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CDC's monkeypox case count passes 1,000: Here's what you need to know

Pox viruses (shown here in this illustration) like monkeypox are oval-shaped with double-strand DNA.
Pox viruses (shown here in this illustration) like monkeypox are oval-shaped with double-strand DNA. (Image credit: ROGER HARRIS/SCIENCE PHOTO LIBRARY via Getty Images)

More than 1,050 monkeypox cases have been detected in the U.S. as of Wednesday (July 13), but based on the availability of diagnostic tests in the country, this may be a significant undercount, some experts say.

So far this year, about 10,800 monkeypox cases have been detected in places where the virus does not typically spread, such as the U.S., according to the Centers for Disease Control and Prevention (opens in new tab) (CDC). Both the global case count and U.S. case count include laboratory-confirmed monkeypox cases and infections attributed to an Orthopoxvirus, the genus of viruses that includes monkeypox; smallpox, which has been eradicated; and the related cowpox and camelpox viruses, which very rarely jump to humans.

The outbreak is being driven by a group of monkeypox viruses known as the West African clade, according to the CDC (opens in new tab). This lineage of viruses rarely causes severe or fatal disease, but children younger than 8, people with weakened immune systems or a history of eczema, and people who are pregnant or breastfeeding face a greater risk of such outcomes.

In late June, the CDC and U.S. Department of Health and Human Services (HHS) announced (opens in new tab) that they'd begun ramping up the nation's capacity for monkeypox testing by supplying tests to five commercial laboratory companies. "Health care providers will be able to use these laboratories by early July and testing capacity through these companies will be ramped up throughout the month," the HHS said.

Related: Monkeypox may have been spreading in UK for years

However, since the first U.S. cases were detected in May, monkeypox testing has generally been hard to come by, so the CDC's official case count is likely misleading, Keletso Makofane, an epidemiologist at Harvard University, told NPR (opens in new tab). That's partially because health care providers previously had to go through a cumbersome process to procure tests, and partially because many providers were only supplying tests to patients whose condition matched a narrow definition of what monkeypox looks like. 

Monkeypox symptoms

With this in mind, the CDC recently updated its guidance as to who should be tested for monkeypox based on their symptoms, Live Science previously reported. In this health alert, the agency noted that many of the recent monkeypox cases in the U.S. have not matched classical descriptions of the disease.

Normally, monkeypox infections are thought to start with flu-like symptoms, including fever, headache, muscle aches, swollen lymph nodes and fatigue. Then, the characteristic "pox" rashes begin to appear, usually around the face and in the oral cavity, and later, on the extremities, including the palms of the hands and soles of the feet. These rashes progress through several stages, starting out as discolored patches of skin and then forming into raised bumps, blisters, and large, pus-filled pimples that eventually scab over and fall off. In most cases, these symptoms resolve in two to four weeks.

In the current outbreak, however, some patient's symptoms have diverged from the normal pattern. For example, some patients developed flu-like symptoms after their skin rashes or didn't experience flu-like symptoms at all, the CDC reported. Some patients initially developed rashes around the genitals and anus, and these skin lesions caused symptoms of painful inflammation and rectal bleeding. And sometimes, patients have had rashes in different stages of progression at the same body site, which is unusual.

Monkeypox rashes can be mistaken for rashes caused by Varicella zoster, the virus that causes chickenpox; or for certain sexually transmitted infections, such as syphilis and herpes, so patients suspected to have these diseases should also be tested for monkeypox, the CDC noted. 

How monkeypox spreads

Monkeypox spreads when people come into contact with an infected person's rashes or materials contaminated with their bodily fluids, such as clothing or linens, according to the World Health Organization (opens in new tab) (WHO). Transmission can also occur through respiratory droplets, meaning spit and mucus, but this mode of transmission usually requires "prolonged" face-to-face contact. In pregnant people, the virus can pass through the placenta and can also be transmitted via close contact to newborns during and after birth.

Related: Smallpox-related viruses are still a threat to humans, experts warn

Preliminary research suggests that the monkeypox viruses driving the current outbreak have a reproduction number, or R-naught (R0), of 0.8, the WHO reported (opens in new tab). That means that a single infected person infects 0.8 more people, on average. That said, the virus's R0 may be greater than 1 among men who have sex with men, as so far, the majority of confirmed cases have been detected in this group. That's not because monkeypox is a sexually transmitted disease or more likely to infect men who have sex with men, but rather because the virus happens to be spreading within this social network. 

Monkeypox treatments and vaccines in the U.S.

There are no drugs specifically approved to treat monkeypox, and many people recover without the need for specific treatment. However, in severe cases, patients may receive antiviral medications intended to treat other infections; for example, they may receive tecovirimat (brand name TPOXX), which is designed to treat smallpox and also works against other orthopoxviruses, according to the CDC (opens in new tab)

Severe monkeypox infections may be also treated with Vaccinia Immune Globulin Intravenous (VIGIV), which contains antibodies taken from the blood of people who were immunized with the smallpox vaccine.

People who have recently been exposed to monkeypox may also be given one of two vaccines — JYNNEOS or ACAM2000 — to reduce the severity of their symptoms or to prevent the illness altogether, according to the CDC (opens in new tab). JYNNEOS, approved for both monkeypox and smallpox, is a newer vaccine and generally preferred over ACAM2000, which carries a risk of severe side effects in immunocompromised people, pregnant people and older adults, The New York Times reported (opens in new tab)

On June 28, the CDC and the HHS launched a campaign to expand vaccine access during the ongoing monkeypox outbreak. All people with confirmed or presumed monkeypox exposures are now eligible for free vaccination, including those "who had close physical contact with someone diagnosed with monkeypox, those who know their sexual partner was diagnosed with monkeypox, and men who have sex with men who have recently had multiple sex partners in a venue where there was known to be monkeypox or in an area where monkeypox is spreading," the statement reads (opens in new tab)

However, the vaccination plan's rollout has not been smooth so far. 

Upon the plan's announcement, experts criticized the rollout as too slow and too limited in scale, The New York Times reported. Already, health and city officials in San Francisco have requested that the federal government quickly distribute more vaccine doses, arguing that the current need vastly outstrips the supply, the San Francisco Chronicle reported (opens in new tab). Similarly, in New York City, vaccine appointments have been filling as quickly as they're released, and Mayor Eric Adams recently wrote to President Joe Biden to ask for more doses to distribute, Gothamist reported (opens in new tab).

Meanwhile, two states with confirmed monkeypox cases — New Mexico and South Dakota — have yet to receive any vaccine doses, CNN reported (opens in new tab) Thursday (June 14). 

Originally published on Live Science. 

Nicoletta Lanese
Nicoletta Lanese

Nicoletta Lanese is a staff writer for Live Science covering health and medicine, along with an assortment of biology, animal, environment and climate stories. She holds degrees in neuroscience and dance from the University of Florida and a graduate certificate in science communication from the University of California, Santa Cruz. Her work has appeared in The Scientist Magazine, Science News, The San Jose Mercury News and Mongabay, among other outlets.