What Is Cholera and its Causes? How to control?
Cholera is a severe acute gastrointestinal infection caused by Vibrio cholera. Th:s curved, actively motile flagellated gram-negative bacilli are killed by the temperature of 100 Degree C in a few seconds but can survive in ice for up to six weeks. The organism that causes cholera is labelled as V. cholera 0 Group 1 or Vibrio cholera 0I (epidemic strain). Vibrios, biochemically similar to the epidemic strain but do not agglutinate in V. cholera 01 antisera, are now referred to as non- 0 Group IV. cholera (non-epidemic strain). The V. cholera non-01 also includes newly discovered V. cholera Bengal_ The El Tor biotype has replaced the classical biotype as the major cause of cholera. This is because El Tor V. cholera is a hardier organism. infection with RI Tor biotype is frequently unrecognised because it may produce milder clinical symptoms; a chronic gall bladder earner state can result in about 3% of all infected results. In 1982 the classical vibrio began to re-establish itself in Bangladesh.
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The fertile. humid valleys of the mighty Ganges and Gangetic plains Of Bengal (Bangladesh and West Bengal) have traditionally been regarded as the home of cholera’. The climatic condition and population density of the Far East Region have maintained it. In these regions devastating epidemics have occurred often following large religious festivals, and pandemics have spread throughout Asia and Europe and even North America. The seventh and the most recent pandemic of cholera beginning in 1961 and caused by El Tor biotype could not get a foothold in Europe as good hygiene prevented its spread in European countries, but it has for the first time become endemic in Near East and Africa. Humans are the only known natural hosts. Transmission is by the faecal-oral route. The organism is passed in stools or vomits of patients with cholera and of the very much larger number of subclinical cases, who excrete it for a few days. Contaminated water plays a major role in the dissemination of cholera; the organism survives up to 2 weeks in freshwater and 8 weeks in saltwater. Transmission is usually through drinking of infected water and eating of shellfish; contamination of food by flies and fingers also occurs.
Cholera vibrios multiply in the lumen of the small intestine and are non-invasive. They secrete a powerful exotoxin (enterotoxin) which stimulates the adenyl cyclase-adenosine monophosphate pathway of the mucosa resulting in an outpouring of massive secretion of isotonic fluid into the intestinal lumen. The toxin is bound irreversibly to the receptor site where it exerts its effect for 24-48 hours. The clinical effects are produced by the toxin. There may be severe diarrhoea with the passage of rice-water stool, acidosis and depletion of sodium and potassium with attendant complications of which hypotension and renal failure are the most important. The incubation period varies from a few hours to 5 days.
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Steps for Controlling cholera during an outbreak of epidemic Guidelines
(1) Confirmation of diagnosis. Demonstration of the rapidly motile vibrios by dark-field illumination of stool slide and subsequent inhibition of their movement with type-specific antisera is diagnostic. (2) Notification. Cholera is notifiable under the International Health Regulation. Its occurrence should immediately be notified to the local and national health authority. (3) Early case finding. An epidemiological study including detection of cases among household contacts, define the extent of the outbreak, and identify the modes of transmission. (4) Treatment centres. If hospital services are not available for severely dehydrated patients not responsive to oral rehydration therapy, temporary treatment centres should be established in a school or local institution. (5) Oral rehydration therapy. Mildly dehydrated patients are treated with (i) ORS- bicarbonate, (ii) ORS-citrate or (iii) ORS-rice based. (6) Intravenous rehydration therapy.’ Required only for severely dehydrated individuals. The IV solutions used are (1) Ringer’s lactate solution (it supplies adequate concentrations of–sodium and potassium and the lactate yields bicarbonate for correction of acidosis). (ii) Dhaka solution/cholera fluid (contains Na+ 3g/litre, k + 0.5g/litre, Cl 3.5g/litre, Acetate 2.8g/litre available in 500m1 or 1000 ml bag for iv injection. (iii) Diarrhoea Treatment Solution (DTS), recommended by WHO, is a polyelectrolyte solution for IV injection (it contains per litre sodium chloride 4 g, sodium acetate 6.5 g, potassium chloride 1 g and glucose 1 g). Several litres are necessary to overcome features of shock. (7) Antimicrobial therapy. Antibiotics, such as tetracycline 250 mg four times daily for 3 days or doxycycline 100 mg twice daily for 3 days helps to eradicate the infection, decrease stool output and shorten the duration of illness. (8) Sanitation measures. (a) Provision of safe drinking water: tube well water; boiling and chlorination; treatment with halogen tablet; (b) Excreta disposal: provision of sanitary latrines; water seal latrines; (c) Food sanitation: sale of foods under hygienic condition; eating of cooked hot food; cleaning and drying of cooking utensils; control of houseflies.9) Chemoprophylaxis. Only for household inmates:.: and contacts with tetracycline. (10) Vaccination: Specific prophylactic vaccination with cholera vaccine; each ml of the vaccine containing-12,000millions killed and preserved vibrios. Primary immunisation consists of 2 equal doses injected sc at an interval of 4-6 weeks. One dose for adults 0.5 ml, children 2-10 years 0.3 ml, children 1-2 years 0.2 ml. The classical cholera vaccine has, however, been found useless for all practical purposes.