A more severe strain of mpox has been detected in the U.S. for the first time

An electron microscopic image of mpox virus particles.

Smith Collection/Gado via Getty Images

hide caption

toggle caption

Smith Collection/Gado via Getty Images

An electron microscopic image of mpox virus particles.

Smith Collection/Gado via Getty Images

A strain of mpox disease that had previously been undetected in the U.S. has been found in California, according to the Centers for Disease Control and Prevention.

California’s health department confirmed the case through lab testing. The patient contracted it after traveling from East Africa, where there has been an outbreak of the clade I strain. The person was treated in San Mateo County and then released. The person is at home recovering, the CDC said Saturday.

The CDC says the strain presents a low risk to the general public. “Casual contact, like you might have during travel, is unlikely to pose significant risks for transmission of mpox,” it said.

The agency advises people to avoid close contact with infected people and surfaces and objects they may have come in contact with, such as clothing, bedding and toothbrushes. Those who are eligible should also be vaccinated, it said.

Earlier this year, the World Health Organization declared mpox a public health emergency of international concern.

It is a disease that is zoonotic, or caused by animals; and endemic, or regularly occurring, in Central and West Africa. It was previously known as monkeypox, but was shortened by the WHO, as critics said the name plays into racist stereotypes and prematurely suggests that monkeys are the main carriers of the disease.

There are two types of mpox, clade I and clade II. They are indistinguishable by their appearance, but clade I diagnoses have typically been more deadly and severe. However, its effects have been less harsh in the current clade I outbreak in Central and East Africa, according to the CDC.

Mpox causes a rash that can manifest on the hands, feet, chest, face or genitals. Symptoms may take 3 to 17 days to show up.