The use of the gene hybridization method for the identification of epidemiologically dangerous strains of cholera vibrios

Using the labeled DNA fragments containing the genes for cholera toxin the strains of cholera vibrios were studied for the presence of cholera toxin genes. Vibrio cholerae strains isolated from natural water reservoirs under the favourable epidemic situation do not contain the cholera toxin genes. The DNA hybridization method was compared with other methods used in research and practical work for estimation of epidemic importance of cholera vibrios.     

An outbreak of cholera (El Tor) in Samarkand Province, Uzbekistan in 1990]

A group outbreak of cholera caused by Vibrio eltor in the Samarkand Province++ in 1990 is analyzed. The retrospective analysis of the isolation of V. cholerae from water of surface reservoirs has been made. The study points out that since the cholera epidemic of 1985 V. cholerae avirulent strains, serogroup O1, have been periodically isolated in the Samarkand Province. The conclusion has been made that the isolation of even avirulent strains only from environmental objects is indicative of the unfavorable epidemiological situation in this area and of the necessity to take measures for improving epidemiological surveillance.     

Global microbial ecology: biogeography and diversity of Vibrios as a model

An environmental source of cholera was hypothesized as early as the late nineteenth century by Robert Koch, but not proven because of the ability of Vibrio cholera, the causative agent of cholera, to enter a dormant phase between epidemics. Standard bacteriological procedures for isolation of the vibrios from the environmental samples, including water, between epidemics generally were unsuccessful. Vibrio cholera, a marine vibrio requiring salt for growth, enters into a dormant 'viable but non-culturable' stage when conditions are unfavourable for growth and reproduction. The association of V. cholera with plankton, notably copepods, provides evidence for the environmental origin of cholera, as well as an explanation for the sporadic and erratic nature of cholera epidemics. Thus, the association of V. cholera with plankton was established only recently, allowing analysis of epidemic patterns of cholera, especially in those countries where cholera is endemic. The sporadic and erratic nature of cholera epidemics can now be related to climate and climate events, such as El Ni?o. Since zooplankton have been shown to harbour the bacterium and zooplankton blooms follow phytoplankton blooms, remote sensing can be employed to determine the relationship of cases of cholera with chlorophyll, as well as sea surface temperature (SST), ocean height, and turbidity. Cholera occurs seasonally in Bangladesh with two annual peaks in the number of cases occurring each year. From the data obtained and analysed to date, when the height of the ocean is high and sea surface temperature is also elevated, cholera cases are numerous. When the height is low and sea surface temperature is also low, little or no cholera is recorded. From the examination of data for the 1992-1993 cholera epidemic in India, preliminary comparisons of cholera data for Calcutta show a similar relationship between cholera cases, ocean height and SST. In conclusion, from results of studies of SST, phytoplankton and zooplankton, and their relationships to incidence of cholera, correlation of selected climatological factors and incidence of V. cholera appears to be significant, bringing the potential of predicting conditions conducive to cholera outbreaks closer to reality.     

On the global stability of a generalized cholera epidemiological model

In this paper, we conduct a careful global stability analysis for a generalized cholera epidemiological model originally proposed in [J. Wang and S. Liao, A generalized cholera model and epidemic/endemic analysis, J. Biol. Dyn. 6 (2012), pp. 568–589]. Cholera is a water- and food-borne infectious disease whose dynamics are complicated by the multiple interactions between the human host, the pathogen, and the environment. Using the geometric approach, we rigorously prove the endemic global stability for the cholera model in three-dimensional (when the pathogen component is a scalar) and four-dimensional (when the pathogen component is a vector) systems. This work unifies the study of global dynamics for several existing deterministic cholera models. The analytical predictions are verified by numerical simulation results.     

Global dynamics of cholera models with differential infectivity

A general compartmental model for cholera is formulated that incorporates two pathways of transmission, namely direct and indirect via contaminated water. Non-linear incidence, multiple stages of infection and multiple states of the pathogen are included, thus the model includes and extends cholera models in the literature. The model is analyzed by determining a basic reproduction number R₀ and proving, by using Lyapunov functions and a graph-theoretic result based on Kirchhoff’s Matrix Tree Theorem, that it determines a sharp threshold. If R₀?1, then cholera dies out; whereas if R₀>1, then the disease tends to a unique endemic equilibrium. When input and death are neglected, the model is used to determine a final size equation or inequality, and simulations illustrate how assumptions on cholera transmission affect the final size of an epidemic.     

Study of the epidemic significance of noncultivated forms of Vibrio cholerae by the polymerase chain reaction]

A specific method of the isolation of the cholera toxin gene by the directional amplification of DNA in the polymerase chain reaction (PCR) has been developed. The product of this reaction has a molecular weight of 440 sequence pairs and is a DNA fragment located on the A-subunit of V. cholerae gene vct. The sensitivity of the method permits the detection of one bacterial cell in the reaction mixture. The method is effective when V. cholerae purified DNA, cell lysates and the DNA of total microflora isolated from the water of natural springs are used. The study of water samples from natural water bodies by the method of PRC has revealed cholera toxin genes of V. cholerae noncultivated forms ni 5 out of 7 water samples taken from natural water bodies at the regions of Azerbaijan endemic for cholera and made it possible to evaluate the number of V. cholerae. The prospects of using PCR for the control of the epidemiological situation in regions endemic for cholera are discussed.     

Dynamics of the isolation and biological properties of Vibrio cholerae cultures,serogroups 01 and 0139, isolated from water reservoirs and sewage water on the territory of the city of Rostov-on-Don

The dynamics of the isolation of V. cholerae cultures from various water objects on the territory of Rostov-on-Don during the period of 1994-2001 was analyzed and biological properties of 14 such cultures were studied. In the absence of epidemic complications during the above-mentioned period, a growth in the amount of V. cholerae isolates, serogroups 01 and 0139, including toxigenic V. cholerae 01, was registered. The microbiological and epidemiological aspects of the monitoring of surface reservoirs and sewage were considered and the expediency of the profound and systematic study of its results for epidemiological surveillance on cholera was emphasized.     

Global stability for cholera epidemic models

Cholera is a water and food borne infectious disease caused by the gram-negative bacterium, Vibrio cholerae. Its dynamics are highly complex owing to the coupling among multiple transmission pathways and different factors in pathogen ecology. Although various mathematical models and clinical studies published in recent years have made important contribution to cholera epidemiology, our knowledge of the disease mechanism remains incomplete at present, largely due to the limited understanding of the dynamics of cholera. In this paper, we conduct global stability analysis for several deterministic cholera epidemic models. These models, incorporating both human population and pathogen V. cholerae concentration, constitute four-dimensional non-linear autonomous systems where the classical Poincaré-Bendixson theory is not applicable. We employ three different techniques, including the monotone dynamical systems, the geometric approach, and Lyapunov functions, to investigate the endemic global stability for several biologically important cases. The analysis and results presented in this paper make building blocks towards a comprehensive study and deeper understanding of the fundamental mechanism in cholera dynamics.     

Cholera vaccination: a decision analysis.

OBJECTIVE: To examine the clinical impact and financial cost of a vaccination program for the prevention of cholera in North Americans travelling to endemic and epidemic regions by means of the principles of decision analysis and a decision tree as well as to illustrate the effect of case attack rates on the cost per case prevented by vaccination. DESIGN: Review of the scientific literature to establish the probabilities of each significant outcome as well as a decision analysis and partial economic evaluation. OUTCOME MEASURES: Clinical impact (attack rates for cholera among vaccinated and nonvaccinated travellers), rates of death associated with cholera and vaccine-associated adverse events (VAAEs), and the number of VAAEs and the vaccine cost per case prevented. MAIN RESULTS: On the basis of our assumptions (including a rate of one case of cholera per 500,000 journeys to endemic regions), to prevent one case of cholera a vaccination program would cost $28.67 million and be associated with 105 VAAEs. CONCLUSION: Routine vaccination of travellers to endemic areas cannot be recommended; however, for people travelling to regions with a high transmission rate vaccination should be considered.     

Flexibility of Oral Cholera Vaccine Dosing—A Randomized Controlled Trial Measuring Immune Responses Following Alternative Vaccination Schedules in a Cholera Hyper-Endemic Zone

BackgroundA bivalent killed whole cell oral cholera vaccine has been found to be safe and efficacious for five years in the cholera endemic setting of Kolkata, India, when given in a two dose schedule, two weeks apart. A randomized controlled trial revealed that the immune response was not significantly increased following the second dose compared to that after the first dose. We aimed to evaluate the impact of an extended four week dosing schedule on vibriocidal response.Conclusions/SignificanceComparable immune responses and safety profiles between the two dosing schedules support the option for increased flexibility of current OCV dosing. Further operational research using a longer dosing regimen will provide answers to improve implementation and delivery of cholera vaccination in endemic and epidemic outbreak scenarios.     

The ABCs (Antibody, B cells, and Carbohydrate epitopes) of cholera immunity: considerations for an improved vaccine

Cholera, a diarrheal disease, is known for explosive epidemics that can quickly kill thousands. Endemic cholera is a seasonal torment that also has a significant mortality. Not all nations with extensive rural communities can achieve the required infrastructure or behavioral changes to prevent epidemic or endemic cholera. For some communities, a single-dose cholera vaccine that protects those at risk is the most efficacious means to reduce morbidity and mortality. It is clear that our understanding of what a protective cholera immune response is has not progressed at the rate our understanding of the pathogenesis and molecular biology of cholera infection has. This review addresses V. cholerae lipopolysaccharide (LPS)-based immunogens because LPS is the only immunogen proven to induce protective antibody in humans. We discuss the role of anti-LPS antibodies in protection from cholera, the importance and the potential role of B cell subsets in protection that is based on their anatomical location and the intrinsic antigen-receptor specificity of various subsets is introduced.     

Model of Vibrio cholerae biofilm as a mechanism of its survival in surface water reservoirs

Vibrio cholerae eltor strains with different epidemic importance isolated from river water in the city of Vladivostok during a cholera outbreak (1999) and in the city of Irkutsk during a safe cholera period (2005) are used in the experiment. A biofilm structure consisting of a peripheral part, bundles, polysaccharide matrix, canals, and polymorphic vibrios is presented by light and luminescent microscopy. The metachromatic pink coloring of the matrix (crystal violet and toluidine blue) or fluorescent reddish orange color (acridine orange) are evidence of acid mucopolysaccharide (glucosaminoglycans) content. The biofilm of a toxigenic strain as opposed to a nontoxigenic one is formed much later, while the elements comprising its structure are more apparent. The viability of vibrio cells during the experiment (90 days) preserving the initial pathogenic potential testifies to the highly adaptable properties of the Vibrio cholerae eltor, which promotes its survival and existence in surface water reservoirs under favorable ecological conditions (optimal temperature, existence of chitin-containing substratum, etc.).     

A generalized cholera model and epidemic-endemic analysis

The transmission of cholera involves both human-to-human and environment-to-human pathways that complicate its dynamics. In this paper, we present a new and unified deterministic model that incorporates a general incidence rate and a general formulation of the pathogen concentration to analyse the dynamics of cholera. Particularly, this work unifies many existing cholera models proposed by different authors. We conduct equilibrium analysis to carefully study the complex epidemic and endemic behaviour of the disease. Our results show that despite the incorporation of the environmental component, there exists a forward transcritical bifurcation at R (0)=1 for the combined human-environment epidemiological model under biologically reasonable conditions.     

The Role of Immunity and Seasonality in Cholera Epidemics

This paper presents a mathematical model for cholera epidemics which comprises seasonality, loss of host immunity, and control mechanisms acting to reduce cholera transmission. A collection of data related to cholera disease allows us to show that outbreaks in endemic areas are subject to a resonant behavior, since the intrinsic oscillation period of the disease (∼1 year) is synchronized with the annual contact rate variation. Moreover, we argue that the short period of the host immunity may be associated to secondary peaks of incidence observed in some regions (a bimodal pattern). Finally, we explore some possible mechanisms of cholera control, and analyze their efficiency. We conclude that, besides mass vaccination—which may be impracticable—improvements in sanitation system and food/personal hygiene are the most effective ways to prevent an epidemic.     

Cholera Threat to Humans in Ghana Is Influenced by Both Global and Regional Climatic Variability

Cholera, an acute diarrheal illness, is caused by infection of the intestine with the bacterium Vibrio cholerae after ingestion of contaminated water or food. The disease had disappeared from most of the developed countries in the last 50 years, but cholera epidemics remain a major public health problem in many developing countries, most often localized in tropical areas. Cholera is an infectious disease for which a relationship between disease temporal patterns and climate has been demonstrated, but only in an endemic context and for local areas of Asia and South America. Until now, similar studies have not been done in an epidemic context, on the African continent, although the largest number of cholera cases has been reported for those countries by the World Health Organization. The wavelet method was used in order to explore periodicity in (i) a long-time monthly cholera incidence in Ghana, West Africa, (ii) proxy environmental variables, and (iii) climatic indices time series, from 1975 to 1995. Cross-analysis were done to explore links between these time series, i.e., between cholera and climate. Results showed strong statistical association (coherency) from the end of the 1980s, between cholera outbreak resurgences in Ghana and the climatic/environmental parameters under scrutiny. Further examination of the existence of common spatial and temporal patterns in infectious diseases on the continent of Africa will permit development of more effective treatment of disease.     

A generalized cholera model and epidemic–endemic analysis

The transmission of cholera involves both human-to-human and environment-to-human pathways that complicate its dynamics. In this paper, we present a new and unified deterministic model that incorporates a general incidence rate and a general formulation of the pathogen concentration to analyse the dynamics of cholera. Particularly, this work unifies many existing cholera models proposed by different authors. We conduct equilibrium analysis to carefully study the complex epidemic and endemic behaviour of the disease. Our results show that despite the incorporation of the environmental component, there exists a forward transcritical bifurcation at R ₀=1 for the combined human–environment epidemiological model under biologically reasonable conditions.     

Seasonal cholera caused by Vibrio cholerae serogroups O1 and O139 in the coastal aquatic environment of Bangladesh

Since Vibrio cholerae O139 first appeared in 1992, both O1 El Tor and O139 have been recognized as the epidemic serogroups, although their geographic distribution, endemicity, and reservoir are not fully understood. To address this lack of information, a study of the epidemiology and ecology of V. cholerae O1 and O139 was carried out in two coastal areas, Bakerganj and Mathbaria, Bangladesh, where cholera occurs seasonally. The results of a biweekly clinical study (January 2004 to May 2005), employing culture methods, and of an ecological study (monthly in Bakerganj and biweekly in Mathbaria from March 2004 to May 2005), employing direct and enrichment culture, colony blot hybridization, and direct fluorescent-antibody methods, showed that cholera is endemic in both Bakerganj and Mathbaria and that V. cholerae O1, O139, and non-O1/non-O139 are autochthonous to the aquatic environment. Although V. cholerae O1 and O139 were isolated from both areas, most noteworthy was the isolation of V. cholerae O139 in March, July, and September 2004 in Mathbaria, where seasonal cholera was clinically linked only to V. cholerae O1. In Mathbaria, V. cholerae O139 emerged as the sole cause of a significant outbreak of cholera in March 2005. V. cholerae O1 reemerged clinically in April 2005 and established dominance over V. cholerae O139, continuing to cause cholera in Mathbaria. In conclusion, the epidemic potential and coastal aquatic reservoir for V. cholerae O139 have been demonstrated. Based on the results of this study, the coastal ecosystem of the Bay of Bengal is concluded to be a significant reservoir for the epidemic serogroups of V. cholerae.     

Demonstration of viable but nonculturable Vibrio cholerae O1 in fresh water environment of India using ciprofloxacin DFA-DVC method

Aim: To demonstrate the presence of culturable and nonculturable viable pathogenic Vibrio cholerae O1 in fresh water environments of a cholera‐endemic region in India. Methods and Results: Conventional culture and ciprofloxacin DFA–DVC were utilized to investigate the existence of V. cholerae O1. We isolated pathogenic culturable V. cholerae O1 from water samples collected from cholera‐affected areas. No culturable V. cholerae O1 was isolated from water and plankton samples from natural fresh water bodies. Ciprofloxacin was used for DFA–DVC as V. cholerae O1 are 100% resistant to nalidixic acid in our region. The viable but nonculturable O1 cells were demonstrated in 2·21 and 40·69% samples from natural water bodies and cholera‐affected areas, respectively. Conclusion: Vibrio cholerae O1 VBNC could be demonstrated using modified DFA–DVC technique. Ciprofloxacin is preferable to nalidixic acid for DVC in view of existing high‐level resistance to nalidixic acid in cholera‐endemic areas. Significance and Impact of the study: We endorse that for public health surveillance, cholera outbreak investigation and disease control water samples in addition to culture should be tested for V. cholerae using DFA–DVC.     

An Optimal Cost Effectiveness Study on Zimbabwe Cholera Seasonal Data from 2008–2011

Incidence of cholera outbreak is a serious issue in underdeveloped and developing countries. In Zimbabwe, after the massive outbreak in 2008–09, cholera cases and deaths are reported every year from some provinces. Substantial number of reported cholera cases in some provinces during and after the epidemic in 2008–09 indicates a plausible presence of seasonality in cholera incidence in those regions. We formulate a compartmental mathematical model with periodic slow-fast transmission rate to study such recurrent occurrences and fitted the model to cumulative cholera cases and deaths for different provinces of Zimbabwe from the beginning of cholera outbreak in 2008–09 to June 2011. Daily and weekly reported cholera incidence data were collected from Zimbabwe epidemiological bulletin, Zimbabwe Daily cholera updates and Office for the Coordination of Humanitarian Affairs Zimbabwe (OCHA, Zimbabwe). For each province, the basic reproduction number () in periodic environment is estimated. To the best of our knowledge, this is probably a pioneering attempt to estimate in periodic environment using real-life data set of cholera epidemic for Zimbabwe. Our estimates of agree with the previous estimate for some provinces but differ significantly for Bulawayo, Mashonaland West, Manicaland, Matabeleland South and Matabeleland North. Seasonal trend in cholera incidence is observed in Harare, Mashonaland West, Mashonaland East, Manicaland and Matabeleland South. Our result suggests that, slow transmission is a dominating factor for cholera transmission in most of these provinces. Our model projects cholera cases and cholera deaths during the end of the epidemic in 2008–09 to January 1, 2012. We also determine an optimal cost-effective control strategy among the four government undertaken interventions namely promoting hand-hygiene & clean water distribution, vaccination, treatment and sanitation for each province.