SAN DIEGO -- While people become sicker and sicker from rattlesnake bites, researchers at the University of California, San Diego are working to combat that trend by developing more potent anti-venom.

Several weeks ago, a bite killed a 5-year-old Schnauzer in Bonita, but it's not just dogs that have been bit that have raised the most alarms.

"It's a definite concern," said Dr. Richard Clark, the director of toxicology at UCSD.

Clark said although a few dozen human bites are reported locally every year, a puzzling trend has emerged.

"We continue to see very bad snake bites, probably worse than last several years previously," he said.

More severe reactions, including breathing problems, low blood pressure, and uncontrollable bleeding have led many to wonder if rattlesnake venom is becoming more potent.

One theory proposes rodents, the rattlesnake's food source, are developing resistance to venom, causing snakes to develop more potent venom by natural selection.

Another theory suggests the rattlesnake has evolved to have more potent venom because of a shrinking habitat and a tougher time finding food over the years.

None of these theories have been proven.

Whatever the cause, UCSD is researching a possible response in the form of more potent anti-venom. A clinical trial began a year and a half ago.

Unlike the conventional anti-venom, the molecules of the new anti-venom are bigger, which means a bigger potential impact on severe and recurring symptoms. The bigger molecules remain in the body long, making the anti-venom more effective.

Clinical trials should be complete by the end of the year. If proven effective, the anti-venom would be a much-needed weapon against venom that may be turning more potent.

Dr. Clark said that every year, there are several rattlesnake-related deaths in California. He said he fears the number could climb, because people with more severe reactions are more at risk for fatal complications.