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The symptoms and causes of monkeypox infections, now diagnosed in more than 750 people

Monkeypox has been reported in 30 non-African countries in what an expert calls "the most important outbreak in the history of monkeypox in the Western Hemisphere."

More than 770 cases of monkeypox have been confirmed across 30 countries outside of Africa, a rare occurrence for the virus.

The U.S. had identified 19 cases across 10 states as of Wednesday. More than 20 European countries have reported cases, according to Global.health, a group that gathers infectious disease data. The highest total is in England, which has around 200 confirmed infections. Spain's tally is above 150 and Portugal has nearly 140 cases.

Additional cases have been reported in Australia, North America, South America and the Middle East. Many countries have more suspected cases awaiting confirmation. No deaths outside Africa have been linked to the current outbreak, but Nigeria reported one monkeypox death in May: a 40-year-old who had underlying health problems and was on immunosuppressive medication.

The suddenness of the virus's spread "suggests there may have been undetected transmission for some time as well as recent amplifying events," according to the World Health Organization. Dr. David Heymann, a leading adviser to the WHO, said last month that two raves in Spain and Belgium may have fueled transmission. Public health authorities in Madrid have also linked Spain’s infections to an outbreak at a sauna.

"This is the most important outbreak in the history of monkeypox in the Western Hemisphere," said Anne Rimoin, an epidemiology professor at UCLA Fielding School of Public Health.

The last time the Western Hemisphere saw a relatively large monkeypox outbreak was in 2003, when the U.S. identified 47 cases. Those patients had been in contact with infected pet prairie dogs, and no people died.

The vast majority of the recent cases have no history of travel to the 11 African countries where monkeypox is endemic, according to the WHO. Most of the cases are among men who have sex with men, but monkeypox is not considered a sexually transmitted infection.

How dangerous is monkeypox?

Monkeypox belongs to the family of poxviruses, which includes smallpox. The disease got its name after scientists discovered it among laboratory monkeys in 1958. The first monkeypox case in a human was diagnosed in 1970.

Since then, most infections have been concentrated in the Democratic Republic of the Congo and Nigeria. The DRC reports thousands of cases annually and Nigeria has reported more than 200 confirmed cases and more than 500 suspected ones since 2017.

The type of monkeypox identified in the recent cases, known as the West African clade, tends to produce milder disease than the other common branch, the Congo Basin clade.

"That’s good news in that, hopefully, there will not be a lot of bad things clinically that happen to people who might be infected," said Dr. Agam Rao, a medical officer at the Centers for Disease Control and Prevention’s Division of High Consequence Pathogens and Pathology.

Around 1 percent of people who have contracted the West African clade in the past have died, compared to up to 10 percent of people who contract the Congo Basin clade, according to the WHO.

Rao said people who get the West African clade "typically recover pretty well" and go "back to their regular lives when it’s over."

What are the symptoms of monkeypox?

Monkeypox symptoms can develop five to 21 days after someone is infected. Most people recover after two to four weeks.

The illness typically starts with flu-like symptoms such as fever, headache, muscle aches and exhaustion, which can last a day or two. Some patients may also experience painful, swollen lymph nodes. A rash often follows one to three days after the fever, progressing from red areas to small bumps on the skin. Those can then turn into blisters that may fill with whitish fluid.

The rash sometimes looks similar to chickenpox, syphilis or herpes. It typically spreads from the face to the limbs, hands, feet and then to the rest of the body, WHO officials said.

"We’re seeing more cases where the rash begins in the genital area — which is not new, that has always been there — but it’s more frequent now and sometimes it tends to stay there," said Dr. Rosamund Lewis, Head of the Smallpox Secretariat at the WHO.

That could make the rash less visible, she added.

How do you get monkeypox? Is it sexually transmitted?

People can get monkeypox from animals, either through bites or scratches or preparing meat from wild game, according to the CDC.

Exposure also comes through close contact with bodily fluids, respiratory droplets, the lesions that form during an infection, or contaminated items like clothing or bedding.

People are most infectious when they have active lesions, according to Jennifer McQuiston, deputy director of the CDC’s High Consequence Pathogens and Pathology division.

"Right now we’re not aware of a real risk for transmission other than when a person has an active rash," she said.

WHO officials said last month that the recent outbreak is likely spreading through exposure to rashes and lesions during sexual activity.

"Many diseases can be spread through sexual contact. You can get a cough or a cold through sexual contact, but it doesn't mean that it's a sexually transmitted disease," said Andy Seale, an advisor with the WHO's HIV, Hepatitis and STIs Program.

The WHO recommends that people with diagnosed infections isolate "until their lesions have crusted, the scab has fallen off and a fresh layer of skin has formed underneath."

What treatments are available?

Rimoin said it makes sense that monkeypox continues to crop up, since there’s less immunity to poxviruses than there was before 1980, when people still received smallpox vaccines.

"It’s not surprising that we’re seeing infections as a result of exposures, given that we no longer have that immunity that we counted on during the eradication of smallpox era," she said.

There is not a proven treatment for monkeypox, but doctors can treat its symptoms, and two antivirals for smallpox could also be considered. Rimoin said supportive care is pretty effective for the West African clade.

Doctors who identify a suspected monkeypox case should report it to the CDC, Rao said, since "any potential treatments that might be provided to the patient are really only available through consultation with public health authorities."

Is there a monkeypox vaccine?

The Food and Drug Administration approved a two-dose vaccine called Jynneos in 2019 for use against monkeypox and smallpox. Older smallpox vaccines have been found to be around 85 percent effective at preventing monkeypox as well.

The U.S. has more than 100 million doses of an older-generation smallpox vaccine called ACAM2000 in the Strategic National Stockpile.

These vaccines may even help reduce symptoms or prevent disease if administered shortly after someone gets infected.

CDC Director Rochelle Walensky said last week that the U.S. is "mobilizing vaccines to states with reported cases," and McQuiston said the shots are going to close contacts of people diagnosed with monkeypox. Other countries, including Denmark, France and England, are taking a similar approach to vaccinations.

"We continue to watch what is happening and think about whether wider vaccination recommendations would make sense," McQuiston said.

She added: "We are working hard to identify cases and we don’t yet know how many there might be. We’re working hard to contain the cases that are happening so they don’t spread onward."