An "extremely rare" illness completely foreign to the state of California has been discovered there, and its appearance is not associated with travel.
On Friday, officials with the health department in Pasadena, California, confirmed a resident had contracted dengue, marking the first locally acquired case in the state not associated with international travel.
"Instead, [it's] an extremely rare case of local transmission in the continental United States," the city said.
Dengue, which is also called bone-break fever, is a viral infection spread from mosquitoes to humans. It's typically found in tropical and sub-tropical climates and is common in many Caribbean tourist destinations, the CDC says.
Local cases can occur in some states with hot and humid climates and where Aedes mosquitoes live, the CDC says. But it's not yet clear how the virus originated in California.
"Although Pasadena is home to the Aedes mosquito, the disease is not established (endemic) in California," the Pasadena Public Health Department said in a press release. "In the U.S., dengue cases are typically seen in travelers who have visited countries where dengue is found."
The health department said the risk of exposure to dengue is very low for residents and that it's an isolated incident, but it still asks people to take steps to prevent all mosquito-borne illnesses. These include wearing insect repellent and covering up in loose-fitted, light-colored clothes.
On the officials' side, the health department said it's conducting surveillance, and teams have offered Pasadena residents information as to how to prevent mosquitoes from breeding around their homes, such as removing any stagnant water that can result in breeding sites.
In addition, the San Gabriel Valley Mosquito and Vector Control District said it's deployed traps to assess the mosquito population over the next few weeks, which so far hasn't yielded any identification of dengue-infected mosquitoes.
About 1 in 4 people infected with dengue will get sick, according to the CDC. Those who do typically get better in one to two weeks, the World Health Organization says, but symptoms during that time may include fever, rash, aches and pains and more.
About 1 in 20 people who get sick will develop severe dengue, which can result in internal bleeding and even death.
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