Effect of prescribed fire for tick control in California chaparral.

Prescribed fire was investigated as a method for controlling ixodid and argasid ticks in chaparral habitats in northern California. Two experimental and two adjacent control plots within a wildlife preserve were monitored for 1 yr postburn. Ticks were collected by flagging vegetation, by CO2-baited pitfall trap, and by live-trapping rodents. Twice as many rodents were caught at control sites compared with burn sites and no dusky-footed woodrats, Neotoma fuscipes Baird, were found in the treatment sites postburn. This species is known to be a reservoir of the agents of Lyme disease, Borrelia burgdorferi sensu stricto Johnson, Schmid, Hyde, Steigerwalt & Brenner, and human granulocytic anaplasmosis, Anaplasma phagocytophilum Dumler, Barbet, Bekker, Dasch, Palmer, Ray, Rikihisa, Rurangirwa. Six ixodid tick species were removed from rodents (Ixodes pacificus Cooley & Kohls, Ixodes jellisoni Cooley & Kohls, Ixodes spinipalpis Hadwen & Nuttall, Ixodes woodi Bishopp, Dermacentor occidentalis Marx, and Dermacentor parumapertus Neumann), two of which transmit bacterial zoonotic agents to people in the far-western United States. There was no decrease in number of ticks per animal trapped at either burn site compared with controls; in fact, the mean number of immature I. pacificus per rodent was significantly higher at one burn site than its control site. Soil refugia may protect ticks from fire-induced mortality; the argasid tick Ornithodoros coriaceus Koch, which lives in soil, was unaffected by the prescribed fire as were I. pacificus and D. occidentalis buried in packets 2.5 cm below ground. We conclude that although prescribed fires in chaparral habitats may diminish local rodent abundance, it does not decrease tick loads on rodents. Furthermore, burning chaparral does not result in a decreased abundance of adult ixodid ticks on vegetation and apparently does not affect argasid or ixodid ticks that are sheltered within soil refugia.

Experimental infection of Columbian black-tailed deer with the Lyme disease spirochete.

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.