US CDC Releases New Guidance on Monkeypox Diagnosis, Warning Early Symptoms Look Similar to STIs

As cases of monkeypox virus (MPXV) continue to rise in the United States, the Centers for Disease Control and Prevention (CDC) have issued new guidance on the virus, especially in the area of diagnosis. Though known for decades, the newest variant of the virus is behaving in unexpected ways.

As of Wednesday, the US has detected 84 cases of MPXV, according to CDC data, and 2,027 cases have been detected across 36 countries. While the virus cannot reach the level of infectiousness of COVID-19, the US has upped its efforts to detect, diagnose, and treat people who have been infected, many of whom are gay and bisexual men who have contracted it during casual sexual encounters.

According to the CDC’s new guidance, MPXV is not a sexually transmitted infection (STI) and is likely spreading due to the close physical contact that happens during sex. However, many of the early symptoms look somewhat similar to STIs such as syphilis and gonorrhea, and part of the CDC’s new guidance is for doctors to more rigorously test people with rashes or lesions that they believe can be explained by an STI.

“It’s important to be aware that monkeypox cases may present similar to some sexually transmitted infections and could be mistaken for other diagnoses,” CDC Director Rochelle Walensky told reporters last week. “Health-care providers should not rule out monkeypox just because a patient has another diagnosis or another STI.”

Since it was discovered in Liberia in 1970, MPXV has generally caused symptoms in patients that are extremely similar to the virus’ much deadlier cousin, smallpox. However, according to the CDC, the newest variant of the virus spreading across Europe and the Americas since last month has some new features, including a persistent rash in the mouth, genitals or anus, and lesions that remain localized instead of spreading across the body. The health agency also notes that multiple types of lesions can be present on a single person, including fluid-filled ones, pus-filled ones, and raised ones.

The lesions remain the most infectious aspect of the virus and touching the skin or the contents of a lesion is enough to cause an infection. Thus, bedding or clothing that has touched the lesions can also cause infection, much as it does in smallpox.

The risk to the public remains low, the CDC said, noting that people exposed to people who were infected, or who traveled to countries with an outbreak, should be extra-vigilant of early symptoms. If someone tests positive for orthopoxvirus, the family of viruses that includes MPXV, they are advised by the CDC to isolate themselves from others until their scabs have fallen off and a fresh layer of skin has formed. The symptoms typically last between two and four weeks.

The World Health Organization (WHO), a UN-affiliated global health agency, referred to the change in viral symptoms as “an unusual situation.”

The MPXV version spreading is a West African variant with a mortality rate of 1% and has caused no deaths in the present outbreak outside of the virus’ endemic range in Central and West Africa. Other variants of the virus can have a mortality rate of as high as 10%, which still pales in comparison to the 30% death rate of the now-eradicated smallpox, a close relative of MPXV.

Because of their similarity, it is believed that the smallpox vaccine can also protect against MPXV, although that has never been tested. According to CNBC, the US has 72,000 doses of the smallpox vaccine Jynneos, which has been approved to treat MPXV, requiring a two-dose administration. The country has been distributing Jynneos to those infected with the virus and has ordered 300,000 more doses of the vaccine. The US also has 100 million doses of an older smallpox vaccine, ACAM2000, in storage, but isn’t using them for MPXV because it can cause a more severe reaction.

Because of its origins in Africa, coverage of the MPXV outbreak has often featured imagery of Africans bearing its trademark lesions, which African doctors have denounced as discriminatory and stigmatizing. As a result, the WHO announced earlier this week that it would rename the virus.