Background Cholera appears to have originated in India. It first spread to Asia in 1817-1823, the first pandemic. The second pandemic reached Europe in
1826-1837, and subsequent to this there were five additional pandemics. The most recent began inexplicably in 1961 with a mild strain, the el Tor biotype, which had been endemic in Indonesia since 1937. More recently, it has become endemic in areas of South America. Vibrio cholerae 0139 is a new strain that emerged in the Indian subcontinent in 1992.
It is mainly to cholera that we owe the introduction of sanitation and the development of 'public health.' Although not a common cause of FP or GE in developed countries, the vibrios, especially V. cholerae, still cause large, mainly waterborne outbreaks in the developing world. It is the only gastrointestinal infection that is internationally notifiable. Because large numbers of organisms are required for infection, case-to-case transmission is uncommon.
Growth and survival The bacteria are aquatic and prefer briny waters. They can be found in many warm plankton-rich coastal waters, including the Mediterranean, Gulf of Mexico, and those of Southeast Asia and South America. Bivalved molluscs concentrate them, as they do many other bacteria. Other fish and shellfish can be contaminated, and inadequate cooking and storage will allow growth sufficient to cause FP. They prefer moist, slightly salty foods. Unfortunately, the el Tor strain is more likely to produce asymptomatic infections, persist longer in the environment, multiply more rapidly in food, and produce less immunity than the classical type. The organism produces an enter-otoxin in the intestine.
Clinical features Cholera, in its most dramatic form, is characterized by an acute outpouring of watery diarrhea (rice water stools) and vomiting causing death within 24 h by acute loss of fluid and electrolytes. However, the clinical syndrome ranges from the symptomless to the mild and less dramatic forms. The organism is not invasive, and if the loss of fluid and salts can be counterbalanced by infusion of equal amounts of fluid supplemented by electrolytes, the patient will survive. Patients with an absence of acid in the stomach, and those with blood group O, are especially prone to severe disease. The incubation period is 1-3 days (range, 12 h-5 days).
Characteristic sequence of events Sewage-contaminated seafood or water is by far the most common source of infection. The vibrio can grow successfully in cooked rice and other grains contaminated by food handlers, and salad vegetables can be contaminated by water. However, the organism often seems to find an 'environmental niche' and may persist in some communities for years.
Diagnosis The organism is usually isolated from the stool using special media. It can also be distinguished by light microscopy, and specific antisera will halt motility of the organisms. Agglutination tests with serum will distinguish 01 from 0139 and other strains. The organism can also be isolated from the environment using enriched media. Toxin production or the presence of the toxin gene can, and should, also be demonstrated. A 4-fold or greater rise in antibody is also helpful in diagnosis.
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