Invasive species aren’t just species—they can also be pathogens. Such is the case with the West Nile virus. A mosquito-borne virus identified in the West Nile subregion in Uganda in 1937—hence the name—West Nile wasn’t much of a concern to people elsewhere until it broke out of Africa in 1999. The first U.S. cases were confirmed in New York City in 1999, and it has now spread throughout much of the world. Though 80% of infections are subclinical—meaning they yield no symptoms—those who do get sick can get very sick.The virus can led to encephalitis—inflammation of the brain and nervous system—and even death, with 286 people dying from West Nile in the U.S. in 2012. There were more than 5,500 cases reported that year, and the scary thing is that as the climate warms, West Nile will continue to spread.
That’s the conclusion of a new study from a team of researchers in the U.S., Britain and Germany, including those at the Center for Tropical Research at UCLA’s Institute of the Environment and Sustainability. In a study published in the journal Global Change Biology, the researchers took climate and species distribution data, and created models that try to project the spread of the virus as the globe warms. West Nile virus is carried by mosquitoes, and infected insects transmit the virus to human beings with a bite. But birds play a role too—if bitten by an infected mosquito, birds can generate high levels of the virus in their bloodstream, and can then transmit it to uninfected mosquitoes, which in turn can infect people. The biggest indicator of whether West Nile virus will occur is the maximum temperature of the warmest month of the year, which is why the virus has caused the most damage in hot southern states like Texas.