For Healthcare Providers


Since B virus was identified in 1932, only 50 people have been documented to have B virus infections; 21 of them died. Most of these people got infected after they were bitten or scratched by a macaque monkey, or when tissue or fluids from a monkey got on their broken skin, such as by needle stick or cut. In 1997, a researcher died from B virus infection after biological material (probably stool) from an infected monkey splashed into her eye.

Hundreds of bites and scratches occur every year in monkey facilities in the United States, but people rarely get infected with B virus. A study of more than 300 animal care workers showed that none had B virus infection, including the 166 workers who had possible exposures to monkeys.

Only one occurrence has been documented of an infected person spreading B virus to another person through direct physical contact with the infected person’s wounds. Among the four patients involved, three were animal handlers (two suffered bite wounds and one had close contact with the sick macaque, but was not injured or exposed to other bodily fluids and did not develop symptoms). The fourth person was the wife of one of the animal handlers. She used an ointment to treat her husband’s wounds and subsequently used it on herself to treat dermatitis. She produced antibodies for B virus but never developed symptoms. The study found no evidence of B virus infection among 130 close contacts of the four patients, healthcare workers, or primate workers. Moreover, even though over 70% of adult macaques have B virus, only a few people in the study developed laboratory evidence of B virus exposure. Thus, transmission of this virus, both human-to-human and primate-to-human, is quite rare.

The Virus

B virus is an alphaherpesvirus commonly found among macaques—a genus of Old World monkeys that serve as the natural host. The virus is found among rhesus macaques, pig-tailed macaques, and cynomolgus monkeys (also called crab-eating or long-tailed macaques).

B virus is also commonly referred to as herpes B, monkey B virus, herpesvirus simiae, and herpesvirus B.

Clinical Features

Symptoms of B virus infection typically occur within 1 month of the patient being exposed, although the actual incubation period can be a little as 3 to 7 days.

Patients with B virus infection will initially present with flu-like symptoms such as fever, muscle ache, fatigue, and headache.

Disease progression depends on the location of the exposure (usually a bite or scratch) and on the number of infectious particles spread during exposure. Vesicular skin lesions sometimes occurs at the exposure site. The patient may also have lymphadenitis (inflamed lymph nodes), lymphangities (infection of lymph vessels), nausea and vomiting, abdominal pain, and hiccups.

The virus can spread to the central nervous system (CNS) and cause the following symptoms:

  • hyperesthesias (increase in sensitivity to stimuli)
  • ataxia (lack of voluntary control of muscle movements)
  • diplopia (double vision)
  • agitation
  • ascending flaccid paralysis (extreme weakness due to reduced muscle tone)

Most patients with CNS complications will die, even with antiviral therapy and supportive care, and those who survive usually suffer serious long-term neurologic problems. Respiratory failure associated with ascending paralysis is the most common cause of death. Respiratory involvement and death can occur 1 day to 3 weeks after symptom onset.

Some people might have a delay in developing acute disease. In rare cases, such delays may range from months to years.


It is critical to be diligent in recognizing symptoms and their progression to help facilitate rapid diagnose of B virus infection in an exposed person.

Both clinical evaluation of symptoms and laboratory testing (ideally showing antibodies or virus positive case) are needed to diagnose B virus in an exposed person.

Serological and virological testing are available for diagnosing B virus infection. For more information, see Laboratory Testing and Diagnosis section.

First Aid and Treatment

First Aid

When a patient has been exposed to a macaque monkey, immediately:

  • Wash and gently scrub the wound or area on the body that had contact with the monkey thoroughly with soap, detergent, or iodine for 15 minutes; and then
  • Run water over the wound or area for 15 to 20 minutes more.

Treatment Criteria

Healthcare providers should take into account the following criteria when deciding whether to implement antiviral therapy:

  1. Type and physical condition of the implicated animal. Only monkeys of the macaque family serve as the natural reservoir for B virus infection. No other primates carry any risk of B virus transmission unless they have become infected by a macaque. Infected macaques do not ordinarily shed B virus. Animals with wounds consistent with B virus infection (fluid-filled blisters on the skin) and animals that are immunocompromised or stressed are far likelier to be excreting virus.
  2. Thoroughness and timeliness of wound cleansing procedure. Wounds that have been cleansed within five minutes of exposure and that have been irrigated for at least 15 full minutes are less likely to lead to B virus infection. Delay in cleansing or inadequate irrigating of the wound increases the risk of infection.
  3. Nature of the wound. Bites or scratches that break the skin, and particularly deep puncture wounds, are considered higher risk than wounds that are superficial and thus more easily cleansed. Wounds to the head, neck, or torso provide potentially rapid access to the central nervous system (CNS) and thus should be considered higher risk. Prophylaxis is recommended for this type of wound, regardless of its severity. Superficial wounds to the extremities are less likely to lead to fatal disease, and antiviral treatment is considered less urgent in these cases.
  4. Exposure to materials that have come into contact with macaques. Accidental needle sticks with syringes that have come into contact with the CNS, eyelids, or mucosa of macaques are considered to carry a high risk of infection. Punctures from needles exposed to the blood of macaques are considered relatively low risk. Scratches resulting from contact with possibly contaminated objects, such as animal cages, are considered to carry a low risk for infection.

It should be stressed, however, that in none of these potential exposures can the risk of infection be considered zero. As such, you should decide whether to treat with antivirals with liberal consideration of the patient’s wishes and concerns.

Patients with a known risk of exposure should be monitored for symptoms, regardless of whether a treatment regimen has been implemented.

Treatment Recommendations

Specific exposure scenarios and the corresponding urgency for post-exposure antiviral treatment, as proposed in the Recommendations for Prevention of and Therapy for Exposure to B virus (Cercopithecine Herpesvirus 1), are as follows:

Treatment is recommended

  • Skin or mucosal exposure – with or without injury – to a high-risk source (e.g., a macaque that is ill, immunocompromised, known to be shedding virus, or has lesions compatible with B virus infection.)
  • Inadequately cleansed skin exposure (where the skin is broken) or mucosal exposure (with or without injury).
  • Laceration of the head, neck, or torso.
  • Deep puncture bite.
  • Needle stick associated with tissue or fluid from the nervous system, lesions suspicious for B virus, eyelids, or mucosa.
  • Puncture or laceration with objects (a) contaminated either with fluid from monkey oral or genital lesions or with nervous system tissues or (b) known to contain B virus.
  • A culture taken after the wound was cleansed tests positive for B virus.

Treatment should be considered

  •  A break in the skin that has been adequately cleaned.
  • Needle stick involving blood from an ill or immunocompromised macaque.
  • Puncture or laceration occurring after exposure to (a) objects contaminated with body fluid (other than that from a lesion) or (b) a possibly infected cell culture.

Treatment is not recommended

  •  Skin exposure in which the skin remains intact.
  • Exposure associated with non-macaque species of non-human primates, unless they were in a situation where they could have been infected by a macaque.

Antiviral Therapy

Recommended dosages for specific antivirals are as follows:

Prophylaxis for exposure to B virus

  •  Valacylovir—1g by mouth every eight hours for 14 days, or
  • Acyclovir—800 mg by mouth five times daily for 14 days

Treatment of B virus infection

  •  With no CNS symptoms
    • Acyclovir—12.5–15 mg/kg intravenously every eight hours, or
    • Ganciclovir—5 mg/kg intravenously every 12 hours


There are no vaccines available protect against B virus infection. Experimental vaccines have been evaluated in animal models, but none are being considered for use in people.