Tuesday, September 6, 2011

Cholera


As an epidemiologist, I must make a special note at the beginning of this post. Modern epidemiology has its origin with this disease. It was the study of cholera, particularly in England during the middle of the 19th century, that laid the groundwork for the statistical analysis of public health data and applied surveillance. It was during a time when the miasma theory of disease transmission prevailed in the medical community. The widely recognized anethesiologist, Dr. John Snow, is largely credited with sparking and pursuing a paradigm shift in disease from one which defined illness as borne of bad, malodorous airs, or "miasmas", to one which would begin to recognize disease as infectious. This new conceptualization recognized disease as directly communicable between people or through vehicles (water, in the case of cholera) that are susceptible to contamination by human interaction.


While, Dr. Snow, was indeed at the forefront of pushing this new, germ theory of disease, the credit should not be allocated to him alone for 2 reasons. First, neither he nor any of his contemporaries could identify the agent that caused cholera, or any other disease for that matter, at the time of his investigations. Robert Koch would be the first to isolate and identify in 1877 a bacterial organism, Bacillus anthracis, that was pathogenic for human disease. In 1883, he subsequently identified Vibrio cholerae as the causative agent for cholera. Second, Dr. Snow did not always apply the greatest of rigor in his epidemiological analyses. It would instead be a priest, Henry Whitehead, who would employ exhaustive shoe-leather epidemiology in the Broad Street community as well as taking a more rigorous statistical approach to applied analysis of the resulting data. Dr. Snow's map of the Broad Street cholera outbreak of 1854 and the pump associated with the contaminated well are now iconic symbols of epidemiology and medical geography. This same map, now in the public domain, is the logo for my podcast, The Germlines:


The Pathogen. Cholera is caused by the gram-negative rod-shaped bacterium, Vibrio cholerae. V. cholerae is a distinctively curved (it's often identified as comma-shaped) bacillus with a flagellum:


Pathogenic V. cholerae is actually limited to a subset of strains within the species, rather than extending to all species members. The pathogenic strains are determined by antisera-specific agglutination and are referred to by their serogroup name. Most disease is caused by the O1 and O139 serogroups. Pathogenic V. cholerae are also classified according to biotype, classical or El Tor, and serotype, which consists of two distinct serotypes, Ogawa and Inaba, and one intermediate serotype, Hikojima. Prior to 1992 it was believed that only O1 strains were responsible for causing cholera. However, in 1992 a new serogroup, O139, emerged in South Asia and has been circulating there ever since but has not spread globally thus far. During human infection V. cholerae infects the small intestine and produces a toxin, known as cholera toxin (CT), which is responsible for the diarrheal disease associated with infection. V. cholerae is of only moderate infectivity as hundreds of millions of organisms are required to induce infection, and it is of low pathogenicity since 75% of infections with the classical biotype strains produce mild or subclinical disease and 93% of the El Tor biotype strains produce mild or subclinical disease. However, the virulence can be quite high: case-fatality in resource poor settings typically ranges from 5% to 10%, but can be as high as 20% during some epidemics if appropriate rehydration therapy is not available. In the best of circumstances the case-fatality is approximately 1%.

It is very important to note that Vibrio bacteria, in general, are free-living in water. They occupy various aquatic environments in various geographic locations, though, when free-living, they demonstrate a greater affinity for warmer more tropical climates. Vibrio species can be found in a range of mostly saltwater, and a few freshwater, environs, occupying a distinct ecologic niche in the water column. In addition, because they are ubiquitous in the marine environment they are frequently found in fish, and especially filter-feeding shellfish. Filter feeders (e.g. oysters, clams, cockles) can demonstrate very high levels of colonization, making them a potentially important reservoir for human infection in some circumstances. The image below, published by Nelson et al., 2009, in Nature Reviews Microbiology, shows the generalized V. cholerae life cycle in both the aquatic and human host settings:



While there is a high degree of genetic homogeneity among the various strains of pathogenic V. cholerae, the strains seem to have the ability to experience remarkable changes in specific gene expression as they transfer from the aquatic environment to the human gut. Studies have demonstrated that many of the pathogenic V. cholerae strains exhibit an increase in infectivity of up to 700 fold for up to 18 hours after passing out in the feces. This is a very interesting cross-niche adaption that V. cholerae has evolved to exploit two distinct ecologies (the ocean versus the human gut), while simultaneously relying on the interaction of these two ecologies for the bacterium's success in either one. We will discuss this concept more below.

The Disease. Simply put, it's watery diarrhea. But it is very bad diarrhea. Vomiting is also common.When diarrhea is present, it is a non-dysenteric diarrhea so there is no blood in the stool. Instead cholera diarrhea is characterized by a very liquid and grayish, "rice-water" stool, which can result in rapid and severe dehydration if the fluid loss is untreated. Cholera is really the only diarrheal disease that can cause severe dehydration resulting in death in healthy, immunocompetent adults. The disease is such a danger because so much fluid is lost so quickly: up to 1 liter per hour during acute infections. As such, rehydration therapy with a focus on re-establishing the electrolyte balance is imperative. The characteristic signs of the dehydration that attends the severe diarrhea are sunken eyes and cheeks and poor skin turgor:


Usually 2% - 5% body fluid loss is required before dehydration is clinically recognizable. In addition to the sunken eyes and poor skin turgor mentioned above, irritability, thirst, increased heart rate and respiration, and no urine volume are also characteristic of this stage. A 10% loss of body fluid marks severe dehydration and is characterized by low blood pressure, diminished pulse, increasingly poor skin turgor, delirium, and frequent loss of consciousness. At this stage the individual is no longer eager to drink and may not even be able to do so. This constitutes a medical emergency and requires immediate oral or intravenous (usually the latter) rehydration therapy.

The Epidemiology and the Landscape. Each year there are between 3 and 5 million incident cases of cholera globally, with approximately 100,000 associated deaths. Each of these deaths is 100% preventable as they are due to dehydration that can be easily treated with appropriate rehydration therapy. The map below was prepared by the World Health Organization (WHO) and shows the countries reporting annual cholera cases by their average case-fatality. Keep in mind that for any specific cholera epidemic, the actual case-fatality may be much higher depending upon the population affected, the local circumstances, the public health response to the source(s) of exposure, and the resources and knowledge available for rehydration therapy.



Cholera may or may not be an ancient disease. The documentation of this disease in populations largely comes down over the last 200 years through the writings of occupying colonizers of peoples in the tropical latitudes, and India in particular. Whether or not cholera emerged in a single location in the Bay of Bengal, which has been the canon of cholera discourse for generations, or existed endemically in multiple locations throughout the watered geography of the world, we cannot say. Either are possible. However, we can say that, during new periods of intense global shipping traffic due to trade and acquisitions of colonizing nations in the 18th and 19th centuries, cholera did spread globally across the world in a series of seven pandemics. However, the responsibility for this emergent disease and subsequent pandemics resides not in the tropical waters of south Asia or anywhere else, but rather in the large-scale movements of resources and people by the colonizers. I make this distinction because there is a very real discourse defined in the histories of cholera that allocates blame for this burgeoning global disease to subaltern populations. Thus we must read critically the standard documentations and chronologies of the seven pandemics as they are typically described. The first pandemic was referred to as the "Asiatic" cholera pandemic beginning in 1817 and running its course by 1824. The name is quite telling, and was, in part, directly responsible for the bureaucratization of lines between race, and between colonizer and colonized, in an emerging globalized world. This first pandemic extended between the Caspian Sea to the west and China to the east. Each subsequent pandemic lasted typically between 10 and 20 years then retreated into endemicity until the relevant V. cholerae strains were supplanted, thus beginning the next pandemic.

We are currently in the seventh pandemic, which began in 1961 and has been dominated by V. cholerae O1, El Tor. Its geographic spread is documented in this map, which also relied on genome sequencing of the bacterium in spatially diverse samples.


Transmission events inferred for the seventh cholera pandemic phylogenetic tree drawn on a global map

While the new serogroup, O139, emerged in the Bay of Bengal in 1992, this has not led to the emergence of an eighth pandemic.

As natural infection with V. cholerae does confer some immunity for a period, endemicity of infection or previous epidemic exposure is relevant to the severity of new epidemics in a given geographic area. In areas that have not had previous exposure to V. cholerae, essentially the entire population is susceptible. This translates to high incidence among both children and adults. Extremely fast transmission of rapid-onset, severe diarrhea across susceptible populations is characteristic of the typical cholera epidemic, and is one of the reasons why it has historically instilled such fear. A recent tragic example of such a situation is the cholera epidemic in Haiti, which began in 2010. Because cholera had been absent from the country for over a century, virtually everyone was susceptible when exposed. As of the middle of August, 2011, this outbreak had resulted in over 419,000 cases of cholera, of which more than 222,000 have been hospitalized and almost 6000 have died, according to the WHO. Again, explosive outbreaks of severe diarrhea among all age groups in susceptible populations is one of the key epidemiologic features of cholera. This unique dynamic may be due to a combination of a high level of susceptibility in the population with the shift in V. cholerae gene expression that leads to a hyperinfectious state of the bacterium when passed in human feces. Here again is the diagram from above to help illuminate the Vibrio life-cycle in this epidemiologic context:


So, cholera is unique because of the way in which ecologies and environments (particularly water and the human gut) converge to produce potentially massive epidemics. V. cholerae occupies specific ecologic niches, all of which are important in defining the landscape, or aqua-scape, epidemiology of cholera. First, it is free-living in the water column; second, it occupies a reservoir niche in fish and shellfish hosts; third, it occupies a niche in the human intestine, in which it undergoes changes in morphology (the production of the flagellum) and changes in infectivity. As such, its transmission is amplified by orders of magnitude, leading to rapid spread across susceptible populations. But always it's close connection with water is maintained: human fecal contamination of water sources account for the single greatest modality of transmission, and subsequently epidemic spread. Therefore, cholera is also firmly grounded in the human social landscape, being sharply delineated by the personal practice of hygiene at the level of the household and the public health practice of infrastructural sanitation at the level of the municipality.

Treatment. Oral rehydration salts mixed with water provide a universal and highly effective treatment. The goal is to reestablish the electrolyte balance in the person suffering the diarrhea episode. In order to stave off what can develop into deadly dehydration (in the case of cholera this can happen in a matter of hours), the individual must replace the fluid lost, AND the salts lost. This is precisely the goal of oral rehydration therapy. Packets of oral rehydration salts containing sodium chloride, potassium chloride, citrate and glucose can be obtained from almost any pharmacist or chemist in most areas of the world. These are simply mixed with water and consumed by the diarrhea-afflicted person. In addition, as much as can be tolerated by the ill person, normal nutrition intake should be maintained throughout the diarrhea episode. It may seem as though the food will go right through you, but the body does obtain some nutrients and this helps the immune system fight the infection. If dehydration is advanced, and/or if the individual is unable to keep fluids down due to vomiting, then intravenous administration of fluids will likely be necessary. With proper rehydration, no one should die from cholera.  


Those suffering from cholera who are undergoing rehydration therapy should be closely monitored for fluid loss during the diarrhea illness. This is typically accomplished using a cholera cot, which is a basic cot with a plastic sheet covering and a hole in the middle that drains into a bucket placed below the hole:






This bucket should contain a measuring stick that quantifies the volume of fluid lost. In this way, health care providers can monitor the volume of fluid loss over time so rehydration therapy can be optimized. 


Prevention and Control. Good sanitation and hygiene are the foundation of cholera prevention. Indeed, public sanitation and public health are both directly derived from the response to cholera in the latter half of the 19th century. However, even after more than 150 years, the world has not yet achieved anything close to an equitable distribution of safe water and so cholera epidemics can still strike with great force, as in Haiti in 2010 or in Zimbabwe in 2008. As such, improved infrastructure that can maintain adequate water resources is a first priority in cholera prevention. Secondarily, personal hygiene at the individual level of the household can also be very important in preventing the spread of cholera: consistent hand washing, boiling water, and thoroughly cooking food are all important in stopping the chain of transmission. However, these latter individual efforts, of course, require that adequate resources exist for such practices. Since both water and fuel for cooking or boiling water are often in short supply in the areas most at risk for widespread epidemics, these practices can be difficult to implement.


Finally, it is important to note that shellfish can be an important reservoir for cholera even in developed countries and should therefore be cooked thoroughly before eating. V. cholerae is endemic along the Gulf Coast of the United States and regular cases of cholera are seen in this area due to eating contaminated shellfish that have not been properly cooked. These isolated cases have not resulted in widespread epidemics because of the effective sanitation infrastructure in place along the Gulf Coast, which keeps any individual infections from contaminating larger water sources.


Here is a very nice animated video by the Department of Entomology at the University of Illinois demonstrating some cholera prevention strategies:




57 comments:

  1. In response to the post, I must say that for over 150 years this disease has known to exist and we understand the mechanism by which it is transmitted, we have the technology available and yet 200,000 people still die because of cholera. Is the technology to clean water accessible? The factors of proper resource allocation and prepardness on the part of government must be enhanced. Poor infrastucture is also a major problem as well.
    I commend the fieldwork that is done by players in the immediate surveillance, monitoring and treatment during a cholera outbreak because the disease can spread so rapidly and must place an immense amount of pressure on those individuals to save lives and stop it in its tracks.
    I believe cholera has been in the news recently out of Somalia. As of 2 weeks ago 37 lives were lost due to the disease...

    ReplyDelete
    Replies
    1. Technology to clean water is available. but not necessarily accessible to everyone. This is the problem with cholera and many of the other gut infections.

      While I agree with you that "proper resource allocation and preparedness on the part of the government" needs to be improved, it is extremely hard to do that. Especially when many of the countries effected are poor and developing.

      Maybe all the developed countries should pick one of the poorer afflicted countries every year and help them develop their clean water technology. This way the cost is reduced for the countries providing help and millions of deaths are prevented (from cholera and other infections). However, this then raised the issue of maintenance and who will be responsible.

      Like you said, the surveillance work is commendable, but it is not nearly enough.

      Delete
  2. Pakistan faced a flood crisis last year in 2010 and the spread of cholera became a threat. Since previous exposure to a disease is related to the severity of an outbreak, I'm wondering if the incidence of cases was lower in Pakistan than other countries that had faced a similar threat because of its proximity to the Bay of Bengal, where cholera may have arose from.

    ReplyDelete
  3. Christopher DonnellySeptember 9, 2011 at 1:35 PM

    To go along with this post, I am wondering what steps global health organizations (the WHO, for example) or governments are doing to prepare for a Cholera outbreak of the new strain, O139, discovered in 1992? The new strand, found in Southeast Asia, seems to be the 8th pandemic waiting to release itself on the world. Even in developed nations, the impact that a cholera outbreak could have huge ramifications, in terms of deaths and hospitalizations, as well as financial burden on healthcare systems. Taking steps to mitigate the effects of preventable disease, such as cholera, needs to be done globally and nations need to support one another in preventing these outbreaks in more susceptible regions.

    Another point to make is the Haiti outbreak that is still occurring. Although the consensus is that the outbreak was not due to the catastrophic earthquake the nation suffered, it brings one question: How can a nation protect itself from diseases such as cholera in times of national disasters? Even if there is no direct relationship between the earthquake and outbreak, the effect on the infrastructure of the medical care in Haiti was surely catastrophic and led to issues in treating the outbreak.

    ReplyDelete
  4. The trouble facing the spread of cholera is the same observed in many diseases. When the threat is not obvious people do very little in the way of prevention. People may become lax about hand washing, waste disposal, or the cleanliness of their water supply. Resources may not be allocated to emergency preparedness for events such as cholera outbreaks. These factors, in addition to the increased number of susceptible people in the population (who have never been exposed) can aid the rapid spread of the disease. Improvements in infrastructure, preparedness, and the implementation of health education programs are necessary for preventing the spread of not just cholera, but most (if not all) communicable diseases.

    ReplyDelete
    Replies
    1. To some extent, I disagree with your statement. Yes, the threat is not obvious, but that could for two reasons, and it depends on the location you're referring to. For example, the US as a developed country already has effective means of water sanitation. The Gulf of Mexico is home to cholera, but because it of our system, its not a threat. To that end, the threat isn't obvious because there is minimal threat in the US. However, things are still done by way of prevention.

      It also sounds as though you also blame the lack of awareness on the victim. What programs are in place in developing countries to bring to light the treat? Those in developing countries that are more susceptible to cholera because of poor sanitation or contaminated drinking water might know that the water is not clean, but they do not have a choice but to consume it, or they do not know how to clean it. They do not have the means to acquire the technology necessary. To that end, I believe that developed countries should do their part in helping aid others to effectively bring an end to cholera.

      Delete
  5. Since "extremely fast transmission of rapid-onset, severe diarrhea across susceptible populations is characteristic of the typical cholera epidemic," surveillance systems seem to be an essential component in mitigating the incidence rates and severity of cholera epidemics. Without a robust active surveillance system, treatment and prevention responses would be slow to act thus needlessly increasing mortality. Is the surveillance of cholera the responsibility of each country or global institutions such as the WHO?

    ReplyDelete
  6. In the Cholera post, I found it very interesting how the organism survives in the environment, and how it depends on the human social aspect and the infrastructure of a country to thrive. After the earthquake hit Haiti in 2010, the already failing infrastructure of the country collapsed even more giving more grounds for cholera to proliferate.  When I visited 3 months after it occurred, the living conditions there were unbearable and in some areas unlivable.  Many of the countryside consisted of tents 3 feet in width, improper bathrooms, and unclean water system.  I wondered then and still do now, if the country was so susceptible to infection after the earthquake, why was there not more focus on expediting the rebuilding process of the living conditions to ensure a safer environment for the people of Haiti? Also, what steps can we take to ensure that countries with weak infrastructures have access to clean water in a disaster, natural or unnatural?  Only 3 months after the earthquake, many locals were already being plagued by minor infections, and yet the proper aid was still not available to them.  Visually, there was not a great effort in place to avoid or lessen the cause of the cholera epidemic in Haiti, and in countries such as Haiti and other lower economic countries there should always be a plan of action to maintain a clean water supply system and septic system.  I do realize that this is the situation in a perfect world, however, outbreaks such as cholera would be less of a threat.  The cholera epidemic in Haiti should encourage Haiti's government and other surrounding countries to strengthen their infrastructure before it contributes or re-contributes to an infectious outbreak.

    ReplyDelete
    Replies
    1. Anika,

      Thanks for sharing your experience. It is both interesting and alarming that V. cholerae can survive and spread at such a rapid pace. Natural disasters like the earthquake in Haiti really set the stage for the emergence of infectious diseases such as cholera. As you mentioned, the earthquake practically destroyed Haiti's infrastructure. The earthquake also may have brought more people in contact with one another, allowing for easier transmission. Close interpersonal contact, along with limited access to clean water, promoted the epidemic. There also may have been limited treatment options during that time; the idea of the cholera cot is ingenious, but I wonder how practical it was in a post-earthquake setting. I'm sure providing sleeping cots for displaced people was a higher priority.

      Delete
  7. It is interesting and poignant that a cholera outbreak lead to the birth of epidemiology. Cholera is more than an isolated organism with the potential to wreak havoc and cause tremendous loss of life in a community. A cholera outbreak is also a manifestation of the fundamental problems in the public health infrastructure of a community. Do major outbreaks even occur in communities in the modern era that have access to clean water, and that have both adequate disease surveillance and health care resources? Should I never eat a raw oyster again?

    ReplyDelete
    Replies
    1. Yes, because Cholera is such a debilitating and more importantly, an easily susceptible disease, it was imperative to restrain it. Cholera is a disease that effects the most basic life source- water and wrecks havoc to the food chain. In developing countries, this is a vital aspect of the quality of life which effects everyone in the population.

      You ask if one should eat a raw oyster... this is not a slight rhetorical question, this is a reality when a person who does not have as strong of an immune system eats food from a location where people have a stronger immune system due to the uncleanliness in the water.

      This is a challenge when traveling to developing countries. where the locals use the tap water thinking its fine and the visiter gets quick food poisoning.

      Delete
    2. Shmuel, people do not have stronger immune systems in locations where water is unclean. In fact, the persistent diarrhea that is common in childhood in many areas with poor water infrastructure typically leads to malnutrition and immune compromise.

      Delete
  8. When it comes to cholera, it seems the most susceptible populations are ones where nutrition itself would not be easy to obtain. While I agree that maintaining adequate nutrition is essential to recovering from any illness, I'm wondering how much it should be stressed in a situation where it's not easily available- seeing that chronic diarrhea severely limits the amount that can actually be absorbed.

    ReplyDelete
    Replies
    1. That's a good point. I agree that susceptible populations are ones with little nutritional sources, however, water reabsorption and hence water is the most essential element/source that must be obtained. Chronic diarrhea does limit the amount of food that can be absorbed but stuffing a person who has cholera with food may not be the best method for recovery. This is so because the increased amount of food in the GI system may promote a hyperosmolar environment in the lumen that further draws out water. This is why the WHO created the oral rehydration formula, which is very effective at promoting water reabsorption as well as provides an isotonic environment of sugar and electrolytes in the GI lumen.

      Delete
  9. Chris said "To go along with this post, I am wondering what steps global health organizations (the WHO, for example) or governments are doing to prepare for a Cholera outbreak of the new strain, O139, discovered in 1992? The new strand, found in Southeast Asia, seems to be the 8th pandemic waiting to release itself on the world. Even in developed nations, the impact that a cholera outbreak could have huge ramifications, in terms of deaths and hospitalizations, as well as financial burden on healthcare systems. Taking steps to mitigate the effects of preventable disease, such as cholera, needs to be done globally and nations need to support one another in preventing these outbreaks in more susceptible regions.

    Another point to make is the Haiti outbreak that is still occurring. Although the consensus is that the outbreak was not due to the catastrophic earthquake the nation suffered, it brings one question: How can a nation protect itself from diseases such as cholera in times of national disasters? Even if there is no direct relationship between the earthquake and outbreak, the effect on the infrastructure of the medical care in Haiti was surely catastrophic and led to issues in treating the outbreak."

    Chris,
    I know that in Somalia UNICEF has been playing a role in trying to mitigate the burden that Cholera is having on children there. UNICEF being a large, international collaboration continues to monitor the situation there.
    visit here: http://www.unicef.org/infobycountry/somalia_59602.html

    I agree with you that the burden of Vibrio Cholera should be fought on an international and global level because it is a global disease. It is not endemic just to one region.

    In reference to disasters and associated outbreaks of cholera, I think it all comes down to resources and preparedness. Resources such as proper infrastructure, sanitation, health delivery etc. And then strategy and preparedness to anticipate disaster and react to massive outbreak... So there are regions of the world that are much more susceptible to mother nature's fury, so international and domestic support I think are needed to plan out and coordinate when and if an outbreak occurs what the best way is of reducing future burden. but you just never know how bad you'll get hit or when (if its an earthquake).
    focus should be on preparedness.

    ReplyDelete
    Replies
    1. While cholera is easily preventable and 100% treatable in normal situations, it becomes more complicated when the outbreak of cholera is associated with natural disasters such as earthquake. I agree that domestic preparedness and international support are the most important in response to the disaster. In the meantime, health education on sanitary and no drinking of contaminated water should be continuously disseminated in the affected regions to prevent a possible outbreak of disease.

      Delete
  10. I believe that cholera is an excellent example of the importance of health education. Chris asks how can a nation protect itself from disease in times of natural disasters? And Anika asks what steps can be taken to ensure that communities have access to clean water?

    I say that educated communities are very important in dealing with both of these issues.
    Through education, people know to use clean water, wash their hands, and to use a toilet or dispose of their waste by other sanitary means.

    There are many things that may seem so common sense to us, but are not properly understood in other communities.

    I'll suggest this article from UNICEF that demonstrates what some educational programs have done in Haiti.
    http://www.unicef.org/emerg/haiti_57135.html
    This program promotes breastfeeding. Prior to this program many mothers believed that the earthquake had affected their breast milk and that it would harm their babies so they stopped breastfeeding, putting their infants at risk for cholera.

    Am I suggesting that education will do away with cholera? No, but it can definitely mitigate the number of cases and burden of the disease.

    ReplyDelete
  11. I agree with Waqas in that surveillance systems are crucial in decreasing the incidence and severity of cholera. I believe that the responsibility of cholera surveillance should be a collective effort between each country, the CDC, and/or the WHO. For example, the Pan American Health Organization analyzes and communicates surveillance data to the CDC from Latin America and the Caribbean. Surveillance data includes cholera as well as other diseases. With such an integration of surveillance systems, therefore, resources may be allocated to areas most in need and further action can be taken to improve overall living conditions. Each country can voice what its people need most and further action can be taken to prevent the spread of communicable diseases.

    ReplyDelete
  12. I agree with George's post about mentioning that a disease with such a long history has allowed us to learn so much about it in regards to where it came from, and how to treat and prevent it. We have so much technology around the world, most that is not even accessible to the public, that can provide clean water and all of the necessary resources to prevent cholera outbreaks. A proper surveillance system should be put into place to prevent any further outbreaks with cholera or other infectious diseases. Andriane had pointed out how Latin America and the Caribbean communicates information from their surveillance systems, and how the information gathered should be a collective effort. This makes a great deal of sense, because if every country had access to all of the information gathered, that particular country's infrastructure will become increasingly stronger in their knowledge and action of preventing cholera.
    Discussing this issue of access to technology and the basic resources brings me back to the infamous question: Is clean water a right or a privilege, and who is that decision maker?

    ReplyDelete
  13. Simple hand washing with soap and water and adequate municipal sanitation are very important measures in the prevention of Vibrio Cholera infection. Sounds simple, but may be difficult to implement. Cholera is a diarrheal disease that should be relatively easily preventable. Children must be taught at an early age about the importance of hand washing in preventing many diseases, including cholera; however, to make the largest impact in saving thousands of lives yearly is to provide adequate sanitation and clean water to people in every community. Having clean water is the better way to save lives in the masses. One example of prevention on a large scale is when fluoride was routinely added to water in developed countries. This has significantly reduced the amount of tooth decay, compared to relying on personal hygiene alone. Effective sanitation along with hand hygiene, boiling water prior to use and thoroughly cooking foods, especially sea food, can prevent cholera infection and possibly eliminate or even eradicate it altogether.

    ReplyDelete
  14. Elizabeth Jennifer LeeSeptember 16, 2011 at 12:38 PM

    I agree with Nicole on the fact that health education is an important tool in prevention of the disease. I also agree with what Stella said about simple ways to prevent Cholera. I heard that treating water with a few drops of household bleach can make it safe to use and drink. This is a relatively inexpensive method of prevention that could work on a community level (one bottle of bleach per community?).

    ReplyDelete
  15. To answer Waqas Shaikh's question, I believe it is the responsibility of each country to implement surveillance measures to prevent and control cholera outbreaks. Ultimately each country is responsible for its citizens, but global institutions such as WHO must support the efforts of the countries with poor infrastructure and the highest incidence rates of cholera. Epidemic outbreaks may affect regions, but can quickly spread to many parts of the world. The world is a "global village" and we must work together to save lives from preventable diseases such as cholera.

    ReplyDelete
    Replies
    1. I like this term you use, "global village" to describe the world and believe it is true that we have the ability to be in constant contact with many areas of the world. With that being said, it is crucial that we all work together to protect against this 100% preventable disease. I think that many times we think of communicable diseases as being a disease or "them" not a disease of "us" but it is necessary to eliminate this thinking and instead understand that an infection anywhere in the world affects all areas of the world. A national surveillance of cholera and other such infectious disease are necessary to keep all people healthy.

      Delete
  16. Jen brought up some good points earlier about the difficulty of obtaining nutrition during a cholera outbreak. Because of the sheer necessity for people to obtain nutrients when facing such severe diarrhea, I believe a main focus of the WHO, UNICEF, public health agencies, and governments should be on the planning of administering oral rehydration salts during such an outbreak for countries that are not already prepared to do so and for countries that are in need of reevaluation of the current effectiveness of access to these salts. The WHO has expressed on their website that 80% of cholera cases can be treated with oral rehydration salts and considering the relative effectiveness and feasibility of stocking up on these tablets, I believe preparing a supply of these salts should be a major concern.

    ReplyDelete
  17. I agree with Nicole. Like other diseases, cholera is mainly spread because of poor water sanitation systems. Proper and clean sanitation is a basic and key component of any health community. Building and maintaining proper sanitation systems will pay dividends not only for preventing cholera but other diarrheal and fecal-oral transmitted diseases. Thus, I think more resources should be devoted to primary prevention interventions such as proper water sanitation instead of secondary and tertiary prevention interventions.

    ReplyDelete
  18. Bobbin - Your response to Jen's comment about the difficulty in attaining nutrient during the outbreak only accounts for areas where there are local health officials that can keep stores of oral rehydration salts.
    If an outbreak occurs in an area with no immediate access to these resources then you will still have people dying and spreading the disease. The world health infrastructure is not strong enough to ensure that every cholera case will be treated properly.

    ReplyDelete
  19. This an other example of a disease that is caused by poor sanitary and living conditions and uncooked mea in this case shellfish. during the last outbreak of cholera in Haiti, people die from a lack of hydration and antibiotics (even though cases were identified early)thatis there were a shortage of IV fluid and medication. Simple precautionary measures such as boiling water and eat well cooked shellfish can tremendously redure the cholera

    ReplyDelete
  20. Stephanie SaettaJuly 12, 2012 at 9:12 PM

    I find the change in gene expression that takes place in the human gut extremely fascinating! Does this have to do with the bacteria communicating with one another? A year ago I would have thought this question was sic-fi nonsense, but there is some amazing research about bacterial communication happening right now. (If you are interested check out: http://www.youtube.com/watch?v=TVfmUfr8VPA)
    If they are "talking," could we develop drugs that block their communication and use them prophylactically in outbreaks?

    ReplyDelete
  21. The gene expression that varies in among V. cholera probably has to do with mutations that occurs. I am also wondering if these organisms can alter their genome via conduction and would therefore need an f+ factor. Since a infected person usually exhibits a 700 fold for up to 18 hours after passing out in the feces the mutations and other forms of genetic alterations would occur quickly. Since it is very difficult if not impossible to eradicate this disease - I agree with Ricardo Guervil that the best warfare to employ is the use of clean water and the proper sanitation.

    Also, I have learned about this disease in many of my public health classes and was only aware of Dr. Snow's contribution and was not aware of Robert Koch who isolated and identified the human strain (Bacillus anthracis) and also identified the causative agent. I found this to be very interesting and am wondering why he has not gained any notoriety in connection to Cholera.

    ReplyDelete
  22. Lots of new information from this post.

    Great to learn about Robert Koch's and Henry Whitehead's involvement in the first Cholera investigation - I only remember learning about John Snow back in my Undergrad Epidemiology class.

    V. Cholerae's ability to mutate in the small intestine to increase its infectivity is very intriguing. I mean, 700-fold is an insane amount. Question, what's the usual time period of immunity after infection?

    "100,000... deaths yearly. Each of these deaths are 100% preventable" - that really resonated with me. I did a presentation on the Cholera outbreak in Haiti last year and I know poor infrastructure and sanitation was instrumental in the rapid spread. I wonder how much effort goes into awareness (of prevention methods) and improving infrastructures in these areas that continue to be plagued with cholera infections. It seems simple enough but I'm sure its much more complicated. I was reading about the cholera outbreak in Sierra Leone last year and less than half of the people living there has access to a private latrine! Its anyone's guess where are all the other people defecating. Of course infections spread like wild fire.

    Loved the animation!

    ReplyDelete
  23. Allison GrossmanJune 13, 2013 at 5:05 PM

    Kizzi, I was also shocked by the sheer number of deaths due to cholera that are preventable. It's astonishing how much illness is preventable, and how many deaths due to illness could have been prevented with treatment. Along with increasing awareness to prevention methods and improving infrastructures, I'm wondering why more people don't have good access to the (pretty simple) treatment. It seems like having a packet of salts in the home and mixing it with a pot of boiled water would be easier than setting up new infrastructure or changing individual and household-level hygiene habits.

    ReplyDelete
  24. I read The Ghost Map by Steven Johnson a couple of years ago and it covered some of the same history of Snow and Whitehead and the triumph of the germ theory of the miasmatic theory. Pretty interesting read, I feel like I should give it a thorough rereading after this ID Epi course. If anyone has any interest, I remember the Epilogue being particularly thoughtful. It was about 20-25 pages ruminating on epidemiology in our modern age of megacities and population boom. It is sad that cholera continues plague so many poor places when it is entirely preventable!

    ReplyDelete
  25. Despite efforts, cholera in Haiti is still a public health issue. The strain of v. cholerae has undergone many mutations. These mutated strains are known to cause more severe dehydration and diarrhea. It is becoming more like the version of cholera from the 1800s which is concerning because it was extremely virulent.

    ReplyDelete
  26. Sheaba Daniel
    Cholera seems to be a preventable disease when there is a focus on sanitation efforts and water infrastructure. Yet this month alone, a cholera outbreak in one village in Nigeria has killed 9 and hospitalized 100 people. The reports noted that the cholera outbreaks in Nigeria seem to occur during the rainy season. As rainwaters sweep through various water sources in the environment, the pathogen is spread as well, putting the community at risk of contracting cholera.

    ReplyDelete
  27. I never knew that virulence of the Vibrio that causes Cholera increased so tremendously in the human gut! Originally I thought its virulence was the same whether in aquatic or the host environment so I guessed I learned something new. I understand that treatment is the replenishment of electrolytes and water but for how long? I guess my question is how long does Cholera take to run its course in the human body? I assume since it has such a rapid onset, that maybe similar to Salmonella poisoning, it will subside within a few days. Are there any antibiotics that can mediate its virulence or is the fact that it can spread so rapidly and have such a quick and severe onset that antibiotics would simply take too long to work?

    ReplyDelete
    Replies
    1. Marc, indeed it is amazing what this infection can do to someone within a short period of time. After an incubation period of 6-48 hours, the onset of severe watery diarrhea begins. To answer some of your questions, you will replace fluid and electrolytes as long as the patient has symptoms (diarrhea) and once they have regained good skin turgor.
      Cholera runs its course in about 2-7 days in the body and recovery depends whether the patient's onw immune system can elliminate the disease or wheter antibiotics are used. The antiboitic of choice is one dose of Doxycycline 200mg.
      Studies have also shown that after someone gets infected with cholera, they usually get immunized for about 3 years.
      Reference: http://www.ncbi.nlm.nih.gov/books/NBK8407/

      Delete
  28. In response to Sheaba, I think that the knowledge is available concerning how to treat and prevent cholera. Being Nigerian myself, I remember being told about cholera as a child. To this day, I can't drink tap water (it has to be boiled). I was reading an article by Michelle Ziegler (http://contagions.wordpress.com/2011/03/01/choleras-chain-of-infection/) that talks about cholera's chain of infection. The article mentions this issue: apart from Nigeria, all across the world, the US included, natural and man-made disasters can put large populations at serious risk of contracting this disease. Of course the risk is practically ubiquitous in countries where the infrastructure is poor, but following disasters (Katrina comes to mind), even developed countries face this issue. In places that are prone to flooding, or that have histories of extreme rainfall to the point where they may have little access to clean water, public health officials should, at least periodically, ensure that the public is cognizant of the risks of transmission, how to avoid it, and how to prepare drinkable water in a worst case scenario.

    ReplyDelete
  29. With increased awareness and education why is the mortality rate still so high? What has been done in the immediate response to those who have experienced the outbreak such as persons in Haiti and most recently, the rapid onset in Ghana? What type of rehydration treatments have been administered, if any have been made available. I also, read briefly an article that in Haiti they are developing a vaccination against cholera. http://www.thebahamasweekly.com/publish/caribbean-news/Haiti_launches_cholera_vaccination_campaign36774.shtml

    ReplyDelete
    Replies
    1. Eradicating or Controlling cholera infection might be a difficult task to do.
      That task needs to include a clean water source, and better health education that involve personal hygiene and a sanitation system supported by government/or local municipalities, and/or developing a vaccine that gives a long term immunity, since infection itself is not giving a life long immunity. All that is basically not happening in most of the countries of the world. So that in comparison Polio infection is controlled/eradicated by the polio vaccine which is comparatively easier and cheaper to initiate and maintain than the costly and almost impossible task of changing the country’s infrastructure and the population behavior especially in poor or developing countries. So I am hopeful that developing a vaccine with high effectiveness and long immunity period will be the quicker/less costly, and better way to control cholera infection of-course in addition to other methods.
      There are 2 oral vaccines available at the moment (Dukoral and shanchol) that are about 50% effective and protection lasts for about 5 years.

      Delete
  30. I am puzzled by the mechanism which cholera uses to increase its infectivity. The fact that transmission of cholera can be greatly reduced by filtering of water and dilution by bleach yet the bacteria that causes this disease can survive the harsh conditions in the stomach and become more virulent. The equilibrium of this pathogen is destroyed at 100 degrees, only a few degrees different from the human body temp. The speed at which dehydration occurs in an affected individual is so serious that it could lead to death.
    One part of the report that I found a bit humorous is the cholera cot. I have never seen this type of apparatus before, along with the bucket and calibrated dip-stick. I suppose it is practical because the infected individual is likely weakened and unable to visit the bathroom at an appropriate time.

    ReplyDelete
  31. Because the primary way cholera is transmitted between humans is water contaminated with infective fecal matter, preventing epidemic spread is as simple as effective waste management right? Shoot, we've had water treatment in the U.S. for a little more than a century.

    I'm being facetious of course, the system that allows us to consistently have access to clean water and to safely dispose of sewage far from where we live without even really thinking about it, was the result of a tremendous amount of public works projects, which, in the South at least, involved so large an undertaking as to require the backing of literally the wealthiest American ever (there's a great episode of Radiolab that talks about Rockefeller, outhouses, and parasites)!

    This month, Sallie Tisdale wrote a small piece in Harper's about a project by the Swiss Federal Institute of Aquatic Science and Technology (EAWAG), to build a toilet that requires no piped water or wired-in electricity, no grid infrastructure at all. Their goal is lofty and they're funded by USAID, the World Bank, the World Health Organization, and the Bill and Melinda Gates Foundation. These major funders are all involved because, for all the miracle cures that have been created in the last century, the innovation that we should manage sewage, arguably thousands of years old, is some of the most effective public health.

    ReplyDelete
    Replies
    1. As a technology advances there is a possibility to fight back a lot of diseases as well as prevent them from happening more frequently. But there is one problem which there is no guarantee that any new technological innovations would be 100% successful to eradicate any disease from the world due to the microbial resistance and technological faults.

      Delete
    2. Thanks for sharing! I looked into the EAWAG Blue Diversion toilet and I think it's especially notable that the design took into consideration the cultural practices of some of the countries that this project might serve i.e. a squatting toilet as opposed to a sit-down one. I've been to countries where countless NGOs have implemented latrines with what we think constitutes a "toilet," yet they sit completely unused and ineffective because these westerners were just imposing their practices on these communities and didn't even think to consider that in their culture people squat while defecating. I'm really looking forward to seeing how this project plays out on a larger scale!

      Delete
  32. This comment has been removed by the author.

    ReplyDelete
  33. Is cholera something that can be flushed out our your system completely once excreted and the person is rehydrated? Or does it also call for antibiotics to get rid of the bacteria?

    Does rehydration therapy create a cycle where the bacteria can reproduce within the gut and continue to cause the necessity for the therapy?

    It is interesting to note that it lives in tropical waters, which often is within occurs in hotter climates where it is already important to be hydrated, does this mean that it is compounded? The map from 2009 showcased an imported case in the US. To that end, once here does that mean that while cholera already causes dehydration, it wouldn’t be to the level in a warmer climate? That is, not only would the climate affect the infectivity, but it would also affect the symptoms experienced.

    ReplyDelete
  34. The animated video was simple yet easily understood for any layperson. The treatment process seems easy enough but I can imagine obtaining these resources (fuel, water, and bleach/chlorine) can be challenging for people in certain countries especially when devastating events happen such as earthquakes and tsunami. Recovery alone is a lengthy process; I can only imagine the other challenge that is faced with battling this disease as well as trying to then establish a sufficient filtration system. Even currently, advanced filtering systems are still making their way to remote villages 5 years after the cholera outbreak in Haiti.

    ReplyDelete
  35. It is interesting to note that filter feeding shellfish such as oysters and clams are important reservoirs for V. cholerae. I wonder what makes the bacteria colonize in these types of organisms. Additionally, which other pathogens cause similar symptoms (dehydration), are similar in mode of transmission and are free living in water?

    ReplyDelete
    Replies
    1. S. Wallace- I wonder if E. Coli would be most similar to the V. cholerae pathogen. They have similar vehicles- food and water, and some symptoms are similar as well between the two. In the E Coli section of this website, there is mention of similar clinical presentation of diarrhea.

      Delete
    2. Hi S. Wallace! There are many pathogenic types of E. Coli, and some types can definitely cause very similar symptoms as V. cholerae diarrhea (although not as watery as cholerae diarrhea). I think the enterotoxigenic E coli (ETEC) causes the most similar symptoms/clinical presentations (watery diarrhea, abdominal cramping) as cholera. In children, enteropathogenic E coli (EPEC) is a common culprit in pediatric diarrheal cases.
      Here's a great link to CDC's info on ETEC:
      http://www.cdc.gov/ncidod/dbmd/diseaseinfo/etec_g.htm

      Delete
  36. A very interesting read! I was intrigued to read this post after visiting Haiti for a few weeks last month to visit family. This post really touched on many issues that I personally reflected on during my trip. While traveling through the country it was very clear that despite the small advances that Haiti has made post the devastating earthquake of 2010, there is still a multitude of rehabilitation that needs to occur. Inadequate water systems and poor sanitation resources still serve as the breeding grounds for this disease. In many areas of the country there is still little separation between water, sanitation, and bathroom usage. This factor aids in creating a catalyst for the cholera when infectivity increases substantially after being released in feces. It is somewhat disheartening to see a place that is in such high need of proper and effective intervention methods while considering that deaths caused by dehydration from this disease are 100% preventable with rehydration therapy. As a disease that can result in death in healthy people, it is important for public health officials to collaborate with local aid organizations for the use of vaccines and other preventive measures to control cholera.

    The animation was also a great resource for preventive methods presented in a clear simplistic manner.

    ReplyDelete
  37. Regardless of technology and medical advances, it is amazing to note that we are in the “seventh pandemic”; this is something that is very humbling. It also makes me rethink the ceviche that I had in San Salvador. The dynamic V. cholerae life cycle is so insidious yet becomes such a powerful bacterium when infecting humans- exhibiting an increase in infectivity of up to 700 fold! Thinking of Haiti in particular, in which cases of cholera have continued to go up since 2010, now 706,089 cases have been reported with 8,592 deaths; a consistent case fatality rate of 1.2%, as reported by the UN in September 2014.
    (http://www.un.org/News/dh/infocus/haiti/Cholera_UN_Factsheet_September_2014.pdf)
    The disappointing part about this is that Haiti’s cholera epidemic has been identified as a top priority by the UN, including rapid response teams equipped with rapid cholera tests. Given what this Infection Landscape blog reports, “that with proper rehydration, no one should die from cholera”, then why is anyone still dying in Haiti from cholera? It seems as though, not enough effort, has been put into rapid aggressive rehydration therapy once infection has occurred.

    ReplyDelete
    Replies
    1. I completely agree with you in that it is mind blowing to think that even after all the technological and medical advances of the 21st century, there are still places, such as Haiti, where cases of cholera continue to rise. It is sad to know that a disease, which is preventable and treatable, is still a main issue in certain countries. In fact, according to the CDC cholera cases have “increased steadily since 2005 and the disease still occurs in many places including Africa, Southeast Asia, and Haiti” (CDC 2014). Access to safe water, adequate sanitation and proper hygiene education should be something that everyone has access to. Even though I know this is not the case, it makes me mad to think that most illnesses and death from diseases such as cholera to this day can be prevented if these basic necessities are provided. The article says: “With proper rehydration, no one should die from cholera” and I have the same question you did: Why are people still dying in Haiti from cholera? What are the people who run these countries and that have the power to change these water, sanitation and hygiene problems doing? I know it may sound dramatic, but it’s reality and being a person with a passion for public health, I just don’t understand how such terrible public health problems still occur in places like Haiti. How did something as basic as having clean water become a luxury?

      Works Cited
      Centers for Disease Control and Prevention. 2014. Retrieved from:
      http://www.cdc.gov/healthywater/global/index.html

      Delete
  38. This is the first time I have ever come across writing regarding Dr. John Snow and the Broad Street Pump that indicates that, "while Dr. Snow was indeed at the forefront of pushing the new, germ theory of disease, the credit should not be allocated to him alone." It was nice to read the names of others who played a role but whose names are not well known. Prior to reading this, I was not aware that neither Dr. Snow nor any of his contemporaries could identify the cholera causing pathogen. It was interesting to know that Dr. Snow did not always apply the greatest of rigor in his epidemiological analyses.
    The reminder to readers that shellfish can be a reservoir for cholera is useful as raw shellfish is commonly eaten worldwide and cooking shellfish thoroughly before eating is a preventative measure that can be easily taken to reduce the incidence of cholera.

    ReplyDelete
  39. Cholera is a disease of poverty. Although there are two-dose vaccinations, the most effective method of prevention is to improve infrastructure. However, with the limited resources, most interventions are focused on treatment first, and then prevention. Therefore, it seems like progress is slow. Developing countries should invest and distribute oral rehydration salts in high-risk populations as a preemptive strategy. Long term interventions require large investments. This is an urgent issue because the environment is changing; rising sea levels and increases in water temperatures can potentially lead to an increase in cholera outbreaks.

    ReplyDelete
    Replies
    1. Good point Kesha, the rising temperatures of the sea is a risk factor that we must be concerned about. The water temperature will be a breeding ground for multiple diseases, Cholera among them. I know Iodine can remove most risks of Cholera from the water. I'm wondering if other elements can too. Perhaps the rising temperatures of the water will dissolve salts deposits on land and thereby cure the water. Wishful thinking?

      While on the topic, global warming can bring diseases to parts of the world that have never been able to breed such diseases. For example, certain vectors, such as mosquitos, are now able to tolerate the climate of more northern regions that were too cold in the past. This can lead to drastic concerns in epidemiology.

      Delete
  40. Infrastructure is essential to maintaining a clean water supply and getting rid of sewage safely. The other point about infrastructure is that getting hospital attention saves lives. It is very simple to deal with the effects of cholera--hydration. However, if you are a long way from safe water and people who know what to do, cholera becomes a killer disease.
    I think cholera will be hard to eradicate because it is free-living in water so its spatial reservoir is huge. It is interesting to think about what effect global warming is having on V. cholera. It seems to prefer warm water and certainly with increased flooding there will be more chance of sewage contaminating water supplies.

    ReplyDelete
  41. The conditions that Cholera thrive in are interesting to me as it is free-living in water plus makes an extraordinary adaptation in the gut as it increasing infectivity. It’s advancement relies on the two preservations in which it can thrive in counties and/or areas with high population density, poor sanitation infrastructures and insufficient access to clean water. This screams to me refugee health. We still see Cholera epidemics explode after natural disasters such as the earthquake in Haiti than many people have mentioned. We also see it strike during political disasters, for example the cholera epidemic in a village of Tanzanian holding Burundian refugees. As overcrowding environment, crippled infrastructure and lack of access to aid make for a cholera breeding ground it is imperative to surveillance the conditions at refugees centers during the current crisis that we see in order for cholera to be less of a threat. Of course in a more perfect world every place would have an economy to develop healthy sanitation infrastructure.
    Are there currently vaccines against cholera than can be administered at refugee centers?

    ReplyDelete

Note: Only a member of this blog may post a comment.