From the April 29, 1998 issue of Berkeleyan, the faculty staff newspaper of the University of California, Berkeley. Volume 26, Number 32.
Stories for April 29, 1998:
Feeding on Its Blood Strips Ticks of Dangerous Lyme Bacterium
by Kathleen Scalise, Public Affairs
posted Apr. 29, 1998
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 lizard’s 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 don’t 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.
Lane’s 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 they’ve 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 it’s 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.
This site is produced and maintained by the Office of Public Affairs,
University of California, Berkeley.
Copyright © 1998, The Regents of the University of California.
For comments concerning this web service please e-mail
berkeleyan@pa.urel.berkeley.edu
Das Original des 2. Texts ist
xxxxxxxxxxxxxxxx
Gegenüber dem Original wurde das Layout ueberarbeitet.
3.9.98, Aribert Deckers
Source: National Institutes of Health and Chronicle
About the Researcher:
Robert S. Lane
Professor and Entomologist
411 Wellman Hall
Phone #: (510) 642-4385
FAX #: (510) 642-7428
blane@nature.berkeley.edu
We have been studying the ecology, epidemiology and control of tick-borne diseases, particularly the spirochete (bacterium) that causes Lyme disease (LD). LD is currently the most commonly reported vector-borne infection in California, the United States, and in other temperate regions of the world. The broad objectives of this research are intended to clarify the basic mechanisms by which the LD spirochete is maintained and distributed including the various modes of transmission to humans and other animals; to determine what behavioral and environmental factors place people at risk for acquiring this spirochete; and to evaluate control methodologies for reducing such risk.
We found that the LD spirochete is maintained in a transmission cycle that differs basically from that in the upper midwestern and northeastern United States. Woodrats and kangaroo rats (vs. white-footed mice) serve as reservoir hosts, 3 species of ticks (vs. one species) maintain and distribute the spirochete, and the spirochetes themselves are generally much more variable than those from the East. Factors that contribute to risk of infection include cutting wood, exposure to leaf litter in hardwood forests, and other outdoor activities that place people in direct contact with the habitats of the primary tick vector. These findings underscore the need for vector ecologists and epidemiologists to study the disease on a regional basis before locally effective control methodologies can be developed and implemented to protect human health.
Additionally, a new species of tick-borne spirochete was discovered during these studies that may be the cause of epizootic bovine abortion, a disease that has been estimated to cause annual losses of $5-15 million to the cattle industry in California alone. Other tick-borne diseases currently or previously investigated by us in collaboration with others include Colorado tick fever, Rocky Mountain spotted fever, ehrlichiosis, relapsing fever, tularemia, human babesiosis, and tick paralysis.
Several ongoing projects are aimed at expanding our knowledge of the relationship of various isolates of LD spirochetes (and other microbial agents) to their tick vectors and vertebrate hosts. Spirochetes isolated from ticks and wildlife are being characterized antigenically and genetically, and the infectivity of selected isolates for vertebrates and ticks determined. The ability of human and nonhuman-biting ticks to acquire, maintain, and transmit the LD spirochete, and the role of rodents and lizards in perpetuating it, are being evaluated experimentally as well as in the field. Intrinsic and extrinsic factors that contribute to the vector efficiency of different ticks and the reservoir competence of rodents also are being assessed. Life history studies of all stages of the western black-legged tick, the primary vector of the LD spirochete to humans in the Far West, are under way preparatory to modelling the population dynamics of this important vector.
Another current focus is to elucidate human risk of exposure to vector ticks along hiking trails and in picnic areas of several heavily-used parklands and other recreational areas in the San Francisco Bay region. Moreover, peridomestic exposure to vector ticks is being evaluated ecologically and seroepidemiologically in rural communities endemic for LD.
The ultimate goal of this research is to use the basic knowledge gleaned from the foregoing projects to develop and implement strategies for reducing human exposure to tick-borne agents. One method currently being tested is the delivery of an oil-based formulation of permethrin to wild rodents via bait stations to reduce the abundance of their associated vector ticks. Another method being evaluated for the same purpose is the use of prescribed (controlled) burning in brushlands where ticks abound. It is anticipated that either one or both of these methods may eventually prove to be useful as part of an integrated program for reducing tick abundance in rural settings or where suburbs abut on natural areas.
Current Graduate Students:
Kurstin Graham
Ted Slowik
Douglas Kain
Caryl Waggett
Current Postdoctoral Fellow:
Chindi Peavey
Current Staff Research Associates:
Leslie Casher
Esther Omi-Olsen
Joyce Kleinjan
Kerry Padgett
Mary Mesirow
Judith Pascocello