(9).
Ixodes dammini has been found to be the main source of Lyme disease in the eastern United States. The white-tailed deer are the likely primary host of the adult I. Dammini tick. Ticks lay their eggs in the spring and then emerged larvae feed in late summer. The larvae remain quiet throughout the winter and develop into nymphs in the spring. The nymphs feed in May and June, just before the peak appearance of human infection in early July. Scientists believe tick larvae acquire the infection from white-foot mice and then transmit it to humans as nymphs. The adults, which feed any time from late fall to the late spring, probably do not account for many human cases because they are large enough to be detected and removed before the spirochete is transmitted. Nymphs cause 70% to 90% of all causes of Lyme disease. They prowl the outdoors in the late spring and summer, when people are doing the same. Because they are so small, they are tough to spot on clothing or skin to remove. (10,2) Fortunately, a nymph bite does not guarantee a case of Lyme disease. The nymph may not be infected. An infected tick, whether nymph or adult, must feed for 24 hours on a human host before injecting its spirochetes. This leaves time to spot and remove them. (4).
If the spirochete does enter a human blood stream, phagocytes are the cells primary first-line defense against bacterial pathogens and will begin their advancement on the foreign organism. A dense infiltration of mature neutrophils has been found at the site of tick bites. However, knowledge about the interaction between Borrelia burgdorferi and the phagocytes is unknown. These microorganisms are internalized by human polymorphonuclear leukocytes and monocytes-macrophages even during the preimmune stage of infection. In fact, immune reaction to Borrelia burgdorferi is not essential, although it facilitates its uptake. Spirochetes are engulfed by conventional or coiling phagocytes and in either case are finally found inside closed phagosomes, where structural alterations of the microorganisms are apparent with microscopical observation.