West Nile Virus
Reportable by Providers and LaboratoriesAbout this Reportable Disease
Infectious agent: West Nile Virus, member of the family Flaviviridae, genus Flavivirus.
Description of illness: West Nile virus (WNV) is a mosquito-borne virus that can cause febrile illness, encephalitis, or meningitis. The incubation period is usually 2 to 6 days. Most people who become infected with WNV will not experience any illness. About 1 in 5 will develop a fever, along with headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people recover completely. However, less than 1% will develop encephalitis or meningitis, with headache, fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis. Recovery may take several weeks or months, and some neurologic effects may be permanent. About 1 in 10 individuals with West Nile encephalitis will die. Persons over 60 years of age are at the greatest risk for severe disease, as well as those with underlying medical conditions. No specific treatment or vaccine exists.
Interactive Disease Data
Laboratory Reporting for this Disease
Reporting requirements apply to all laboratories located within Tennessee, as well as laboratories outside of Tennessee that test residents of Tennessee, including laboratories located within healthcare facilities. Healthcare providers and laboratories in the same healthcare facility both have a duty to report. The type of organisms and analytes laboratories must report to TDH for 2026 are indicated, and there are several ways laboratories can report results to TDH.
- Manually report results to TDH by faxing or mailing a completed PH-1600 form to your local health department, or faxing to the state health office at (615) 741-3857
- Automatically submit results to TDH via electronic laboratory reporting (ELR), which automates the process of sharing data with TDH using interoperability standards.
- See the ELR Onboarding Handbook for details on the onboarding process, checklist, frequently asked questions, business rules, message format, and vocabulary.
- To initiate the ELR onboarding process with TDH, register in the Trading Partner Registration (TPR) system TPR provides documentation for Promoting Interoperability (PI) attestation and milestone letters to document onboarding progress. Contact MU.Health@tn.gov for assistance.
- Submit online via NBS. NBS is TDH's reportable disease system. To request an NBS account for reporting Complete this user survey to request an NBS account for reporting.
- Blood lead levels can be sent via fax ( (615) 741-3857), entered online, or reported using the instructions at this link.
Information about this Reportable Disease for Healthcare Providers
Clinical Summary
- Scope and agent: West Nile virus (WNV) is a mosquito-borne flavivirus and a leading cause of arboviral disease in the United States. Birds are the primary reservoir; humans are incidental hosts.
- Clinical presentation: Most infections are asymptomatic. About 20% develop an acute febrile illness (West Nile fever). Fewer than 1% develop neuroinvasive disease, including meningitis, encephalitis, or acute flaccid paralysis, which may present with altered mental status, neurologic deficits, or weakness.
- Transmission and seasonality: Spread occurs through bites of infected Culex mosquitoes, primarily in summer and early fall. Rare transmission routes include blood transfusion and organ transplantation. Not spread through casual contact.
- Clinical approach: Consider WNV in patients with aseptic meningitis, encephalitis, or acute flaccid paralysis during mosquito season. Diagnosis is typically made by WNV-specific IgM testing in serum or CSF. Treatment is supportive. Prompt reporting to public health is required.
Healthcare Provider Reporting
Healthcare reporting requirements apply to all providers located within Tennessee, as well as providers whose patients reside in Tennessee.
Providers must report cases of all diseases and conditions listed through one of these methods:
• Mail or fax a completed PH-1600 form to your local health department or fax to the state health office at (615) 741-3857
• Send automatically via electronic case reporting (eCR). See this TDH webpage for more information on eCR, register at the Trader Partner Registration website, or contact MU.Health@tn.gov for assistance.
• Submit online via NBS. NBS is TDH's reportable disease system. To request an NBS account for reporting Complete this user survey to request an NBS account for reporting.
• Blood lead levels can be sent via fax ( (615) 741-3857), entered online, or reported using the instructions at this link.
Information about this Reportable Disease for the Public
What Is It
West Nile virus is a virus spread to people through the bite of an infected mosquito. It is most common during the warmer months, especially summer and early fall.
How It Spreads
People get West Nile virus from mosquito bites. Mosquitoes become infected when they feed on infected birds and can then spread the virus to humans. West Nile virus is not spread through casual contact like touching or coughing.
Symptoms
Most people infected with the West Nile virus do not feel sick.
About 1 in 5 people may develop:
- Fever
- Headache
- Body aches
- Joint pain
- Vomiting or diarrhea
- Rash
- Fatigue
A small number of people (less than 1 in 100) can develop serious illness affecting the brain or nervous system, such as:
- Severe headache
- Stiff neck
- Confusion
- Muscle weakness
- Tremors
- Seizures
- Paralysis
Seek medical care right away if you or someone you know has symptoms of serious illness.
Who Is at Higher Risk
People at higher risk include:
- Adults over age 60
- People with weakened immune systems
- People with certain chronic medical conditions
Prevention
There is no vaccine for the West Nile virus. The best way to prevent infection is to avoid mosquito bites:
- Use EPA-registered insect repellent.
- Wear long sleeves and pants when outdoors.
- Use window and door screens.
- Remove standing water around your home (such as in buckets, flowerpots, and birdbaths).
- Community mosquito control programs also help reduce the risk of spread.
This Page Last Updated: March 25, 2026 at 8:53 PM