Lizard May Act As Lyme Disease Panacea
by Kathleen Scalise, Public Affairs
Ticks harboring the Lyme disease bacterium can be cleansed of the 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.
Lizards are doing humanity a great service here, said Robert Lane, professor of insect biology in the College of Natural Resources and principal investigator on the tick research. The findings were published in April in California Agriculture and before that in the Journal of Parasitology. The lizards blood contains a substance probably a heat-sensitive protein that kills the Lyme disease spirochete, a kind of bacterium, said Lane.
Even better news, the newly discovered protein apparently leaches into the mid-gut of infected nymphal ticks as they feed and destroys spirochetes stored there, permanently cleansing the ticks before they mature to adult size.
The western fence lizard is an even more important host of immature nymphal ticks that transmit Lyme disease in Northern California than most rodents, said Lane.
But unlike wood rats and some other wild rodents, western fence lizards dont contract the Lyme disease bacterium when infected ticks attach, said Lane. The newly discovered spirochete-killing factor in their blood, not yet identified, seems to prevent infection.
In California, the western black-legged tick is the primary carrier of Borrelia burgdorferi, the bacterium causing Lyme disease. The lizard protein cleans the tick gut in the nymphal stage of tick development an immature stage at which the tick is usually smaller than 1/20th of an inch in length.
Tiny though they are, these ticks can do big damage, causing most cases of Lyme disease in California, where the disease occurs sporadically in people who frequent tick-infested areas during the spring and summer.
In California, some populations of western black-legged ticks are three to four times more likely to carry the dangerous Lyme disease spirochete as nymphs than as adults. This is contrary to logic, since you would expect that the older the tick is, the more likely it is to be infected, said Lane. To reach the adult stage, a tick must have fed twice before, whereas to reach the nymphal stage, it must have fed only once, leaving less opportunity for exposure to infection.
Lanes recent study of Tilden Park in the East Bay showed that in one area 1.3 percent of adult ticks carry the Lyme disease bacterium, compared to 5.7 percent of nymphal ticks. 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 points out that along most of the trails surveyed at Tilden, the infection rate in adult ticks was as low as zero percent in some areas. As for picnic areas, several yielded few ticks year around, showing the risk there is lower than along trails. All in all, the risk of being infected with Lyme disease following a tick bite in Tilden is very low.
Nymphal ticks are most active from April through July, Lane said. They live in shady, moist wooded areas carpeted with dead leaves and organic matter. People are most likely to contract Lyme disease from nymphal ticks while gardening, picnicking, resting or otherwise enjoying the outdoors in such areas.
Because of their small size, nymphal ticks are hard to detect on human skin, said Lane. You could easily have them and not know it. Probably only 20 to 30 percent of people who acquire Lyme disease as a result of a nymphal bite are aware that theyve been bitten.
Despite the new lizard finding, people should not go out into the woods and collect lizards and put them in their backyards to protect themselves from Lyme disease, said Lane. Not only would this be ineffective because Lyme disease in California primarily is contracted in rural or semi-rural areas occupied by various kinds of wildlife including lizards, but there are problems with moving lizards from one locality to another and its an illegal activity, Lane said.
Lane collaborated with Berkeley researcher Gary Quistad on the recent work, which was funded by the National Institutes of Health.
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