In the past two weeks, mosquitoes carrying West Nile virus were detected in nine of 12 Staten Island ZIP codes, according to recent trap data.

Philadelphia health officials are warning residents after West Nile virus was found in mosquitoes in Northeast Philadelphia earlier this month.

West Nile virus is a viral disease that is transmitted by mosquitoes. The virus is a member of the Flaviviruses, which also includes Zika, dengue and yellow fever viruses. The virus was first identified in the West Nile district of Uganda in 1937,