The state Health Department said Thursday two cases of dengue fever were locally acquired on the Big Island, and officials are investigating four additional possible cases.

“Although dengue is not endemic to Hawaii, we do have the mosquito species capable of transmitting the disease,” state epidemiologist Dr. Sarah Park in a news release. “It’s likely an infected traveler infected the local mosquito population, which led to this cluster, so we want the public to be aware of this mosquito-borne disease and the steps they can take to prevent infection.”

The tally for confirmed dengue fever cases in Hawaii so far this year is now 15. There were 14 cases last year.

Further testing and confirmation with the Centers for Disease Control and Prevention are pending.

The department has sent out a medical advisory to clinicians in Hawaii County.

Hawaii District health officer Aaron Ueno said in a news release, “Our local environmental health assessments have not found significant mosquito activity in the affected area.”

He added, “As a precautionary measure the department is conducting mosquito prevention activities such as spraying with consent from property owners.”

The dengue virus is transmitted through the bite of an infected mosquito. Symptoms, which usually begin within a week of a bite, include fever, joint or muscle pains, headache or pain behind the eyes, and rash.