the patient developed an episode of diarrhoea and anorexia matching symptoms observed in infected adult cattle.
Investigating Routes of Transmission
Graft transmission has been ruled out due to a negative polymerase chain reaction test on the graft alongside prior positive blood samples. Researchers are actively investigating three alternative transmission hypotheses. Vector-borne transmission via Culicoides species biting midges near the patient’s rural home remains the primary hypothesis, mirroring how the virus spread among European livestock. Alternative arthropod vectors, blood transfusions, and food-borne transmission via raw milk or cheese are considered less likely, though investigations remain ongoing.
Experts Monitor Virus Risk and Call for Surveillance
While the fatal case highlights the neuro-invasive potential of the pathogen in vulnerable populations, researchers emphasize that the finding does not currently indicate a serious risk for the general immunocompetent population. Experts at the Federal Office for Food Safety and Veterinary Affairs and other European veterinary agencies continue to monitor the epidemiology of the virus. The documented fatality has prompted calls for enhanced surveillance systems across both human and animal healthcare networks in Europe to track potential vector-borne spread.
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