West Nile virus (WNV) activity typically peaks in late summer and early autumn as mosquito populations remain active and temperatures stay warm. According to the Centers for Disease Control and Prevention (CDC), the virus is the leading cause of mosquito-borne disease in the continental United States, with most human cases occurring between July and October. Public health officials monitor local surveillance data to track viral prevalence in mosquito pools, birds, and humans to mitigate transmission risks.
How is West Nile virus transmitted?
The virus spreads primarily through the bite of an infected Culex species mosquito. Mosquitoes become carriers after feeding on infected birds. The CDC notes that transmission does not occur through casual contact, such as touching or kissing, nor through handling live or dead infected birds. While rare, the virus can spread through organ transplants, blood transfusions, and from mother to child during pregnancy or breastfeeding.
What are the symptoms of infection?
Most people infected with West Nile virus—about 80%—do not develop any symptoms. For those who do, the Mayo Clinic reports that symptoms typically appear two to 14 days after a bite.
Common symptoms include:
- Fever
- Headache
- Body aches and joint pain
- Vomiting or diarrhea
- Fatigue or skin rash
A small percentage of individuals, roughly one in 150, develop severe, life-threatening neurological illnesses, such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes surrounding the brain and spinal cord). Those over age 60 or with underlying medical conditions, such as cancer, diabetes, or kidney disease, face a higher risk of severe outcomes.
How can you prevent mosquito bites?
Reducing exposure to mosquito bites remains the most effective strategy for preventing infection. The Environmental Protection Agency (EPA) recommends using insect repellents containing active ingredients like DEET, picaridin, or oil of lemon eucalyptus, which are registered as effective and safe when used according to label instructions.
Other recommended preventative measures include:
- Wearing long-sleeved shirts and long pants during peak mosquito hours, typically dusk and dawn.
- Installing or repairing window and door screens to keep mosquitoes outside.
- Emptying standing water from containers like flower pots, buckets, and bird baths weekly, as these serve as breeding grounds for mosquitoes.
Is there a vaccine or specific treatment?
There is currently no vaccine to prevent West Nile virus in humans and no specific antiviral medication to treat the infection. According to the CDC, clinical management focuses on supportive care, which may include hospitalization, intravenous fluids, pain medication, and nursing care to manage symptoms. Individuals who experience symptoms such as high fever, severe headache, neck stiffness, or confusion should seek medical attention promptly.