Specific features of the typhoid fever epidemic process in organized collective

During the chronic water epidemic of typhoid fever in Tajikistan in 1996-1997 specific features of the epidemic process dynamics in groups of servicemen were studied in several cities. The infective agent was proved to be transmitted by the alimentary route and through everyday contacts, the water route of transmission playing the most important role. The early clinical and epidemiological signs of the water outbreak of typhoid fever and the risk factors were established. The clinical and epidemiological aspects of vaccination were analyzed.     

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.     

Epidemiology, transmission dynamics and control of SARS: the 2002-2003 epidemic

This paper reviews current understanding of the epidemiology, transmission dynamics and control of the aetiological agent of severe acute respiratory syndrome (SARS). We present analyses of data on key parameters and distributions and discuss the processes of data capture, analysis and public health policy formulation during the SARS epidemic are discussed. The low transmissibility of the virus, combined with the onset of peak infectiousness following the onset of clinical symptoms of disease, transpired to make simple public health measures, such as isolating patients and quarantining their contacts, very effective in the control of the SARS epidemic. We conclude that we were lucky this time round, but may not be so with the next epidemic outbreak of a novel aetiological agent. We present analyses that help to further understanding of what intervention measures are likely to work best with infectious agents of defined biological and epidemiological properties. These lessons learnt from the SARS experience are presented in an epidemiological and public health context.     

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.     

The mechanism of the development of the epidemic process in Sonne dysentery

An epidemic outbreak of Sonne dysentery has been studied. The data of epidemiological monitoring before and after the epidemic have been analyzed. The real prognostication value of controlling the biological properties of Shigella sonnei and the increase of their intrapopulation heterogeneity at the period of the activation of the epidemic process of Sonne dysentery has been established.     

Prevention of acute intestinal infections based on the epidemiological surveillance system

The development of the system of epidemiological surveillance and its introduction into the practical work of the district sanitary and epidemiological station made it possible to decrease morbidity in acute intestinal infections 2.4 times in comparison with preceding years, as well as to put an end to the outbreaks of these infections. The work proved the advantage of epidemiological diagnosis permitting the introduction of measures which prevent the formation of the epidemic strain of the infective agent and thus affect the seasonal rise of morbidity.     

Crimean-Congo hemorrhagic fever in Rostov Province: the epidemiological characteristics of an outbreak

The results of the epidemiological analysis of the outbreak of hemorrhagic fever which was caused by Crimean-Congo hemorrhagic fever virus and occurred during the period of July 3-19, 1999, in the Oblivskaya district of Rostov Province are presented. The specific epidemiological features of the outbreak have been determined. The possible versions of the appearance of the focus of infection and the role of Ixodes ticks in the circulation of the infective agent are discussed.     

Variational data assimilation with epidemic models

Mathematical modelling is playing an increasing role in developing an understanding of the dynamics of communicable disease and assisting the construction and implementation of intervention strategies. The threat of novel emergent pathogens in human and animal hosts implies the requirement for methods that can robustly estimate epidemiological parameters and provide forecasts. Here, a technique called variational data assimilation is introduced as a means of optimally melding dynamic epidemic models with epidemiological observations and data to provide forecasts and parameter estimates. Using data from a simulated epidemic process the method is used to estimate the start time of an epidemic, to provide a forecast of future epidemic behaviour and estimate the basic reproductive ratio. A feature of the method is that it uses a basic continuous-time SIR model, which is often the first point of departure for epidemiological modelling during the early stages of an outbreak. The method is illustrated by application to data gathered during an outbreak of influenza in a school environment.     

Etiology of the epidemic outbreak of community-acquired pneumonia in children in St. Petersburg

In September-December 1998 the epidemic rise of outhospital pneumonia (EP) among children was observed in St. Petersburg, which led to a twofold increase in morbidity rate this year. The study of the etiology of EP during the period of 1998-2001 confirmed the prime role of Streptococcus pneumoniae (74.5%) and, for the first time in Russia, revealed the epidemic outbreak of acute chlamydiosis (Chlamydia pneumoniae), diagnosed in 67.3% of children, the maximum occurrence (87.5%) in 1998 with only 19% of the patients having the disease in the form of monoinfection. The prevalence of S. pneumoniae and C. pneumoniae in the etiology of EP and more severe course of mixed infection suggested that these infective agents played a leading role in the epidemic outbreak of acute respiratory infections in St. Petersburg.     

Community Involvement in Dengue Outbreak Control: An Integrated Rigorous Intervention Strategy

BackgroundAn explosive outbreak of dengue fever occurred in Guangdong Province, China in 2014. A community-based integrated intervention was applied to control this outbreak in the capital city Guangzhou, where dengue epidemic was mainly caused by imported cases.ConclusionsThis study suggests that an integrated dengue intervention program has significant effects to control a dengue outbreak in areas where dengue epidemic was mainly caused by imported dengue cases.     

Biological properties of Vibrio cholerae as a part of epidemiologic surveillance of cholera

Systematic dynamic surveillance of the complex of biological properties of V. cholerae makes it possible to find out specific features of this infective agent, to improve diagnostics and to use the data thus obtained for epidemiological surveillance on cholera. The study of the complex of biological properties of V. cholerae O1, its ecological relationships and interactions give evidence to assert that microbiological aspects as one of the primary tasks in monitoring water ecosystems, as well as the necessity of surveillance on strains isolated from humans. Different properties of V. cholerae should be determined irrespective of the object, time and territory of their isolation in the process of epidemiological surveillance on cholera.     

Virulence variation among epidemic and non-epidemic strains of Saint Louis encephalitis virus circulating in Argentina

Saint Louis encephalitis virus caused an outbreak of febrile illness and encephalitis cases in Córdoba, Argentina, in 2005. During this outbreak, the strain CbaAr-4005 was isolated from Culex quinquefasciatus mosquitoes. We hypothesised that this epidemic variant would be more virulent in a mouse model than two other non-epidemic strains (78V-6507 and CorAn-9275) isolated under different epidemiological conditions. To test this hypothesis, we performed a biological characterisation in a murine model, including mortality, morbidity and infection percentages and lethal infection indices using the three strains. Mice were separated into age groups (7, 10 and 21-day-old mice) and analysed after infection. The strain CbaAr-4005 was the most infective and lethal of the three variants, whereas the other two strains exhibited a decreasing mortality percentage with increasing animal age. The strain CbaAr-4005 produced the highest morbidity percentages and no significant differences among age groups were observed. The epidemic strain caused signs of illness in all inoculated animals and showed narrower ranges from the onset of symptoms than the other strains. CbaAr-4005 was the most virulent for Swiss albino mice. Our results highlight the importance of performing biological characterisations of arbovirus strains likely to be responsible for emerging or reemerging human diseases.     

Lattice Model for Influenza Spreading with Spontaneous Behavioral Changes

Individual behavioral response to the spreading of an epidemic plays a crucial role in the progression of the epidemic itself. The risk perception induces individuals to adopt a protective behavior, as for instance reducing their social contacts, adopting more restrictive hygienic measures or undergoing prophylaxis procedures. In this paper, starting with a previously developed lattice-gas SIR model, we construct a coupled behavior-disease model for influenza spreading with spontaneous behavioral changes. The focus is on self-initiated behavioral changes that alter the susceptibility to the disease, without altering the contact patterns among individuals. Three different mechanisms of awareness spreading are analyzed: the local spreading due to the presence in the neighborhood of infective individuals; the global spreading due to the news published by the mass media and to educational campaigns implemented at institutional level; the local spreading occurring through the “thought contagion” among aware and unaware individuals. The peculiarity of the present approach is that the awareness spreading model is calibrated on available data on awareness and concern of the population about the risk of contagion. In particular, the model is validated against the A(H1N1) epidemic outbreak in Italy during the season, by making use of the awareness data gathered by the behavioral risk factor surveillance system (PASSI). We find that, increasing the accordance between the simulated awareness spreading and the PASSI data on risk perception, the agreement between simulated and experimental epidemiological data improves as well. Furthermore, we show that, within our model, the primary mechanism to reproduce a realistic evolution of the awareness during an epidemic, is the one due to globally available information. This result highlights how crucial is the role of mass media and educational campaigns in influencing the epidemic spreading of infectious diseases.     

Isolation and identification of Crimean-Congo hemorrhagic fever virus in the Stavropol territory

The results of the isolation and identification of the causative agent of a haemorrhagic fever outbreak in the Stavropol Territory are presented. The virus isolated from blood of haemorrhagic fever patients by virological methods was identified in serological and molecular tests as Crimean haemorrhagic fever virus. This epidemiological analysis testify to increased activity of the natural focus of Crimean-Congo haemorrhagic fever in this area due to a number of natural and other factors leading to intensification of its epidemic realization.     

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.     

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.     

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.     

A Bayesian Inference Framework to Reconstruct Transmission Trees Using Epidemiological and Genetic Data

The accurate identification of the route of transmission taken by an infectious agent through a host population is critical to understanding its epidemiology and informing measures for its control. However, reconstruction of transmission routes during an epidemic is often an underdetermined problem: data about the location and timings of infections can be incomplete, inaccurate, and compatible with a large number of different transmission scenarios. For fast-evolving pathogens like RNA viruses, inference can be strengthened by using genetic data, nowadays easily and affordably generated. However, significant statistical challenges remain to be overcome in the full integration of these different data types if transmission trees are to be reliably estimated. We present here a framework leading to a bayesian inference scheme that combines genetic and epidemiological data, able to reconstruct most likely transmission patterns and infection dates. After testing our approach with simulated data, we apply the method to two UK epidemics of Foot-and-Mouth Disease Virus (FMDV): the 2007 outbreak, and a subset of the large 2001 epidemic. In the first case, we are able to confirm the role of a specific premise as the link between the two phases of the epidemics, while transmissions more densely clustered in space and time remain harder to resolve. When we consider data collected from the 2001 epidemic during a time of national emergency, our inference scheme robustly infers transmission chains, and uncovers the presence of undetected premises, thus providing a useful tool for epidemiological studies in real time. The generation of genetic data is becoming routine in epidemiological investigations, but the development of analytical tools maximizing the value of these data remains a priority. Our method, while applied here in the context of FMDV, is general and with slight modification can be used in any situation where both spatiotemporal and genetic data are available.     

Distinguishing epidemic waves from disease spillover in a wildlife population

Serengeti lions frequently experience viral outbreaks. In 1994, one-third of Serengeti lions died from canine distemper virus (CDV). Based on the limited epidemiological data available from this period, it has been unclear whether the 1994 outbreak was propagated by lion-to-lion transmission alone or involved multiple introductions from other sympatric carnivore species. More broadly, we do not know whether contacts between lions allow any pathogen with a relatively short infectious period to percolate through the population (i.e. reach epidemic proportions). We built one of the most realistic contact network models for a wildlife population to date, based on detailed behavioural and movement data from a long-term lion study population. The model allowed us to identify previously unrecognized biases in the sparse data from the 1994 outbreak and develop methods for judiciously inferring disease dynamics from typical wildlife samples. Our analysis of the model in light of the 1994 outbreak data strongly suggest that, although lions are sufficiently well connected to sustain epidemics of CDV-like diseases, the 1994 epidemic was fuelled by multiple spillovers from other carnivore species, such as jackals and hyenas.