Monkeypox Confirmed in the U.S. and Europe. What You Need to Know

Monkeypox is a viral infection that first presents with a basic suite of flu-like symptoms: fever, chills and body aches (sound familiar?). It may also cause fatigue and swollen lymph nodes. But its most distinct symptom by far is a pimple-like rash that can cover the entire body — including the palms and soles of feet of the person infected. The illness usually lasts for two to three weeks, and monkeypox has an incubation period of five to 12 days.

The monkeypox virus is a member of the Orthopoxvirus family, which includes both the smallpox and cowpox viruses. While all these viruses are serious, monkeypox is significantly less virulent than smallpox, despite causing similar symptoms.

"Monkeypox has so far about 11 percent mortality in individuals who do not have prior smallpox vaccination," says Dr. Andrea McCollum, an epidemiologist at the U.S. Centers for Disease Control and Prevention (CDC), "but smallpox could have, you know, upward of 80 or 90 percent mortality."

Smallpox has the distinction of being the first disease to be eradicated by a modern vaccine. The World Health Organization (WHO) launched an intense vaccination program in 1967. The last known infection was in Somalia in 1977, and by 1980, the virus was declared functionally eliminated. The smallpox vaccine is about 85 percent effective against monkeypox, according to the CDC.

Monkeypox, however, has not been eradicated. Because the world has done so well eradicating smallpox, countries have stopped vaccinating for it, and that means fewer people have immunity from monkeypox, as well. This has led to dozens of monkeypox outbreaks in West Africa and central Africa. The Congo alone had as many as 4,600 cases in 2020, according to a February 2022 study published in Neglected Tropical Diseases.

But where does monkeypox come from, and how does it spread?

Contrary to its name, monkeypox is not usually spread by monkeys; it was given the moniker after it was first isolated from a monkey colony in 1958. The virus is typically spread by small rodents such as dormice, rats, and tree and rope squirrels. Scientists still haven't pinned down which species is the natural reservoir for the disease, though some kind of rodent seems likely.

In 1970, the first case of monkeypox in humans was recorded in the Democratic Republic of the Congo. To this day, the DRC and other Central and West African countries, including Nigeria, see the vast majority of monkeypox outbreaks. Cases usually crop up in heavily forested, rural areas. "These are populations that are routinely hunting wild animals or have close contact with wild animals in the forest," McCollum says.

Once a human contracts monkeypox, they can pass it to other humans via respiratory droplets or contact with skin lesions. It is much less contagious than COVID-19 or other respiratory viruses when spread through the air, but it can linger on surfaces. Typically, close family members or caregivers of people with monkeypox are at the highest risk of becoming infected. Animal-to-human transmission also can occur when someone is bitten or scratched by an infected animal or if they eat infected bush meat.

So how likely is monkeypox to become a pandemic? In short, it's not likely, but we should continue to be cautious.

Like the patient in Massachusetts, seven of the eight confirmed cases in the U.K. had not traveled to Africa, and had no contact with the one patient who was known to have traveled to Nigeria, the U.K. Health Security Agency (UKHSA) said. That suggests they caught the virus in England. The UKHSA also said more than half of the cases in London are in gay or bisexual men. It is urging men who are gay and bisexual to be aware of any unusual rashes or lesions and to contact a sexual health service immediately.

"This [outbreak] is rare and unusual," Dr. Susan Hopkins, UKHSA chief medical adviser, said in a statement Monday, May 16. "UKHSA is rapidly investigating the source of these infections because the evidence suggests that there may be transmission of the monkeypox virus in the community, spread by close contact."

"Many of these global reports of monkeypox cases are occurring within sexual networks," Inger Damon, M.D., Ph.D., said in a statement. Damon is the director of the CDC's division of High-Consequence Pathogens and Pathology and a poxvirus expert with more than 20 years' experience. "However, health care providers should be alert to any rash that has features typical of monkeypox. We're asking the public to contact their health care provider if they have a new rash and are concerned about monkeypox."

The United States has had a monkeypox outbreak in the past," McCollum says. That was in 2003, and it was accidentally imported into the U.S. along with several small West African mammals as part of the "pocket pet" industry. The mammals, which included Gambian giant pouched rats, were housed alongside a pack of prairie dogs also destined for the pet trade.

Prairie dogs (and their fleas) are notorious for transmitting zoonotic diseases, including bubonic plague — the little rodents picked up the monkeypox virus easily. The infected prairie dogs were then sold to a Wisconsin family from a company called Phil's Pocket Pets in Villa Park, Illinois.

In the end, more than 45 people across six states contracted the virus. The spread prompted the CDC to bust out a few reserve smallpox vaccines that the U.S. government had stockpiled in case of a bioterrorism attack. The smallpox and monkeypox viruses' similar physiology means that a dose of the smallpox vaccine can confer some immunity.

Fortunately, there were no fatalities from the 2003 outbreak. However, the incident did lead to a ban on the sale of Gambian giant pouched rats and other West African rodents.

Today, the U.S. wouldn't necessarily need to dip into its smallpox vaccine stores to fight a monkeypox outbreak. In 2019, the Federal Drug Administration approved Jynneos, its first-ever monkeypox vaccine. Like the smallpox vaccine, it uses a weakened — or attenuated — version of the vaccinia virus (a related poxvirus) to stimulate an immune response.

The one-shot vaccine is available for anyone 18 and older and also provides protection against smallpox. Jynneos is available as part of the Strategic National Stockpile (SNS) supply of life-saving pharmaceuticals, which are for use in a public health emergency, or for anyone determined to be at high risk of either smallpox or monkeypox infection.

One concern during this outbreak is with so many new cases, scientist worry the virus could be evolving and mutating, similar to how COVID-19 has. The outbreak in Europe, where cases appear to be acquired via sexual contact, suggests a novel route of transmission. This has completely new implications for how to respond to and control any monkeypox outbreak.

We live in a highly interconnected world, where a local epidemic in one corner can easily to spill over to another. "It's a good example of how diseases don't have borders," McCollum says.