It's more contagious than the measles.
It causes hysteria and shortness of breath.
When together, the afflicted create a sound that makes a Beatles ovation at Shea Stadium seem like a golf clap after a fifth-hole bogie.
Tim Tebow fever shook the floor and walls in Denver on Sunday afternoon, but thanks to their fourth-quarter execution, the Chargers didn't crack, surviving the episode, if a bit worse for the wear, in a 29-24 win at Sports Authority Field at Mile High.
A Malcom Floyd 38-yard catch on third-and-10 and an unnecessary roughness penalty set up kicker Nick Novak's career-high fifth field goal with 24 seconds remaining.
That's when second-year quarterback Tebow, for whom the fan demand has been palpable on radio shows, newspapers and city billboards, attempted to cap a rally attempt from a 26-10 fourth-quarter deficit.
The 24-year-old completed a 20-yard and then 31-yard pass to lead the Broncos to the Chargers' 29-yard line. The defense pressured and withstood Tebow's last-second 29-yard heave into the end zone that skipped just past wide receiver Matthew Willis.
The Chargers improved to 4-1 before their bye, as the Broncos sunk to 1-4.
"The thing I like most about our football team," coach Norv Turner said, "and I told them this, we make the stop when we have to make the stop, we make the throw when we have to make the throw, we make the catch when we have to make the catch, and we make the kick when we have to make the kick. What that does is build great confidence.
"Now, we know in between, there's a lot of things we have to get better at. But if you have the confidence that when it's in the last four minutes, last two minutes, that you're going to get the stop or get the first down or make the kick, it gives you a chance, mentally, to win any game."
The Chargers played down the stretch without their top two running backs. Concussion symptoms forced Mike Tolbert out of the game, and Ryan Mathews followed him to the sideline with a calf strain after rushing for a career-high 125 yards.
Tebow ran for a touchdown and threw for another after replacing Kyle Orton to start the third quarter. Orton was awful in the first half, completing six of 13 passes for 34 yards with no touchdowns and an interception.
Despite the disappointment, the crowd chanted "Tebow! Tebow!" as fans filed out of the stadium.
Tebow's quarterback rating was 101.7 compared to Orton's 21.0 despite completing four of his 10 passes for 79 yards. He also ran six times for 38 yards.
Chargers quarterback Philip Rivers was 18 of 29 for 250 yards with one touchdown and an interception. He was sacked a season-high five times.
The Chargers had a tough time in the red zone in the first half, gaining 9 yards on a dozen snaps inside the Broncos' 20 and settling for three chip-shot field goals.
Cassius Vaughn returned an interception 55 yards for a touchdown that gave Denver a 7-6 lead.
Rivers' pass bounced off wide receiver Patrick Crayton's hands and Vaughn plucked the fluttering football out of the air and raced untouched into the end zone for Denver's first defensive touchdown since Champ Bailey's 70-yarder against San Francisco on Dec. 31, 2006.
Vaughn, however, was beaten badly by Malcom Floyd on a 43-yard touchdown with 13 seconds left in the first half that put the Chargers ahead 23-10. Floyd broke free from Vaughn down the right sideline, and rookie safety Quinton Carter, subbing for injured Brian Dawkins (neck) couldn't come over the top fast enough.
That score came after the Broncos burned just 45 seconds off the clock after getting the ball at their 20 with 1:47 left before halftime in what turned out to be Orton's final series of the day.