Since 2017, Nigeria has had sporadic cases of monkeypox, mostly in urban areas, she says. The country has had 46 cases in 2022 as of April 30.

From time to time, travelers have carried monkeypox from Nigeria to other countries, but those have been mainly isolated cases. This outbreak may also have started with a traveler.

Genetic evidence from viruses isolated from patients in Portugal, the United Kingdom and the United States suggests that the multinational outbreak may have had a single source, researchers from Portugal reported May 23 at Virological.org.

“Our virus definitely comes from Portugal,” says Philippe Selhorst, a virologist at the Institute of Tropical Medicine in Antwerp, Belgium, who posted the genetic makeup of the monkeypox virus from a Belgian patient to Virological.org on May 20. The DNA sequence of the virus is very similar to ones from Portugal. The patient had traveled to Lisbon shortly before developing a rash, further solidifying the link.  

Because monkeypox has DNA as its genetic material, it mutates more slowly than RNA viruses, such as dengue or SARS-CoV-2, the coronavirus that causes COVID-19. “I would expect all cases … in the outbreak to be very similar,” Selhorst says.

Still, virologists have noted mutations in the virus taken from different patients. That’s to be expected. “There’s always going to be differences between viruses,” he says. “The question is: ‘Is that difference relevant?’” Nothing in the viral DNA indicates that the virus has mutated to spread more easily from person-to-person, Selhorst says.

How is the virus spreading?

This outbreak seems to be driven by human-to-human transmission. “This virus has used a sexual network to spread around the world,” says Amesh Adalja, an infectious diseases physician and a senior scholar at the Johns Hopkins Center for Health Security.

That doesn’t mean monkeypox is a sexually transmitted disease — one that is passed through semen or other bodily fluids exchanged during sex, he says. “You can catch the flu if you make out with somebody, and people kiss during sex, but that doesn’t make influenza a sexually transmitted infection.” Similarly, close skin-to-skin contact during sex can spread monkeypox.

People infected with monkeypox may not have a visible rash, but could have lesions in their mouth or throats that harbor the virus and may pass the infection through saliva, the CDC’s Brooks said. Selhorst and colleagues are collecting semen and other body fluids from people infected with monkeypox to see if it is possible for the virus to be sexually transmitted.

In this outbreak, rashes have appeared first in people’s groin and anal regions, and have been mistaken for herpes or other STDs, Brooks said during the news briefing. And monkeypox cases are sometimes confused with chicken pox, Yinka-Ogunleye says. Doctors need to be aware that a patient with a rash may have something more exotic, Adalja and Hopkins colleague Tom Inglesby warned May 23 in the Annals of Internal Medicine. If monkeypox is suspected, doctors should contact their state or local health department.

How can the outbreak be stopped?

In Nigeria, monkeypox outbreaks are controlled by isolating infected people and tracing close contacts, Yinka-Ogunleye says. Vaccines and antiviral medications are not available there for limiting the disease’s impact or spread, she says. Most of the time medication is not needed, as the body eventually clears the virus on its own, but people may be given other drugs as part of supportive care.

In Europe and the United States, close contacts of infected people may be vaccinated with either ACAM2000, an older vaccine against smallpox, or with a newer vaccine called Jynneos. Made by vaccine company Bavarian Nordic, Jynneos was approved by the U.S. Food and Drug Administration in 2019 for use against smallpox and monkeypox. That vaccine has fewer side effects than the older vaccine and is safer for people with eczema or weakened immune systems.

More than 1,000 doses of Jynneos are available in the United States’ Strategic National Stockpile, Jennifer McQuiston, deputy director of the CDC’s Division of High Consequence Pathogens and Pathology said during the CDC news briefing. And the company expects to produce more soon. More than 100 million doses of the older vaccine are available.

So far, cases in this outbreak have been mild. But two antiviral drugs, called brincidofovir and tecovirimat, developed against smallpox might be used to treat severe monkeypox cases (SN: 5/2/18).

Most of the evidence that the drugs will work against monkeypox come from animal studies. But in a tiny study in the United Kingdom, three people who got brincidofovir as monkeypox treatment developed liver problems and had to be taken off the drug, researchers report May 24 in Lancet Infectious Diseases. One person given tecovirimat spent only 10 days in the hospital, compared with six other patients who stayed in the hospital between 22 and 39 days because they were still producing virus. Those numbers are too small to draw any conclusions about the treatment’s effectiveness.

People previously vaccinated against smallpox may still have some protection against monkeypox, too, says Aaron Glatt, an infectious diseases epidemiologist at Mt. Sinai South Nassau in Oceanside, N.Y., and a spokesperson for the Infectious Diseases Society of America. But those numbers are dwindling. Smallpox was declared eradicated in 1980 and most countries stopped vaccinating against the virus in the 1970s. That means many people 50 and younger have no immunity to smallpox or monkeypox.

“This is a negative to the eradication of smallpox,” he says. “But in the overall scheme of things, it’s a positive that we eradicated smallpox. Even if we have a handful of monkeypox cases as a consequence of not vaccinating for smallpox, it is [still] a very, very good exchange.”

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