The Delaware County Health Department is evaluating three probable human cases of West Nile virus, according to Patch. The department told the publication that the cases had not been confirmed and that evaluations were continuing. No information about the patients’ conditions was available.
Mosquito surveillance
West Nile virus has been found in more than 100 groups of mosquitoes trapped in Delaware County this season, Patch reported. The county’s mosquito program conducts surveillance from spring through fall and uses traps to monitor mosquito activity and identify areas where the virus may be present, according to the Delaware County Health Department.
The county’s findings are part of broader West Nile activity reported across southeastern Pennsylvania. The Pennsylvania Department of Environmental Protection had recorded virus-carrying mosquitoes in 46 of the state’s 67 counties, including every county in the southeastern region, when the Philadelphia Department of Public Health issued its September update. Philadelphia had reported four human cases at that point.
Seasonal risk and historical context
According to the Pennsylvania Department of Health, human West Nile infections are most commonly seen from July through September, with risk continuing until the first hard frost. As a statewide historical reference, Pennsylvania reported 34 neuroinvasive and non-neuroinvasive West Nile cases during the 2022 season, according to the department.
Health effects
Most people infected with West Nile virus do not develop symptoms. About 20 percent develop fever or flu-like illness, while fewer than 1 percent develop severe neuroinvasive disease, which can involve inflammation of the brain or spinal cord, according to CDC clinical data cited in the article’s reporting. The available information does not indicate whether Delaware County’s probable cases will be confirmed or what symptoms, if any, the patients have experienced.
Human West Nile cases occur in Delaware County in most years, according to CBS News Philadelphia. The county’s highest total in the five-year period cited by the health department was four confirmed infections in 2021.
Reducing exposure
Residents can reduce mosquito breeding around their homes by draining standing water each week, the Delaware County Health Department advises. The county also recommends using EPA-registered repellent containing DEET, Picaridin or oil of lemon eucalyptus, according to its West Nile guidance.
The county’s response combines surveillance, habitat reduction and larviciding. Those measures account for roughly 95 percent of mosquito management, while adulticide spraying may be used when trapping data indicate an acute public-health threat, according to the Delaware County Health Department. The county says it does not spray solely in response to nuisance complaints.
