Sunday, March 30, 2008


What is cholera?

Cholera is an acute diarrheal infection of the intestine caused by ingestion of the bacterium Vibrio cholerae;(v.cholerae is responsible for releasing the toxin called cholerae toxin or {CT}which in turn is responsible for causing the mucosal cells to hypersecrete water and electrolytes into the lumen of the gastrointestinal tract. The result is profuse watery diarrhea, leading to dramatic fluid loss "rice water stools"is its hallmark)- which is fluids and mucous flecks.

Transmission occurs through direct faecal-oral route/ contamination or through ingestion of contaminated water and food and not limited to exposure of disrupted skin and mucosal surfaces to contaminated water. The disease is characterized in its most severe form by profuse watery diarrhea, vomiting, and leg cramps. In these persons, rapid loss of body fluids leads to dehydration and hypotention leading to shock. Without treatment, death can occur within hours due to severe dehydration and kidney failure.

The extremely short incubation period - two hours to five days - enhances the potentially explosive pattern of outbreaks, as the number of cases can rise very quickly. About 75% of people infected with cholera do not develop any symptoms. However, the pathogens stay in their faeces for 7 to 14 days and are shed back into the environment, potentially infecting other individuals. Cholera is an extremely virulent disease that affects both children and adults. Unlike other diarrhoeal diseases, it can kill healthy adults within hours. Individuals with lower immunity, such as malnourished children or people living with HIV and the elderly are at greater risk of death if infected by cholera.

How does a person get cholera?

Two serogroups of V. cholerae - O1 and O139 - can cause outbreaks. The main reservoirs are human beings and aquatic sources, often associated with algal blooms (plankton). Recent studies indicate that global warming might create a favourable environment for V. cholerae and increase the incidence of the disease in vulnerable areas. V. cholerae O1 causes the majority of outbreaks worldwide. The serogroup O139, first identified in Bangladesh in 1992, possesses the same virulence factors as O1, and creates a similar clinical picture. Currently, the presence of O139 has been detected only in South-East and East Asia, but it is still unclear whether V. cholerae O139 will extend to other regions. Careful epidemiological monitoring of the situation is recommended and should be reinforced. Other strains of V. cholerae apart from O1 and O139 can cause mild diarrhoea but do not develop into epidemics. A person may get cholera by drinking water or eating food contaminated with the v. bacterium. In an epidemic, the source of the contamination is usually the feces of an infected person. The disease can spread rapidly in areas with inadequate treatment of sewage and drinking water.

The v. bacterium may also live in the environment in brackish rivers and coastal waters. Under cooked sea food e.g. Shellfish if eaten raw have been reported as a source of cholera. The disease is not likely to spread directly from one person to another; therefore, casual contact with an infected person is not at risk of becoming ill. However, eating in one plate or preparing meals with persons who are carriers and failed to wash their hands after a long visit to the bathroom/latrine is deemed unsafe.

ALL in all- Cholera is mainly transmitted through contaminated water and food and is closely linked to inadequate environmental management. The absence or shortage of safe water and sufficient sanitation combined with a generally poor environmental status are the main causes of spread of the disease. Typical at-risk areas include peri-urban slums, where basic infrastructure is not available, as well as camps for internally displaced people or refugees, where minimum requirements of clean water and sanitation are not met.

However, it is important to stress that the belief that cholera epidemics are caused by dead bodies after disasters, whether natural or man-made, is false. Nonetheless, rumours and panic are often rife in the aftermath of a disaster. On the other hand, the consequences of a disaster -- such as disruption of water and sanitation systems or massive displacement of population to inadequate and overcrowded camps -- can increase the risk of transmission, should the pathogen be present or introduced.
What to do to avoid getting cholera when you are a way from home?

Drink only water that you have boiled or treated with chlorine or iodine. Other safe beverages include tea and coffee made with boiled water.
Eat only foods that have been thoroughly cooked and are still hot, or fruit that you have peeled yourself. Avoid undercooked or raw fish or shellfish, including ceviche.Make sure all vegetables are cooked avoid salads. Avoid foods and beverages from street vendors-the likes of Muturas.
A simple rule of thumb is "Boil it, cook it, peel it, or forget it"

Is a vaccine available to prevent cholera?
Oral cholera vaccines:

The use of the parenteral cholera vaccine has never been recommended by World health organization due to its low protective efficacy and the high occurrence of severe adverse reactions. An internationally licensed oral cholera vaccine (OCV) is currently available on the market and is suitable for travellers. This vaccine was proven safe and effective (85–90% after six months in all age groups, declining to 62% at one year among adults) and is available for individuals aged two years and above. It is administered in two doses 10-15 days apart and given in 150 ml of safe water. One such example of recently developed oral vaccine for cholera is Dukoral from SBL Vaccines. It is licensed and available. The vaccine appears to provide somewhat better immunity and have fewer adverse effects than the previously available vaccine.

Prevention and control of Cholera outbreaks:

Among people developing symptoms, 80% of episodes are of mild or moderate severity. Among the remaining cases, 10%-20% develop severe watery diarrhoea with signs of dehydration. If untreated, as many as one in two people may die. With proper treatment, the fatality rate should stay below 1%.

Measures for the prevention of cholera have not changed much in recent decades, and mostly consist of providing clean water and proper sanitation to populations potentially affected. Health education and good food hygiene are equally important. In particular, systematic hand washing should be taught. Once an outbreak is detected, the usual intervention strategy is to reduce mortality by ensuring prompt access to treatment and controlling the spread of the disease.

The majority of patients - up to 80% - can be treated adequately through the administration of oral rehydration salts- repackaged mixture of sugar and salts to be mixed with water and drunk in large amounts (standard sachets). Very severely dehydrated patients are treated through the administration of intravenous fluids, preferably Ringer lactate. Appropriate antibiotics can be given to severe cases to diminish the duration of diarrhoea, reduce the volume of rehydration fluids needed and shorten the duration of vibrio excretion. Routine treatment of a community with antibiotics, or "mass chemoprophylaxis", has no effect on the spread of cholera and can have adverse effects by increasing antimicrobial resistance. In order to ensure timely access to treatment, cholera treatment centres should be set up among the affected populations whenever feasible.The provision of safe water and sanitation is a formidable challenge but remains the critical factor in reducing the impact of cholera outbreaks.

Recommended control methods, including standardized case management, have proven effective in reducing the case-fatality rate. Comprehensive surveillance data are of paramount importance to guide the interventions and adapt them to each specific situation. In addition, cholera prevention and control is not an issue to be dealt by the health sector alone. Water, sanitation, education and communication are among the other sectors usually involved. A comprehensive multidisciplinary approach should be adopted for dealing with a potential cholera outbreak.

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