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.     

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.     

Phase changes in the population of group A streptococci and their influence on the course of the epidemic process of tonsillitis

This work presents the data on the complex evaluation of the population of group A streptococci, studied at each of four phases (reservation, epidemic transformation, epidemic spread, reservational transformation) of the course of the epidemic process of streptococcal infection of the respiratory tracts (tonsillitis) in an organized group of adults. The characterization of the phases of the infective agent in accordance with the level of the carrier state, the size of streptococcal foci and the virulence of streptococci is given. Thus, the study shows that the heterogeneity of group A streptococci with respect to their virulence reaches its maximum level at the phases of reservation and epidemic spread and its minimum level at the phases of epidemic and reservational transformation. The size of streptococcal foci in carriers and the virulence of streptococci isolated from them are the inter-related unidirectional signs of the population of the infective agent and, at the same time, the main factors responsible for the phase character of the epidemic process and the morbidity level in tonsillitis.     

An assessment of epidemic outbreaks of salmonellosis connected with poultry plant production]

The causes of the simultaneous rise of salmonellosis morbidity induced by S. enteritidis among the population of three towns in the Perm region were studied. The study revealed the leading role of eggs and chicken meat as factors contributing to the transfer of this infection to the population of different territories, commonly supplied with the products of one poultry plant. The contamination of eggs and chickens with S. enteritidis occurred at the plant due to Salmonella infection of chickens, parallel with the use of nonbalanced mixed fodder, originally intended for feeding swine. Analysis of the epidemic and epizootic processes of Salmonella infection in this epidemic situation made it possible to reliably establish the factors contributing to the transfer of the infective agent and the site of contamination.     

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 results of a serological study of viral hepatitis patients and healthy subjects under the conditions of a high-intensity epidemic process in hepatitis A

The activity of the involvement of preschool children of different ages in organized groups into the epidemic process of hepatitis A and the state of population immunity in elderly persons have been studied. Under the conditions of the intensive development of the epidemic process the active involvement of preschool children into this process as early as at the age of 1-2 years has been noted. At periods between epidemics the active circulation of the infective agent in the presence of decreased manifestations of the disease has been revealed.     

The manifestations of the epidemic process in shigellosis and their theoretical interpretation]

This work, based on the retrospective analysis of shigellosis morbidity among organized groups of adults, as well as the whole population of the city, demonstrates the manifestations of the epidemic process. Water supply was common in the city, while water consumption was autonomous. The organized groups of adults did not use the products of the local milk-processing factory. The following facts were established. The dynamics of morbidity in Flexner's dysentery showed the change of dominating variants of the infective agent, which reflected the action of internal mechanisms of the development of the epidemic process. The role of Sonne dysentery in the total structure of shigellosis morbidity did not correlate with the consumption of milk and milk products. The theory of the self-regulation of the parasitic system and the theory of correspondence served as the basis for the theoretical interpretation of the manifestations of the epidemic process of Shigella infections. To ascertain the real correspondence of individual Shigella species to concrete transmission factors, further investigation are necessary.     

Retrospective epidemiologic diagnosis of viral non-A, non-B hepatitis with a fecal-oral mechanism of transmission of the causative agent

The possibility of the retrospective epidemiological diagnosis of viral hepatitis non A, non B with the fecal-oral mechanism of the transfer of infection in three cities of Central Asia on the basis of the analysis of the dynamics of registered hepatitis A morbidity is shown. With the irregularity of morbidity levels among the total population being characteristic of all three cities, in Andizhan one rise in morbidity within a period of 3 years (1975-1978) and in Tashauz one rise within a period of 5 years (1975-1980) were registered. The analysis of the dynamics of morbidity observed in individual age and social groups showed that these rises, especially those registered in 1976 in Andizhan and in 1977 in Tashauz, were determined by morbidity levels among school children and adults. This is also true for a rise in morbidity rate registered in Tashauz in 1985. In Andizhan the highest morbidity rates among adults were registered in districts insufficiently equipped with modern amenities. Cases of infection registered as hepatitis A (HA) among persons immune to HA at territories with high intensity of the epidemic process of HA at the above-mentioned periods seem to be due to viral hepatitis non A, non B with the fecal-oral mechanism of the transmission of the infective agent.     

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.     

Epizootic characteristic of rabies today

During the 23 year period rabies was registered in the Moscow region in 163 cases among foxes, 22 cases among racoon-like dogs, 92 cases among dogs, 54 cases among cats. In 1991-2000 ten cases of rabies were registered among other wild animal other than foxes and raccoon-like dogs (hares, hedge-hogs, polecats, badgers, hamsters, martens, rats). Under today conditions the generalized epizootological pattern of rabies is characterized by the vector "natural foci-->anthropurgic foci" with wild and domestic animals playing an alternative role in the epizootic process and the circulation of the infective agent. Wild carnivorous animals maintain natural focal infection in time and space, while all domestic animals are a direct or indirect ecological impasse and took no part in the maintenance of the infection. Foxes are the main source of infection for the animals of the anthropurgic cycle: they play a special role in the development of the epizootic situation in the region as the main reservoir and source of the causative agent of rabies as a natural focal infection. Among other wild animals, raccoon-like dogs are involved into epizootic and epidemic chains. Dogs are the main objects to be infected in the anthropurgic cycles, while cats--a progressing group of risk. During the period of 25 years a decrease in the probability of natural rabies was noted.     

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.     

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.     

Control of emerging infectious diseases using responsive imperfect vaccination and isolation

This paper is concerned with a stochastic model for the spread of an SEIR (susceptible --> exposed (= latent) --> infective --> removed) epidemic among a population partitioned into households, featuring different rates of infection for within and between households. The model incorporates responsive vaccination and isolation policies, based upon the appearance of diagnosed cases in households. Different models for imperfect vaccine response are considered. A threshold parameter R*, which determines whether or not a major epidemic can occur, and the probability of a major epidemic are obtained for different infectious and latent period distributions. Simpler expressions for these quantities are obtained in the limiting case of infinite within-household infection rate. Numerical studies suggest that the choice of infectious period distribution and whether or not latent individuals are vaccine-sensitive have a material influence on the spread of the epidemic, while, for given vaccine efficacy, the choice of vaccine action model is less influential. They also suggest that an effective isolation policy has a more significant impact than vaccination. The results show that R* alone is not sufficient to summarise the potential for an epidemic.     

The dynamics of the formation of an infection focus in the intestines

The problem of the stability of the development of Shigella population in the intestine, depending on the dose of the infective agent, is analyzed. The agent is reproduced in the intestinal mucosa in short cycles, starting with adhesion and followed by penetration, intracellular multiplication and, finally, emission of free bacteria and hulled tops of villi with Shigella intracellular microcolonies. This form of emission maintains high concentration of bacteria and ensures, in case of the adhesion of hulled material, high local concentration provoking the repetition of the cycle. Depending on the dose, chains of cycles either progressively develop or maintain a constant level, or become extinct. Stable development of the chains of infectious cycles forms a focus of infection in the body (in the intestine). The growth of the populations of infective agents in live tissues, following the chain of cycles, produces a new type of microbial culture, differing from the types obtained by batch and flow cultivation. The aggregation and accumulation of infective agents in the hulled material is the particular case of the formation of infections, highly active particles and accumulations of infective agents, ensuring the development of infection with a relatively small number of organisms.     

Specific features of the HIV infection epidemic in Moscow

Retrospective analysis of the epidemic of HIV infection in Moscow allowed to mark out two periods: the first--from 1987 to 1993 and the second one--from 1994 to 2000. The characteristic feature of the first period of the epidemic was the sexual transmission of the agent mainly among homosexuals; the most affected group were persons aged 20-39 years and the number of AIDS patient decreased with a simultaneous growth in lethality. During the second stage of the HIV infection epidemic changes in the prevailing transmission routes of the agent occurred: injection drug addicts took the leading role. Changes in the ratio of HIV-infected men and women took place along with active involvement of persons aged 13-18 years into the epidemic process. The established changes in the epidemiological situation require corrections in the strategy and tactics of epidemic control and prophylactic measures.     

The Kermack-McKendrick epidemic model revisited

The Kermack-McKendrick epidemic model of 1927 is an age of infection model, that is, a model in which the infectivity of an individual depends on the time since the individual became infective. A special case, which is formulated as a two-dimensional system of ordinary differential ordinary differential equations, has often been called the Kermack-McKendrick model. One of the products of the SARS epidemic of 2002-2003 was a variety of epidemic models including general contact rates, quarantine, and isolation. These models can be viewed as age of infection epidemic models and analyzed using the approach of the full Kermack-McKendrick model. All these models share the basic properties that there is a threshold between disappearance of the disease and an epidemic outbreak, and that an epidemic will die out without infecting the entire population.     

A stochastic model for the development of an AIDS epidemic in a heterosexual population.

A non-age-dependent model, describing the evolution of a bisexual population, is developed in this paper and applied to projecting an AIDS epidemic in a heterosexual population. Included in the formulation are frequency- and non-frequency-dependent rules of partnership formation as well as five states of HIV disease, affecting the probability of infection per sexual contact. Results from computer experiments, designed to study the development of an AIDS epidemic in a heterosexual population fed by single males with a 50% prevalence of HIV infection prior to becoming active in heterosexual partnerships, are reported. In these experiments, the only source of HIV infection for females was sexual contacts with infected males within partnerships. Data on the probability of infection per sexual contact with an infected partner and the number of sexual contacts per month were incorporated into the model. However, the numbers used for the initial population of singles, couples, and those becoming sexually active per month were hypothetical. Even though the prevalence of HIV infection among males entering heterosexual partnerships was high, after 30 years the projected prevalence of HIV infection among females ranged from about 10 to 15% depending in part on the expected duration of partnerships and on whether the frequency- or non-frequency-dependent model was used. In these experiments, solutions of the embedded, nonlinear, deterministic equations for the incidence of HIV infection and the cumulative number of deaths due to AIDS proved to be good measures of central tendency for the sample functions of the stochastic population process.     

Erysipeloid as an occupational disease of workers in shoe enterprises

An outbreak of erysipeloid among the workers of a shoe factory is described. The spread of infection occurred due to contact with infected raw materials, which was confirmed by the isolation of Erysipelotrix rhusiopathiae from washings made from chrome and Russia leather supplied by different tanneries, as well as from casein glue. The raw materials could be additionally infected by rodents, in particular by common voles; the above-mentioned infective agent had been repeatedly isolated from these animals on the territory of this region. Leather was also infected in the process of soaking: the infective agent was isolated from the water of soaking baths. For the first time the routes of the spread of erysipeloid infection among shoe factory workers were bacteriologically confirmed. The recommended complex of sanitary, medical and antiepidemic measures led to the liquidation of the outbreak and thus proved to be effective. The authors draw the attention of epidemiologists, sanitary inspectors, occupational pathologists and heads of medical centers at shoe factories to the necessity of preventing the spread of occupational erysipeloid infection among the workers, as well as to the necessity for dermatologists, surgeons and infectionists, most frequently dealing with erysipeloid patients, to be correctly oriented in respect to this infection.     

Meningococcal infection in the Uzbek SSR

The epidemiological characteristics of meningococcal infection in Uzbekistan during the period of 8 years since its last epidemic rise in 1972 is presented. Differences in the intensity of the epidemic process among the urban and rural population due to a considerable isolation of most of the rural populated localities from the district centers and the low population density in the republic have been established. The seasonal distribution of the infection had a winter-spring character in urban areas and a spring character in rural areas. 63.4% of all cases were children under 14 years. In cities a high morbidity level among adolescents and young people was determined mainly by visitors from rural areas. A high epidemiological importance of healthy carriers, predominantly schoolchildren and young people was established. The immunological studies of humoral immunity in different groups of the population indicate that the process of immunization was more rapid in cities.     

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.