Cholera is caused by strains of the bacteria Vibrio cholerae. There are more than 100 species of Vibrio cholerae, only a few of which are known to cause cholera. The bacteria usually causes severe acute diarrhea with liquid stools and repeated vomiting.
The watery diarreah is typically pale and cloudy in appearance and is also known of as "rice water stool," in reference to its similarity to water that has been used to wash rice. This diarreah is teeming with bacteria which can contaminate drinking water in the case of poor sanitation and infect other people who drink the water.
Transmission of cholera
The bacteria causing cholera is present in stool or other effluent that may seep into and contaminate waterways, soil or sources of drinking water. Drinking infected water or even just using it to wash foods, kitchen utensils or culinary items can lead to transmission of the infection.
The bacteria may also attach to zooplankton present in salt water, brackish water and even fresh water. The bacteria latch onto the chitinous exoskeleton of these plankton.
Ingestion and survival in humans
Once the bacteria is ingested on eating contaminated food or water, it has to survive the journey through the digestive tract. Around two thirds of the bacteria ingested can survive the strong acid that is produced by the lining of the stomach walls. Once these bacteria pass into the small intestine, they begin to produce long tail-like structures called flagella that help them propagate and move through intestinal mucus until they reach the intestinal walls. On reaching the intestinal walls, the bacteria produce finger like projections called frimbriae or pili on their surface which they use to hold on to the intestinal walls. Here, the bacteria start to produce the toxic proteins that cause the watery diarrhea and this acts as a vessel for carrying out new multiplying bacteria into the external environment where it may be ingested by another host. Symptoms of cholera may begin within as little as 2 hours after infection or as much as 5 days afterwards.
Reviewed by Sally Robertson, BSc