West Nile Virus: A Mosquito-Borne Disease in a Warming World

West Nile is back — and it’s spreading

West Nile virus infections are spiking in the U.S. this year, with late summer and early autumn driving most cases. But this isn’t just a local blip. West Nile is part of a global pattern: mosquito-borne viruses are thriving in more places, for longer parts of the year, as climates trend warmer, wetter, and more erratic. Whether these shifts are primarily natural cycles or human-driven, the practical result is the same — mosquito ecology is changing, and viruses are following.

What makes West Nile different

• Wildlife reservoir: WNV cycles between birds and mosquitoes. Humans are dead-end hosts (we get sick but don’t pass it on).
• Mostly mild — sometimes severe: Many infections are silent; a small fraction lead to neuroinvasive disease (encephalitis, meningitis, paralysis).
• Seasonal risk: Late summer/early fall peaks, especially after warm, wet periods (or even droughts that concentrate birds and mosquitoes around limited water sources).

The wider pattern

• Dengue & Zika: Human-amplified outbreaks, expanding beyond the tropics as Aedes mosquitoes move into new regions.
• Yellow fever & Japanese encephalitis: Wildlife reservoirs (monkeys; birds/pigs) keep risk alive; vaccination programs are key where available.
• Ross River virus: Wildlife cycle (kangaroos, wallabies, birds) — climate and rainfall strongly influence outbreaks.

Why climate matters (whatever the cause)

• Warmer temps → faster mosquito breeding and viral replication.
• Heavy rain/floods → more standing water (breeding sites).
• Droughts → birds, animals, and mosquitoes cluster together.
• Range expansion → mosquitoes establish in areas once too cool.

What you can do

• Use EPA-registered repellents (DEET, picaridin, oil of lemon eucalyptus).
• Long sleeves/pants at dusk and dawn; use window/door screens.
• Remove standing water (gutters, pots, birdbaths); cover rain barrels.

For a practical reference with symptoms, prevention, and care, see our companion guide: “West Nile Virus (WNV)”.