The U.S. is experiencing one of its worst West Nile outbreaks in years, with the mayor in Dallas declaring a state of emergency. Here's what you need to know about this mosquito-borne virus.
What is it? West Nile virus is an infection transmitted by mosquitoes, although in very small cases it has been spread through blood transfusions, organ transplants, breastfeeding and during pregnancy from mother to baby.
What's the history? West Nile virus was first detected in a woman in the West Nile district of Uganda in 1937. It spread to North America in 1999.
How do I prevent it? The easiest way to avoid West Nile is to prevent mosquito bites through insect repellent, wearing long sleeves and pants outdoors and having good screens on all doors and windows.
Also, get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Replace the water in bird baths weekly and drill holes in the bottoms of tire swings for drainage.
What are the symptoms? About 80 percent of people infected have no symptoms, but those that do experience fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash.
About one in 150 people infected will develop severe symptoms. They can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
How is it treated? There's no specific treatment for West Nile. Mild symptoms will go away on their own after a few days, while very ill patients must go to the hospital for intravenous fluids, help with breathing and nursing care.
What is the risk of getting very sick? Your chance of developing complications or severe illness from West Nile increases if you are over 50 or you have a weakened immune system, such as if you have cancer or are pregnant.
How bad is it this year? The U.S. is experiencing its biggest spike in West Nile since 2004, with 241 cases reported so far this year. Twenty-six people have died.
Where is it worst? Forty-two states have reported West Nile cases, but Texas is bearing the brunt of this year's outbreak, with 14 deaths reported there so far. It's also bad in Mississippi and Oklahoma.