The disease was named after one of the towns in Connecticut in which the illness appeared. Stephen W. Barthold, Ph.D., director of the Center for Comparative Medicine at the University of California-Davis, has been studying these bacteria for a number of years. These ticks and the bacteria they carry are not selective about the hosts they latch onto, Barthold said, and they infect mice, birds, and people, among others. In the eastern U.S., ticks transmit Lyme disease primarily during the nymph stage, probably because they are smaller than adult ticks and less likely to be noticed. Ticks must feed on the host for at least 12 to 24 hours before they can transmit bacteria.
Nymphs are less than two millimeters in size.
They are most likely to transmit bacteria after two or more days of feeding. Adult ticks can also transmit the disease, but because they are larger and more likely to be seen and removed within a few hours, they rarely have time to transmit Lyme disease to humans. They are more likely to spread the disease to dogs, horses, and other animals that are not checked as often for ticks. In the eastern U.S., adult ticks are most active during the cooler months of the year when fewer humans are outdoors. Kerwin E. Hyland, Ph.D., professor emeritus of biological sciences at the University of Rhode Island, said deer ticks position themselves on the tips of grasses and shrubs and latch onto people or animals that brush against the vegetation.