[Standards for reviewing preparations in the study of ixodid tick nymphs by dark-field microscopy in borreliosis foci].

The results of dark-field microscopy of 73 positive preparations from the unfed Ixodes persulcatus Sch. nymphs collected in the Perm Region of Russia have been analysed. The preparations were prepared by cutting the ticks placed into a physiological saline drop with needles. The numbers of Borrelia in the preparations varied from 0.4 to 173.6 per 100 microscopic fields (mean 22.9). It has been demonstrated that if all the standard conditions are fulfilled (magnification 600), drop volume 0.005 mil covering 18 x 18 mm glasses), it is practically impossible to overlook an infected nymph while examining 250 microscopic fields in such a preparation. The above-described conditions ensure valid reliable results of Borrelia calculation and their concentration measurements. The differences in the individual Borrelia infection rates in nymphs may be expressed by using the scale: low (up to 10), moderate (10.1-50), and high (above 50 Borrelia per 100 microscopic fields).