Vibrio Cholerae And Cholera Molecular To Global Perspectives Pdf

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Vibrio cholerae and Cholera: Molecular to Global Perspectives

Specifically, there is marked disagreement about whether to use oral cholera vaccines in these settings, despite the improved safety and effectiveness profiles of these vaccines. Setting and Participants. Main Outcome Measures. The provision of an adequate quantity of purified water and the establishment of suitable facilities for defecation pending appropriate sanitation systems are important measures to help prevent outbreaks of cholera in refugee settings.

Such variation is in part a consequence of the disparate availability of resources needed to effectively manage such outbreaks. Clearly, more effective strategies to prevent cholera are needed.

At present, use of additional interventions to assist in the control of cholera outbreaks in refugee settings is not recommended. Mass antibiotic chemoprophylaxis is considered ineffective and may be associated with the emergence of drug-resistant organisms. To address this controversy, we report a cost-effectiveness analysis of several alternative intervention strategies, including vaccination, to control cholera outbreaks in sub-Saharan refugee settings.

Although not always attained, the provision of basic primary health care; safe, potable water; latrines; food; and oral rehydration solution is considered routine in all refugee settings. This baseline standard of care does not include any supplementary intervention to prevent or treat cholera. The algorithm for the possible outcomes following each of the above intervention strategies is depicted in Figure 1. If an outbreak of cholera occurs, based on the attack rate, a certain proportion of the population will develop cholera.

If a vaccination program is in effect, the fraction of the population developing cholera will also depend on vaccine coverage and the protective efficacy of the vaccine. The outcomes under analysis include severe and nonsevere cases of cholera and deaths from cholera.

A severe case is defined as one requiring intravenous fluids for treatment. Our cost-effectiveness analysis, in which the final indices of intervention performance are expressed as cost per case prevented and cost per death averted, was chosen over a cost-benefit analysis since estimation of the value of human life and other indirect costs, such as lost productivity, were beyond the scope of this research.

Estimates for parameters and probabilities used in our base case analysis are based on unpublished, detailed epidemiologic information from 21 cholera outbreaks in Mozambican refugee camps in Malawi collected between and by MSF and Epicentre. Table 1 provides a summary of these estimates; those estimates for which data could not be obtained from these sources were derived from published studies or were provided by the authors.

The setting chosen for this analysis is a hypothetical refugee camp with persons situated in a cholera-endemic area of sub-Saharan Africa. For all refugee camps documented by MSF and Epicentre to have had a cholera outbreak, the median cumulative fraction of refugees who developed cholera during the first 2 years following the first cholera case in each camp was 3. To derive other expected epidemiologic parameters, including week-specific attack rates, we overlaid the contours from the 21 epidemic curves for which detailed epidemiologic information was available and constructed a temporal distribution of the cumulative cases, representing the contribution of all 21 epidemics.

To obtain a representative epidemic curve of approximately median duration and yet maintain the original cumulative attack rate, we added the week-specific attack rates for each 2-week period and applied this sum to a truncated 1-week period. Intravenous rehydration is the mainstay of treatment to prevent death in severe cholera cases. Oral rehydration solution is used for mild and moderate cases of dehydration.

Doxycycline is administered to all patients and their close contacts. The time lag to recognize the epidemic and have the treatment centers operational is expected to be 1 week with PT.

The time lag to institute treatment is expected to be 1 week longer with RT ie, 2 weeks. Although several oral cholera vaccines are under development and evaluation, only vaccines containing killed whole cells have been evaluated in populations with endemic cholera. In this analysis we assume that vaccination will be targeted to all age groups older than 12 months, that the vaccine will be administered in 2 doses separated by at least 2 weeks, and that vaccination will reduce the number of cholera cases in an epidemic but not the probability of whether a cholera epidemic occurs in the 2-year time horizon.

Vaccine coverage is expected to be better with RV, with which there is an elevated perceived risk of disease by the refugees. With PV as the intervention, it is assumed that in-migrants over the 2-year time horizon would be vaccinated at the time of entry to the camp by existing health care providers.

Table 1 includes cost estimates entailed in vaccination and treatment in dollars used in the base case analysis. Except for cost of vaccine, all estimates are based on actual costs incurred by MSF. Only direct costs are included in the model. The treatment costs include the variable costs of drugs and treatment supplies eg, doxycycline, oral rehydration solution, and Ringer lactate and the fixed costs of freight, transportation, human resources, construction materials, and other equipment eg, laboratory supplies, disinfectants, nursing material, stationery, lighting, tents, water pump, pipes, and water tank.

The vaccination costs include the cost of vaccine, buffer, storage of vaccine in refrigerators, freight, vaccinators, supervisors, recorders, guards, vehicles, and other supplies eg, vaccine carriers, cups, and vaccination cards. Table 1 includes a plausible range for each of the variables we have elected to incorporate into 1-way sensitivity analyses. For an epidemic curve of 40 weeks' duration, we used the original temporal distribution of the cumulative cases representing the contribution of all 21 epidemics.

To obtain a representative epidemic curve of 4 weeks' duration and yet maintain the original cumulative attack rate, we added the week-specific attack rates for each week period and applied this sum to a truncated 1-week period. The results of the base case analysis are summarized in Table 2. If vaccination is to be incorporated into a treatment strategy, strategies combining a vaccination intervention with RT are expected to prevent no further cholera cases, prevent fewer cholera deaths, and cost more than the same vaccination intervention combined with PT.

At extreme values in the 1-way sensitivity analyses, strategies that incorporated RT were found to be less effective and to cost more than corresponding strategies that incorporated PT.

For strategies incorporating vaccination, the indices of cost-effectiveness were found to be most sensitive to the epidemic attack rate, vaccine coverage, cost of vaccine, vaccine protective efficacy in those 5 years of age or older, epidemic duration, time lag for vaccine effect, and time lag for treatment effect. For the extreme values of each of these variables, the incremental cost per case prevented and cost per extra death averted of adding either PV or RV to PT are presented in Table 3.

Other than the results shown in Table 3 , we did not find any significant impact on the results of our base case analysis during sensitivity analyses for all the other variables listed in Table 1. Irrespective of whether PV or RV was added to PT, the only situation in which vaccination incorporated into a treatment strategy was found to be inherently more cost-effective than the treatment strategy alone was when the cost of vaccine fell sufficiently.

In any chosen strategy, PT, the intervention currently recommended by MSF, would be preferred over RT, since irrespective of whether a vaccination intervention is adopted or not, strategies that incorporate PT are expected to cost less and to be more effective than corresponding strategies that incorporate RT. These observations persisted throughout the sensitivity analyses.

If vaccination were to be incorporated into an intervention strategy, PT plus PV, the strategy found to be more cost-effective in the base case analysis, would be preferred over PT plus RV. During sensitivity analyses, PT plus PV remained more cost-effective than PT plus RV except when the duration of the cholera epidemic was prolonged to 40 weeks or when the time lag for vaccine effect was reduced to 3 weeks. Since the duration of a cholera epidemic cannot be predicted, the only practical situation in which PT plus RV could be considered a more cost-effective option would be when the time lag for vaccine effect was expected to be 3 weeks or less.

In such a situation, the marginally superior cost-effectiveness of PT plus RV should be weighed against the possibility that the concurrent treatment of cases and use of reactive vaccination might disrupt both activities, a disruption we did not account for in our analyses. At the onset of a cholera epidemic, the sooner the treatment centers can be made fully operational, the smaller the expected number of deaths. With PT, if this time lag is reduced to less than 1 week, the expected incremental cost per extra death prevented of adding a vaccination campaign will become greater.

In such a situation, the major impact of vaccination is expected to be the reduction of cholera cases. This cost saving or negative incremental cost of adding PV to PT occurs when the money saved in treatment costs due to the fewer cases requiring treatment following vaccination is greater than the cost of the vaccination program itself.

Several assumptions in our model have worked to diminish the predicted cost-effectiveness of strategies incorporating vaccination compared with treatment alone. Unless relief agencies with comparable expertise in managing cholera cases respond to a given epidemic, it is unlikely that the CFR will be as low.

Furthermore, because of inadequate data, additional expected benefits from vaccination, such as induction of herd immunity and other manifestations of reduced transmission, cross-protection against diarrhea from enterotoxigenic Escherichia coli , and protection of vaccinated out-migrants against cholera, have not been included in our analysis.

On the other hand, there are also potential adverse effects of a vaccination campaign that we have not addressed. A vaccination campaign against cholera may interfere with other essential public health measures being instituted in the refugee camp concurrently. These public health measures include the provision of potable water, sanitation, and basic primary health care eg, treatment of other illnesses, such as malaria; vaccination of children against measles; and attention to appropriate nutrition.

In addition, following a vaccination campaign, vaccinated individuals may be lulled into a false sense of security and may not pursue other preventive measures, thereby putting themselves at an increased risk of infection by pathogens transmitted via feces. It is important not to generalize the results of this analysis to all conceivable refugee settings. The refugee camps incorporated into our analyses could be considered as relatively established, and they provided what we have referred to as a baseline standard of care.

In certain catastrophic situations, as illustrated by the massive epidemic of cholera early in the Goma, Zaire, refugee crisis of , 5 there may be no adequate health infrastructure, food, or potable water. While such devastating conditions last, it is implausible that any supplementary vaccination program to prevent cholera can be implemented.

Cholera epidemics continue to occur in refugee settings despite current efforts to implement nonvaccine prevention strategies.

Unless changes are made to these current strategies or additional nonvaccine prevention strategies are employed, it is reasonable to expect continued outbreaks of cholera in refugee settings. In our analyses, we have not evaluated the potential effectiveness and costs of nonvaccine prevention strategies beyond those currently employed on a routine basis.

We chose the BS-WC including rBS-WC cholera vaccine for this analysis, since it is the only oral cholera vaccine to have been evaluated in populations with endemic cholera. Once published data regarding the clinical performance of the live attenuated CVD HgR vaccine in a cholera-endemic setting become available, our model can be adapted to incorporate this vaccine into the analysis.

It is foreseeable that economies of scale in the production of the rBS-WC vaccine could result in a lower cost per dose. Furthermore, it is reassuring that a developing country such as Vietnam is reported to be producing a killed oral cholera vaccine below this cost threshold.

These effectiveness studies could also serve to address collectively many of the aforementioned limitations of this analysis. Our sensitivity analyses have also revealed that the cost-effectiveness of vaccination is significantly diminished as vaccine coverage falls. Therefore, if vaccination is to be incorporated into an intervention strategy, all possible measures that are known to improve vaccine coverage should be undertaken. Active support provided by refugee community health workers has been shown to be associated with high immunization coverage in refugee camps in Somalia.

Our website uses cookies to enhance your experience. View Large Download. Figure 1. Figure 2. Figure 3. Table 1. Table 2. Table 3. An analysis of mortality trends among refugee populations in Somalia, Sudan, and Thailand. Bull World Health Organ. Google Scholar.

An outbreak of cholera in a refugee camp in Africa. Eur J Epidemiol. Refugees and displaced persons. Centers for Disease Control and Prevention. Famine-affected, refugee, and displaced populations: recommendations for public health issues. Goma Epidemiology Group. Public health impact of Rwandan refugee crisis: what happened in Goma, Zaire, in July, ? Practical field epidemiology to investigate a cholera outbreak in a Mozambican refugee camp in Malawi, J Trop Med Hyg.

Vibrio cholerae and cholera : molecular to global perspectives

Vibrio cholerae and Cholera: Molecular to Global Perspectives , edited by Wachsmuth, Blake and Olsvik, provides an extensive, multiauthored textbook of cholera, its bacteriology, pathophysiology, epidemiology and molecular biology that has been made disturbingly timely by the spread of the seventh pandemic throughout Latin America since , the emergence of the new 8th pandemic of O epidemic cholera in Asia since last year and the rampant epidemic among Rwandan refugees this summer. The comprehensive description of progress since then provides sometimes difficult, but important, epidemiologic and molecular details which fuel current efforts at controlling what appear to be increasing problems with cholera in the s. Sign in Sign up. Members Institutions Cost. Advanced Search Help. Print ISSN:

Vibrio cholerae and Cholera: Molecular to Global Perspectives

Joachim Reidl, Karl E. The facultative human pathogen Vibrio cholerae can be isolated from estuarine and aquatic environments. In former centuries cholera was a permanent threat even to the highly developed populations of Europe, North America, and the northern part of Asia.

Vibrio cholerae and Cholera: Molecular to Global Perspectives

Zimbabwe offers the most recent example of the tragedy that befalls a country and its people when cholera strikes. The — outbreak rapidly spread across every province and brought rates of mortality similar to those witnessed as a consequence of cholera infections a hundred years ago. In this Review we highlight the advances that will help to unravel how interactions between the host, the bacterial pathogen and the lytic bacteriophage might propel and quench cholera outbreaks in endemic settings and in emergent epidemic regions such as Zimbabwe.

Specifically, there is marked disagreement about whether to use oral cholera vaccines in these settings, despite the improved safety and effectiveness profiles of these vaccines. Setting and Participants. Main Outcome Measures.

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Wachsmuth and P. Wachsmuth , P. Olsvik Published Biology. View PDF.

Cholera transmission: the host, pathogen and bacteriophage dynamic

Drasar, Vibrio cholerae and cholera: molecular to global perspectives. Wachsmuth, P. Olsvik editors.

To assess their pathogenic potential, we analyzed environmental strains of V. Analysis of 14 environmental strains, including 3 strains carrying a new allele of the tcpA gene, 9 strains carrying a new allele of the toxT gene, and 2 strains carrying conventional tcpA and toxT genes, showed that all strains colonized infant mice with various efficiencies in competition with a control El Tor biotype strain of V. These results suggested that the new alleles of the tcpA and toxT genes found in environmental strains of V. Detection of functional homologs of the TCP island genes in environmental strains may have implications for understanding the origin and evolution of virulence genes of V.

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NCBI Bookshelf. Baron S, editor. Medical Microbiology. Cholera is a potentially epidemic and life-threatening secretory diarrhea characterized by numerous, voluminous watery stools, often accompanied by vomiting, and resulting in hypovolemic shock and acidosis. It is caused by certain members of the species Vibrio cholerae which can also cause mild or inapparent infections.

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Wachsmuth and P. Wachsmuth , P.

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