Monkeypox cases started to appear around the world in May, and the virus hasn’t stopped spreading since.
As of Thursday, there were over 20,000 confirmed cases in 77 countries, according to the Centers for Disease Control and Prevention. The United States had 4,638 cases, including 115 in Massachusetts.
The state Department of Public Health (DPH) said Thursday that there have been 36 cases in adult males in Massachusetts within the past seven days. The new cases were diagnosed between July 21 and July 27.
The virus — a milder relative of smallpox that was first discovered in monkeys — has until now rarely been seen outside Central and West Africa.
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The World Health Organization declared the outbreak a public health emergency on Saturday, indicating that it is an “extraordinary event” — and requires a response.
We spoke to experts to find out who’s most at risk, where to get tested, and what else the public needs to know.
How severe are the symptoms?
“The symptoms of monkeypox can start like many other viral infections, with a fever, a feeling of malaise, muscle aches, and pains,” said Dr. Daniel Kuritzkes, chief of the Division of Infectious Diseases at Brigham & Women’s Hospital. “Eventually, most people will develop a rash.”
The rash is distinctive. “It’s not just red skin,” said Kuritzkes. “It’s these small blisters, or what we call vesicles, that appear.”
The lesions are filled with fluid, and often look like pimples, said Nikki Alcala, a public health nurse at Fenway Health. They can appear anywhere on the body — external or internal.
A study published last week in the New England Journal of Medicine found that 95 percent of patients developed the rash, though most had fewer than 10 lesions.
Dr. Keletso Makofane, an epidemiologist at Harvard’s FXB Center for Health and Human Rights who worked on the study, said monkeypox “ranges in severity,” and the level of discomfort “depends where the lesions are.”
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Lesions in the rectum are often “debilitating” because they impede bowel movements. Lesions in the throat make it difficult to eat and drink.
“For some people, the pain is so excruciating that they have difficulty functioning,” Makofane said.
For most individuals, the rash lasts two to four weeks and resolves on its own. The lesions start to scab and often itch as they heal.
How is it transmitted?
“The main path for transmission is close person-to-person contact, and that typically means skin-to-skin contact with open lesions,” Kuritzkes said.
Monkeypox also spreads through contact with items like sheets, towels, and clothes that have been used by someone with the virus.
It takes “quite some time” for monkeypox to spread via respiratory routes or through face-to-face contact, like conversations — “much longer than what we think about as close contact for the transmission of COVID-19,” said Kuritzkes.
Before this outbreak, monkeypox wasn’t known to spread through sexual contact, said Dr. Martin Hirsch, an infectious disease doctor at Massachusetts General Hospital. Now, the majority of confirmed cases are among men who have sex with men.
In the study in the New England Journal of Medicine, 98 percent of infected individuals were gay or bisexual men, and 95 percent of suspected transmission occurred through sexual activity.
Nonetheless, experts emphasize that sex isn’t the sole route of infection.
“It’s contact transmission, and it’s not just gay men that are at risk,” said Alcala.
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Can you catch monkeypox while riding the T?
“That would be highly unlikely,” Kuritzkes said. “It’s very unlikely that by holding onto the same handle, strap, or pole that you’re going to end up contracting monkeypox on the T, nor by breathing the same air.”
In a crowded car at rush hour, though, commuters might make contact with someone else’s skin. If they have lesions, it’s possible they could transmit monkeypox, said Kuritzkes.
“Wearing long sleeves would be protective,” he said.
How else can people protect themselves?
People should wash their hands and avoid close skin-to-skin contact with anyone who has a rash that could be monkeypox, said Dr. Erica Shenoy, associate chief of the Infection Control Unit at Mass. General.
Experts also recommend individuals limit the number of sexual partners.
“It’s highly, highly unlikely that people who are in monogamous relationships have anything to worry about, regardless of what kind of sex they’re having,” said Kuritzkes.
It’s important for people to know who their partners are, whom they have been with, and whether they have any monkeypox symptoms, he said.
A condom only provides partial protection, because the infection isn’t limited to the exchange of secretions. “The issue is the pox lesions — lesions that may be on the genitals but may also be elsewhere, on the stomach or the hands or the arms,” said Kuritzkes.
Where can you get tested?
Testing for monkeypox — which involves swabbing lesions or scabs — is available through the Massachusetts State Public Health Laboratory and commercial and reference laboratories, according to a memo from state officials on Tuesday.
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Providers at clinics or hospitals must take the samples and send them to the labs.
The state laboratory, which is in Jamaica Plain, typically processes tests and returns results to providers within 24 hours, according to a spokeswoman for DPH.
The commercial labs list a longer turnaround time — about two to three days — since specimens have to be sent out of state.
While awaiting results, individuals should cover any lesions, wear a mask, use a separate bedroom and bathroom, and disinfect shared surfaces. Anyone who tests positive for the virus should continue to isolate until they recover.
What is the treatment?
There are three treatments, all of which are antivirals, approved by the Food and Drug Administration to treat smallpox, that are also effective against monkeypox, said Kuritzkes.
“Most people don’t actually need treatment, but treatment has been given to those who have severe symptoms,” he said.
The drug used most often in the United States is tecovirimat, also known as TPOXX, said Kuritzkes. It has been distributed to states from the strategic stockpile kept by the government.
According to Hirsch, the drug is still in short supply.
Who is eligible for a vaccine?
People who are “known contacts” or “presumed contacts” of individuals with monkeypox are eligible for the JYNNEOS vaccine, according to the Massachusetts Department of Public Health. The vaccine is administered in two doses, a minimum of 28 days apart.
The shots are recommended within four days of exposure to prevent the onset of monkeypox, and within 14 days of exposure to reduce the severity of the disease. People who’ve had multiple sexual partners in the past 14 days in an area with monkeypox are also eligible.
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The shots are administered by appointment only at about a dozen clinics around the state — including Fenway Health, MGH’s Sexual Health Clinic, Boston Medical Center, and Cambridge Health Alliance. The complete list is available on a state website.
Massachusetts received 2,004 doses of vaccine from the CDC on July 5, and “more vaccine is expected to become available in coming weeks,” per a state website.
How worrisome is monkeypox?
“I don’t want anyone to worry,” said Shenoy. “I want them to be aware, alert, and know what to do if they develop symptoms that might be consistent with monkeypox” — isolate and test.
Experts agreed that monkeypox is cause for concern, but not of the same severity as COVID-19.
“It’s very concerning that we’ve seen such a big increase in the numbers of cases,” Kuritzkes said. “This isn’t quite going up as exponentially in the way that we saw [COVID-19] explode, but it certainly has the potential to cause a major epidemic.”
Unlike COVID, there also haven’t been any deaths from monkeypox in the United States.
“To that extent, it’s not as bad as COVID,” said Makofane. Nonetheless, monkeypox is “a serious illness.”
Camille Caldera was a Globe intern in 2022.Follow her on Twitter @camille_caldera.