First human infection with Shamonda virus confirmed in France after fatal encephalitis

The World Health Organization has reported the first laboratory-confirmed human infection with Shamonda virus anywhere in the world, a fatal case of encephalitis in eastern France in a virus that until this year was known only in animals. France's national focal point notified WHO on 20 October 2026, and the UN agency published the details in a Disease Outbreak News notice on 2 November [s1].

The patient was an immunocompromised older man who had been hospitalised on 18 August for an underlying illness [s1]. He developed neurological signs on 23 September — visual disturbances, confusion, loss of consciousness and seizures — and was diagnosed with severe encephalitis two days later, when cerebrospinal fluid was collected [s1]. He died on 8 October. Metagenomic sequencing of the 25 September fluid samples identified Shamonda virus, and French health authorities were notified on 7 October [s1].

How the case was confirmed

The evidence that this was a genuine human infection rather than a laboratory artefact is unusually detailed for a first-of-its-kind report. Retrospective RT-PCR testing of serum collected between early July and October, as well as faecal, urine, saliva and respiratory samples, confirmed the presence of viral RNA, and post-mortem biopsies of the brain, liver and spleen showed very high viral genomic loads [s1]. A wide panel of tests for other encephalitis pathogens came back negative [s1]. The recovered sequence belonged to the SHAV-EU1 genotype, covered roughly 90% of the genome and was 99% identical to a virus circulating in neighbouring Switzerland [s1].

The man lived in rural eastern France, where animal infection has been documented since July, and had not travelled abroad in the preceding year [s1]. He had received multiple blood transfusions between February and October, but testing of the linked donors by the French Blood Establishment and the national arbovirus reference centre was negative, making transfusion-associated transmission unlikely though not formally excluded [s1]. Investigators have not pinned down how he was infected; mosquito exposure was reported, and vector-borne transmission is considered the most plausible route, with food-borne transmission still under investigation [s1].

An animal virus new to Europe

Shamonda virus sits in the Simbu serogroup of the genus Orthobunyavirus and belongs to the same species as Schmallenberg virus, the midge-borne pathogen already established in European livestock [s1]. It was first isolated from cattle in Nigeria in the 1960s and had never been linked to human disease before this case [s1]. Its arrival in Europe is recent: the virus was detected on the continent only in the summer of 2026, when an acute, non-fatal syndrome marked by sharp drops in milk yield, diarrhoea, fever and lethargy began spreading through dairy herds in southern Germany and Switzerland [s2].

By the end of July, more than 100 affected farms had been reported to the cattle health service in the German state of Baden-Württemberg alone, with within-herd illness rates reaching as high as 100% but no animal deaths [s2]. Veterinary laboratories ruled out bluetongue, Schmallenberg and a long list of other viruses by PCR before pan-Simbuvirus testing and metagenomic sequencing recovered a complete Shamonda genome [s2]. By 20 October, animal detections in metropolitan France spanned 54 departments, predominantly in cattle, and WHO listed confirmed or suspected infections in cattle, horses and alpacas across Belgium, France, Germany, the Netherlands and Switzerland, with further detections since reported in Austria, Ireland, Jersey, Liechtenstein, Portugal, Slovenia and Spain [s1].

Risk still cannot be quantified

Like Schmallenberg, Shamonda is thought to spread through the bites of Culicoides midges rather than directly between animals, and no specific antiviral or vaccine exists [s1]. WHO is careful to say that a single human case cannot establish how often the virus infects people, how severe those infections are, or whether healthy adults are at risk [s1]. The seasonal decline in midge activity may lower vector-borne transmission in northern Europe over the coming months, but the agency stops short of calling the public health risk low — it says the risk "cannot yet be reliably assessed or quantified" and that the assessment will be revised if more cases appear [s1].

For now WHO recommends a coordinated One Health response: continued animal surveillance, serosurveys in humans, enhanced entomological studies to identify the vectors, and testing for Shamonda in patients with compatible symptoms and plausible exposure [s1]. No further human cases have been detected [s1]. The notice is a reminder of how closely Europe's warming climate and the shifting range of biting midges are tied to which animal viruses reach people — the same ecological pathway that carried bluetongue and Schmallenberg across the continent before it.