U.S. health officials issued a warning to travelers about a mosquito-borne illness being transmitted in parts of southeast China.

The Centers for Disease Control and Prevention said there is an outbreak of chikungunya in Guangdong province. Most cases have been reported in the city of Foshan.

Most people infected with the virus develop fever, joint pain, headache, muscle pain, rash, joint swelling and other symptoms, the CDC said Friday in a travel warning. Symptoms usually begin three to seven days after a person has been bitten by an infected mosquito.

The CDC said most people recover in about a week, and there is no treatment. In some cases, severe joint pain can last for several months to years following acute illness.

Newborns and older adults, as well as people with medical conditions such as heart disease and diabetes, are more prone to severe illness. Death is rare, the CDC said.

China held a national conference last month on ways to prevent and treat the virus. From July 20 to July 26, 2,940 new local cases were reported in Guangdong province, China’s National Health Commission said in a news release Thursday. The cases were mild, with no reports of severe illness or deaths.

Insect repellents and wearing clothing that covers the skin can help protect people from mosquito bites. Vaccination is recommended for people who are visiting areas with outbreaks, the CDC said. There are two approved vaccines in the United States.

The virus was first detected in Tanzania in 1952, according to the World Health Organization. Since 2004, outbreaks have become more frequent and widespread.

It has been found in Asia, Africa, Europe and North and South America.