Herpesvirus simiae, often known as B virus or monkey B virus, is a herpes virus that may infect monkeys and apes, including macaques and chimpanzees. The virus is predominantly found in Southeast Asia and may be transmitted to humans by interactions with infected animals, such as bites or scratches.
It is unusual among non-human herpesviruses in that it is neurotropic and neurovirulent in a foreign human host. Untreated B virus infections in humans have a high mortality rate (80%), providing unique and potentially fatal challenges for anybody interacting with affected animals.