Department of Entomological Sciences, University of California, Department of Health and Human Services, Public Health Service, National Institutes of Health, National Institute of Allergy and Infectious Diseases, Laboratory of Pathobiology, Rocky Mountain Laboratories, Berkeley, California 94720
Transovarial and transstadial passage of Borrelia burgdorferi was demonstrated for the first time in the western black-legged tick, Ixodes pacificus. One of three field-collected females with spirochetes in ovarial tissues produced 100% infected progeny that maintained the spirochetes transstadially and in 4 of 5 cases passed them via eggs to as many as 97% of F2 filial ticks. The progeny infected ovarially and by subsequent transstadial passage had generalized tissue infections that exhibited reduced immunofluorescence staining reactivity with a fluorescein isothiocyanate-labeled polyclonal antibody. Attempts to isolate the spirochete from ticks in BSK medium or various modifications of it were unsuccessful. Spirochetes in tissue smears of all three parasitic stages of the F1 generation were nonreactive with a monoclonal antibody (H5332) specific for B. burgdorferi, whereas those present in tissue smears of F2 larvae bound with it.