Short Note on Cholera

Cholera is an acute infection of the gut, caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae O1 or O139.  Other serogroups of Vibrio cholerae may cause diarrheal disease and other infections but are not associated with epidemic cholera. Vibrio parahaemolyticus is an important cause of enteritis.

It has a short incubation period of 1-5 days and produces an enterotoxin that causes copious (voluminous watery stools), painless, watery diarrhea often accompanied by vomiting which can lead to  dehydration (hypovolemic shock or acidosis) that can kill within hours if left untreated.

Cholera is a preventable disease and up to 80% cases of cholera can be successfully treated with oral rehydration salts (ORS). According to World Health Organization up to about 75% of people infected with Vibrio cholerae O1 or O139 don’t develop any symptoms.

People at risk:  Risk of cholera is highest in areas where basic infrastructure is not available such as peri-urban slums, refugees with limited access to safe drinking water and proper waste disposal. People with low immunity – such as malnourished children or people living with HIV – are at a greater risk of death if infected.

Signs and Symptoms

About 75% of people infected with V. cholerae do not develop any symptoms, although the bacteria are present in their faeces for 7–14 days after infection and are shed back into the environment. Among people who develop symptoms, 80% have mild or moderate symptoms, while around 20% develop acute watery diarrhea with severe dehydration.

Following an incubation period of 6-48 hours, cholera begins with the abrupt onset of watery diarrhea which is followed by several diarrheal episodes which may be accompanied by vomiting. This leads to hypovolemic shock.
Muscle cramps may occur as water and electrolytes are lost from body tissues. The outcome of the disease depends upon the extent of water and electrolyte loss and adequacy of water and electrolyte repletion therapy. If untreated, death can occur from hypovolemic shock, metabolic acidosis and uremia.

About Vibrio cholerae

Vibrios are Gram negative curved rods (comma shaped). They are highly motile (darting type of motility) with single polar flagellum (monotrichous).  Vibrios are sensitive to low pH and die rapidly in solution below pH 6. Vibrios tolerate alkaline media (alkaline peoptone broth of pH 8.5) is used for enrichment) that kills most intestinal commensal.

Vibrio cholerae strains:

Two serogroups of V. cholerae O1 and O139  cause outbreaks. V. cholerae O1 causes the majority of outbreaks, while O139 is confined to South-East Asia. Non-O1 and non-O139 V. cholerae can cause mild diarrhoea but do not generate epidemics.

Source: World Health Organisation/Medical Microbiology by Samuel Baron/CDC Websit