Lizards Slow Lyme Disease in West
Ticks bite them - and leave with purified blood
Sabin Russell, San Francisco Chronicle, April 17, 1998
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
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.
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.
Lab tests showed that when infected nymphs fed on the lizards, and then metamorphosed into adult ticks, they were no longer infected.
According to Robert Murray, epidemiologist at the state health department's Division of Communicable Disease Control, the percentage of infected deer ticks in high Lyme disease areas such as Connecticut is 30 to 60 percent. But the percentage of black-legged ticks -- the closely related cousins that carry Lyme disease in California -- is only 1 to 2 percent, and only as high as 6 percent in areas such as Mendocino county, where the most Lyme disease cases are found.
In California, only about one in every 200,000 persons is infected with Lyme disease. In Connecticut, where Lyme disease was first discovered in the rural town of Lyme, the rate is 100 times higher.
Lyme disease does occur in California, particularly in coastal zones that provide a moist, forested environment favored by the ticks. In Mendocino County, the rate is about 50 per 200,000, and in Humboldt County, it is 20 per 200,000.
Scientists caution that Lane's findings do not prove the case that the lizard helps protect western Americans from Lyme disease. "It may be one of many factors," said Kramer.
Melissa Kaplan notes: Of course, to those of us Westerners who do have Lyme disease, the fact that our cute little blue belly Sceloporous lizards de-Borrelia ticks doesn't do us a lot of good, not until we can get some of their anti-Borrelia proteins for ourselves!
TICKS AND LYME DISEASE
UC Berkeley entomologist Robert Lane has discovered that a substance found in the blood of the common western fence lizard kills Lyme disease bacteria in the gut of juvenile ticks that feed on it. It may help explain why there is far less Lyme disease in California than in the eastern United States, where the lizard does not live. The western fence lizard -- a commonly found species dubbed the blue belly lizard in California, can carry an average of 30 juvenile black legged ticks, which are about the size of a poppy seed. Three stages of tick development Larval Ticks pass through three stages of development. During each stage they eat one ``blood meal.'' Larval ticks become infected with Lyme disease when they feed on rodents.
Adult black-legged ticks move off the forest floor and onto plants and grasses. Those who feasted on lizards as nymphs are less likely to transmit Lyme disease to humans.
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