Two Philadelphians have been diagnosed with West Nile virus, health department says

Two people in Philadelphia were diagnosed with West Nile virus after experiencing symptoms of the mosquito-borne illness late last month, city health officials said Tuesday.

The cases are the first to be identified this season in Philadelphia, according to an alert sent to health-care providers.

Both Philadelphia patients had developed a serious neurological condition, a rare side effect of the virus that occurs in less than 1% of patients.

Most West Nile cases are asymptomatic, but in about 20% of cases, people become noticeably ill, according to the U.S. Centers for Disease Control and Prevention.

In Pennsylvania, cases of West Nile in humans have also been reported this summer in Allegheny, Bucks, Butler, Lancaster, and Schuylkill Counties.

In the Philadelphia cases, both patients were hospitalized for acute flaccid myelitis, which causes sudden weakness in the arms and legs and a loss of muscle tone and reflexes. The health department’s alert did not provide any further detail on their condition.

West Nile can also cause encephalitis, an inflammation of the brain, and meningitis, an inflammation of the membrane surrounding the brain and spinal cord. About 10% of people who develop severe illness from the virus will die, according to the CDC.

But most West Nile patients who show symptoms will instead develop milder symptoms such as a fever, headaches, joint pains, and vomiting, although the CDC warns that fatigue from even milder cases can last months.

Philadelphia logged 11 cases of West Nile in 2022, one of which was fatal. In 2023, the city saw five symptomatic patients, one of whom died.

More mosquitos have been testing positive for the virus in the city this year, health officials said, adding that the risk of West Nile infections in humans will be higher over the next few weeks and through October.

Preventing West Nile infections requires controlling mosquitos in an area, and city health officials regularly spray for mosquitos and destroy the places where mosquitos breed: in standing water, overgrown bushes, and tall grass.

On an individual level, wearing bug spray with at least 20% DEET while walking in brush, tall grasses, or wooded areas can help prevent bites and infections. Philadelphians can also make sure screens on windows and doors are secure and remove standing water outside their homes.

Physicians should report suspected and confirmed cases of West Nile virus to the health department immediately by calling 215-685-6741 during business hours, or 215-686-4514 after hours. Residents can report mosquito problems and sightings of dead birds, which can also be a sign of the virus circulating, to the health department’s Mosquito Complaint hotline at 215-685-9000.