It is almost exactly a year ago that perhaps the most wide-ranging review of the state of our knowledge on vibrio cholera was published in the prestigious journal Nature Reviews Microbiology by Nelson et al (2009). Given that Haiti is experiencing an incipient epidemic (see McNeil & Sontag 2010), it might prove useful to review the facts.
- Cholera is spread primarily by water contaminated by bacteria known as Vibrio cholerae, although contaminated seafood, especially raw shellfish, will give it to you as well.
- Cholera is overwhelmingly a disease of Third World countries with overcrowded populations with poor isolation of water for drinking and cooking apart from water used to flush feces and wash clothes soiled by diarrhea. Cholera is very frequent in Bangladesh (Emch et al 2010), southern India (Das 2010), southeast Asia (Lenglet et al 2010) certain sub-Saharan African cities (Lusaka, see Gettlemen 2009), and parts of Latin America (Alamet et al 2010). Eastern Europe and Russia are also susceptible when water and sewer infrastructure crumbles owing to age or poor maintenance (Cromley 2010). Crowding alone rarely provides sufficient conditions for cholera. Hong Kong & Singapore are tremendously crowded places, but sanitary systems have been updated and made robust enough to withstand certain shocks, so chances for cholera outbreaks there are reduced. Despite being located on a peninsula where cholera is endemic, Singapore, a city-state of 4.8 million people, had only 7 cases of vibrio cholera in 2007, and to the degree it can be confirmed, raw seafood seemed to be the primary culprit although contaminated beverages were also implicated in one case (Wong, James & Goh 2010).
- Cholera is considered to be a perfect model for public health experts and mathematically inclined epidemiologists (Azaele et al 2010) to use to predict and map epidemics, owing to its having had repeated outbreaks over long periods of time, many of which were well documented in terms of the number of victims, locations, weather conditions, and demographics (Bertuzzo et al 2010, Ruiz-Moreno et al 2010). Three factors in addition to poverty and overcrowding almost mathematically tend to predict outbreaks. 1. Unusually heavy rains, which cause sewage and drinking water to mix (Sasaki et al 2009) 2. Spikes of high temperatures which favor the multiplication of the bacterium (Islam et al 2009). 3. Physical shocks such as earthquakes, volcanoes, tsunamis, and floods so deep that buried pipelines are crushed from overhead weight and/or dams break (Guha-Sapir & Gijsbert van Panhuis 2009). It is sadly no surprise that earthquake-damaged Haiti is experiencing an epidemic, but almost astonishing that cholera has not broken out to any extent in vastly more flooded Pakistan, which has experienced many of these contributing factors but fortunately temperatures there are heading downwards in a way that may limit vibrio proliferation.
- Vibrio cholera typically has a sort of bullet-shaped or elliptical body, often developing a whipping tail or flagellum that propels it. It uses the flagellum to penetrate membranes, and seems to thrive in those slick aquatic (but occasionally visceral) scummy surfaces that are called biofilms (Kamruzzaman et al 2010).
- The bacterium otherwise has what amounts to a two step life cycle. It lives and reproduces relatively slowly in sewage-type water, but once a patient ingests as little a single glass of this sort of water (unwittingly containing millions to billions of unseen particles), it can begin a new and hyper-virulent life cycle in the body, if it beats certain of the body’s defenses.
- Curiously the biggest initial defense is stomach acid (Nalin et al 1978). There is some evidence that a diet high in certain acidic foods or acidic natural products confers some disease resistance (Rahim et al 2010).
- Once the bacteria survives to make it to the small intestine, it uses its flagella to propel the head of the bacterium into the lining of the small intestine. There the bacterium’s “head” release some toxins. These toxins cause the cells lining the intestine to rupture and release free floating proteins, fats & carbohydrates, which enable the bacterium to feed and multiply very rapidly. In fact, once the vibrio sustain an intestinal presence not only does the patient become very sick, but the bacteria that emanates from his or her stool become hyper-infectious, reproducing much more rapidly than in ordinarily contaminated water, and causing person-to-person transmission to happen more quickly and resulting in the most severe of symptoms (Merrell et al 2002).
- Intestinal tissue damage, from marauding vibrio, however, is not the immediate cause of death. Rather it is the massive diarrhea of a consistency and appearance of what is typically described in the medical literature as “rice water:” i.e. Water that looks like it was left over after you had boiled rice in it. What that water contains, besides tens of trillions of hyper-infectious vibrio is a great quantity of electrolytes (dissolved salts and trace minerals) without which the body cannot function, as well as vast quantities of water (sometimes quarts at a time) that have to be replaced or the patient will die of dehydration, which is ironic since it often seems as if the patients are practically swimming in their own watery waste.
- While antibiotics will help a patient, particularly if the right ones are matched to the right subtypes of cholera, the patient must first survive the onslaught of their fluid and electrolyte loss through the immediate force-feeding of oral rehydration therapy. The composition of the remedial solutions often consists of fairly simple concoction of water, salt, sugar, and well-cooked rice. The chances for recovery go up from around 50% to as high as 99% if the patient is well hydrated through a crisis period lasting several days (Atia & Buchman 2010). It’s key, of course, that the water used to make these is uncontaminated!
- Certain age groups and people with certain blood types seem to have a special propensity for bad outcomes during cholera epidemics. Children under the age of 5 (Bryce et al 2005) , and people with blood type O are especially hard hit (e.g. Swerdlow et al 2005).
- What can be done to limit the spread or damage caused by vibrio cholera? While most vaccines developed to date are of limited effectiveness, a certain level of immunity is conferred if everyone is vaccinated in an endemic area, at least as long as the locally infective subtype does not mutate greatly ( Ali et al 2005). The idea that we could release viruses that feed on vibrio into the local water supplies of an area undergoing an epidemic has some merit, since it has been found that seasonal outbreaks of cholera tend to be quashed when the viruses that feed on them also multiply to such a degree that they damp down the epidemic (Faruque et al 2005). But ultimately the most effective “cure” for cholera is most likely to be industrialization which increases incomes for individuals and budgets for the local authorities while it improves water supplies primarily for reasons of manufacturing, with its side benefit of building durable separate systems for piping in and storing drinking water and processing and piping away urine and feces contaminated waste water (Hamlin 2009). This complex, indirect, and largely capitalist approach surprisingly better explains long term successes in controlling outbreaks than theories of popular uproar, reform movements, and grass roots public health outreach.
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