Macacine alphaherpesvirus 1, commonly known as Virus B, is a rare but serious zoonotic pathogen. It primarily resides in macaque monkeys, its natural hosts. While causing mild or asymptomatic infections in these primates, Virus B can lead to severe and potentially fatal disease if transmitted to humans. Awareness of this virus, its transmission, and appropriate responses is important for those who may encounter macaques.
Understanding Virus B
Macacine alphaherpesvirus 1, also known as B virus or Herpes B virus, belongs to the Alphaherpesvirinae subfamily within the Herpesviridae family. It is in the same genus, Simplexvirus, as human herpes simplex viruses (HSV-1 and HSV-2). This double-stranded DNA, enveloped virus measures approximately 160 to 180 nanometers in diameter. It was first identified in 1932 following a human fatality.
Various macaque species, including rhesus (Macaca mulatta), cynomolgus (Macaca fascicularis), and pig-tailed macaques (Macaca nemestrina), are natural hosts for Virus B. These monkeys are predominantly found in Asia, where the virus is enzootic. Macaque colonies have also been introduced to regions like Florida, the Isle of Mauritius, and Gibraltar, establishing the virus there.
How Virus B Spreads
Transmission of Macacine alphaherpesvirus 1 from macaques to humans primarily occurs through direct contact with infected animals or their bodily fluids. Bites and scratches from macaques are common routes of infection, as the virus can be shed in saliva and other secretions. Contact with macaque tissues, such as central nervous system tissue or fluids from oral or genital lesions, can also lead to transmission.
Indirect exposure can occur through contaminated fomites, such as needlesticks, cuts from broken tissue culture bottles containing infected monkey cells, or scratches from contaminated cages. While rare, a single case of human-to-human transmission has been documented, attributed to shared medication that contaminated a broken skin site. High-risk groups include laboratory personnel, veterinarians, and primate handlers who work closely with macaques in research or sanctuary settings.
Recognizing Symptoms of Virus B Infection
Initial symptoms of Macacine alphaherpesvirus 1 infection in humans can resemble a flu-like illness, appearing within two to 30 days post-exposure, with most cases presenting within five to 21 days. These generalized symptoms include fever, headache, muscle pain (myalgia), and nausea. Localized vesicular eruptions, similar to herpes simplex virus lesions, may also develop at or near the exposure site.
As the infection progresses, neurological symptoms follow within three to seven days of symptom onset. These can include neurological signs at the exposure site, such as numbness, tingling, itching, or pain. More generalized neurological signs may involve:
Meningismus (neck stiffness)
Confusion
Double vision (diplopia)
Difficulty swallowing (dysphagia)
Dizziness
Slurred speech (dysarthria)
Cranial nerve palsies
Problems with coordination (ataxia)
If left untreated, the virus can spread along sensory nerves into the spinal cord and ascend to the brain, leading to severe encephalomyelitis and respiratory failure, which can be fatal.
Diagnosis and Treatment for Virus B
Accurate and prompt diagnosis of Macacine alphaherpesvirus 1 infection is important due to its severe outcomes in humans. Diagnostic procedures include molecular tests such as real-time polymerase chain reaction (PCR), which detects viral DNA in samples like cerebrospinal fluid, blister fluid, or oral and genital swabs. Metagenomic next-generation sequencing (mNGS) can also confirm viral DNA.
Viral culture from clinical samples is another diagnostic method, though it requires specialized biosafety level 3 or 4 containment facilities and can take one to seven days for results. Serological tests, such as enzyme-linked immunosorbent assay (ELISA), can detect antibodies against the virus, but their sensitivity and specificity may vary, and they do not necessarily indicate active viral shedding. Immediate antiviral treatment is crucial; medications like acyclovir, ganciclovir, and valacyclovir are used. Early administration of these drugs can reduce the mortality rate from an estimated 70-80% in untreated cases to less than 20%.
Preventing Virus B Infection
Preventing Macacine alphaherpesvirus 1 infection involves adhering to safety protocols for individuals who may come into contact with macaques. Avoiding direct contact with these animals, especially those in captivity, is a primary preventive measure. When contact is unavoidable, wearing appropriate personal protective equipment (PPE), including gloves, masks, and eye protection, is recommended to minimize exposure to bodily fluids.
Immediate and thorough wound care is an important first response following any potential exposure, such as a bite or scratch. The wound should be cleaned vigorously with detergent and water for at least 15 minutes, or mucous membranes should be flushed with saline for the same duration. Post-exposure prophylaxis (PEP) with antiviral medications, such as valacyclovir (often preferred), acyclovir, or famciclovir, should be initiated as soon as possible, ideally within hours and certainly within five days of exposure, due to the virus’s rapid progression.