Lyme Disease-Transmitting Ticks Depends on Activity
By Judy McBride
September 5, 2001
Outdoor enthusiasts would likely
pick up fewer ticks that transmit Lyme disease from a brisk walk in the woods
than from sitting on fallen logs or kneeling in or handling leaf litter.
Blacklegged deer tick nymphs lurk in these venues, waiting for animals or
people to latch onto.
The nymphs--tick youths--are the main vectors of Lyme disease. But at less
than one-sixteenth of an inch long, their tiny, black bodies are barely visible
and seldom felt. So Agricultural Research
Service entomologist John F. Carroll wanted to assess the relative risk of
picking up blacklegged deer tick nymphs from different activities. He chose
moderately infested woods a few miles from his laboratory at ARS
Henry A. Wallace Beltsville (Md.)
Agricultural Research Center.
Carroll usually wears boots, tucks his pantlegs into his socks and covers
the exposed sock with tape because ticks can get a better hold on material.
Although the nymphs got on his footwear, many were brushed off as he walked
along. About the same number of ticks were on his boots after a five-minute
walk as after a 30-second one. Wearing sneakers with the sock tops exposed
afforded somewhat less protection than the boots and tape, he and ARS
statistician Matt Kramer recently reported in the Journal of Medical Entomology.
But the type of footwear appears to be less important than the type of
activity. The researchers found tick nymphs on 87 percent of fallen logs they
sampled. They specifically tested large logs that would make good seats for
tired hikers or climbing kids. Fallen logs make a good hiding place for mice
and other rodents that serve as a reservoir for the Lyme disease bacterium,
according to Carroll. Stone walls might pose a similar risk.
Kneeling or placing hands in leaf litter--activities that campers, kids at
play and homeowners clearing underbrush and leaves are likely to do--also
increases risk. The researchers picked up many more nymphs from slowly crawling
on their hands and knees for 30 seconds than from walking half a minute. The
ticks clung to their pant legs and hands, with the majority on their pants.
ARS is the chief agency for scientific research in the
U.S. Department of Agriculture. Carroll
works in the Beltsville center's
Epidemiology, and Systematics Laboratory.