RESERVOIR COMPETENCE OF THE RICE RAT (RODENTIA, CRICETIDAE) FOR BORRELIA-BURGDORFERI

The reservoir competence of the rice rat, Oryzomys palustris, for Borr elia burgdorferi is described. Infected Ixodes scapularis Say (I. damm ini, Spielman, Clifford, Piesman & Corwin) nymphs were used to infect animals. Borrelia infection was diagnosed by xenodiagnostic feeding of noninfected I. scapularis larvae and by reisolation of the spirochete s from blood and other tissues. Rice rats acquired B. burgdorferi and maintained spirochete infection for 5-9 wk. B. burgdorferi were cultur ed from samples of skin and urinary bladders from all animals killed o n day 21 (three rats), 35 (three rats), or 56 (three rats) after infec tion. The spirochetes were also detected in blood samples obtained 1 a nd 2 wk after exposure. Spirochetes that persisted for 5 wk in lice ra ts did not lose their infectivity for golden Syrian hamsters. The prep atent period for infecting xenodiagnostic ticks was 1 wk. Overall, 75. 6% of I. scapularis larvae (n = 694) that fed on infected rice rats ac quired B. burgdorferi. Prevalence of infection reached 83% in ticks th at fed on tick-exposed animals during the 2nd-4th wk, 68% during the 5 th wk, and 17.4% during the 9th wk. The duration of rice rat infectivi ty for ticks exceeded 2 mo. I. scapularis nymphs infected as larvae on rice rats transmitted B. burgdorferi. Taken together, these studies c onfirm the reservoir competence of the rice rat for B. burgdorferi.