The National Academies

The National Academies: What You Need To Know About Infectious Disease

What You Need To Know About Infectious Disease

West Nile Virus

West Nile virus is an arthropod-borne virus, or arbovirus, most commonly spread by the bite of an infected mosquito that contracted the virus after feeding on infected birds. In a very small number of cases, West Nile virus also has been spread through blood transfusions, organ transplants, breastfeeding, and even during pregnancy, from mother to baby. West Nile virus is not, however, spread through casual person-to-person contact s or from handling live or infected birds, though proper safety precautions should be taken when working with infected animals.

West Nile virus has been documented in Europe, the Middle East, Africa, parts of India, and Australia. It arrived in North America—the continental United States and Canada—in 1999. According to preliminary data from 2016, there were 1,938 cases reported in the United States and 92 deaths.

Approximately 80 percent of people who are infected with West Nile virus will not show any symptoms at all. Up to 20 percent of the people who become infected have symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and back. Most people who develop these symptoms recover completely, but fatigue and weakness can last for weeks or even months. Less than 1 percent of infected people will develop serious neurologic illnesses, such as encephalitis and meningitis. Symptoms of those illnesses include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis.

There is no specific treatment for West Nile virus. In cases with milder symptoms, such as fever and aches, people usually get better on their own, without treatment. In more severe cases, people usually need to go to the hospital, where they can receive supportive treatment, including intravenous fluids, help with breathing, and nursing care.


Explore Other Topics

What do you know about infectious disease?

Which are larger?

  • Correct!

    Bacteria are 10 to 100 times larger than viruses.

  • Sorry, that’s incorrect.

    Bacteria are 10 to 100 times larger than viruses.

Infectious Disease Defined


An infectious agent that is only capable of replicating itself inside the living cells of other organisms.

View our full glossary