Ticks: Where Ticks Come From (cont.)
After each activity, in scenes strikingly reminiscent of primate grooming behavior, the researchers meticulously picked off and counted the ticks on their clothing and bodies. They also used an adhesive lint roller to pick up ticks that might otherwise have escaped their attention. All told, they found a total of 86 nymphal ticks on their bodies during the field trials.
"Activities that were riskiest involved considerable contact with wood," said Steinlein. "Of the six behaviors we analyzed, sitting still on leaf litter was the least riskiest behavior, resulting in tick exposure only eight percent of the time."
Why the difference between wood products and leaf litter? The clue may be in an important animal host for the larvae and nymphs of the western black-legged tick.
"The western fence lizard is an important host for the ticks, and the lizards often use logs in sunlit areas as basking sites," said Lane. "Nymphal ticks that are seeking hosts to feed upon may be going to the place where they'll have the greatest chance of finding a lizard. Humans or pets that happen to come along for a picnic lunch or a short rest on a log may be putting themselves in harm's way."
DNA tests revealed that 3 to 4% of the ticks the researchers found on their bodies, as well as through drag sampling leaf litter with a white flannel cloth, tested positive for B. burgdorferi and another, less prevalent human disease-causing bacterium Anaplasma phagocytophilum. Estimates from prior studies of ticks infected with B. burgdorferi in Mendocino County are higher, ranging from 5 to 10% on average, with some spots occasionally yielding rates of 15% or higher.
Tick infection rates normally are significantly higher in the northeastern and upper midwestern United States, where most cases of Lyme disease occur. Lane cautioned that the findings in this study are not intended to be applicable to forested areas in other regions of the country.
But for people frequenting areas of California where Lyme disease is endemic, the researchers recommend precautions to prevent tick exposure.
"I would avoid prolonged contact with wood as well as with leaf-litter areas, and I would strongly suggest that people inspect themselves carefully after spending time in tick-infested areas," said Lane. "Moreover, I would advise people to continue checking their skin for two to three days after the potential exposure. Nymphal ticks are so hard to see in the beginning - probably less than one in three people bitten by nymphs ever discovers the tick that bit them. But they become easier to detect once they start swelling up a bit after they've had a blood meal.
"Animal studies suggest that it usually takes longer than one day after the tick becomes attached for the bacteria to be transmitted to the host, so the sooner the tick is found and removed, the better," said Lane.
The National Institutes of Health and the U.S. Centers for Disease Control and Prevention helped support this research.
Source: UC Berkeley News Release, Apr. 8, 2004
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