Primate Cercopithecine Herpesvirus (Herpes B Virus) Study Guide

Overview and Clinical Importance

Cercopithecine herpesvirus 1 (CeHV-1), commonly known as Herpes B virus or Monkey B virus, is an alphaherpesvirus endemic to Asian macaques. It is the only nonhuman primate herpesvirus known to be highly pathogenic in humans, with an untreated mortality rate exceeding 70-80%. This zoonotic pathogen represents one of the most feared occupational hazards for laboratory animal personnel, veterinarians, and researchers working with macaques.

In macaques, infection is typically asymptomatic or causes mild disease analogous to herpes simplex virus (HSV) infection in humans. However, when transmitted to humans through bites, scratches, or mucosal exposure, the virus can cause fatal encephalomyelitis. Since its first identification in 1932 following the death of researcher William Brebner, approximately 50 human cases have been documented, with 21 fatalities.

Etiology and Classification

Viral Characteristics

B virus belongs to Family Herpesviridae, Subfamily Alphaherpesvirinae, Genus Simplexvirus. The virus has been officially renamed Macacine alphaherpesvirus 1 by the International Committee on Taxonomy of Viruses (ICTV).

Epidemiology

Natural Hosts

B virus is endemic in Old World macaques of the genus Macaca. The primary reservoir species include:

• Rhesus macaques (Macaca mulatta)
• Cynomolgus macaques (Macaca fascicularis)
• Pig-tailed macaques (Macaca nemestrina)
• Japanese macaques (Macaca fuscata)
• Stumptail macaques (Macaca arctoides)

Seroprevalence and Transmission

Clinical Presentation

Clinical Signs in Macaques

In the natural host, B virus infection is typically mild and self-limiting, analogous to HSV infection in humans. Most infected macaques are asymptomatic carriers.

When Lesions Occur (Rare)

• Oral lesions: Vesicles and ulcers on oral mucosa, lips, tongue; gingivostomatitis
• Ocular lesions: Conjunctivitis of varying severity
• Genital lesions: Vesicles on prepuce or vulva (reactivation from lumbosacral ganglia)

Clinical Signs in Humans (Zoonotic Infection)

Human infection with B virus is a medical emergency. Untreated infection has a mortality rate of 70-80%. The incubation period is typically 2-5 weeks but can be as short as 3-7 days.

Clinical Progression in Humans

Pathogenesis

B virus pathogenesis differs dramatically between macaques (natural hosts) and humans (accidental hosts).

In Macaques

• Primary infection occurs via oral or genital mucosa
• Virus replicates in epithelial cells, causing mild local lesions
• Virus travels retrograde via sensory neurons to ganglia
• Establishes LIFELONG LATENCY in trigeminal or lumbosacral ganglia
• Periodic reactivation and shedding, often asymptomatic

In Humans

• Entry via bite, scratch, needle stick, or mucosal splash
• Local replication at inoculation site (vesicular lesions may form)
• Axonal transport to CNS via peripheral nerves
• Progressive ENCEPHALOMYELITIS with ascending myelitis
• Brainstem involvement leads to respiratory failure

Transmission and Risk Factors

Routes of Human Exposure

High-Risk Scenarios

• Exposure to macaque with visible herpetic lesions
• Wounds to head, neck, or torso (rapid CNS access)
• Deep puncture wounds difficult to clean
• Delayed or inadequate wound cleansing
• Exposure during breeding season (increased shedding)
• Immunocompromised, stressed, or ill macaque source

Diagnosis

In Macaques

Routine screening of macaques for B virus is NOT recommended because seronegative animals can be shedding virus, and seropositive animals may not be actively shedding. All macaques should be treated as potentially infected.

In Humans

• PCR of CSF: Most sensitive test for CNS disease; viral DNA detectable when neurological symptoms present
• Viral culture: Can isolate from wound site, CSF, conjunctival fluid; requires BSL-4 laboratory
• Serology: Paired serum samples (acute and convalescent); 4-fold rise in titer is diagnostic; seroconversion may take weeks
• CSF analysis: Pleocytosis, elevated protein; antibodies may be detected in CSF

Treatment and Post-Exposure Prophylaxis

Immediate First Aid (CRITICAL)

Wound cleansing is the MOST IMPORTANT factor in preventing infection. The 15-minute scrubbing time is more critical than the type of solution used.

Post-Exposure Prophylaxis (PEP)

Treatment of Established Infection

Prevention

Laboratory and Facility Safety

• Treat ALL macaques as potentially infected regardless of serostatus
• PPE: Long sleeves, gloves, face shield/goggles, surgical mask
• Maintain cages free of sharp edges
• Limit access to macaque housing areas
• Establish institutional exposure protocols with first aid supplies
• Regular training of all personnel in contact with macaques
• Annual serum banking for exposed workers

Specific Pathogen Free (SPF) Colonies

NIH-funded efforts have established B virus-free macaque colonies. Animals are tested and segregated. Identification of herpetic lesions warrants removal from SPF status.

Memory Aids

B Virus = BITES, BRAINS, BAD

• Bites and scratches from macaques
• Brain involvement (encephalomyelitis)
• Bad prognosis without treatment (greater than 70% mortality)

First Aid: SCRUB 15, FLUSH 15

• SCRUB wound with soap for 15 minutes
• FLUSH with running water for 15-20 more minutes

Treatment Mnemonic: VAG

• Valacyclovir = PEP (prophylaxis)
• Acyclovir IV = No CNS symptoms
• Ganciclovir IV = CNS disease (first choice)

Prognosis