Transovarially Acquired Lyme Disease Spirochetes (Borrelia Burgdorferi) in Field-Collected Larval Ixodes Dammini (Acari: Ixodidae)1

To determine whether larval Ixodes dammini are infected transovarially by Lyme disease spirochetes (Borrelia burgdorferi), we swept larval I. dammini from vegetation in 4 regions of Massachusetts, USA, where the spirochetes are endemic. Larvae were permitted to feed on noninfected hamsters. After molting to the nymphal stage, 274 were examined for spirochetes. Two nymphs were found to be infected. The rarity of transovarial infection (0.7%) suggests that transovarial passage is of limited importance in maintaining B. burgdorferi in nature, but that it may provide a mechanism for transporting spirochetes to new sites.