Monkey B Virus vs. Monkeypox: What's the Difference?

Two rare but potentially lethal illnesses with "monkey" in the name are leading to confusion.

Two rare viruses with the phrase "monkey" in their name occasionally make headlines: monkeypox and monkey B virus. While both of these viruses contain the word "monkey," they're not the same. They're "totally different viruses," David Cennimo, MD, associate professor of medicine, adult and pediatric infectious diseases, at the Rutgers New Jersey Medical School, told Health. Here's what you need to know about these rare viruses, and if you could be at risk.

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Completely Different Causes

According to the CDC, monkeypox is caused by the monkeypox virus, which is in the same genus as the variola virus, the cause of smallpox. The monkey B virus is a form of the herpes B virus, Richard Watkins, MD, an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University, told Health. It's worth noting, according to Dr. David Cennimo: "Monkeys are not the primary host. It is rodents."

Monkey B virus infections in people are rare and typically caused by macaque monkeys, the CDC says. While chimpanzees and capuchin monkeys can catch the B virus, they often die from the infection.

"Monkeypox and herpes B are two totally distinct viruses," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, told Health.

Monkeypox and Monkey B Virus Are Both Rare

Monkeypox is a rare illness that's even more rare in the US, according to the CDC. The virus is generally most common in certain central and western African countries, according to CDC data, but it has appeared in the US. An outbreak of the virus in 2003 in America caused 47 cases.

Monkey B virus infections in people are also rare, with only 50 documented infections ever identified as of 2019, the CDC says. Most people were infected after getting bit or scratched by a monkey, or when tissue or fluids from an infected monkey got on their broken skin, such as via a needle stick or cut. "Herpes B is primarily a threat to workers who work with Old World monkeys," Dr. Amesh Adalja said. (Old World monkeys are found in Africa and Asia.) "Facilities have protocols in place for exposures."

Some Overlapping Symptoms

Monkeypox symptoms include:

  • Fever
  • Headache
  • Muscle aches
  • Backache
  • Swollen lymph nodes
  • Chills
  • Exhaustion

These symptoms are accompanied by a rash that progresses through several stages, ending in scabs that fall off. Some people only experience the rash. The illness usually lasts from two to four weeks, according to the CDC.

Monkey B virus is "severe," Dr. David Cennimo said. The CDC says that the first symptoms are usually flu-like, including:

  • Fever and chills
  • Muscle aches
  • Fatigue
  • Headache

After that, you may develop small blisters on the area of your body that had contact with the monkey, along with these symptoms:

  • Shortness of breath
  • Nausea and vomiting
  • Abdominal pain
  • Hiccups

If the disease progresses, the virus will spread and cause swelling of the brain and spinal cord, resulting in symptoms like:

  • Pain, numbness, and itching near the infection site
  • Problems with muscle coordination
  • Brain damage and severe damage to the nervous system

People can also develop breathing issues and subsequently die from the infection, usually one day to three weeks after they first have symptoms.

Both Can Be Deadly

According to the CDC, one in 10 people in Africa who catch monkeypox die from the virus, but certain types of the virus—such as the type identified in the 2022 global outbreak—are much less deadly. Of the 50 documented cases of people who have contracted monkey B virus, 21 have died, the CDC says.

Worry About Contracting Monkey B Virus or Monkeypox

Dr. Amesh Adalja pointed out that documented cases of the monkey B virus have happened in laboratory researchers who specifically work on monkeys. If that doesn't describe you, Dr. Amesh Adalja said, the virus is unlikely to be a risk.

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