Berkeley Magazine, Fall 1998


Ticks harboring the Lyme disease bacterium can be cleansed of infection when they feed on the blood of the common Western fence lizard, Berkeley researchers have discovered. The new finding may explain why Lyme disease is less common in California but epidemic in some northeastern states, where lizards are rare.

Even better news, the newly discovered protective agent apparently leaches into the mid-gut of infected nymphal ticks as the tick feeds and destroys spirochetes stored there, permanently cleansing the ticks before they mature to adult size.

"Lizards are doing humanity a great service here," said Robert Lane, professor of insect biology at Berkeley's College of Natural Resources and principal investigator for the tick research. "The lizard's blood contains a substance -- probably a heat-sensitive protein -- that kills the Lyme disease spirochete, a kind of bacterium."

In California, the Western black-legged tick is the primary carrier of Borrelia burgdorferi, the bacterium causing Lyme disease. Cleansing of the tick gut by the lizard protein occurs in the nymphal stage of tick development, which is an immature stage usually smaller than 1/20th of an inch in length.

Tiny though they are, these ticks cause most of the Lyme disease in California, where the disease occurs sporadically in people who frequent tick-infested areas during the spring and summer.

Lane's recent study of Tilden Park in the San Francisco Bay Area showed that, in one area, 1.3 percent of adult ticks -- compared to 5.7 percent of nymphal ticks -- carried the Lyme disease bacterium. These rates are much lower than in the northeastern U.S., where, for instance, 50 percent of adult ticks and 25 percent of nymphal ticks carry the disease in parts of Rhode Island, Massachusetts, Connecticut and New York.

Lane found that, along most of the trails surveyed at Tilden Park, the infection rate in adult ticks was even lower, as low as zero percent in some areas. As for picnic areas, the risk there was lower than along the trails. All in all, the risk of being infected with Lyme disease following a tick bite in Tilden Park is very low, said Lane.

Despite the new lizard finding, Lane cautions that people should not go into the woods to collect lizards and put them in their backyards to protect themselves from Lyme disease. It wouldn't help because Lyme disease in California is contracted mainly in rural or semi-rural areas. But also, moving the lizards is illegal.

Western Fence Lizard

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