West Nile Fever: The Mosquito-Borne Illness You Should Know About

West Nile Virus and West Nile Fever

West Nile Virus (WNV) is a mosquito-borne virus that can cause illness in humans ranging from mild flu-like symptoms to serious neurological complications. It's most commonly spread through the bite of an infected mosquito, particularly in warmer months.

West Nile Fever is the infection caused by the West Nile Virus, which is a a flavivirus related to Zika and dengue virus.

While most people infected with WNV don’t feel sick at all, about 1 in 5 will develop symptoms like fever, fatigue, and body aches. In rare cases, it can lead to serious conditions such as meningitis or encephalitis, especially in older adults or those with weakened immune systems.

West Nile Virus in Animals and the Environment

West Nile Virus doesn’t just affect humans. Birds are the primary hosts of the virus, and the infection cycle starts with mosquitoes feeding on infected birds. Over 300 species of birds have been known to carry WNV, but crows, jays, and robins are among the most commonly affected.

Horses are also at risk. Just like humans, most horses infected with WNV will recover, but some may develop neurological symptoms, such as weakness, tremors, or difficulty standing. Fortunately, there is a vaccine available for horses, which is an important preventive tool in equine health.

In terms of the environment, outbreaks of WNV are closely tied to mosquito activity, which can be influenced by rainfall, temperature, and climate conditions. This means that regions with warm, wet weather are more likely to see cases. Local and national health authorities monitor bird populations and mosquito pools to track the virus and issue warnings when risk is high.

What You Can Do:

If you find a dead bird, especially a crow or jay, contact your local health department. Reporting these cases helps public health officials monitor the spread of West Nile Virus in your community.

How Does West Nile Virus Spread?

The primary way West Nile Virus spreads is through mosquito bites. Here’s how it works: mosquitoes become infected when they bite birds carrying the virus. Then, the infected mosquito can pass it to humans or animals. It cannot spread through casual contact like touching or kissing.

Other, much less common, ways WNV can spread include:

• Blood transfusions

• Organ transplants

• From mother to baby during pregnancy, delivery, or breastfeeding

West Nile Virus Symptoms: What to Watch For

Most infections (70-80%) cause no symptoms, but when they occur, they typically appear 2–14 days after a mosquito bite.

Mild to Moderate Symptoms (West Nile Fever)

These usually resolve on their own but can last weeks:

• Flu-like fatigue – Sudden exhaustion, often mistaken for a seasonal virus.

• "Breakbone" aches – Severe joint/muscle pain (hence the nickname).

• Rash – Flat, pink spots on the torso, arms, or legs (appears in ~50% of symptomatic cases).

• Swollen lymph nodes – Especially in the neck or armpits.

Severe Neuroinvasive Disease (1 in 150 cases)

The virus attacks the nervous system, causing:

• Meningitis – High fever, stiff neck, light sensitivity.

• Encephalitis – Confusion, tremors, seizures, or paralysis (like polio-like weakness in limbs).

• Coma or death (in rare cases, particularly in older adults or immunocompromised individuals).

When to Seek Help

Mild symptoms: Rest and hydrate, but see a doctor if fatigue persists beyond 2 weeks.
Severe symptoms: The severe forms—like encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes around the brain and spinal cord)—require immediate medical attention. Go to the ER immediately for stiff neck, confusion, or muscle weakness.

Why Some Get Sicker

Risk factors for severe illness:

• Age over 60

• Chronic conditions (cancer, diabetes, hypertension)

• Organ transplant recipients

Note: No specific treatment exists—supportive care is key. Prevention (mosquito repellent, removing standing water) is critical!

Who is at Risk?

Anyone can get infected, but older adults, people with chronic illnesses, and those with weakened immune systems are at greater risk for serious complications. Living or traveling in areas where WNV is active also increases your risk—especially during mosquito season.

Diagnosis and Treatment

West Nile Virus is diagnosed with blood tests that detect antibodies or the virus itself. In more serious cases, spinal fluid may also be tested.

There’s no specific treatment or vaccine for WNV. Most mild cases go away on their own with rest, fluids, and over-the-counter pain relievers. For severe cases, hospitalization may be needed for supportive care, such as IV fluids, pain management, and monitoring.

Prevention Tips

The best way to protect yourself from West Nile Virus is to avoid mosquito bites:

• Use insect repellents with DEET, picaridin, or oil of lemon eucalyptus

• Wear long-sleeved shirts and pants when outdoors

• Use mosquito screens on windows and doors

• Empty standing water from flowerpots, buckets, and birdbaths

• Stay indoors at dawn and dusk when mosquitoes are most active

Final Thoughts

West Nile Virus is usually mild, but it can become serious in certain individuals. Awareness and prevention are your best defense. If you experience symptoms after a mosquito bite, especially during summer or early fall, talk to your doctor.

Sources:

• Centers for Disease Control and Prevention (CDC):
  https://www.cdc.gov/westnile/symptoms/index.html
  https://www.cdc.gov/westnile/index.html

• World Health Organization (WHO):
  https://www.who.int/news-room/fact-sheets/detail/west-nile-virus

• Mayo Clinic:
  https://www.mayoclinic.org/diseases-conditions/west-nile-virus/symptoms-causes/syc-20350320

• National Institute of Allergy and Infectious Diseases (NIAID): https://www.niaid.nih.gov/diseases-conditions/west-nile-virus

• MedlinePlus (U.S. National Library of Medicine): https://medlineplus.gov/westnilevirus.html