A virus spread by squirrels has taken the lives of at least three men in Germany. The victims, all squirrel handlers, caught the disease after handling exotic versions of the animals, health officials report.

Variegated squirrels are capable of transmitting the newly recognized disease to humans, researchers determined. This rare type of squirrel is native to Central America and southern Mexico. The animals do not live in the wild in North America.

Researchers are uncertain how the animals became infected with the variegated squirrel 1 bornavirus (VSBV-1) or even whether or not it came from Central America with the rodents. The animals all appeared to be healthy when the infections were passed onto human handlers.

"A new bornavirus that can be transmitted to humans and cause severe disease has been detected in variegated squirrels. The study shows that exotic animal species can have the risk of transmitting novel zoonotic viruses to humans from close contact," said Martin Beer, head of virus diagnostics at the Friedrich-Loeffler Institute in Insel Riems, Germany.

The victims each developed a case of swelling of the brain, known as encephalitis, and died two to four months after being infected by the rodents. The victims all perished between 2011 and 2013, after one was bitten and the other two were scratched by the animals. Analysis of the brains of the victims and squirrels revealed the animals and their handlers were both infected by the previously unknown virus.

Health care officials report that all three men who died from the squirrel virus were over the age of 60 and were experiencing other health conditions that may have worsened their physical response to the viral invader. They were all members of the same squirrel breeding association and knew each other socially.

Bornaviruses normally affect birds, sheep and horses, and researchers have long questioned whether or not the microorganisms can result in illness among infected human beings.

Symptoms of infection include the chills, weakness and fever, followed by difficulty in walking and general confusion. Encephalitis is usually brought on by a viral infection, but tests for the usual causes of the condition turned up negative, leading health workers to determine a previously undetected virus was to blame. However, the tests performed do not definitely prove the VSBV-1 virus caused the deadly cases of encephalitis.

The bornavirus is not believed to be able to spread to more common varieties of squirrels, nor can it be transmitted from person to person. Researchers caution people should not handle or feed variegated squirrels, living or dead.

Analysis of the trio of deaths from squirrel virus in Germany was profiled in the New England Journal of Medicine.

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