Lyme disease affects approximately 30,000 Americans every year, mostly in the Northeast — although that geographical range is spreading.

Researchers at the University of Pennsylvania have found that people are unlikely to contract the same strain of the tick-borne bacteria twice.

Penn assistant professor of biology Dustin Brisson says early antibiotic treatment typically clears up the Borrelia burgdorferi infection without harm. But if diagnosis lags, serious complications can arise.

"These complications can involve the nervous system, the heart, joints, and they can be really debilitating," said Brisson.

To learn more about how the body handles the infection, particularly in the rare cases when a person gets the disease more than once, Brisson used statistical modeling in conjunction with patient data previously collected by colleagues.

"We simulated hundreds of thousands of sets of patients to see what we could expect with regard to how many patients are infected multiple times and those that are infected multiple times, how many of those are infected by the same strain," said Brisson.

To fit the real patient data, Brisson's model had to assume people would develop strain-specific immunity that lasted at least six years. Because there are five main strains that infect humans, that means checking for ticks should still be a priority for anyone with a prior case. But Brisson said the finding is promising.

"People should be encouraged that a vaccine is possible, at least in a strain-specific way," said Brisson, "and general vaccines or vaccines that are against all the important strains could potentially be on the horizon."

For now, if Lyme disease is suspected, Brisson said the best thing to do is save the tick for testing.