[The optimization of a method for assessing the contagiosity and the degree of individual infectiousness of ticks with Borrelia].

The results of dark-ground microscopy of 478 positive preparations from Ixodes persulcatus Sch. and I. ricinus L., gathered in the active natural foci of Lyme's disease in Leningrad Province, have been analysed. The preparation was prepared by cutting ticks placed into a drop of physiologic saline, with needles. It has been demonstrated that if all the standard conditions are fulfilled (magnification 600, drop volume 0.02 ml, covering glasses, 18 x 18 mm) it is practically impossible to overlook an infected tick during examination of 200-250 visual fields in such a preparation. The conditions described above ensure reliable results of Borrelia calculation and their concentration assessment. Differences in the degree of individual vector infestation may be expressed using a scale: low (up to 10), medium (10.1-50), high (50.1-250) and very high (above 250 Borrelia per 100 visual fields).