B-virus (Macacine alphaherpesvirus 1; McHV-1; formerly Macacine herpesvirus 1, Cercopithecine herpesvirus 1, CHV-1), Herpesvirus simiae, or Herpes virus B is the Simplexvirus infecting macaque monkeys. B virus is very similar to HSV-1, and as such, this neurotropic virus is not found in the blood.
In the natural host, the virus exhibits pathogenesis similar to that of cold sores in humans. Conversely, when humans are zoonotically infected with B virus, patients can present with a severe encephalitis, resulting in permanent neurological dysfunction or death. Severity of the disease increases for untreated patients, with a case fatality rate of approximately 80%. Early diagnosis and subsequent treatment are crucial to human survival of the infection.
B virus is the only identified old-world-monkey herpesvirus that displays severe pathogenicity in humans. There have been a number of accidental infections and fatalities of researchers working with rhesus monkeys (Rhesus macaque). Personal protective equipment is necessary when working with macaques, especially with animals that have tested positive for the virus. Bites, scratches, and exposures to mucous membranes, including the eye, have led to infection when not cleaned immediately.
B virus infection is extremely rare, but it can lead to severe brain damage or death if it is not treated immediately. People typically get infected with B virus if they are bitten or scratched by an infected macaque monkey, or have contact with the monkey's eyes, nose, or mouth. Only one case has been documented of an infected person spreading B virus to another person. As of 2020, there have been 50 documented cases of human B virus infection since the identification of the virus in 1932, 21 of which led to death. At least 20 of the patients developed some degree of encephalitis.
History
Macacine alphaherpesvirus 1 was first identified in 1932 following the death of William Brebner, a young physician who was bitten by a rhesus monkey while doing research on polio. He had healed from the bite but later developed a febrile illness, resulting in localized erythema, lymphangitis, lymphadenitis and, ultimately, transverse myelitis. Neurologic tissues obtained during autopsy revealed the presence of an ultrafilterable agent that appeared similar to HSV-1. This isolate was originally termed "W virus."
Within a year of Brebner's death, Albert Sabin identified a novel virus from the same samples, which he later named B virus. Sabin further described the lethality of Macacine alphaherpesvirus 1 by showing that infectivity was independent of the route of inoculation. Additionally, it was observed that Macacine alphaherpesvirus 1 induced immunologic responses similar to HSV-1 and shared similarities to HVP-2 and Langur herpesvirus, two other nonhuman primate alphaherpesviruses.
By 1959, Macacine alphaherpesvirus 1 was identified as the causative agent in 17 human cases, 12 of which resulted in death. Approximately 50 cases had been identified by 2002, although only 26 were well documented. Improvements in handling human cases have been made in the past several decades. Between 1987 and 2004, the mortality rate decreased, largely due to the addition of new forms of treatment and improved diagnosis. There have been a total of five fatalities related to Macacine alphaherpesvirus 1 in this period.
Researchers working with macaque monkeys continue to face danger from B virus infections. The last identified case of human B virus infection occurred in 2021, when a veterinarian in China became infected while performing two dissections on rhesus monkeys and subsequently died. Two years previously, a researcher working with monkeys at a Japanese pharmaceutical company became infected and critically ill. The last known fatality in the United States occurred in 1997 when researcher Elizabeth Griffin was splashed in the eye by an infected rhesus monkey while working at the Yerkes National Primate Research Center.
Traveling to an area where macaques are known carriers of the virus and interacting in close contact in areas such as temples poses a risk of exposure. However, even in endemic areas, human cases are rare. There have been no known cases of Macacine alphaherpesvirus 1 in travelers.