Monkey B Virus: What to Know

Medically Reviewed by Jennifer Robinson, MD on September 20, 2023
4 min read

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.

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.

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.

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.

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.

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.

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).

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