West Nile Virus: Symptoms, Treatment & Prevention

West Nile Virus Facts

  • West Nile virus (WNV) is the leading cause of mosquito-borne disease in North Americans and can cause flu-like symptoms.
  • West Nile virus is non-contagious and is transmitted to humans and animals mostly through infected mosquitoes.
  • 8 out of 10 cases of West Nile virus would show no symptoms and go unreported.
  • Only 20% of WNV cases would show signs and symptoms that include mild fever, headache and body aches, nausea and vomiting, diarrhea, fatigue, swollen lymph nodes, and skin rash.
  • Severe neurological infections could occur in only 1 out of 150 people affected with the West Nile virus and can lead to coma, convulsions, tremors, and even permanent conditions like vision loss, paralysis or muscle weakness.
  • People aged 50 and above, or those with certain medical conditions such as hypertension, diabetes, kidney disease, and cancer, are at a higher risk of developing the West Nile virus symptoms.
  • In 2018, total 11 cases of West Nile virus were reported in Orange County, 6 of them belonged to age group 50-65.

Image of a Man and Mosquito with the List of West Nile Virus Symptoms

West Nile Virus Intro

The West Nile virus is among the most commonly spread infections in people passed through mosquito bites. In North America, occurrences of West Nile virus (WNV) is primarily observed during summer through fall. In southern climates that experience milder temperatures, West Nile virus can be spread year-round.

The cases of WNV have been reported throughout the central United States. In Orange County alone, total 11 cases of West Nile virus were reported in 2018, which also included one death by the illness. Thankfully, no new cases of the West Nile fever or infection have been reported this year. However, with summer approaching it’s better to be alert so that you and your family can remain safe.

How Is West Nile Virus Transmitted to Humans?

Usually, West Nile virus gets transmitted to humans and animals through infected mosquitoes. You can’t acquire it from chance interaction with an infected person or animal. Few, extremely rare cases of West Nile virus have been reported to transmit through other channels, including organ replacement, blood transfusion, mother to infant during pregnancy or breastfeeding, and virus exposure in a lab.

The majority of West Nile virus infections occur during hot weather conditions when mosquitoes are most active. The infection is passed on to the mosquitoes when they feed on infected birds. See below for the CDC’s explanation of the West Nile virus transmission cycle.

Image of West Nile Virus Transmission Cycle by CDC

Image Source: Centers for Disease Control & Prevention

What Are the Signs & Symptoms of West Nile Virus Infection?

The incubation period – the length of time between when an infected mosquito bites you and when the first signs and symptoms of the illness would appear – for the West Nile virus ranges between 2 to 14 days. Only about 8 out of 10 people infected with WNV will not show any symptoms. The remaining 20% would show milder flu-like symptoms like fever, headache, joint pains, diarrhea, or rash.

However, in rare cases (only in 1 out of 150 cases), people infected with the West Nile virus would show severe, occasionally fatal, ailment including but not limited to:

  • A high temperature
  • Tremor
  • Disorientation
  • Coma
  • Seizures or convulsions
  • Severe vision loss
  • Numbness
  • Paralysis or muscle weaknesses

Who Is at Risk of Acquiring West Nile Virus Infection?

People who generally stay outdoors for long durations are at maximum risk of infection. The mosquitoes that spread West Nile virus are predominantly active at dawn and dusk, so remaining outdoors during those periods elevates the risk of infection.

People aged 50 and above are more prone to develop the West Nile disease symptoms, but it"s not evident whether they are especially susceptible to infection.

Infants and pregnant women are not at greater risk of West Nile virus infection.

What Are the Health Risks Involved with West Nile Virus Infection?

Regardless of your infection, the possibility of developing a severe illness due to West Nile virus is minimal because only less than 1 percent of the infected population becomes severely ill. Moreover, most individuals who do get sick fully recover. The following puts you at possible risk of developing a severe or life-threating infection:

  • Being older puts you at higher risk
  • Suffering from diseases including cancer, diabetes, and more
  • Receiving an organ transplant

How Do Health Care Providers Detect the West Nile Virus Infection?

Health care providers will send your blood sample for lab tests if you are suspected to have a West Nile virus infection.

What Is the Required Treatment for West Nile Virus?

There is no definite treatment for WNV disease; however clinical management is supportive. Mild signs of West Nile fever typically resolve on their own. For acute infection, symptoms can include severe headaches, a stiff neck, bafflement or confusion that can be treated by seeking prompt medical attention. Usually, a severe infection requires hospitalization.

Visit your family doctor, or an urgent care clinic near you if you experience any symptoms of the West Nile virus.

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Gina Nguyen, MD

Dr. Nguyen is a medical director at Family Care Center Costa Mesa. She has implemented standards of care for underserved population and helped the clinic achieve NCQA (National Committee of Quality Assurance) Level 2 recognition and FQHC (Federally Qualified Health Care Center) status. Now, her focus is on providing the highest quality care to patients and improving lifestyle choices to reduce or eliminate health problems.