Monkey B Virus: What to Know

Medically Reviewed by Brunilda Nazario, MD on July 20, 2021

What Is the Monkey B Virus?

It is a virus that’s common in macaque monkeys and transmitted in rare cases to humans, where it may cause serious illness. Your doctor might call it herpes virus B, or simply B virus. Other possible names include simian B virus, H simiae encephalomyelitis, Cercopithecine herpesvirus type I, or herpes simiae.

How Does the B Virus Pass From Monkeys to Humans?

Macaque monkeys, including rhesus macaques and pig-tailed macaques, are the most common host for the herpes B virus. They don’t tend to get sick from it, or if they do, they only have very mild symptoms.

Humans can get it from a bite or scratch from one of these monkeys or from contact with the monkey’s bodily substances like saliva, feces, urine, or other tissue, especially brain tissue. This might happen through the eyes, nose, mouth, or a cut or wound. A contaminated needle stick or the sharp edges of a monkey cage could also pass on the virus.

What Are the Symptoms of Monkey B Virus in Humans?

You might notice symptoms within 3 to 7 days of exposure, but they could start as much as a month later. You will typically first notice flu-like symptoms that can include:

Other possible symptoms include:

In addition, the area of the bite, scratch, or other exposure often develops small blisters. You may also notice pain, itching, and numbness in that area.

How Common Is Monkey B Virus in Humans?

It’s very rare. Scientists know of only about 50 cases of human infection with B virus since 1932, when they first identified it. Most of these happened after a bite or scratch from a monkey or exposure to fluids through broken skin.

Still, simple exposure doesn’t mean you will get the virus. Hundreds of bites and scratches happen every year in monkey facilities in the U.S. with no infection.

And, of course, most people don’t have regular contact with these particular monkeys. Those most at risk are veterinarians, lab workers, and others who work regularly with macaque monkeys or specimens from the animals like saliva, cell cultures, urine, or other bodily fluids and tissue.

How Serious Is Monkey B Virus Infection in Humans?

It’s very serious. It can cause breathing problems and inflame your brain and spinal cord, which can damage your nervous system and lead to death.

Of the approximately 50 people known to have contracted herpes B virus since the 1930s, 21 of them died.

What Should You Do After Possible Exposure to B Virus?

Start first aid in the area right away. That means: Use iodine, soap, or detergent to thoroughly wash and, if possible, gently scrub the bite, scratch, wound, or body area that touched the monkey for 15 minutes. Continue to rinse the area with water for another 15 to 20 minutes.

Get to a health care provider as soon as possible and tell them of your possible exposure to the B virus through a macaque monkey.

How Do Doctors Diagnose and Treat Monkey B Virus in Humans?

Your doctor will ask you about your symptoms and examine you, especially the wound or area of exposure. More serious wounds or needle sticks raise the risk of infection.

They will ask you in detail about how it happened and how you know the type of monkey. They might also ask you exactly what you did right after you were exposed (first aid measures).

A lab test can sometimes show special antibodies that your body produces in response to a B virus infection. In some cases, they might take a culture of a wound or exposure site to see if B virus is present.

Doctors typically treat B virus infection with antiviral medications given through a needle (IV medications).

What Can You Do to Prevent B Virus Infection?

There are no vaccines for humans that protect against B virus.

If you work closely with macaques, you can help minimize the risk of infection if you follow the rules and protocols of your lab or facility. These might include:

  • Humane restraint methods that cut down on bites and scratches
  • Use of proper protective clothing, gloves, and face shield
  • Immediate first aid and medical attention for any bites, scratches, or other exposures
  • Careful cleaning of external surfaces exposed to the monkeys or their tissue or bodily fluids
WebMD Medical Reference



Boston Public Health Commission: “Herpes B Virus.”

CDC: “B Virus (herpes B, monkey B virus, herpesvirus simiae, and herpesvirus B).”

National Organization for Rare Disorders: “Simian B Virus Infection.”

University of Virginia’s Occupational Health Program: “Monkey B Virus: A Guide to the Causes, Transmission, and Prevention of Cercopithecine herpesvirus.”

Virginia Department of Health: “B Virus.”

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