[The mathematical modelling of a dynamic epidemic process with a change in the infectivity of the causative agent of an infectious disease]. / Matematicheskoe modelirovanie dinamiki épidemicheskogo protsessa pri izmenenii zaraznosti vozbuditelia infektsionnoi bolezni.

The influence of changes in epidemic parameters on the time course of the disease manifestations was under study. An attempt to determine the relationship between such epidemic signs as the infectiousness of the parasite population (the transfer factor P) and morbidity and to study the influence of P on the seasonal and cyclic patterns of morbidity by modeling the process was made. The relationship between the quantitative parameters of "infectiousness" and "infectiousness profile" of the causative agent and morbidity was established. Seasonal and cyclic fluctuations of the modeled epidemic process were explained by the annual changes, constituting some percent shares of its constant value.

[A mathematical model of the epidemic process in anthroponotic infection with stable and homogeneous factors]. / Matematicheskaia model' épidemicheskogo protsessa antroponoznoi infektsii pri stabil'nykh i odnorodnykh faktorakh.

A very simple mathematical model of the epidemic process of human infection in the presence of stable and homogeneous factors has been created and analyzed. The theoretical possibility of describing the detailed course of the epidemic process by means of this model, permitting the consideration of inner parameters which cannot be determined in any other way, has been shown. The study has revealed that the approximation of the model to the real epidemic process is connected with the introduction of the notion of the heterogeneity of the parasite and host populations into the axiomatics of modeling.

[A comparative analysis of the Salmonella typhi strains isolated from patients and bacterial carriers]. / Sravnitel'nyi analiz shtammov Salmonella typhi, vydelennykh ot bol'nykh i bakterionositelei.

The comparative analysis of 133 S. typhi clinical strains isolated from patients and carriers in Dnepropetrovsk Province in 1978-1987 was carried out. As shown by this analysis, 10 Vi phage types were represented in the set of strains under study, phage types A and F1 being the most numerous ones. Phage type F1 occurred less frequently among the strains isolated from carriers. 31.1% of the strains were found to contain plasmids with different molecular weight ranging from 96 to 0.5 MD. The occurrence of plasmid-containing strains remained at the same level during the whole period under study. Low-molecular plasmids occurred more frequently in the strains isolated from carriers. The minimal suppressive concentrations of a number of antibiotics, such as penicillin, ampicillin, monomycin, chloramphenicol, tetracycline, rifampicin and streptomycin, were determined. 7% of the strains were resistant to penicillin, 9% to monomycin, 15%--to tetracycline and 2.6% to chloramphenicol. The correlation between penicillin and monomycin resistance of the strains and the presence of the plasmid with a molecular weight of 60 MD in these strains was established. All strains were shown to be highly variable in the degree of their virulence: from 10(2) to 10(8). The strains isolated from patients possessed greater virulence.

[Phenomenology and molecular mechanisms of Shigella sonnei dissociation: its variability in model in vivo and in vitro systems]. / Fenomenologiia i molekuliarnye mekhanizmy dissotsiatsii Shigella sonnei: izmenchivost' v model'nykh sistemakh in vivo i in vitro.

The dynamics of the accumulation of phase II S. sonnei in the infectious process in germ-free rats, during cultivation and in subcultures was studied. The in vivo variability of S. sonnei showed a sharply defined phasic character of the process with the periods of the apparent absence of phase II, the increase of its occurrence and stabilization with the preservation of S-forms in minor amounts. Kanamycin-resistant phase II accumulated in vivo more rapidly than in vitro. Cultivation with sodium desoxycholate was found to accelerate the process of disassociation. The characteristic feature of all dissociants detected in all systems was their plasmid profile: in phase I, plasmids of 120 and 60 Md, as well as small plasmids, were detected; in phase II disassociants, plasmid with a molecular weight of 120 Md was absent. The restriction analysis of total plasmid DNA by means of restrictase EcoR1 showed the absence of 3 fragments in phase II while other 13 fragments were retained. These results open prospects for the molecular cloning of the gene antigen of phase II.