Shigellosis in the USSR: the etiological role of Shigella dysenteriae

The etiological role of S. dysenteriae in Shigella infections at different territories of the USSR in 1983-1987 is analyzed. The study shows that S. dysenteriae pertain to territories with unfavorable water supply of the population. At some of these territories, in particular the Uzbek SSR, Grigor'ev-Shiga dysentery seems to gain ground and the restoration of the area of its spread occurs. In recent years the penetration of Grigor'ev-Shiga dysentery from abroad became more frequent in the presence of the pandemic of this dysentery in the world, which caused the appearance of the disease in 17 out of 27 basic territories of the All-Union Center of Shigella Infections. The ways for increasing the control of this infection are outlined.     

The world-wide pandemic and drug resistance of the causative agent of Grigor'ev-Shiga dysentery

One of the factors facilitating the global pandemic of Grigor'ev-Shiga dysentery is considered in detail. All Shigella dysenteriae 1 strains, irrespective of the geographical zone of their spread, showed medicinal resistance. As pandemic developed, the spectrum of medicinal resistance constantly increased in all hyperendemic foci. The presence of pronounced relationships between the strains circulating in each of three hyperendemic foci and the strains circulating in different hyperendemic foci could be observed. The necessity of paying greater attention to this dangerous infectious disease, and especially to the problems related to the medicinal resistance of its causative agents, is emphasized.     

Shigella differentiation according to R factor affiliation with incompatibility groups taking into account antibiotic resistance spectra

The study on 198 Shigella strains isolated from dysentery patients and cultures from 3 different dysentery foci showed a possibility of intraspecies typing of the causative agents according to the R factor incompatibility groups with regard to the antibiotic resistance spectra. The procedure was most effective in defining the similarity of the strain origin from the epidemiological foci.     

Conditions and factors determining the etiological structure of dysentery and its changes. Report 1. Epidemiological theory of etiological selectivity of the main (primary) pathways of infection and their differences in various nosological forms of dysentery]

The authors present the elaborated and formed epidemiological theory ("conformity theory") according to which the etiological structure of dysentery is determined by the etiological selectivity of the main (primary) waves of transmission of the infection differing in various nosological forms of dysentery. In Grigoriev-Shiga dysentery the domestic way of the spread of infection plays the main role, in Flexner and Newcastle dysentery--the water way, and in Sonne dysentery--the food way (particularly through the milk). Evolution of the etiological structure of dysentery serves as the reflection of evolution of the principal ways of transmission. The complex of prophylactic and antiepidemic measures in individual noslogical forms of dysentery should be differentiated and be directed in epidemiological sense to the neutralization of the corresponding main (primary) way of transmission of the infection.     

Evaluation of the epidemiological effectiveness of hospitalization of patients with dysentery]

The authors present materials on the study of epidemiological efficacy of hospitalization of dysentery patients by statistical analysis (calculation of tendencies, rates of increase, etc.) of the indices of focal morbidity per 1000 contacts in the total number of foci characterized by various periods of isolation of the first patient. The work was carried out on materials of two towns considerably differing by the extent of organization of public services and amenities. The results obtained pointed to the relative epidemiological efficacy of hospitalization of dysentery patients particularly marked at the territory with less favourable living conditions.     

Epidemiologic features of acute viral respiratory infections in familial foci]

A study was made of the epidemiological peculiarities of viral respiratory infections of various etiology in the familial foci with the use of a methodical approach permitting to detect the true spread of infection in the familial foci, with consideration to the subclinical forme fruste of the disease and "carrier state". It appeared that in the familial foci the infectiousness of the majority of respiratory viral infections was greater than in the closed collective bodies uniting persons of the same age. The age composition of the family influences the manifestness (particularly in parainfluenza infection) and the intensity of the epidemic process characterized by the coefficient of the secondary affections. The type of the apartment, the floor on which it is located, and the number of persons residing in it had no significant influence on the spread of the viral infections in the familial foci. A definite role in this process is played by the level of specific serum antibodies in the members of the family surrounding the patient. The association of morbidity level with the antibody level proved to be the most distinct in children with influenza and adenoviral infection; this association was less significant in adults.     

Use of intraspecific differentiation of Sh. sonnei for the purpose of studying patterns in the epidemic process of dysentery]

The use of complex typing of Sh. sonnei by the colicinogenic and enzymatic properties in epidemiological analysis of dysentery caused by Sh. sonnei, apart from establishment of epidemiological connections in the foci, offered a possibility of introducing significant corrections in the determination of the sizes and duration of existence of the epidemic foci, as well as in detection of the sources and factors of transmission of the infection established in epidemiological examination. Typing of Sh. sonnei also aided in ascertaining that, apart from general regularities in the individual territories, the epidemic process in individual groups of the population and in different seasons of the year could also course autonomously.     

Eltor cholera in Latin America

Cholera epidemics in South and Central America in the period 1991-1999 are characterized. The mechanisms of existence of Vibrio eltor in environmental objects have been substantiated. The causes and conditions of endemic foci formation which determine the infection spread not only within the countries of the subcontinent, but also far beyond its borders are shown. The effectiveness of cholera control interventions is evaluated.     

Screening of Trypanosoma brucei gambiense in Domestic Livestock and Tsetse Flies from an Insular Endemic Focus (Luba,Equatorial Guinea)

Background

Sleeping sickness is spread over 36 Sub-Saharan African countries. In West and Central Africa, the disease is caused by Trypanosoma brucei gambiense, which produces a chronic clinical manifestation. The Luba focus (Bioko Island, Equatorial Guinea) has not reported autochthonous sleeping sickness cases since 1995, but given the complexity of the epidemiological cycle, the elimination of the parasite in the environment is difficult to categorically ensure.

Methodology/Principal Findings

The aim of this work is to assess, by a molecular approach (Polymerase Chain Reaction, PCR), the possible permanence of T. b. gambiense in the vector (Glossina spp.) and domestic fauna in order to improve our understanding of the epidemiological situation of the disease in an isolated focus considered to be under control.The results obtained show the absence of the parasite in peridomestic livestock but its presence, although at very low rate, in the vector. On the other hand, interesting entomological data highlight that an elevated concentration of tsetse flies was observed in two out of the ten villages considered to be in the focus.

Conclusions

These findings demonstrate that even in conditions of apparent control, a complete parasite clearance is difficult to achieve. Further investigations must be focused on animal reservoirs which could allow the parasites to persist without leading to human cases. In Luba, where domestic livestock are scarcer than other foci in mainland Equatorial Guinea, the epidemiological significance of wild fauna should be assessed to establish their role in the maintenance of the infection.     

Effectiveness of social hygiene and organized preventive measures in dysentery in preschool institutions]

The work presents the data on the development and realization of the complex of social and hygienic, as well as organizational and preventive measures for dysentery control at institutions for children of preschool age in one of the regions of our country. This complex comprises the improvement of "epidemiological" knowledge of the staff, preventive orientation in the work of the epidemiological section of the local Sanitary Epidemiological Station, the spread of sanitary and hygienic knowledge children and in their families, the improvement of material and technical equipment of children's institutions. The complex proved to be highly effective: at institutions for children of preschool age morbidity -ate in dysentery decrease 4--5 times, and its specific falue dropped from 40% to 5.4%, the frequency of positive results given by tests for the presence of intestinal microflora in washings from various objects decreased more than 25 times. Morbidity rate at institutions for children of preschool age decreased 4--5 times as compared with that among children not attending such institutions. The above data suggest the necessity of introducing this experience in other regions of our country.     

Persistence and resurgence of sleeping sickness caused by Trypanosoma brucei gambiense in historic foci. Biomathematical approach of an epidemiologic enigma

Since the end of the 19th century, historic endemic foci of Trypanosoma brucei gambiense sleeping sickness have proven very persistent. A five-compartment mathematical model with open vector populations was developed in order to study the dynamics of this disease in Central Africa. Of particular interest is the rate at which the disease spreads or goes to extinction at the beginning of an epidemic outbreak. A measure of this rate is the initial halving/doubling time T(o) of the numbers infected; T(o) is a doubling time when the basic reproduction number Ro > 1 and a halving time when Ro < 1. For realistic parameter values, T(o) can be quite large (i.e. several years or even decades) which corresponds to a persistent low-level endemic brought about by an Ro either just above 1 (slow spread) or just below 1 (slow extinction). A resurgence of historical foci can then be caused by a small shift in parameter values that brings Ro well above 1 and decreases T(o). In addition, when Ro is less than 1 (in the absence of vector migrations), simulations show that a very small percentage of infected immigrant flies can bring about high prevalence rates in the human population. The model is validated with field data from historical Congolese, Central and West African foci of the past.     

Epidemiological surveillance on natural-borne infections in the Ulyanovsk region

The analysis of natural foci of haemorrhagic fever with renal syndrome (HFRS) and tick-borne borreliosis on the territory of the Ulyanovsk region is presented. Reduced rat control interventions result in a wide spread of these and other infections with natural focality. Monitoring of natural foci of HFRS, tick-borne borreliosis and arbovirus infections, their typing and determination of main reservoirs are the most promising among epidemiological surveillance methods.     

The etiological structure of shigellosis in the former USSR--an indicator of the activity of the main routes of infection transmission]

The data on the etiological structure of Shigella infections in the USSR in 1988-1989 are presented. The study showed the dominating role of S. flexneri with S. sonnei also retaining great importance in Shigella infections. The process of the liquidation of S. dysenteriae and S. boydii infections began in some large cities. The domination of dysentery caused by S. flexneri and a high typhoid rate, particularly in Central Asia, were due to poor water supply of the population. The spread of dysentery caused by S. sonnei was completely independent of the water factor. The decisive role in the transmission of S. sonnei in infective doses was explained by decentralized milk supply.     

Data on the epidemiology of rotavirus infection

The findings of epidemiological study of rotavirus infections among children in Gorki over the period of 1981-1985 are analyzed. The age of the patients is specified, as are the disease seasonal patterns and the incidence rates of its manifest and asymptomatic forms, and of carriership cases among healthy children in different foci of this infection.     

Contrasting landscape epidemiology of two sympatric rabies virus strains

Viral strain evolution and disease emergence are influenced by anthropogenic change to the environment. We investigated viral characteristics, host ecology, and landscape features in the rabies‐striped skunk disease system of the central Great Plains to determine how these factors interact to influence disease emergence. We amplified portions of the N and G genes of rabies viral RNA from 269 samples extracted from striped skunk brains throughout the distribution of two different rabies strains for which striped skunks were the reservoir. Because the distribution of these two strains overlapped on the landscape and were present in the same host population, we could evaluate how viral properties influenced epidemiological patterns in the area of sympatry. We found that South Central Skunk rabies (SCSK) exhibited intense purifying selection and high infectivity, which are both characteristics of an epizootic virus. Conversely, North Central Skunk rabies (NCSK) exhibited relaxed purifying selection and comparatively lower infectivity, suggesting the presence of an enzootic virus. The host population in the area of sympatry was highly admixed, and skunks among allopatric and sympatric areas had similar effective population sizes. Spatial analysis indicated that landscape features had minimal influence on NCSK movement across the landscape, but those same features were partial barriers to the spread of SCSK. We conclude that NCSK and SCSK have different epidemiological properties that interact differently with both host and landscape features to influence rabies spread in the central Great Plains. We suggest a holistic approach for future studies of emerging infectious diseases that includes studies of viral properties, host characteristics, and spatial features.     

Everyday contact spread of viral hepatitis B

The results obtained in the study of the characteristic features of the spread of viral hepatitis B under the conditions of family foci are presented. Children with viral hepatitis B have been found to infect 4-5 persons per 1,000 contacts, while adults infect not more than 1 person per 1,000 contacts. The results of the study have led to the conclusion that the idea of the potential danger of hepatitis B patients as the source of infection depends on the forms of the infectious process taken into account in evaluating its epidemiological significance. Latent cases of hepatitis B virus infection appear more frequently among the contacts of sick children than among those of sick adults, but the manifest forms of the disease are more frequently caused by infection contacted from sick adults.     

Formation of the dysentery epidemic process in three small towns]

Data are presented concerning the epidemiological analysis of Sonnei dysentery outbreaks in three towns connected by common nutrition and water supply. The epidemic processes in these populated localites were strongly interrelated. Possibilities of the effect of the water factor on the extent of Sonnei dysentery incidence were studied as well. The results of studies led to the conclusion on the presence of numerous action forms of the water factor which should be taken into consideration in carrying out prophylactic and antiepidemic measures in Sonnei dysentery.     

La Trypanosomose Humaine Africaine dans l’espace ivoiro-burkinabé : optimisation des stratégies de surveillance épidémiologique

The objective of this paper was to describe recent data from Burkina Faso and Côte d’Ivoire on Human African Trypanosomosis medical monitoring in order to (i) update the disease situation in these two countries that have been sharing important migratory, economic and epidemiological links for more than a century and (ii) to define the future strategic plans to achieve the goal of a sustainable control/elimination process. Results of active and passive surveillance indicate that all sleeping sickness patients diagnosed these last years in Burkina Faso were imported cases from Côte d’Ivoire. Nevertheless the re-introduction of the parasite is effective and the risk of a resumption of transmission exists. In Côte d’Ivoire, few cases are still diagnosed in several historical foci and the fear exists that the disease could reemerge in these foci or spread to other areas. In order to achieve a sustainable elimination of sleeping sickness in these two countries, control entities have to adapt their strategy to the different epidemiological contexts. At the exception of specific cases, the current disease prevalence no longer justifies the use of expensive medical surveys by exhaustive screening of the population. New disease control strategies, based on the exchange of epidemiological information between the two countries and integrated to the regular national health systems are required to target priority intervention areas. Follow-up in time of both treated patients and serological suspects that are potential asymptomatic carriers of parasite is also important. In parallel, researchers need to better characterize the respective roles of the human and animal reservoir in the maintenance of transmission and evaluate the different control strategies taken by National Control Programs in term of cost/effectiveness to help optimize them.     

Revealing the Micro-scale Signature of Endemic Zoonotic Disease Transmission in an African Urban Setting

The development of novel approaches that combine epidemiological and genomic data provides new opportunities to reveal the spatiotemporal dynamics of infectious diseases and determine the processes responsible for their spread and maintenance. Taking advantage of detailed epidemiological time series and viral sequence data from more than 20 years reported by the National Reference Centre for Rabies of Bangui, the capital city of Central African Republic, we used a combination of mathematical modeling and phylogenetic analysis to determine the spatiotemporal dynamics of rabies in domestic dogs as well as the frequency of extinction and introduction events in an African city. We show that although dog rabies virus (RABV) appears to be endemic in Bangui, its epidemiology is in fact shaped by the regular extinction of local chains of transmission coupled with the introduction of new lineages, generating successive waves of spread. Notably, the effective reproduction number during each wave was rarely above the critical value of 1, such that rabies is not self-sustaining in Bangui. In turn, this suggests that rabies at local geographic scales is driven by human-mediated dispersal of RABV among sparsely connected peri-urban and rural areas as opposed to dispersion in a relatively large homogenous urban dog population. This combined epidemiological and genomic approach enables development of a comprehensive framework for understanding disease persistence and informing control measures, indicating that control measures are probably best targeted towards areas neighbouring the city that appear as the source of frequent incursions seeding outbreaks in Bangui.