A deadly disease spread by shrews has been killing humans for decades and going unnoticed, according to scientists.
Doctors say at least 14 patients in Germany have died from encephalitis caused by Borna disease virus 1.
But it is feared the total could be much higher, given the shrews that carry the bug are found in Austria, Switzerland and Liechtenstein.
Experts are now calling for more research into the spread of the virus, to work out if it really is behind even more unexplained human deaths.
Encephalitis makes the brain swell up and can cause a fever, headache, vomiting, seizures, limb weakness and loss of consciousness.
The Borna disease virus is carried by bi-coloured white-toothed shrews in Germany, Austria and Switzerland, and can cause serious illness in horses, sheep and humans if they contract it, according to scientists (stock image)
Experts at Regensburg University Hospital in Germany studied the medical records of 56 people who died between 1999 and 2019.
The group all had encephalitis and lived in in the south of Germany, where the Borna disease-carrying bi-coloured white-toothed shrews roam naturally.
Eight of them were found to have Borna disease virus 1, bringing the confirmed total of human cases to 14.
Six older cases of Borna virus were not dated but were diagnosed in the same region and only one of them recovered.
The eight new patients all died within two months of being diagnosed with encephalitis, which affects around 6,000 people each year in the UK and 25,000 in the US.
Their illnesses tended to begin with a fever, headache and confusion, and progress to unsteady walking, memory loss, seizures, deep coma and eventually death.
The others had encephalitis which stemmed from other causes – viruses such as herpes, measles, mumps and rubella may also cause the deadly brain illness.
Professor Barbara Schmidt, one of the researchers, said: 'Our findings indicate Borna disease virus infection has to be considered a severe and potentially lethal human disease transmitted from a wildlife reservoir.
The virus was recorded in shrews and pet animals – believed to be cats – across Germany, Switzerland and Austria, with all eight human cases in the study found in the south of Germany (human cases shown as squares)
Encephalitis is an uncommon but serious condition in which the brain becomes