VECTOR COMPETENCE OF RHIPICEPHALUS-SANGUINEUS AND DERMACENTOR-VARIABILIS FOR AMERICAN ISOLATES OF BABESIA-GIBSONI

To determine the identity of the tick vector of enzootic Babesia gibso ni in California, two common ixodid ticks were allowed to engorge upon B. gibsoni infected dogs. Sporozoites were observed in the salivary g lands of prefed nymphal Rhipicephalus sanguineus ticks that fed as lar vae on B. gibsoni-infected dogs. A higher proportion (31%) of nymphal ticks that prefed on an uninfected dog for 48 hours contained sporozoi tes in their salivary glands than did ticks which had fed for 24 hours (13%). Sporozoites were not observed in the salivary glands of prefed R. sanguineus nymphs which were derived from the eggs of adult female s that fed on an infected dog, in adults that were fed as nymph on an infected dog, or in the nymphal and adult uninfected controls. Dermace ntor variabilis ticks appeared not to become infected. Although attemp ts to transmit B. gibsoni to susceptible, splenectomized dogs were uns uccessful, R. sanguineus would appear to be the most likely tick vecto r to maintain this piroplasm in California.