A laboratory model of the parasitic system of
Lyme borreliosis (LB) with Ixodes persulcatus and Borrelia burgdorferi s.s. underwent 5 epizootic cycles (Cycle I transition of Borreliae by the scheme a tick–>a mouse–>a tick corresponds to the seasonal cycle). A group of 5-6 mice was inoculated with the suspension of infected nymphs by the intracutaneously route and 35-45 days later intact tick larvae or nymphs were fed on them. In the first three cycles, 40-100% of mice in a group (a total of 33 of 59) were susceptible, but 3 of 11 groups of mice were not inoculated. 20-50% of larvae and 75-92% of nymphs were susceptible on the infected mice. The mean geometric abundance of borreliae was 2.8-6.3 cells per 100 fields of vision in the nymphs infected in the larval phase and 16.1-29.5 cells in the image phase. In cycle IV, 2 of 6 groups of mice were unsusceptible to borreliae and 5 of the 17 mice from 4 groups got infected. One mouse died from
Lyme borreliosis when larvae were fed on it. The nymphs remolted from underfed larvae were infected in 62.2% of cases, the mean geometric abundance in these nymphs was 5.7% per 100 fields of vision. A total of 3.2-14.7% of the ticks fed on the remaining 4 mice were infected and the abundance of boreliae was 1-2 per 100 fields of vision. In cycle V, one of 12 mice got infected, the infection rate in nymphs was 9.1%, the abundance of borreliae was 1 per 100 fields of vision. Thus, as the number of epizootic cycles increases, the proportion of infected mice, that of ticks infected on these mice on feeding, and the abundance of borreliae in the infected ticks decrease. Moreover, there was a reduction in the length of borreliae reduced from 17-18 mm to 10-11 mm and in the duration of multiplication and preservation of borreliae in the infected ticks and there was concurrently an increase in the duration of development of an infectious process in mice. It is suggested that the population of borreliae consists of 2 morphophysiological groups or more. During cultivation of the laboratory model of the parasitic system of
Lyme borreliosis, a group of borrelia that are short and slightly pathogenic for mice had got many points in its favour. A five-fold procedure of artificial election of precisely defining this group set the model on the verge of disappearance. The capacity of the populations of borreliae to alter their properties rapidly and fundamentally suggests that there might be violent annual fluctuations in human morbidity.