Cholera: Introduction, Causative Agent, Pathogenicity, Symptoms, Lab Diagnosis, Treatment, Prevention, and Keynotes

Introduction

Cholera is an infectious disease that is caused by the Gram-negative bacterium, Vibrio cholerae. It is responsible for severe watery diarrhea, which can lead to dehydration and even death if untreated. Cholera occurs due to eating food or drinking water contaminated V. cholerae. 13 lakhs to 40 lakhs cases are reported each year according to WHO worldwide. It is mostly found in places with poor sanitation, crowding, war, and extreme scarcity of food (famine). The most common locations include parts of Africa, South Asia, and Latin America.

Causative Agent of Cholera

Vibrio cholerae

Pathogenesis

The incubation period of cholera is a few hours to 5 days. Vibrio cholerae multiply rapidly in the large intestine where it releases the cholera toxin. The toxin penetrates into the intestinal wall and prevents the absorption of water by the intestine creating hypovolemic shock and dehydration.

Lab Diagnosis of Cholera

Microscopy: Darting motility test of stool is positive.

Culture: Growth on MacConkey agar with non-lactose fermenter colony while on TCBS agar yellow colony as shown above picture.

String Test: Positive

Biochemical Tests

Serotyping

Vibrio cholerae Rapid Diagnostic Test Procedure for Serotypes O1 and O139

Latex Agglutination

PCR

Symptoms

Symptoms may occur from mild to even very serious. 20 percent of cases have severe watery diarrhea accompanied by vomiting, which can quickly lead to dehydration. Even though many infected people may have minimal or no symptoms, they can still contribute to the spread of the infection. The signs and symptoms due to dehydration may occur as-

1. Rapid heart rate
2. Loss of skin elasticity
3. Dry mucous membranes (mouth, throat, nose, and even eyelids)
4. Low blood pressure
5. Thirst
6. Muscle cramps
7. If it is not treated, dehydration can lead to shock and death in a matter of hours.

Treatment and Prevention

Treatment with antimicrobial agents/antibiotics should start only after the initial rehydration therapy and
correction of acidosis. Antibiotics have a secondary role in the treatment of cholera by shortening the length of cholera diarrhea as well as the excretion of vibrios. Tetracycline is the usual drug of choice. Alternate to tetracycline, ciprofloxacin, and norfloxacin (quinolones) have shown excellent in vitro activity
against Vibrio.

The FDA has approved Vaxchora (lyophilized CVD 103-HgR) vaccine which is a single-dose live oral vaccine
for the age group 18–64 years old also there is no cholera vaccine that provides 100% protection, and thus the vaccination is not recommended as a prophylactic measure in preventing it by the WHO.

Boiled or chemically disinfected or bottled water may protect from cholera for the following purposes-

• Drinking
• Making food or drinks
• Preparing ice
• Brushing your teeth
• Washing face and hands
• Washing dishes and utensils that are used to eat or prepare food.
• Washing fruits and vegetables

Avoid raw foods for using like-

• Unpeeled fruits and vegetables
• Unpasteurized milk and milk items
• Raw or undercooked meat or shellfish
• Fish caught in tropical reefs may be contaminated with Vibrio cholerae bacilli.

Pictures

Rice water stool of Cholera patient

Hanging Drop Preparation for Darting motility of Vibrio cholerae

Hanging drop positive for Darting motility of Vibrio cholerae

Cholera Dipstick Test Positive Demonstration

Pure well-isolated V. cholerae yellow colony on TCBS medium

String test positive Vibrio cholerae demonstration

Gram-negative comma or curved shaped or fish in stream appearance of Vibrio cholerae in Gram staining of culture microscopy

Vibrio cholerae Biochemical Reactions in TSI, SIM, Citrate, and Urea agar demonstration

Oxidation-fermentation (OF) test and Decaboxylase test of V. cholerae

Vibrio cholerae antisera for serotping

Vibrio cholerae serotyping for O139 ( Bengal) demonstration

Vibrio cholerae colony characteristics on MacConkey agar

Vibrio cholerae colony morphology on blood agar

Vibrio Cholerae haemodigestion on blood agar after 3 days of incubation

Vibrio cholerae growth on nutrient agar demonstration

Keynotes on Cholera

• Serogroup O1 and O139 of V. choerae are responsible to cause outbreaks.
• The biotype EL Tor and serotype Ogawa are the principal causes of epidemic cholera in developing countries.
• 20% of cases cholera cases lead to severe life-threatening fatal conditions.
• Cholera is also known as “blue death”.
• Cholera can not be eradicated permanently from the globe since its causative agent V. cholerae is the native species of the aquatic environment.
• The antigenic variation of the V. cholerae strains is one of the major shortcomings and restrictions in developing a 100% protective vaccination against cholera.
• Hydration is the pillar of treatment for cholera.
• If anyone develops severe, watery diarrhea and vomiting especially after eating raw shellfish or traveling to a country where cholera is epidemic. He/she needs medical help immediately since cholera is highly treatable, but because dehydration can happen quickly and therefore it is important to get cholera treatment properly away.

Further Reading

1. https://www.frontiersin.org/articles/10.3389/fcimb.2020.561296/full
2. https://www.intechopen.com/chapters/59438
3. https://www.cdc.gov/cholera/illness.htm
4. https://www.webmd.com/a-to-z-guides/cholera
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7671094/