West Nile Virus is Moving Up in the World
Global temperatures are rising. You hear this all the time because, based on certain numbers, it's true. But what are these numbers?
The metric used by NASA's Goddard Institute for Space Studies (GISS) and the National Oceanic and Atmospheric Administration (NOAA) is the "global mean surface temperature anomaly". Sounds like something made up to give Spock some dialogue. But it just means how much hotter the Earth is compared to a long-term average.
What average? To test if current years are unusually warm, scientists usually compare them to the average global surface temperature between 1951 - 1980. We have solid data for those years. Anytime before that, data wasn't as accurate or consistently gathered. Although, you might see a "pre-industrial baseline" which covers 1850-1900. Oddly enough, the average global surface temperature in both periods was around 57°F. Things weren't changing all that much. Until now.
Using either baseline, each of the past ten years rank among the warmest on record. And the trend overall is showing -- you guessed it -- global temperatures are rising. The year 2000 was 0.76°F warmer than the pre-industrial average. By 2023, the Earth was 2.12°F warmer. That made it the warmest year ever recorded.
But is two degrees warmer something to worry about?
Well, it's just an average. It reflects much wider swings around the globe. (The Arctic is warming over 4°F on average). Behind this global number, huge changes in Earth's climate are happening locally -- more heatwaves, droughts, extreme weather, habitat loss, and a significant shift in climate zones, which bring diseases that thrive in warmer climates closer to where we live.
It's why the United Kingdom just reported its first case of West Nile virus ever.
West Nile virus is primarily spread by mosquitoes that love warm weather. Hotter temperatures speed up the mosquito life cycle and the virus's incubation period inside the mosquito, increasing the chances of transmission.
The virus used to be confined to Africa and the Middle East. But as global weather warmed, it spread to the southern United States and southern Europe. With this new UK finding, the range for the virus continues to expand.
The UK Health Security Agency (UKHSA) announced it on May 21, 2025. Scientists found the presence of viral genetic material in two mosquito samples in the wetlands of Retford, Nottinghamshire.
But there's no need to worry.
Agencies call the situation very low risk. There's no evidence the virus is still spreading among the birds or mosquitoes. More importantly, there are no reports of humans getting it. West Nile virus has appeared in the UK, but it's not yet a threat.
Same exact thing happened in the United States. West Nile had never appeared in the country. Then, in the summer of 1999, local health officials in New York City noticed an unusual number of crows and other birds were dying. There was a virus spreading. By August, the virus was confirmed was West Nile.
No need to worry. Except within three years the virus had spread from a 6-county area around New York City to the West Coast of the U.S., covering 44 states and five Canadian provinces. By 2002, there were 2,258 cases of humans infected.
But again, this is not cause for panic. Humans infected with West Nile virus usually never even know it. There are no symptoms at all. So, no problem. And for those few who do get sick, the illness is usually mild. Fever, headache, stuff humans can deal with by taking off the shelf meds.
Except -- in a very small percentage of people who get the virus -- it isn't so easy. The virus gets into the victim's brain or nervous system and causes swelling or infection of the brain and the protective layers around the spinal cord. It causes seizures, and difficulty moving. It can be life threatening.
But this is very rare -- West Nile virus is only fatal in the most severe cases. Less than 0.1% of infected people die -- fewer than 1 in 1,000. So there's really nothing to worry about.
Although, since the 1999 outbreak in North America, West Nile virus has caused 60,000 human infections and more than 3,000 deaths.
UK officials stress that for this kind of outbreak to occur, there would need to be a critical mass of infected birds and mosquitoes, with enough warm weather to sustain multiple cycles of transmission. The UK's cool climate keeps this process at bay. Summer temperatures average a cool 59°F. It can take up to 100 days for the virus to develop inside a mosquito when it's that cool, and that's longer than the insect's lifespan.
So really, there's no need to worry. As long as global temperatures don't continue to rise.
Because there is one important thing to know about West Nile virus. There's no vaccine or antiviral for it. Doctors can treat the symptoms, help with the pain, provide supportive care.
But if you get the fatal kind, there's nothing they can do.
