West Nile Virus Home > West Nile Virus Transmission

The most common way of transmitting West Nile virus is through the bite of an infected mosquito. In rare cases, West Nile virus can be spread through blood transfusions, organ transplants, or breastfeeding. If symptoms of West Nile virus occur, they typically develop between 3 and 14 days after transmission.

How Is West Nile Virus Transmitted?

Most often, West Nile virus is spread by the bite of an infected mosquito. West Nile virus is not spread through casual contact, such as touching or kissing a person with the virus.

Transmission Through an Infected Mosquito

The main cause of human infection with West Nile virus is through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds.
Even in areas where the virus is circulating, very few mosquitoes are infected with the West Nile virus. Even if the mosquito is infected, less than 1 percent of people who get bitten and become infected will get severely ill. The chances of you becoming severely ill from a single mosquito bite are extremely small.

Transmitting West Nile Virus Through Transfusions, Transplants, and Pregnancy

Additional causes of human infection became apparent during the 2002 West Nile epidemic. These additional causes of transmission include:
  • Blood transfusions
  • Organ transplants
  • Breastfeeding
  • During pregnancy, from mother to baby.
It is important to note that these other methods of transmission represent a very small number of cases.

Incubation Period for West Nile Virus

People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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