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SAN DIEGO — County officials confirmed Friday that they’ve identified the year’s first instance of West Nile virus after a Cooper’s hawk tested positive.

Officials with the county’s Vector Control Program only found small amounts of the virus in the hawk’s tissues, leading them to believe it was an old infection. Last year, only one county resident contracted West Nile virus and ultimately survived, but the virus has spread to as many as 44 residents as recently as 2015. Six people died due to the virus that year.

The virus is usually carried by birds, but mosquitoes can transmit it to other animals, including humans, by biting them. Symptoms of West Nile can include headache, fever, nausea, skin rash or swollen glands, according to Vector Control officials. Native and invasive mosquito species can also carry viruses like dengue and Zika.

Vector Control officials advised residents to combat local mosquito populations by emptying household items like buckets and plant saucers that may hold standing water. When outside, residents are advised to wear insect repellant that contains ingredients like picaridin or oil of lemon eucalyptus.

Residents can also obtain mosquitofish from the county for free to control larvae and breeding in items like swimming pools and bird baths that may contain standing water.

The county also encouraged residents to report local mosquito activity, dead birds and possible breeding areas to the Vector Control Program, which can be reached at (858) 694-2888. Residents can learn more about the county’s efforts to counter local mosquito activity at its Fight the Bite webpage.