May 26, 2008 -- PHOENIX (AP) - A rattlesnake strikes.

The victim experiences extreme pain at the location of the bite, nausea, sometimes diarrhea. Then the mouth and throat swell, making it difficult to breath. The victim gets lightheaded, collapses and goes into shock -- all within minutes of the strike.

The potentially deadly symptoms used to be fairly rare, but toxicologists in Arizona, Colorado and California say they're seeing some or all of them more than ever, and that they could be contributing to an increase in fatal rattlesnake bites in Arizona.

At least five people have died from rattlesnake bites in Arizona since 2002 -- three or four of them from the extreme symptoms, said Steve Curry, director of medical toxicology at the Banner Poison Control Center in Phoenix.

Curry could recall just five fatal rattlesnake bites in the two decades before 2002.

Scientists and toxicologists can take guesses at what's behind the spike in extreme symptoms, but no one yet knows what's going on. Some say it could be a change in snake venom, a change in the snakes themselves, or something altogether different.

"This is a brand new phenomenon," said Jeffrey Brent, clinical professor of medicine at the University of Colorado Health Sciences Center. "It should spur a considerable amount of research in the area."

Brent said he hadn't seen the extreme symptoms in patients until last year, when there were five. "They came pretty darn close to dying," he said. "They were extremely, extremely sick."

He said there haven't been any such bites so far this year, but that the season is just getting started.

Rattlesnake bite victims in California began showing symptoms of weakness, breathing trouble and low blood pressure this year, said Richard Clark, director of the division of medical toxicology at the University of California-San Diego.

He said about a dozen people have been affected and one patient has died since January.

In Arizona, Curry said those who haven't died from the extreme symptoms become critically ill and often take months to recover.

"We're seeing patients now because of the severe shock they've been in, who have had severe strokes, and who have had loss of some intestines because of impaired blood flow and who have gone into kidney failure," he said. "These are things that we did not see at all in years past, but now we see them a few times each summer."

In each state, the snakes responsible for the bites have been different. It's the Southern Pacific Rattlesnake in California, the prairie rattlesnake in Colorado and the Mojave in Arizona.

In letters last week, Arizona authorities notified hundreds of physicians and emergency rooms of the extreme symptoms, which can be mistaken for other ailments and delay the injection of antivenin. Colorado and California authorities say they're taking a wait-and-see approach to the situation.

Russ Johnson, president of the Phoenix Herpetological Society, said he's been bitten twice by rattlers, and one nearly cost him his life.

He said he was handling a Western Diamondback at his home when it struck in 2001, and because one of the snake's fangs got caught in his knuckle, he got a full dose of venom.

"She just lit me up," he said. "I've had burns, broken bones, but this is intense and it is unrelenting."

Johnson said it took 26 vials of antivenin to treat him. His symptoms included swelling, dizziness, sensitivity to light and nausea, and the middle finger on his right hand turned black.

He still can't bend it. "It took me six months to hold a paper cup of water without dropping it, and I still can't have road rage on the right-hand side."

(Copyright 2008 by The Associated Press. All Rights Reserved.)