Officials say the cases were found through testing of blood donors.
No information on the patients has been released, but officials say they were asymptomatic.
"Those mosquitoes that are born also can be born much more quickly," said Ryan McNeil with the Fresno Mosquito and Vector Control District. "Their cycle going from an egg to an adult, to impact human beings is quite quick in these higher temperatures."
Mosquito Abatement Districts in Fresno County report that 56 of its samples tested positive for the virus.
The California Department of Public Health reports that as of July 5, there were zero cases of the West Nile Virus in people across the state.
But on Wednesday, the Fresno County department of Public Health confirmed three cases of the disease after screening donated blood.
"Here at the health department, we'll trace those," said Leticia Berber with the Fresno County Public Health. "We'll interview those individuals to see if they traveled, where they were."
Public Health officials said it's not uncommon to see West Nile Virus in donated blood.
McNeil said since March, crews have been setting hundreds of traps and checking out neighborhoods that could be a hotspot for mosquitos.
"Those neighborhoods that have more lush or mature landscaping, therefore more water to maintain, though, that landscaping have typically been a little bit higher," said McNeil. "The area around Fresno High and Old Fig Garden in our district in particular, historically, those two areas have been above average in mosquito production where we have found that disease."
According to CDPH, last year there were a total 473 infected cases of the West Nile Virus in the state. The state reported 433 symptomatic cases in humans. Nineteen people died from the disease in 2023, including one person from Fresno County.
"There's no medication for this virus," said Berber. "If you do get infected with the virus, all we can do is give you medication to feel better."
In Northwest Fresno, Ian Ledesma said his dad makes sure to take care of the pond outside their home, so it doesn't become a breeding ground for the pesky bug.
"We'll put chlorine tablets, and it will keep the little bugs away," said Ledesma.
"Anything that can hold water needs to have that water removed," said McNeil.
"Bird baths, we recommend, and other fountains to either have a working pump. Pools to have a working pump or to change out that water in those fountains."
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