After the Lyme pathogen was identified, scientists in the Northeast traced the relatively simple two-year life cycle of the disease in nature, as depicted below. In the first year, adult blacklegged ticks feed and mate on the ears and hide of deer, laying eggs that drop to the forest floor in late spring. The uninfected larvae acquire Borrelia only after taking a blood meal from infected white-footed mice previously bitten by other infected ticks. In the second year, infected larvae fall from the mice to the ground, growing into adolescent nymphs. The nymphs then quest, moving to the tips of long grass and brush to wait for their next blood meal to wander by: a dog, a deer, or that accidental human host.
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