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Food-Info.net> Topics > Food Safety > Bacteria > Overview of food-borne bacteria

Vibrio cholerae

General characteristics

There are two varieties of V. cholerae , that are potentially pathogenic to humans. The main type causing cholera is V. cholerae O1, the other types are known as non-O1.

V. cholerae O1 is responsible for Asiatic or epidemic cholera. Outbreaks are very rare in Europe and North America, and occur mainly in (sub)-tropical regions. Cholera is always associated with polluted water or (shell)fish originating from polluted waters.

V. cholerae non-O1 infects only humans and other primates. It is related to V. cholerae O1, but causes a disease reported to be less severe than cholera. Both pathogenic and non-pathogenic strains of the organism are normal inhabitants of marine and estuarine environment. This organism has been referred to as non-cholera vibrio (NCV) and nonagglutinable vibrio (NAG) in the past.

Disease symptoms

Cholera is the name of the infection caused by V. cholerae .

Symptoms of Asiatic cholera may vary from mild, watery diarrhoea to acute diarrhoea, with characteristic rice water stools. Onset of the illness is generally sudden, with incubation periods varying from 6 hours to 5 days. Abdominal cramps, nausea, vomiting, dehydration, and shock; after severe fluid and electrolyte loss, death may occur. Illness is caused by the ingestion of viable bacteria, which attach to the small intestine and produce cholera toxin. The production of cholera toxin by the attached bacteria results in the watery diarrhoea associated with this illness.

Infective dose -- Human volunteer feeding studies utilizing healthy individuals have demonstrated that approximately one million organisms must be ingested to cause illness. Antacid consumption markedly lowers the infective dose.

Symptoms of V. cholerae non-O1 are diarrhoea, abdominal cramps, and fever symptoms associated, with vomiting and nausea occurring in approximately 25% of infected individuals. Approximately 25% of infected individuals will have blood and mucus in their stools. Diarrhoea may, in some cases, be quite severe, lasting 6-7 days. Diarrhoea will usually occur within 48 hours following ingestion of the organism. It is unknown how the organism causes the illness, although an enterotoxin is suspected as well as an invasive mechanism. Disease is caused when the organism attaches itself to the small intestine of infected individuals and perhaps subsequently invades.

Infective dose - It is suspected that large numbers (more than one million) of the organism must be ingested to cause illness.

Diagnosis

Cholera can be confirmed only by the isolation of the causative organism from the diarrheic stools of infected individuals.

Diagnosis of a V. cholerae non-Ol infection is made by culturing the organism from an individual's diarrheic stool or from the blood of patients with septicaemia.

Associated foods

Cholera is generally a disease spread by poor sanitation, resulting in contaminated water supplies.

This is clearly the main mechanism for the spread of cholera in poor communities in South America.

The good sanitation facilities in Europe and the U.S. are responsible for the near eradication of epidemic cholera. Sporadic cases occur when shellfish harvested from faecally polluted coastal waters are consumed raw. Cholera may also be transmitted by shellfish harvested from nonpolluted waters since V. cholerae O1 is part of the autochthonous microbiota of these waters.

Shellfish harvested from coastal waters frequently contain V. cholerae serogroup non-O1.

Consumption of raw, improperly cooked or cooked, re-contaminated shellfish may lead to infection.

Prevention

Poor hygiene, polluted water and improper hygienic food handling are the main causes. Proper heating (boiling) of water and good sanitation thus can prevent V.cholerae infections to a large extend.

Risk populations

All people are believed to be susceptible to infection, but individuals with damaged or undeveloped immunity, reduced gastric acidity, or malnutrition may suffer more severe forms of the illness.

All individuals who consume raw shellfish are susceptible to diarrhoea caused by this organism.

Sources:

The bad bug book : http://www.cfsan.fda.gov/~mow/intro.html

 



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