Incompetence of roe deer as reservoirs of the Lyme borreliosis spirochete.

To determine whether the roe deer, Capreolus capreolus L. may serve as a reservoir host for the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, evidence of spirochetal infection was sought in nymphal Ixodes ricinus (L.) that had engorged as larvae on roe deer. Sixteen roe deer were shot in Lyme disease enzootic areas of south-central Sweden during August-November 1990 and August 1991. An average of 276 (range, 84-658) larvae of I. ricinus was collected from each of 12 deer shot in August. Of those ticks that had fed on deer and then developed to the nymphal stage, the gut contents of 238 were examined by phase-contrast microscopy. All these ticks were negative for spirochetes, whereas 4.2% contained Trypanosoma cf. cervi Kingston & Morton and 15.1% contained the nematode Dipetalonema rugosicauda Meszaros & Sugar. A total of 396 nymphal ticks was collected by blanket-dragging during May-June 1991 and examined for spirochetes; 9.1% of these host-seeking nymphs were infected with spirochetes. Although the roe deer serves as a principal blood source for all stages of I. ricinus, it does not appear to serve as a major reservoir of B. burgdorferi.