An explosive outbreak of respiratory streptococcal infection with a droplet transmission mechanism

The data obtained in the study of an explosive outbreak of acute respiratory diseases, tonsillitis and scarlet fever in one of schools in Moscow have made it possible to exclude the alimentary mechanism of its development and to demonstrate the role of the droplet mechanism of transmission in the appearance of its outbreak. The epidemiological analysis of the outbreak has permitted the formulation of the hypothesis on the conditions of the formation and spread of the epidemic variant of the infective agent; this hypothesis corresponds to the available data in literature on the qualitative changes of the infective agent in the course of the epidemic process. The study has shown that the prophylaxis of the explosive outbreaks of respiratory streptococcal infections must be ensured by the system of epidemiological surveillance with timely intervention into the epidemiological process at its early stages.     

The epidemic process in mumps infection

Manifestations of the epidemic process of a parotitis infection can be explained by the theory of the self regulation of parasitic systems. A characteristic feature of epidemic parotitis is the formation of epidemic foci in the absence of parotitis cases and without the penetration of the infective agent from the outside. The epidemic wave of parotitis infection decreases as the virulence of the infective agent attenuates due to its passage through persons gaining immunity in the course of the epidemic. The avirulent infective agent persists in the body of some immune carriers till a sufficient stratum of susceptible subjects accumulates in the chain of the agent circulation. The analysis points to the autonomous character of the epidemic process not only among the urban and rural population, but also among separate social and age groups of the population within one town or settlement. The findings evidence an independent formation of the epidemic variant of the infective agent in individual schools and preschool institutions.     

Manifestations of angina morbidity as a reflection of the self-regulation of the epidemic process in streptococcal infection

The data on the application of the principles of the self regulation of the epidemic process for understanding the annual dynamics of angina morbidity in organized groups of adults are presented. In this case the reservation of group A streptococci occurs in chronic (resident) carriers, whose proportion was found to be 15.8 +/- 2.6%. The epidemic manifestations of morbidity are regulated mainly by the concentration of newly arrived members in the groups, i. e. by the size of the stratum providing the optimum conditions for the parasitization of the streptococcal population. The annual morbidity levels depend essentially not only on the heterogeneity of the group members with respect to their susceptibility to streptococcal infection, but also on the conditions of their accommodation, affecting the transmission of droplet infection. The role of individual risk factors in the variation of the quantitative characteristics of the angina morbidity manifestations under study is calculated.     

Analysis of the possible mechanisms of the action of socioeconomic factors on the epidemic process whose biological base is an open parasitic system

The mechanism of action of socioeconomic factors on the epidemic process have been analyzed on the basis of the study of the influence, exerted on the biological properties of infective agents by environmental factors resulting from human activities, and the theory of the self-regulation of the parasitic system. Such mechanisms can be subdivided into the mechanisms affecting the epidemiological triad (the source of infection, the mechanism of transfer, and the susceptibility of the population) and the mechanisms facilitating the formation of infective agents with selective advantages (decreased virulence, resistance to antimicrobial preparations, etc.) under the influence of environmental factors resulting from human activities. The former mechanisms suppress and tend to localize the epidemic process, while the latter ones activate this process under the conditions becoming more complicated for the spread of the infective agent.     

The OF characteristics of streptococci group A and immunity to streptococcal infection based on the results of OF and anti-OF tests

The influence of the OF activity of group A streptococci on their specific pathogenic properties has been shown, which is manifested by increased virulence of these streptococci for children of younger age groups and by a two times higher isolation rate of OF+ strains in tonsillitis than in scarlet fever. The possibility of the indirect evaluation of the content of anti-M-antibodies by the results of the anti-OF test has been revealed, which permits using this test instead of the bactericidal test, more complicated, in the study of immunity to infection induced by group A OF+ streptococci. Among the main methods of laboratory support of epidemiological surveillance on streptococcal infection, the introduction of the highly discriminating OF typing and the anti-OF test into practical use is recommended.     

Effect of the influenza A virus on the sensitivity of mice to infection caused by Streptococcus group B

Study of the capacity of group B streptococci for causing the development of infection in mice has revealed the virulence of the cultures for mice to be determined by the serovar of the streptococcus, the infective dose, and the amount of type-specific polysaccharide. Under the conditions of mixed viral-bacterial infection, influenza A virus was shown to influence the development of bacterial infection in the animals in two ways: to increase the virulence of an avirulent strain and to decrease the pathogenicity of a virulent one in streptococcal monoinfections. Simultaneously with viral infection, the stimulation of the multiplication of an avirulent strain in the lungs of mice was observed, while in the control groups of the animals the elimination of bacteria from the lungs was registered. No additional accumulation of the infective virus in the lungs of mice in the presence of streptococci was found.     

Epidemiology of group A streptococcal infections--their changing frequency and severity

The frequency and severity of streptococcal infections and their sequelae have declined dramatically in the past century, yet the prevalence of streptococcal infections is still high. The reasons for this decline must be intimately related to host resistance, virulence of the agent, and environmental factors, especially crowding. Close examination of these fundamental influences does not reveal any evidence that humans have become less resistant to streptococcal infections, but they react less violently. There is some evidence that the agent may have lost a degree of its virulence. The decline in morbidity and mortality due to streptococcal infections began long before antibiotics, especially penicillin, were available. However, penicillin has proved to be an important factor in prevention of streptococcal infections, especially in rheumatic fever prophylaxis. There are certain indications that repeated streptococcal infections due to similar M types, occurring in young children over the past several decades, have resulted in some degree of immunity as well as the possible evolution of less virulent, but not less infectious, strains of group A streptococci. Also, a decrease in crowding would be expected to result in fewer streptococcal infections. Although there are more people in the world than at any other time in the history of man, urban population density in the western world, at least, is less than in the late 1800s and early 1900s.     

Significance of the heterogeneity of respiratory syncytial viral populations in the development of the epidemic process

The manifestations of the epidemic process in respiratory syncytial (RS) virus infection induced by the strains of the infective agent, differing in their capacity for reproduction at 39 degrees and 37 degrees C and in their sensitivity to antibodies, were compared. The observation of children in a group (about 80 children simultaneously) with the systematic serological and virological examination of sick and healthy children was the main method in this investigation. The circulation of RS viruses with greater capacity for reproduction at 39 degrees and 37 degrees C and lesser sensitivity to antibodies, i.e. viruses with greater virulence, was accompanied by the increased intensity of manifestations of the epidemic process. An increase in the heterogeneity of RS virus populations isolated at the same period of observation was accompanied by the intensification of the epidemic process, which was manifested by increased morbidity rate and a higher level of contamination in children, an increase in the incidence of outbreaks and in the frequency of RS virus reinfection.     

Immunoepidemiological characteristics of the duration of a meningococcal carrier state

The duration of meningococcal carriership in children and adults in the foci of infection and outside such foci and the immunological characteristics relating to group-specific meningococcal antigens A, C, X, Y and Z at different periods after the detection of the infective agent in the nasopharynx have been studied. Carrier state has been shown to last, on the average, 11 days. The duration of the release of meningococci from the nasopharynx has proved to be influenced by the epidemic situation in a given group. Differences in the time course of the immunological reorganization of the body in response to antigenic challenge in prolonged and short-term carrier state have been detected. These data suggest that rapid immune response to meningococcal antigens in the process of short-term carrier state is probably one of the factors preventing the prolonged colonization of the nasopharynx by the infective agent.     

Immunological factors in the evolution of the epidemic process in meningococcal infection

The results obtained in 1987 in the study of the immunostructure of the population of Yaroslavl with respect to meningococcal polysaccharides, groups, A, B, C, and lipopolysaccharide are presented in comparison with earlier results obtained in 1976. The regulating role of the immunological factor in the evolution of the epidemic process of meningococcal infection has been confirmed. The level of antibodies to meningococcal polysaccharides, groups A and B, has been found to reflect the intensity of the circulation of the infective agent among the population. The comparison of the results of investigations carried out in 1976 and 1987 has revealed the essential role of the lipopolysaccharide antigen in the formation of the postinfection immunity of the population to meningococcal infection, irrespective of the group of the infective agent.     

The epidemic process of an acute streptococcal respiratory infection in large organized collectives of children

The study of the specific features of the development of the epidemic process of scarlet fever, tonsillitis, and acute respiratory diseases (ARD) in two large organized groups of children revealed the presence of some differences which depended on the character of prophylactic measures taken in these groups. Thus, in the absence of prophylaxis with bicillin a pronounced increase in the level of carriership, accompanied by an increase in the infective capacity of carriers, was noted. This resulted in a high level and unfavorable dynamics of morbidity in scarlet fever, tonsillitis, and ARD. On the contrary, the use of prophylaxis with bicillin ensured the stability of the level of carriership, while the infective capacity of carriers was not pronounced. At the same time a rise in ARD morbidity was insignificant, and morbidity in scarlet fever and tonsillitis was reduced to nil.     

Effect of a streptococcal allergen on the rosette-forming capacity of the T-lymphocytes in erysipelas patients

The reaction of antigen-dependent E-rosette formation with the hemolytic streptococcal antigen in erysipelas patients is indicative of the ambiguous role of the specific immunological transformation of the body in respect of the infective agent antigens in different clinical forms of the disease and is of prognostic importance as regards the chronic transformation of the infectious process and the development of the relapses of the disease.     

Cholera morbidity problems in 1 of the departments of the Democratic and Popular Republic of Algeria

A total of 1,078 cases of bacteriologically confirmed cholera were analyzed at the period of 1979-1983. In 1981 Vibrio eltor, serotype Inaba, replaced V. cholerae, serotype Ogawa, and became the prevailing infective agent. Every year young children and persons over 50 years of age were most actively involved into the epidemic process. The peak of seasonal morbidity was observed in September-October. The appearance of the foci of infection in families was found to be slightly pronounced in cholera. 85.3% of the families had only a single case of cholera. The cases of cholera with the fatal termination of the disease were registered mostly at the beginning of the seasonal rise of morbidity and at its peak.     

Susceptibility of chicken embryos to group A streptococci: Correlation with fibrinogen binding

Abstract One problem in investigating group A streptococcal infections and virulence is the lack of appropriate in vivo models. In this study we introduce the chicken embryo model for determining virulence of Streptococcus pyogenes . We found that M protein positive strains, if administered intravenously, were highly virulent for 12-day-old chicken embryos. The LD₅₀ of the strains tested could be correlated directly with the amount of cell wall exposed M protein, which has been determined by the capacity of streptococci to bind fibrinogen and by the ability of streptococci to survive in fresh normal human blood. The number of colony forming units (cfu) of M⁺ strains necessary to kill 50% of embryonated eggs was significantly lower (<10² cfu) than for M⁻ variants (>10⁴ cfu). Albumin and/or IgG binding to streptococcal cells, which can also take place in proteins of the M protein family which do not bind to fibrinogen, did not show that clear correlation to the virulence in chicken embryos that did fibrinogen binding. Application of anti-streptococcal M protein antisera from chicken and rabbit reduced the lethality of the chicken embryos. In contrast, no correlation was found between lethality of chicken embryos and the in vitro production of erythrogenic toxins by the administered strains. Thus the results indicate that the presence of M-protein with its fibrinogen binding activity on the streptococcal cell surface is necessary for virulence of group A streptococci in the chicken embryo model.     

Pulse electrophoresis of serogroup A streptocci isolated in Moscow

Pulse electrophoresis of group A streptococci (GAS) isolated in 1998 - 2004 in Moscow from patients during outbreaks of tonsillitis in child institutions, military unit and also from sporadic cases in children and adults was performed. During analysis of 48 strains 16 pulse electrotypes were recognized. These data allow to consider that in different child institutions (and other groups) accumulation and spreading of most adapted to such environment variants of GAS are take place and population structure of GAS in such institutions is unique on molecular and other characteristics. This study showed that complex typing of GAS (use of pulse electrophoresis and PCR for detection of erythrogenic toxins A and C) will help to improve molecular-epidemiologic surveillance for streptococcal group A infection, development of recommendations on reduction of morbidity from this infection and also to decrease risk of its severe forms, complications and mortality.     

Patterns in the epidemic process of scarlet fever in various territories differing in respect of climate and geography]

Observations carried out in Ashkhabad and Petrozavodsk permitted to reveal specific features of the epidemic process in scarlet fever at the territories differing in climato-geographic respect. This was expressed in a different level of morbidity, differences in the character of periodicity, seasonality and age structure of morbidity. Along with this there were noted differences in the spread of the carrier state of hemolytic streptococcus and of their biological properties, and also in the process of immunity formation in the population. The data obtained suggest that one of the causes of epidemiological differences in scarlet fever detected in the southern and the northern districts were peculiarities of the immunological reactivity of the population and a difference in the carrier state of the highly toxigenic streptococci.     

Typing of Streptococcus group A isolated from patients and healthy persons

The typing of 80% of 381 streptococcal strains, group A, under study was accomplished with a set of diagnostic anti-T sera obtained from the Sevak Institute (Czechoslovakia). None of the T-types could be related with certainty to the localization of the infective agent in the human body (the pharynx, the skin). Different T-types were shown to circulate in definite regions of the USSR. To enhance the differentiating capacity of T-typing, the enzymatic (lipoproteinase and NADase) activity of the strains was determined, thus permitting the subdivision of the T-types into still smaller groups. The typing of OF+ strains of unknown M-specificity could be carried out by means of the blood sera of healthy persons, containing antibodies to streptococcal lipoproteinase. The conclusion on the expediency of using the determination of lipoproteinase and NADase as an additional marker in the typing of group A streptococci was made.     

Current data on the cloning of virulence factors of pathogenic Streptococci

The data on the cloning of the main pathogenic determinants of group A streptococci including M-protein, erythrogenic toxin, streptokinase, streptolysin O are analyzed. The scientific importance and the possible ways to use the data obtained after cloning are discussed. The hypothesis on the operon system of a number of streptococcal virulence factors regulation is discussed. Construction of vector systems for streptococcal genes cloning is summarized.     

Manifestations of genotypic and phenotypic heterogeneity in populations of Shigella sonnei and of humans at different phases of the development of the epidemic process

The study of the structure and developmental dynamics of S. sonnei populations and the state of local immunity to this infection in children under school age has revealed that the interaction of the heterogeneous populations of the parasite and the host is the internal motive force of the self-regulating phasic development of the epidemic process. In the course of this process complementary changes in the virulence of the infective agent and in the immunoresistance of children are generated on the basis of negative feed-back.     

The factors of bacterial pathogenicity and their role in the development of the infectious process

The latest data concerning the characterization of the pathogenicity factors of bacteria and the evaluation of their role in the realization of definite phases of the development of the infectious process are presented. The infectious process is regarded as the result of the complicated simultaneous interaction of microorganisms and different cells and tissues of the host body. The problems of the polydeterminant character of pathogenicity factors, tho possibility of the joint action of different factors at one and the same stage of the development of the infectious process and, vice versa, the action of the same factors at different stages of the interaction of the infective agent and the susceptible host are discussed. Modern data on the genetic control of pathogenicity factors, on the localization of their genetic determinants on the chromosome and the virulence plasmids, information of pathogenicity "islets" which jointly determine the pathogenic potential of the infective agent are given. The emphasis is made on fact that the general principle of the genetic control of bacterial pathogenicity is complicated relationship between chromosomal and nonchromosomal determinants; some of them form a part of genetic pathogenicity "islets", simultaneously regulating and expressing the pathogenicity factors of the infective agent.