The principal route of human infection with West Nile Virus is through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. The virus eventually finds its way into the mosquito’s salivary glands. During subsequent blood meals, the virus may be injected into humans and animals, where it can multiply and possibly cause illness.
Additional routes of infection have become apparent during the 2002 West Nile epidemic. It is important to note that these other methods of transmission represent a very small proportion of cases. A recent investigation has confirmed WNV transmission through transplanted organs. Investigations of other patients who developed WNV infection within several weeks of receiving blood products or organs are ongoing to determine whether WNV was transmitted by transfusion or transplantation in any of these cases.
These is one reported case of trans-placental (mother-to-child) WNV transmission. although transmission of WNV and similar viruses to laboratory workers is not a new phenomenon, two recent cases of WNV infection of laboratory workers have been reported.