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Making Sense of ... Cholera

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Cholera

What is cholera?

Cholera is an acute, diarrheal disease caused by the bacterium Vibrio cholerae, in most cases, from contaminated water. It may be mild and transient,

Where is cholera usually found?

Cholera is now very rare in industrialized nations; the last serious outbreak in the US occurred in 1911. However, the disease is still endemic in the developing world, including the Indian subcontinent and sub-Saharan Africa.

How common is cholera?

In areas with inadequate sanitation, cholera is endemic. Many prefer to refer to a 30 year epidemic, on the basis that the disease does change with time, and spreads in waves from country to country. But the the underlying links between disease and untreated water is perennial and unchanging. The incidence in central America and Asia is declining, but major improvements in sewage and water systems will be required in many developing countries before the word 'eradication' can be considered. Only in the last few years have charities and governments recognized that water treatment is a vital component of any aid package; not just for cholera, but for a slate of water-borne diseases.

How is cholera transmitted?

Cholera occurs naturally in water-borne life, such as plankton, and so is initially ingested by drinking contaminated water, or eating uncooked fish or seafood from such water.

Cholera is then transmitted feces contaminated with the bacterium. This may occur when untreated sewage is released into waterways or groundwater, further contaminating the water and food taken from it or washed in it.

Can cholera be spread from person-to-person?

Direct person-to-person spread is unlikely, but poor hygiene practices, particluarly with the resulting diarrhea, can result in direct contamination of food or water used by others. This is how epidemics begin; the disease can spread rapidly in areas with a combination of poor education, untreated water and inadequate treatment of sewage.

Who is most at risk from cholera?

The prime risk factor is being in an area which has endemic cholera or poor water and sewage facilities. While few 'westerners' are at serious risk, careless or unthinking travellers to such areas do have an increased risk, and regularly bring the disease home.

Susceptibility to cholera depends on many individual factors, but four features significantly increase risk:

  • A large amount of the bacteria need to be ingested for infection to occur; repeated drinking of contaminated water will increase the risk.
  • Those with weakened immune systems, including older people and infants.
  • Risk is affected by blood type. People with type O blood are most susceptible, then B, then A; those with type AB are least likely to be affected.
  • Increased susceptibility has been observed in those with lower gastric acidity, either from antacids or malnourishment.

The risks vary in inverse proportion to the resources available for disease management; the reported overall 'case-fatality rate' (CFR) has dropped to about 1.5% overall, but while the CFR for South Africa is very low (about 0.25%), rates of up to 30% have been observed in other parts of Africa.

What are the symptoms of cholera?

Cholera is characterized by sudden, painless, profuse watery diarrhea and vomiting. The amount of fluid lost may be considerable, and is in proportion to the severity of the infection. In severe infections, the diarrhea can causes a fluid loss of more than one litre per hour. Within hours, severe dehydration, with intense thirst, muscle cramp, weakness, and negligable urine production will usually follow. Untreated choleral dehydration may lead to kidney failure, shock, coma, and death.

Symptoms usually subside in a few days, and most people are free of the bacteria in two weeks, but a few become long-term carriers.

Symptoms are largely confined to the intestines, and the diarrhea is caused by the enterotoxins that V. cholerae produces. The effects may be mild and transient, but in about one in 20 infected people, the disease will progress as described above.

What are the long term effects of cholera?

The debilitating effects of the disease may take a considerable time to resolve; in a few cases, irreversible kidney failure may be a result of dehydration.

What is the mortality rate for cholera?

Cholera has a short incubation period, 2-3 days, and can be rapidly fatal if untreated. The death rate may be as high as 50%, and some epidemics ahve had a 90% mortality rate. But with effective treatment, mortality is less than 1%.

For comparison, the 1849 St. Louis epidemic resulted in 4,557 deaths in a population of 63,000. That's just 7.2% of the total population, many years before effective treatment was devised; but that figure may be misleading, as we do not know how many people actually contracted the disease.

How is cholera diagnosed?

The disease starts has a distinctive pattern, and diagnosis will initially be made by clinical signs of a patient in a cholera area.

The diagnosis will be confirmed by culturing bacteria from rectal swabs or fresh stool samples.

Dipsticks have been developed for rapid diagnosis, enabling a diagnosis within a few minutes.

Is there a treatment for cholera?

Immediate rehydration is the key to management of cholera. It is the loss of fluid and salts through diarrhea that is life-threatening.

Oral rehydration solution, developed by the World health Organization, is a mixture of sugar and salts, which is mixed with clean water and drunk in large amounts. In some cases, intravenous rehydration may be required. With prompt treatment, fatality is rare.

Antibiotics may diminish the severity and duration of the illness, rehydration is the life saver.

Anyone who develops severe diarrhea and vomiting in cholera areas should seek immediate medical attention.

Is there a way to prevent infection?

  • Avoid unnecessary travel to affected areas.
  • Drink boiled water or water treated with chlorine or iodine, or drinks made with boiled water or carbonated, bottled beverages.
  • Do not add ice to drinks; the ice may be contaminated
  • Eat foods that have been thoroughly cooked and are still hot, or freshly peeled fruit.
  • Avoid undercooked or raw fish or shellfish, including ceviche.
  • Avoid salads.
  • Avoid foods and beverages from street vendors.
  • If in any doubt, only consume the items above that you have prepared for yourself.
  • Do not bring perishable seafood home.

What is the cholera vaccine?

The vaccine is not recommended for travelers because of the brief and incomplete immunity it confers. An oral vaccine for cholera has been licensed and is available in some countries; it appears to provide better immunity with fewer adverse effects than the previously available vaccine.

Studies have suggested that the use of oral vaccines in endemic areas can substantially reduce the incidence of the disease.1,2

Not all recipients of the vaccine will be fully protected against cholera, particularly for certain strains which no vaccine is effective against. Where effective, the vaccine has a life of a few months.

What is the protocol for cholera vaccination?

The risk of cholera to educated and careful travelers is so low that the disadvantesof vaccination probably outweigh the benefit.

Who should get vaccinated against cholera?

Currently, no country or territory requires vaccination against cholera as a condition for entry. in some circumstances, local authorities may require documentation of this vaccination. A single dose of oral vaccine will satisfy local requirements.

Are there adverse reactions to the cholera vaccine?

The most frequently reported undesirable reactions, such diarrhoea, abdominal pain, abdominal cramps, stomach/abdominal gurgling (gas), abdominal discomfort, headache, occur in about one in one thousand people

Rarer effects (between one and ten in 10,000), include fever, malaise, nausea, vomiting, loss of /or poor appetite, respiratory symptoms and dizziness.

Very rare efects include fatigue/drowsiness, flu-syndrome, dyspnoea, dyspepsia, flatulence, urticaria, shivers, joint pain, sore throat, reduced sense of taste, sweating, insomnia, dehydration, hypertension, paraesthesia, asthenia, angioedema, fainting, rash, pruritus, lymphadenitis and arthralgia. Though these are very rare, when compared with common sense precautions, most people would probably decline a vaccine that is is not fully effective against many syrains of the disease!

Can cholera be controlled environmentally?

Although cholera is a potentially fatal disease, it is easily prevented. In the North America and Western Europe, cholera is no longer a threat, simply because of modern water supply and sanitation methods.

Simple sanitation is all that is required to avoid an outbreak, and can often stop an epidemic.

Action needs to be taken at each point of transmission:

  • Water sources: Education, and warnings displayed at contaminated water sources.
  • Sterilization: Boiling, filtering, and chlorination of water before use.
  • Affected individuals: hygiene and safe and efficient disposal of waste.
  • Sewage: Treatment of raw sewage before release into the environment.

Education and sanitation are the key weapons in the prevention of cholera.

Is there legal protection for workers and others?

Cholera is usually a gepgraphic risk, as much as a behavioural one; those who travel to affected areas need to heed advice and take precautions; in most cases, a legal fight for compensation would have little hope of success.

But being infected with cholera in a non-cholera area may well be the result of negligence in water supply, food preparation, or perhaps hygiene. Take advice!

What can be learned from history?

For one hundred years, cholera and its means of spread have benn fully understood. And yet scientists still speak of sixth, seventh and eighth epidemic; academically, they are, of course, correct. But for such a readily preventable disease, microscopic differences in bug types are nothing, compared to dealing with dirty water.

"History repeats itself, first as tragedy, second as farce." - But we can choose to learn from the tragedy, and avoid the farce. It would be a shame in thirty years, to have to say "What experience and history teach is this - that people and governments never have learned anything from history, or acted on principles deduced from it."

Bibliography and Further Information Sources

References

  1. Longini , I. M., et al., (2007) Controlling Endemic Cholera with Oral Vaccines
    PLoS Med. 2007 November; 4(11): e336
  2. Reyburn, R., et al., (2011) The Case for Reactive Mass Oral Cholera Vaccinations
    PLoS Negl Trop Dis. 2011 January; 5(1): e952

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

First Published: 27 November 2006
Last updated: 20 April 2012
© Andrew Heenan 2006 et seq
 

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