Mpox: What You Need to Know

[Originally published: July 11, 2022. Updated: Nov. 18, 2024.]

Mpox (formerly known as monkeypox), an infectious disease typically found in parts of Central and Western Africa, has again been labeled a global health emergency by the World Health Organization (WHO).

Mpox became a global concern in 2022 when a type of the virus spread to other countries. That outbreak led to more than 90,000 cases worldwide, including more than 32,000 in the United States.

In 2023, the WHO declared an end to the global health emergency based on a decline in new cases and steady progress in controlling the spread of the disease, even though it continued to circulate in the community.

Now, public health officials around the world are concerned about a new strain of the virus that has driven up the number of cases and deaths in the Democratic Republic of Congo and other African countries. The first reported case from this strain was detected in California in mid-November.

Although it can affect anyone, most mpox cases from the 2022 outbreak were sexually transmitted and reported in men who have sex with men (MSM). The 2022 outbreak was caused by a strain called Clade IIb. The current outbreak is caused by Clade I, a strain that can also be sexually transmitted, cause more severe illness, and lead to death in up to 10% of those infected.

For reasons not yet known, the virus, since 2022, is behaving in ways never before seen, with cases occurring in countries that don’t normally see it. Before this, mpox was also not known to spread easily among people or to infect large groups at once. Now, it can spread through close contact.

We talked with Marwan Azar, MD, a Yale Medicine infectious diseases specialist about what we know so far about this new strain of mpox.

Similar to smallpox, but less severe, mpox was discovered in 1958 when two outbreaks of a pox-like disease occurred in colonies of monkeys kept for research in Denmark, according to the Centers for Disease Control and Prevention (CDC).

Despite being originally called “monkeypox,” the source of the disease is not known. However, African rodents and non-human primates, like monkeys, may carry it and infect humans. The first human case was reported in 1970. “The disease has been renamed ‘mpox’ to avoid racist and discriminatory connotations related to the original name,” says Dr. Azar.

Until 2022, nearly all cases in people outside of Africa have been linked to imported animals or with travel to other countries where the disease is common.

Normally, someone infected with mpox first presents with a nonspecific flu-like illness, including fever, headache, and malaise, Dr. Azar says. “Swollen lymph nodes can be a telltale sign, after which a rash appears. The rash usually starts off like a spot.”

The first lesions, according to the CDC, develop on the tongue and in the mouth before spreading to the skin and becoming raised. The lesions, which fill with pus, remain for five to seven days before beginning to crust. They typically scab over by the end of the second week and remain for about another week before starting to fall off. An infected person is contagious from the start of the flu-like symptoms until all scabs have fallen off.

“The rash traditionally seen with mpox starts in the center of the body, the face, or the head, and then moves outward to the extremities. That is the classic presentation,” Dr. Azar says. “But with the 2022 worldwide outbreak, it did not always follow this pattern. In many cases, lesions were only seen in the genital area or around the anus. It’s important to recognize that these lesions could be mistaken for sexually transmitted diseases, such as syphilis or herpes, which also have lesions in those areas.”

Those infected might only experience a rash. Others may get a rash first, followed by other symptoms. Most illnesses clear up in two to four weeks. If you have new or unexplained rashes, sores, or other symptoms, you should see your health care provider.

Mpox can spread in different ways. Before the 2022 outbreak, the most common method was by direct contact with infected animals by way of a bite, scratch, or feces, or by preparing/eating meat or using products from an infected animal.

In the past, human-to-human transmission was rare, Dr. Azar says.

What was troubling about the 2022 cases is that mpox appeared to be spreading through close contact with an infectious rash, scab, or bodily fluids. It can also be transmitted through respiratory secretions during prolonged face-to-face contact or during intimate physical contact, including kissing, cuddling, or sex. It is not yet known if it is spread through semen or vaginal fluids.

Additional transmission can occur from touching clothing, linens, or other items that came in contact with an infectious rash or body fluids. Pregnant women can also transmit the virus to their fetus.

There are several different ways people can prevent mpox infection, including avoiding close, skin-to-skin contact with a mpox rash; not handling or touching bedding, clothing, or towels of a person who has mpox; and washing hands often with soap and water or using an alcohol-based hand sanitizer, especially after contact with people sick with the virus.

Individuals who are at increased risk (MSM with certain high-risk sexual exposures) are encouraged to receive two doses of the Jynneos™ vaccine (more on vaccination below). Vaccination reduces the chances of contracting the infection and of severe illness, hospitalization, and death. Vaccination is also an important tool in preventing the spread of mpox.

Dr. Azar advises the general public and health professionals to visit the CDC pages on mpox to familiarize themselves with signs and symptoms, prevention techniques, many of which are similar to prevention strategies for COVID-19, and information about who would most benefit from vaccination.

Yes. According to the CDC, mpox can spread to anyone through close, personal, skin-to-skin contact, which can happen when you have sex. Examples include:

• Oral, anal, and vaginal sex or touching the genitals (penis, testicles, labia, and vagina) or anus (butt) of a person with mpox
• Hugging, massage, and kissing
• Touching fabrics and objects that were used by a person with mpox and that have not been disinfected, such as bedding, towels, fetish gear, and sex toys

Doctors can diagnose mpox based on a patient’s history and a physical exam; anyone who suspects they might have the virus should contact their health care provider. The virus can be confirmed with a PCR test that is available at specialized labs. Your health care provider can work with the state department of public health if testing is deemed necessary, Dr. Azar says.

Those who are sick with mpox should isolate at home. For those with an active rash or other symptoms, stay in a room or area separate from family and pets when possible.

While there are no specific treatments for mpox infections, antiviral drugs licensed for smallpox use are effective and can be used against mpox. These might be advised for people more likely to get very ill, including those with weak immune systems.

Two vaccines licensed by the Food and Drug Administration (FDA) are available for preventing mpox. Jynneos is a two-dose vaccine (separated by four weeks), which is up to 85% effective in preventing mpox after two doses and is recommended for those who are at increased risk of exposure to mpox and those who have been exposed to mpox in the past two weeks.

The other vaccine, called ACAM2000, is a modern iteration of an old smallpox vaccine. The WHO celebrated the eradication of smallpox in humans in 1980. Now stored in a national stockpile, the vaccine has been used for mpox, but there are drawbacks: it can lead to serious illness in people with compromised immune systems. It is not the preferred vaccine for mpox at this time.

“With regards to mpox—previously, the vast majority of cases were from contact with animals, usually rodents. I believe our encroachment on the natural world has brought us into closer contact with animal species we had never been close to before,” Dr. Azar says. “And when animals’ ecosystems are destroyed, they move closer to urban environments. That has facilitated the transfer of viruses that mostly circulate in animal species. And since humans have not been exposed to them, there is very little pre-existing immunity to these viruses, which makes us more susceptible.”