Also, the tick must be attached to the human for at least 48 hours before the infection is transmitted. If the tick is removed within 24-48 hours and before it is engorged with blood, human infection will be very rare. In the spring, tick eggs mature into larvae, which feed on mice. If the mouse is infected, the larva may pick up the spirochete. Nymphs feed on the dusky-footed wood rat, deer, and other mammals including domestic pets and humans.
Nymphs are most active in spring and summer.
The spirochetes multiply in the nymph midgut, but then may pass through the gut wall into the lymph stream and lodge in its salivary glands. The spirochete may then be transmitted to a human or other mammal via tick saliva. Most of the blood meal is not ingested until the final day. Thus, the nymph remains small and hard to detect until just before detachment. Adult ticks also feed on mammals and humans.