CHOLERA: CAUSES, SYMPTOMS, DIAGNOSIS AND TREATMENT

Published in Microbiology
Tuesday, 09 January 2018 13:31
CHOLERA is a specific infectious disease that affects the lower portion of the intestine and is characterized by violent purging, vomiting, muscular cramp, suppression of urine and rapid collapse. It can a terrifying disease with massive diarrhea. The patient’s fluid losses are enormous every day with severe rapid dehydration, death comes within hours.

ETIOLOGY
 
  • Site: GIT (Gastrointestinal Track)
  • Agent: VIBRIO CHOLERA
 
MORPHOLOGICAL CHARACTER
 
Gram-negative, curved rods, non-capsulated, non-spore, motile by means of flagella (polar) they occur singly.
 
CULTURAL CHARACTER
 
  1. They produce smooth, convex, round, colonies which appear opaque and granular in transmitted light.
  2. They can grow on many kinds of media including enriching media contains bile salt and asparagine.
  3. They particularly grow on TCB agar (Thiosulfate Citrate Bile Salt agar) and produce yellow colonies.
  4. They are readily killed by acid and optimum pH for growth is 8.5-9.5.

BIOCHEMICAL CHARACTER
 
They ferment sucrose and maltose but not arabinose. They are oxidase positive which make them different from enteric Gram-negative rods. Some are halotolerant while others are halophilic require presence of NaCl for their growth.
 
ANTIGENIC CHARACTER
 
  • Vibrio Cholera contains two types of antigen flagellar (H) and somatic (O).
  • Vibrio Cholera contains two types of antigen flagellar (H) and somatic (O).
  • All Vibrios shared a single heat labile H antigen.
  • The O antigen is composed of heat stable polysaccharides and are classified into 6 serogroups and are further classified into 60 serotypes on the basis of O antigen.
  • One serotype of Vibrio Cholera bacilli is responsible for epidemic cholera and is subdivided into two types.
    (1) Classical (2) El Tor
  • El Tor types Vibrios were different from the classical types in their ability to cause lysis of goa or sheep erythrocyte in a test known as Grieg Test.
  • Each of the two biotypes of 01 serotypes of Vibrio is comprised of two or three antigenic factor A, B, and C
  • Factor A and B are found in serotype Ogawa, A and C in serotype Inaba and A, B and C in serotype Hikojima.
 
CHOLERA TOXIN
 
V. Cholera elaborated an enterotoxin that is responsible for the loss of fluid is Cholera, called CHOLERAGEN. It is a polymeric protein with a molecular weight 84,000 daltons containing two major domains. The domain "A" with molecular weight 28,000 daltons, play the key role in the biological activity of the Choleragen. The domain "B" is also known as CHOLERAGENOID with a molecular weight 56,000 daltons bind the toxin to its receptors on host cell surface. it is also the immunologically active region of the toxin.
 
Vibrio Cholera has been shown to produce a second toxin called ZONULA OCCULUDENS TOXIN (ZOT). This toxin disintegrates the tight junction between enterocytes, allowing escape of water and electrolytes.
 
MODE OF ACTION OF TOXIN
 
The toxin subunit "A" and "B" promote the entry of subunit "A" into the cell, "B" subunit is responsible for attachment of toxin to the epithelial cell of the small intestine. This subunit alters the activity of the regulatory protein, that controls the activity of enzyme, Adenylate Cyclase. This enzyme converts the ATP (Adenosine Tri-Phosphate) into CAMP (Cyclic Adenosine 5 Mono Phosphate). This increase in cyclic AMP level causes loss of water, electrolytes and result in diarrhea. This may lead to death because of dehydration and acidosis.

PATHOGENESIS
 
Cholera occurs in epidemic form under the condition of overcrowding, floods, wars, and famine. Humans are the only known natural hosts. A person may have to ingest 108 – 1010 organism to become infected. Vibrio Cholera is transferred from one person to another by ingestion of contaminated water or foodstuff. The contact with the carrier can also contribute to epidemics.
 
The Cholera bacilli find their way into the small intestine where they proliferate and elaborate the Choleragen. The toxin elevates the produces a massive secretion of isotonic fluid into the lumen of the intestine.

CLINICAL FINDING
 
The incubation period is few hours to 4 days. After incubation, there is sudden onset of nausea, vomiting, diarrhea with abdominal cramps, rapid dehydration and loss of fluid electrolytes. Mortality rate without treatment is 25% to 50%.
 
LABORATORY DIAGNOSIS
 
Diagnosis of Cholera patient by physical examination of stool, direct microscopic examination. Culture technique and also by agglutination method.
 
SMEAR
 
Smear made from stool sample is not distinctive however darkfield microscopy or phase contrast microscopy can show motile Vibrios.
 
CULTURE
 
There is rapid growth on peptone agar, TCB’s near pH 9 colony can be picked after 18-24 hours of incubation.
 
AGGLUTINATION
 
Agglutination test using anti O group on serum and also by the biochemical reaction.
 
EPIDEMIOLOGY
 
Man is the only host of Cholera disease and spread of infection is from person to person with contaminated water, food or flies. In many intensive 1% to 5% of exposed susceptible person developed the disease. The carrier state seldom exceeds 3 to 4 weeks.
 
PREVENTION
 
  1. Good water supply. Proper treatment of water should be there before supply to the town.
  2. Proper treatment of sewerage system.
  3. Personal hygiene and proper sanitation.
 
TREATMENT
 
Individual infected with Cholera require rehydration adequately by giving a solution of Oral Rehydration Salts (ORS) containing sodium chloride, sodium bicarbonate, potassium chloride and glucose. During the epidemic, 80-90% of diarrhea patient can be treated by oral rehydration alone but the patient who becomes severely dehydrate must be given intravenous fluid.

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CHOLERA: CAUSES, SYMPTOMS, DIAGNOSIS AND TREATMENT

CHOLERA: CAUSES, SYMPTOMS, DIAGNOSIS AND TREATMENT

CHOLERA is a specific infectious disease that affects the lower portion of the intestine and is char...

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