Health officials have recently reported a cluster of acute fatal encephalitis in three squirrel breeders possibly related to an infection with a newly identified bornavirus is an unusual event.

 Variegated Squirrel Public domain image/Proceedings of the Zoological Society of London
Variegated Squirrel
Public domain image/Proceedings of the Zoological Society of London

All infected persons bred variegated squirrels, a type of tree squirrel common to Central America that can be kept as an exotic pet.  A bornavirus strain different from all currently known bornaviruses so far was found in the patients and in a squirrel belonging to one of the patients.

The cases are still under investigation and there is no proof yet of a direct relationship between the presence of the bornavirus and the encephalitis, hence, a zoonotic infection with bornavirus has not been confirmed, the European Centre for Disease Prevention and Control (ECDC) reports.

However, European health officials still advise there could be a higher risk of exposure to infection for variegated squirrel breeders, their family members and the owners of variegated squirrel pets.

Borna disease virus (BDV) infections were first described in the 18th century and were named after the town of Borna, near Leipzig, Germany, where an epizootic condition was described in 1885 among military horses presenting with a fatal neurologic disease. BDV can infect many vertebrate species including rhesus monkeys, horses, sheep, cattle, goats, rabbits, deer, llamas, alpacas, cats, rats, mice, shrews, gerbils, dogs, and ostriches. BDV related avian bornaviruses (ABV) have been recently described in psittacine birds, Canada geese, trumpeter and mute swans, and canary birds.

Animal BDV infections have been described in central Europe, the United Kingdom, Israel, Japan, Sweden, Finland, Australia, and the United States of America. In animals, BDV infection may lead to an acute or sub-acute disease with meningo-encephalitis or mild manifestations with alteration or impairment of nerve-cell functions.

Few documented possible human infections with bornaviruses describe symptoms such as diverse psychiatric disorders in people infected with the virus. However, the existing evidence is insufficient to prove the potential bornavirus infection in humans and its connection with the said psychiatric disorders, mainly because of the complexity of the laboratory procedures related to diagnosing the bornavirus.