Cholera

Cholera is an acute diarrheal disease caused by bacterium Vibrio cholerae. Cases range from symptomless to severe infections. The majority of infections are mild or asymptomatic. Typical cases are characterized by the sudden onset of profuse, effortless, watery diarrhea followed by vomiting, rapid dehydration, muscular cramps and suppression of urine. Unless there is rapid replacement of fluid and electrolytes, the case fatality may be as high as 30 to 40 percent.

Epidemiological features

Cholera is both an epidemic and endemic disease. The epidemicity and endemicity of a disease will depend on the characteristics of the agent, those of the environment. Characteristics of the agent which influence its distribution include its ability to survive in a given environment, its virulence, the average number of organisms required to cause infection, etc. Global experience has shown that the introduction of cholera into any country cannot be prevented, but cholera can create a problem only in areas where sanitation is defective.

Epidemics of cholera are characteristically abrupt and often create an acute public health problem. They have a high potential to spread fast and cause deaths. The epidemic reaches a peak and subsides gradually as the "force of infection" declines. often-times, by the time control measures are instituted the epidemic has already reached its peak and is waning. Thus, cholera epidemic in a community is self-limiting. This is attributed to the acquisition of temporary immunity, as well as due to the occurrence of a large number of subclinical cases.

In areas where cholera is endemic, it does not show a stable endemicity. It undergoes seasonal fluctuations as well as epidemic outbreaks. The seasonal variation differs between countries and even between regions of the same country.

Causative agent of cholera

• The organism that causes cholera is labelled as Vibrio cholerae. Vibrio cholerae is primarily divided into over 200 serogroups based on the O-antigen, but only O1 and O139 cause epidemic cholera.
• Vibrio cholerae are killed within 30 minutes by heating at 56 degree Celsius or within a few seconds by boiling. They remain in ice for 4-6 weeks or longer.
• Drying and sunshine will kill them in a few hours. They are easily destroyed by coal tar disinfectants such as cresol. Bleaching powder is another good disinfectant which kills vibrio cholerae instantly at 6 mg/liter.
• The vibrio multiply in the lumen of the small intestine and produce an exotoxin (enterotoxin). This toxin produces diarrhea through its effect on the adenylate cyclase-cyclic AMP system of mucosal cells of the small intestine. The exotoxin has no effect on any other tissue except the intestinal epithelial cells.
• The human being is the only known reservoir of cholera infection. He may be a case or carrier.
• Cholera is dose-related infection. Infection occurs when the number of vibrio ingested exceeds the dose that is infective for the individual.

Periods of communicability of infection

A case of cholera is infectious for a period of 7-10 days. Convalescent carriers are infectious for 2-3 weeks. The chronic carrier state may last from a month up to 10 years r more.

Carriers in cholera

A cholera carrier may be defined as an apparently healthy person who is excreting Vibrio cholerae O1 (classical or EI Tor) in stools. Four types of cholera carriers have been described:

Types of carriers of cholera

Host factors in cholera

• Cholera affects all ages and both sexes. In endemic areas, attack rate is highest in children.
• Gastric acidity is an effective barrier. The vibrio is destroyed in an acidity of pH 5 or lower.
• Movement of population results in increased risk of exposure to infection.
• The incidence of cholera tends to be the highest in the lower socio-economic groups, and this is attributable mainly to poor hygiene.
• An attack of cholera is followed by immunity to reinfection, but the duration and degree of immunity are not known.

Environmental factor in cholera transmission

Vibrio transmission is readily possible in a community with poor environmental sanitation. The environmental factors of importance include contaminated water and food.

Mode of transmission of cholera

Transmission of cholera occurs from man to man via:

1. Fecally contaminated water.
2. Contaminated food and drinks.
3. Direct contact with infected person.

Incubation period of cholera

From a few hours upto 5 days, but commonly 1-2 days.

Clinical features of cholera

• Epidemiological studies have shown that more than 90 percent of cholera cases are mild and clinically indistinguishable from other acute diarrhea. The classical form of severe cholera occurs in only 5-10 percent of cases.
• Affected person suffer from profuse, painless, watery diarrhea followed by vomiting.
• The patient may pass as many as 40 stools in a day.
• The stools may have a "rice water" appearance.
• Presence of signs of dehydration like sunken eyes, hollow cheeks, scaphoid abdomen, sub-normal temperature, washerman's hands, and feet, absent pulse, unrecordable blood pressure, loss of skin elasticity, shallow and quick respirations.
• The output of urine decreases and may ultimately cease.
• The patient becomes restless, and complains of intense thirst and cramps in legs and abdomen.
• Some time death may occur due to dehydration and acidosis resulting from diarrhea.
• If death not occur, the patient begins to show signs of clinical improvement after few days.

Diagnosis of cholera

To diagnose the cholera a fresh specimen of stool should be collected for laboratory examination and microscopic examination of vibrio cholera presence conform the disease.

Treatment of cholera

• Cholera is now the most effectively treated disease. Mortality rates have been brought down to less than 1 percent by effective rehydration therapy.
• The mildly dehydrated patients should be treated at home with oral rehydration fluid.
• Severely dehydrated patients, requiring intravenous fluids, should be transferred to the nearest treatment centre or hospital.
• The antibiotics is also given in treatment of cholera. The commonly used antibiotics for the treatment of cholera are flouroquinolones, tetracycline, azithromycin, ampicilline and trimethoprim sulfamethoxazole.
• If diarrhea persists after 48 hours of treatment, resistance to antibiotic should be suspected.
• General sanitation measures must be applied at the onset of an outbreak of cholera. As water is the most important vehicle of transmission of cholera, all steps must be taken to provide properly treated or otherwise safe water to the community for all purpose (drinking. washing, and cooking).
• Proper excreta disposal and proper food sanitation is important to prevent the infection transmission.
• The vaccine is also available to prevent the cholera. There are three types of oral cholera vaccine are available: (a) Dukoral (WC-rBS), (b) Sanchol and mORCVAX and (c) Euvichol.