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Lizards and mammals were trapped and examined for ticks from August 1992 to June 1993 in two habitat types, chaparral and woodland-grass, in northern California. Five tick species were collected from mammals (Dermacentor occidentalis, Haemaphysalis leporispalustris, Ixodes pacificus, I. spinipalpis, I. woodi), but only I. pacificus was found on lizards. Dermacentor occidentalis, I. pacificus, and I. woodi occurred in both habitats, whereas H. leporispalustris and I. spinipalpis were found only on animals trapped in chaparral. The tick species most commonly encountered on mammals was D. occidentalis in chaparral and I. pacificus in woodland-grass. Peak infestation of mammals occurred in spring for I. pacificus immatures and H. leporispalustris, summer for D. occidentalis immatures, fall through spring for I. woodi immatures, and fall through winter for I. spinipalpis. The primary aim of the study was to quantify the relative importance of the western fence lizard (Sceloporus occidentalis), which is reservoir-incompetent for Borrelia burgdorferi sensu lato (s.l.), and mammalian B. burgdorferi s.l.-reservoirs as hosts for the immature stages of I. pacificus in spring. The estimated relative utilization by I. pacificus of the western fence lizard versus mammals was 88% for larvae and 99% for nymphs in chaparral in May. When tick infestation data were corrected for a two-fold lower efficiency of field examinations for rodents than for lizards, the western fence lizard still accounted for 78% of larval and 98% of nymphal feedings. In woodland-grass, 46% of 100 I. pacificus larvae and 100% of 52 nymphs recovered from mammals or western fence lizards during May-June were collected from the lizards. However, this may represent an underestimate of the importance of the western fence lizard as a larval host in this habitat because inclement weather during the late May sampling period doubtless resulted in significantly decreased lizard activity. In conclusion, the western fence lizard was more heavily utilized by I. pacificus immatures, especially nymphs, than were rodents.

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The course of Borrelia burgdorferi-infection in Columbian black-tailed deer. (Odocoileus hemionus columbianus), its effect on the health of these animals, and their reservoir competence for fleas were evaluated experimentally. Four yearling females inoculated intramuscularly with 10(8) organisms of the CA4 strain of B. burgdorferi, and two yearling males unexposed to spirochetes, were monitored daily for 3 mo. Spirochetes were reisolated from the blood of three does at 14 or 70 days postinjection, and from several tissues of the fourth doe at necropsy. Considerable antigenic heterogeneity was observed among the reisolates as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Only two of the four infected deer developed significant antibodies (> or = 1:128) to B. burgdorferi with titers persisting for < or = 2 mo. Hematological values were highly variable and the degree of variation observed was much greater than that reported previously for Columbian black-tailed deer or other subspecies of mule deer. Infected deer did not manifest signs of Lyme disease. On histologic examination of eight tissues per deer, we observed a minimal hepatic lesion in all animals exposed to B. burgdorferi. No spirochetes were detected in 367 fleas (Pulex irritans) that had naturally infested these deer; thus this flea probably is an inefficient host of B. burgdorferi.