Lizards Slow Lyme Disease in Western U.S.

Posted on Nov 11, 2013

Lizards Slow Lyme Disease in Western U.S.

It may sound like witchcraft, but Berkeley scientists have found that ticks who feast on the blood of the common western fence lizard are purged of any Lyme disease bacteria hiding in their gut.

The newly published findings may explain why there is less tick-borne Lyme disease in California than in the eastern United States, where the debilitating illness was first discovered and given its name.

Researchers suspect that a yet- to-be-identified protein in the lizard’s blood destroys the microbes that would otherwise flourish in the tick’s belly and can be later transmitted to human victims.

“We’ve speculated on this for years, and now we have fairly good evidence that this is the case,” said Robert Lane, a University of California at Berkeley insect biologist who has been studying ticks and Lyme disease for more than a decade.

Lane and his colleague Gary Quistad conducted a series of laboratory experiments using young Lyme disease-infected ticks and fence lizards. In the nymphal stage during which they feed on the blood of lizards, the ticks are only about the size of a poppy seed. But it is common to find 30 to 40 at one time sharing the blood of a single fence lizard.

Although infected adult female ticks pose a serious threat of transmitting Lyme disease to humans, the smaller nymphal ticks are the most dangerous because they are harder to find and are still capable of transmitting the disease.

Lane had determined eight years ago that the lizards appeared to be immune to Lyme disease despite infestation with tick nymphs. His latest research, published recently in the Journal of Parasitology, suggest why this happens.

The experiments first ruled out the possibility that antibodies produced by the lizard’s immune system were able to neutralize the Lyme disease bacteria.

Test tube experiments found that Lyme disease bacteria bathed in lizard’s blood died within one hour, while control samples grown in mouse blood lasted three days.

In another experiment, the researchers heated lizard blood to the boiling point, and found that it no longer killed the bacteria in a test tube. The sum of these tests points to what Lane calls a “spirochete-killing factor” that is probably a large protein.

“It’s an extremely important paper,” said Vicky Kramer, chief of the vector-borne disease section of the California Department of Health Services.

Researchers are now trying to determine the precise nature of the Lyme disease-killing protein, and perhaps find out if it can be used to create a treatment for the disease. Lane said he has not yet discussed his findings with biotechnology companies.

California health officials long have been pleasantly puzzled by the fact that Lyme disease is a relative rarity in the state, despite an abundance of ticks. Lane points out that in the eastern regions with higher Lyme disease rates, “they don’t have fence lizards there.”

Berkeley’s Tilden Park served as the field laboratory for Lane, where he previously also uncovered a curious quirk about Lyme disease and the black-legged ticks that carry it there: the infection rates for young ticks, while low, was three to four times higher than the rate in adult ticks. The latest findings again suggest why: When young nymphal ticks feed on the fence lizards, the mysterious protein not only protects the lizard from infection — it actually leaches into the tick’s gut and kills the bacteria there.