Four people in Oregon were infected with a rare tick-borne virus, known as Colorado tick fever, in a single month, according to a new report.

That's an unusually high number of cases for the state, which typically sees one or fewer cases of Colorado tick fever per year, according to the report, published today (March 28) by the Centers for Disease Control and Prevention (CDC).

According to the CDC, all four cases occurred in May 2018. The patients lived in three neighboring counties in central Oregon; three of them were men in their 70s and the fourth was a woman in her 50s.The symptoms in all the patients included fever and low white-blood-cell count; three were hospitalized, the report said.

The patients tested positive for Colorado tick fever virus — a virus that is spread by the bite of the Rocky Mountain wood tick (Dermacentor andersoni). This pest is typically found in parts of the western U.S. and western Canada, at elevations around 4,000 to 10,000 feet (1,219 to 3,048 meters) above sea level. (Colorado tick fever virus is not related to Rocky Mountain spotted fever, another tick-borne disease that can be spread by the same tick.) [10 Important Ways to Avoid Summer Tick Bites]

Colorado tick fever is rare, with only 83 cases reported in the U.S. from 2002 to 2012, according to the CDC. The most common symptoms are fever, chills, headache, body aches and fatigue.

The patients all reported spending a lot of time outdoors working in wooded or bushy areas and recalled having a tick bite two weeks before their symptoms started.

There's no specific treatment for Colorado tick fever, but all of the patients recovered from their illnesses, the CDC reported.

The study authors stated that, after checking medical records at the same hospital where the patients were treated, they noted one suspicious case of a man in his 60s who had symptoms consistent with the virus in the summer of 2018. Indeed, when the researchers followed up with him, they learned that the man had been bitten by a tick before he got sick. When the scientists tested his blood, the results were positive for antibodies against Colorado tick fever virus, meaning the man had the virus at some point.

That brings the total number of Colorado tick fever cases in Oregon to four confirmed and one suspected case during the spring and summer of 2018.

In the report, the CDC noted that the increase in Colorado tick fever cases in Oregon in 2018 might have been due to increased tick activity in the area, or to increased awareness of and testing for the disease, the report said.

"Health departments need to reinforce tick prevention measures," the researchers wrote.. They suggested using insect repellant, wearing long sleeves and long pants, avoiding wooded and bushy areas, and performing tick checks after spending time outdoors. CDC said.

Originally published on Live Science.