Infection of field-collected <i>Ixodes ricinus</i> (Acari: Ixodidae) larvae with <i>Borrelia burgdorferi</i> in Switzerland

Free-living larvae from natural areas in five regions in Switzerland were collected to determine the infection rate of <i>Ixodes ricinus</i> L. larvae by <i>Borrelia burgdorferi</i> Johnson. Larvae were examined for the spirochetes using direct fluorescent antibody assay. Of 652 larvae examined, spirochetes were detected in 20 (3.1%). No differences in infection rate among sites were detected. The low prevalence of <i>B. burgdorferi</i> in larvae, compared with higher infection rate in nymphs (12.8%) and adults (14.5%), suggests that transovarial transmission is inefficient. These results suggest that <i>I. ricinus</i> can serve as a reservoir for <i>B. burgdorferi</i> in nature. Further study is needed on the relative importance of ticks, compared with mammals and birds, as reservoirs for <i>B. burgdorferi</i>.