It has since spread throughout the contiguous United States, but instances are rare. The virus is also found in parts of Asia, the Middle East and Africa. It was first discovered in Uganda in 1937.
The Centers for Disease Control and Prevention report that 2,085 cases of West Nile Virus were reported in 2014, the last year available for statistical purposes. The cases were reported to have occurred in 43 states and the District of Columbia, resulting in 84 deaths.
The virus is believed to be transmitted to humans by mosquito bites during warm weather, when mosquitos are most active. The incubation period is about three to 14 days from the time of the bite to the point when symptoms appear.
Mosquitos are infected when they feed on an infected bird. Once a human is infected with West Nile Virus, it can spread through blood transfusions, organ transplants, and via transference from mother to child during fetal gestation or breastfeeding, although it’s unclear whether that happens in all cases.
To date, handling animals infected with the West Nile Virus is not believed to be a cause of the disease’s transmission.
Fortunately, most mosquitos do not have the West Nile Virus, and even an infected mosquito may not transmit the virus. Even if the mosquito does pass along the virus, many people show no symptoms of the disease.