Transmission of Borrelia burgdorferi by Ixodes pacificus nymphs and reservoir competence of deer mice (Peromyscus maniculatus) infected by tick-bite.

The transmission of Borrelia burgdorferi to deer mice (Peromyscus maniculatus) by Ixodes pacificus nymphs was investigated experimentally. Deer mice were exposed to infected nymphs for 24, 48, or 72 hr, or until ticks had fed to repletion (> or = 96 hr). Infection status of hosts was assessed 4 wk later by culture of ear-punch biopsies in BSK II medium and by indirect immunofluorescence. Eight mice exposed to ticks for 24 hr did not become Infected. In contrast, infection was acquired by 1 of 9 (11%), 2 of 8 (25%), and 8 of 10 (80%) mice exposed for 48, 72, and > or = 96 hr, respectively. Eight weeks after exposure to infected nymphs, the infectivity of 5 deer mice for I. pacificus larvae was assessed. Overall, 33% of I. pacificus larvae fed on these mice acquired and transstadially passed spirochetes. We conclude that most I. pacificus nymphs require 4 days or longer to transmit spirochetes to deer mice, and that larvae efficiently acquire and maintain spirochetes from mice that have been infected by tick-bite.